Lab_2_Exp_2

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Experiment 2 Group 5 Page 1 EEL4119L Electronics Laboratory II Experiment 2 By Pablo Sanchez James Saville Niv Barazani Nabil Elsrouji Charles Florestal October 1, 2019
Experiment 2 Group 5 Page 2 Table of Contents Table of Contents .......................................................................................................................... 2 ABSTRACT ................................................................................................................................... 4 EQUIPMENT AND TOOLS ....................................................................................................... 4 COMPONENTS ............................................................................................................................ 4 Part A: Voltage-Series Negative Feedback Amplifier ............................................................... 5 Introduction ..................................................................................................................................... 5 Objective ......................................................................................................................................... 6 Simulation ....................................................................................................................................... 6 Experiment ...................................................................................................................................... 8 Conclusion .................................................................................................................................... 14 Part C: Current-Shunt Feedback Amplifier ............................................................................ 14 Part 1 – Simulations of Circuit Schematics .............................................................................. 14 Part 2 – Measurements of Circuit Without Feedback ............................................................... 21 Part 3 – Measurements of Circuit with Feedback ..................................................................... 28 Introduction ................................................................................................................................. 35 Figure D1: AC Sweep Analysis of Voltage-Shunt Amplifier without Feedback Schematic ................................................................................................................................................... 35 Table D2: Simulation Component Values for Voltage-Shunt Amplifier with Feedback ............................................................................................................................................... 36 Figure D2: AC Sweep Analysis of Case A Schematic .......................................................... 37 Table D3: Active Mode Table for AC Sweet Analysis of Case A ................................... 37 Figure D3: AC Analysis Gain in dB of Case A ......................................................................... 38 Figure D4: AC Sweep Analysis Rin of Case A ......................................................................... 39 Figure D5: AC Sweep Analysis of Voltage-Shunt Amplifier with Feedback Schematic ...... 40 Table D4: Active Mode Table for AC Sweet Analysis of Case B .................................... 40 Figure D6: AC Sweep Analysis Gain in dB for Case B ........................................................... 41 Figure D7: AC Sweep Analysis Rin of Case B ......................................................................... 42 Table D5: Voltage-Shunt Feedback Amplifier Simulation Summary ............................... 43 Table D7: DC Voltage Levels at Transistor Pins for Case A .............................................. 44 Figure D8: Mid-Band Gain for Voltage Shunt Amplifier without Feedback at f = 1KHz .. 45 Figure D9: Oscilloscope Image of the Higher Cut-off Frequency (f = 525KHz) of Voltage Shunt Feedback Amplifier without Feedback .......................................................................... 45 Figure D10: Oscilloscope Image of the Lower Cut-off Frequency (f = 115Hz) of Voltage Shunt Feedback Amplifier without Feedback .......................................................................... 46
Experiment 2 Group 5 Page 3 Table D8: AC Frequency Response of Voltage Shunt Feedback Amplifier without Feedback .................................................................................................................................. 47 Figure D11: Excel Graph of AC Frequency Response of Voltage-Shunt Feedback Amplifier without Feedback ........................................................................................................................ 47 Table D9: Measured Component Values for Voltage-Shunt Amplifier with Feedback .. 48 Table D10: DC Voltage Levels at Transistor Pins for Case B ............................................ 48 Figure D12: Mid-Band Gain for Voltage Shunt Amplifier with Feedback at f = 1KHz ...... 48 Figure D14: Oscilloscope Image of the Lower Cutoff Frequency (f = 475Hz) of Voltage Shunt Feedback Amplifier with Feedback ............................................................................... 49 Table D11: AC Frequency Response of Voltage-Shunt Feedback Amplifier with Feedback .................................................................................................................................. 50 Figure D15: Excel Graph of AC Frequency Response of Voltage-Shunt Feedback Amplifier with Feedback .............................................................................................................................. 50 Table D12: Measured Voltage-Shunt Feedback Amplifier Summary ............................... 51 Figure D16: Image of PCB; Voltage-Shunt Feedback Amplifier without Feedback (Case A) ....................................................................................................................................................... 52 Figure D17: Image of PCB; Voltage-Shunt Feedback Amplifier with Feedback (Case B) . 53 Figure D18: Image of Breadboard; Voltage-Shunt Feedback Amplifier without Feedback (Case A) ........................................................................................................................................ 54 Figure D19: Image of Breadboard; Voltage-Shunt Feedback Amplifier with Feedback (Case B) ........................................................................................................................................ 55 Part E: Series-Shunt Feedback Amplifier ................................................................................ 57 ADS Simulations ...................................................................................................................... 57 Case (a): PCB Shunt feedback Amplifier without Feedback .................................................... 64 Case (b): PCB Shunt feedback Amplifier with Feedback ........................................................ 70 Conclusion ................................................................................................................................ 75 Lab Report Questions ................................................................................................................. 76 Acknowledgements ..................................................................................................................... 79
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Experiment 2 Group 5 Page 4 ABSTRACT Feedback in electronics can affect the overall device in a lot of ways. Some parameters that it can affect are input/output impedances, current and voltage gain, and how wide the bandwidth of the mid-band gain the device has. There are two different types of feedback; positive and negative feedback. A circuit with negative feedback has its pros and cons. The benefit of having negative feedback is that it increases the bandwidth. But the drawback is that it decreases input/output impedance and gain. With positive feedback, it can affect the circuit in an undesirable way and possibly cause oscillations. In this experiment, we will observe different negative feedback amplifier and see how having a negative feedback affects the circuit compared to not having a feedback at all. We will perform frequency, bias point stability, and record voltage gain when comparing an amplifier with negative feedback to an amplifier without feedback. Throughout the experiment, we need to make sure that the input and output are not close to being in phase since that concludes the circuit is very unstable and will oscillate. EQUIPMENT AND TOOLS Equipment and Tools are provided by Florida Atlantic University and we give our thanks to them for providing the tools we need to conduct this experiment. ● Dual Display Digital Multimeter - GW INSTEK GDM-8245 ● Function Generator - GW INSTEK GFG-3015 ● 3 Channel DC Power Supply - GW INSTEK GPS-3303 ● Two Channel Digital Storage Oscilloscope - Textronix TDS 2012C ● BNC to Alligator Clips Cable ● Voltmeter Probe ● Advanced Design System (ADS) ● BNC Cables ● Banana to Pin Cables COMPONENTS ● ¼ W +/-1% Tolerance Resistors with Metal Film ● ¼ W Capacitors ● Q2N3904 NPN BJT ● Electronic Breadboard ● PCBs fabricated by JLCPCB ● Cables
Experiment 2 Group 5 Page 5 Part A: Voltage-Series Negative Feedback Amplifier Introduction Here we have the Voltage-Series Negative Feedback Amplifier, as illustrated in Figure A1. This circuit has a lot of gain and is able to amplify a very small signal in the millivolts to desired volt ranges. Since the design of this circuit is to provide a large gain of around 65 dB (we will talk more about it in later sections), a voltage divider network was added to the input of the circuit to attenuate the signal. Following the input signal we have our first stage transistor amplifier with a diode attached to the base for thermal coupling and a voltage divider network for forward biasing the transistor. The transistor have a few capacitors and resistors tied to the emitter for stability and a resistor at the collector for current limiting. The output of the amplified signal through the first stage is fed through a capacitor and into the base of the second stage transistor amplifier. The output of the second stage amplifier through a capacitor is fed back to the first stage transistor resistor and capacitor split network to serve as our negative feedback line. Capacitors are added to our power supply to stabilize from any voltage ripple. This circuit is prone to oscillating therefore it is imperative to take care when building this circuit. Figure A1: Voltage- series negative feedback amplifier, with Rf (R6) of 10MΩ (Represents no feedback case).
Experiment 2 Group 5 Page 6 Objective For this experiment we are looking to get a better understanding of the voltage-series negative feedback amplifier. To do so, we will first build the filter in the ADS, Figure A1 illustrate as such with the given component values. Then we will run the simulation to plot the gain at the output of the filter, this will enable us to determine the mid band gain, the lower and upper pass-band frequencies, and more analysis. We do this for both the non-feedback and feedback system. After completing our simulations and getting our measurements we will move onto building our design on a breadboard and continue with recording our data. At this point we will be able to compare our simulation results with our built experimental data. As mentioned before this design is prone for oscillation, therefore there was several factors that had to be taking into when building the circuit on the breadboard. Simulation For our simulation we built the design from Figure A1 into the ADS software. The 10 MΩ resistor line in our circuit is served to provide our non - feedback system. Running our simulation, plotting both the input impedance of our circuit and the frequency response of the output of the circuit we get the graphs shown in Figure A2. For the frequency response, you can see that the marker m1 set at 4.185 kHz gives us the maximum gain for our circuit. While the m2 and m3 gives us the low band-pass and high band-pass frequencies at 60.564 kHz and 60.542 kHz, respectively. The input impedance plotted from the input of the first stage transistor input, it can be seen that when the frequency increases pass the mid band region the input impedance drops rapidly.
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Experiment 2 Group 5 Page 7 Figure A2: Frequency Response and Input Impedance of Voltage-Series Negative Feedback amplifier design (Represents no feedback case). Figure A3: Voltage-series negative feedback amplifier, with feedback. We continue to our next simulation where we swap the 10MΩ resistor with a 4.7 kΩ resistor. This serves to give us our feedback system. The design is shown in Figure A3. Graphing the frequency response and input impedance of this circuit we get what is shown in Figure A4. From the frequency response we can see that the graph widen quite a bit given us a low band-pass frequency at approximately 3 Hz and a high band-pass frequency at approximately 10.5 MHz. It also lowered our mid band gain significantly to approximately 6 dB. The two peaks in our graph shows where two points in which the circuit may oscillate. The input impedance graph shows dips at two possible oscillation points and remain relatively constant within the mid band region.
Experiment 2 Group 5 Page 8 Figure A4: Frequency Response and Input Impedance of Voltage-Series Negative Feedback amplifier design (Represents no feedback case). Without Feedback With Feedback Input Impedance at 1kHz 15kΩ 500kΩ Gain (Mid-Band) in dB 63.6 dB 6 dB Lower cut-off frequency(fL) 60 Hz 3 Hz Higher cut-off frequency(fH) 280.8 kHz 10 MHz Bandwidth(fH-fL) 280.7 kHz 10 MHz Gain-Bandwidth Product 17.8M 60M Figure A5: Data of Voltage-Series negative feedback amplifier design. Experiment After our simulation, we then built our circuit on the breadboard. Considering that there are many factors that can cause oscillation to this design performance, we shorten the leads on the parts and put them relatively close to one another. Also taking into consideration that there can be external devices operating next to the circuit that can cause interference, we decided to record our data when there was no activities in the laboratory but our own. Figure A5 shows our circuit’s breadboard and it connected to our oscilloscope. The components of the circuit was measured while building the circuit and this is recorded onto Table A1.
Experiment 2 Group 5 Page 9 Figure A6: Breadboard design of the Voltage-Series negative feedback amplifier (Perfboard version also). BreadBoard Resistor Nominal Value(kΩ) Measured Value(kΩ) R1 2.7 2.695 R2 2.2 2.196 R3 100 100 R4 66 66.03 R5 2.2 2.197 R6 44 44.45 R8 130 129.65 R9 3.3 3.296 R12 0.15 0.1503 R13 180 179.06 R14 20 19.94 Rload 47 46.87 Rf1 10000 9915 Rf2 4.7 4.677 BreadBoard Capacitor Nominal Value(F) Measured Value(F) C2 100u 99.93u C3 100u 99.77u C4 10u 10.16u C5 100u 100.1u
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Experiment 2 Group 5 Page 10 C7 100u 100.9u C9 0.01u 10.46n C10 100u 99.77u Cs 300p 303p Table A1: Resistor and Capacitor values. We begin collecting our input and output data on our breadboard design. This is the non- feedback circuit containing the 10 MΩ resistor. Our results are found in Table A2 below. Figure A7: Oscilloscope reading at 1 kHz Frequency Response of non-feedback circuit.
Experiment 2 Group 5 Page 11 Figure A8: Oscilloscope reading of lower cut-off frequency of the non-feedback circuit. Figure A9: Oscilloscope reading of higher cut-off frequency of the non-feedback circuit. Breadboard Without Feedback Rf = 10MΩ CH1-CH2 Frequency(Hz) Vin(V) Vout(V) Vout/Vin Gain (dB) Phase Shift 10 0.0031 0.64 206.4516 46.29637 -132 12 0.0011 0.296 269.0909 48.59798 -132 14 0.00256 0.808 315.625 49.98343 -117 25 0.0033 1.76 533.3333 54.53997 89.1 75 0.00344 4.52 1313.953 62.3716 52.3 100 0.00344 5.12 1488.372 63.45423 42.3 500 0.00344 6.12 1779.07 65.00386 10.4 800 0.00344 6.24 1813.953 65.17252 4.66 2000 0.00344 6.36 1848.837 65.33797 1.73 5000 0.00344 6.36 1848.837 65.33797 3.77 10000 0.00344 6.36 1848.837 65.33797 7.32 15000 0.0036 6.4 1777.778 64.99755 17.7 20000 0.00368 6.4 1739.13 64.80664 20.5 25000 0.00384 6.4 1666.667 64.43697 25.8 35000 0.004 6.4 1600 64.0824 33.2 45000 0.0045 6.4 1422.222 63.05935 68.1 100000 0.00464 4.32 931.0345 59.37932 64.1 600000 0.0011 0.18 163.6364 44.2776 -132 650000 0.0011 0.18 163.6364 44.2776 -142 1000000 0.0011 0.1 90.90909 39.17215 -131 Table A2: Frequency Response of Voltage-Series negative feedback amplifier (no feedback).
Experiment 2 Group 5 Page 12 Figure A10: Frequency response of non-feedback circuit over a range of frequencies. We continued recording the data for circuit but now with the feedback system by switching the 10 MΩ with the 4.7 kΩ. Our data is found in Table A3. Figure A11: Oscilloscope reading at 1 kHz Frequency Response of non-feedback circuit. 0 10 20 30 40 50 60 70 10 25 500 5000 20000 45000 650000 Gain(dB) Frequency (Hz) Frequency Response without FB
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Experiment 2 Group 5 Page 13 Figure A12: Oscilloscope reading of lower cut-off frequency of the feedback circuit. Figure A13: Oscilloscope reading of higher cut-off frequency of the feedback circuit. Breadboard With Feedback Rf = 4.7kΩ CH1-CH2 Frequency() Vin Vout Vout/Vin Gain Phase Shift 10 0.004 0.04 10 20 -77.4 12 0.004 0.046 11.5 21.21396 62 14 0.001 0.076 76 37.61627 -34.2 25 0.00514 0.126 24.51362 27.78815 -50.7 75 0.0044 0.127 28.86364 29.20702 19.3 100 0.0044 0.125 28.40909 29.06915 15.4 500 0.0048 0.128 26.66667 28.51937 6.77 800 0.0042 0.127 30.2381 29.61109 1.73 2000 0.0044 0.127 28.86364 29.20702 -5.76 5000 0.0044 0.128 29.09091 29.27515 -3.24 10000 0.0044 0.126 28.63636 29.13836 -1.43 15000 0.0048 0.127 26.45833 28.45125 -7.57 20000 0.0044 0.127 28.86364 29.20702 -5.18 25000 0.0044 0.124 28.18182 28.99938 -5.75 35000 0.0042 0.122 29.04762 29.26221 -7.78 45000 0.0042 0.119 28.33333 29.04595 -3.89 100000 0.0036 0.0968 26.88889 28.59146 -7.56 600000 0.001 0.03 30 29.54243 -177 650000 0.001 0.03 30 29.54243 -166 1000000 0.00088 0.023 26.13636 28.3449 -5.77 Table A3: Frequency Response of Voltage-Series negative feedback amplifier (with feedback).
Experiment 2 Group 5 Page 14 Figure A14: Frequency response of feedback circuit over a range of frequencies. Conclusion There are noticeable differences from our ADS simulation and our recorded data from our breadboard design. The ADS simulation frequency response is relatively smooth for the non-feedback design and had two peaks for the feedback design. We noticed in the ADS simulation that when we added feedback the gain reduced by a significant amount and the bandwidth widen also by a large amount. Our breadboard design data was of course not exactly of that from our ADS simulation. This can be due to slight noise and of course our circuit components are not that of exact value to the ADS component values. Both the simulation and experimental design data showed that when a feedback system is added, the bandwidth does widen significantly and the gain is lowered. While the non- feedback circuit retain a mid-band gain of around 63-65 dB in both the ADS simulation and the breadboard recorded data. The mid-band gain in our feedback circuit varies significantly, where the ADS gain is about 6 dB the breadboard design gain is around 29 dB. Part C: Current-Shunt Feedback Amplifier Part 1 – Simulations of Circuit Schematics 0 5 10 15 20 25 30 35 40 10 25 500 5000 20000 45000 650000 Gain(dB) Frequency (Hz) Frequency Response with FB
Experiment 2 Group 5 Page 15 Figure 1 – Schematics of Current-Shunt FB Amplifier (Rf = 10 Mega Ohm) In this experiment we were given a reference design for the Current-Shunt Feedback Amplifier. We began by capturing this schematic into the ADS schematic capturing software. After capturing the schematic (using the 10 MOhm value for Rf), I ran the AC simulation to populate the DC Bias measurements onto the schematic. Quickly looking at the DC bias voltages points out that both transistors are on in the active forward mode because for Q1 and Q2, 𝑉 ? > 𝑉 ? > 𝑉 𝐸 .
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Experiment 2 Group 5 Page 16 Figure 2 – AC Sweep Simulation Current-Shunt FB Amplifier (Rf = 10 Mega Ohm) After capturing the circuit schematic and reviewing the DC Bias voltages, I continued on with the AC Sweep simulation and created a plot of the Gain. ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) I found the flat area of the curve to indicate a mid-band gain of ~36.8dB. By moving the markers, I was able to locate the lower and upper cutoff frequencies at 8.8 Hz, and 3.38 MHz respectively. The lower cutoff frequency is negligible when calculating the bandwidth due to the large difference in order of magnitude. The bandwidth of this circuit is approximately the high cutoff frequency, 3.38Mhz.
Experiment 2 Group 5 Page 17 Figure 3 – Input Impedance of Current-Shunt FB Amplifier (Rf = 10 Mega Ohm) Continuing with the analysis, I created a plot showing the input impedance in relation to frequency. The input impedance is caused by the input capacitor Cin. 𝑅 𝑖? = (𝑉 𝑖? − 𝑉 𝑏 ) ? 𝑖? Here we can see that as the input frequency approaches 0Hz or DC voltage, the input impedance approaches infinity. I added marker m1 to show the input impedance at the lower cutoff frequency.
Experiment 2 Group 5 Page 18 After completing the first AC Sweep analysis it is time to change the feedback resistor from 10 Mega Ohms to 2.4 kOhms. Figure 4 – Schematics of Current-Shunt FB Amplifier (Rf = 2.4 kOhm) Here we have the original schematics from Figure 1 modified with a 2.4k feedback resistor. After updating the schematic (using the 2.4 kOhm value for Rf), I ran the AC simulation again to populate the DC Bias measurements onto the schematic. Still, the DC bias voltages reveal that both transistors are on in the active forward mode because for both Q1 and Q2, 𝑉 ? > 𝑉 ? > 𝑉 𝐸 .
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Experiment 2 Group 5 Page 19 Figure 5 – AC Sweep Simulation Current-Shunt FB Amplifier (Rf = 2.4 kOhm) After updating and reviewing the circuit schematic, I continued on with the second AC Sweep simulation and created a plot of the Gain. ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) I found the flat area of the curve to indicate a mid-band gain of ~32.9dB. By moving the markers, I was able to locate the lower and upper cutoff frequencies at 163.4 Hz, and 3.659 MHz respectively. Again, the lower cutoff frequency is negligible when calculating the bandwidth due to the large difference in order of magnitude. The bandwidth of this circuit is approximately the high cutoff frequency, 3.659Mhz.
Experiment 2 Group 5 Page 20 Figure 6 – Input Impedance of Current-Shunt FB Amplifier (Rf = 2.4 kOhm) Next, I created a plot showing the input impedance in relation to frequency. The input impedance is caused by the input capacitor Cin. 𝑅 𝑖? = (𝑉 𝑖? − 𝑉 𝑏 ) ? 𝑖? Here we can see that as the input frequency approaches 0Hz or DC voltage, the input impedance approaches infinity. I added marker m1 to show the input impedance at the lower cutoff frequency. Without Feedback With Feedback Input Impedence at 1kHz 0 Ohms 0 Ohms Gain (Mid-Band) in dB 36.877 dB 32.935 dB Lower cut-off frequency (𝑓 𝐿 ) 8.844 Hz 163.4 Hz Higher cut-off frequency (𝑓 ? ) 3.388 MHz 3.659 MHz Bandwidth (𝑓 ? − 𝑓 𝐿 ) ~3.388 MHz ~ 3.659 MHz Gain-Bandwidth Product 1.25E8 1.21E8 Figure 7 – Table of Simulated Values Summary The table in figure 7 summarizes the values encountered during the AC Sweep simulations.
Experiment 2 Group 5 Page 21 Part 2 – Measurements of Circuit Without Feedback After simulating the design, I decided to have PCB’s made according to the schematics tested. KiCAD was used to do the PCB Layout, and the gerber files were then sent out to a vendor. Figure 8 – The Schematic Output from the PCB Design Software Figure 8 shows the schematic from the PCB design software, the locations of the test points, and also the reference names used for each component. Figure 9 – Printed Circuit Board Figure 9 shows the received board before assembly.
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Experiment 2 Group 5 Page 22 Reference Nominal Value Measured Value R1 82k 81.9k R2 47k 46.71k R3 33k 32.91k R4 100 100.9 R5 34k 33.96k R6 47k 46.96k R7 55k 54.69k R8 10M 10.02M R9 14k 13.98k R10 25k 24.83k C1 10uF 9.8uF C2 100uF 96uF C3 10uF 10.6uF C4 10uF 9.03uF Figure 9 – Table of Measured Values Figure 9 shows the values of the components used to construct the current-shunt feedback amplifier. After assembling the circuit, I continued on to take the measurements over frequency.
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Experiment 2 Group 5 Page 23 After assembling the circuit, I connected the bench PSU, the oscilloscope, and the function generator to the circuit. I configured the function generator to a frequency of 1 kHz with a sine wave function. I set the offset to 0VDC, and configured the amplitude of the function generator to 20mV. Figure 10 – Scope Image of 1kHz input In Figure 10, we can see that the input amplitude is 48mV p-p, and the output is 1.18V p-p. The mid band gain can be calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 1.18 0.048 ) = 27.669 Next I began to sweep the frequency input until I noticed a 3dB decrease in gain. Assuming that the input voltage stays constant, the expected output voltage for the upper and lower cutoff frequencies would be: 0.048 × 10 ( 27.669𝑑?−3𝑑? 20 ) = 𝑉 ??? = 0.8354𝑉
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Experiment 2 Group 5 Page 24 Figure 11 – Scope Image of Lower Cutoff Frequency In figure 11, we can see that at 80 Hz, we have an input voltage of 48.8mV p-p, and an output voltage of 0.832V p-p. The gain is then calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 0.832 0.0488 ) = 24.634?? Next I continued to sweep above 1kHz to locate the upper cutoff frequency.
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Experiment 2 Group 5 Page 25 Figure 12 – Scope Image of Upper Cutoff Frequency In figure 12, we can see that at 63.3 kHz, we have an input voltage of 48mV p-p, and an output voltage of 0.824V p-p. The gain is then calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 0.824 0.048 ) = 24.694?? Armed with the upper and lower cutoff frequencies, we are able to calculate the bandwidth as: ?𝑎??𝑤𝑖??ℎ = 𝑓 ? − 𝑓 𝐿 = 63300 ?𝑧 − 80 ?𝑧 = 63220 ?𝑧 We can then find the Gain Bandwidth product as: ?𝑎𝑖? − ?𝑎??𝑤𝑖??ℎ ?𝑟????? = ?𝑎𝑖? × ?𝑎??𝑤𝑖??ℎ = 27.669 ?? × 63220 ?𝑧 = 1.75?6
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Experiment 2 Group 5 Page 26 With Feedback Rf = 1MΩ and Cf = 10μF CH1 to CH2 Frequency (Hz) Vin (V p- p) Vout (V p- p) Vout/Vin Gain (dB) Phase Shift (Degrees) 10 0.0520 0.360 6.923 16.806 139.30 12 0.0448 0.220 4.911 13.823 171.20 14 0.0464 0.280 6.034 15.613 95.08 25 0.0496 0.400 8.065 18.132 -67.24 75 0.0512 0.840 16.406 24.300 -120.20 100 0.0512 0.980 19.141 25.639 -111.10 500 0.0520 1.160 22.308 26.969 -29.93 800 0.0520 1.180 22.692 27.118 -29.42 2000 0.0520 1.200 23.077 27.264 -50.50 5000 0.0528 1.180 22.348 26.985 60.78 10000 0.0512 1.160 22.656 27.104 177.10 15000 0.0528 1.140 21.591 26.685 10.74 20000 0.0520 1.140 21.923 26.818 -50.94 25000 0.0512 1.100 21.484 26.642 -74.22 35000 0.0488 1.060 21.721 26.738 -143.50 45000 0.0496 0.980 19.758 25.915 -142.20 100000 0.0496 0.664 13.387 22.534 -146.20 600000 0.0440 0.188 4.273 12.614 -127.30 650000 0.0448 0.180 4.018 12.080 -119.90 10000000 0.0456 0.140 3.070 9.743 -119.00 Figure 13 – Frequency Response and Phase Shift Measurements Figure 13 is a table of measured frequencies to assess the frequency response and phase shift of the amplifier. After measuring each frequency and documenting the results, I then plotted the data into a scatter plot.
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Experiment 2 Group 5 Page 27 Figure 14 – Plotted Measured Data from Figure 14 Figure 14 shows the measured gain in dB plotted over frequency. Figure 15 – Assembled PCB Figure 15 shows the PCB assembled with the components from the table in figure 9. 0.000 5.000 10.000 15.000 20.000 25.000 30.000 1 10 100 1000 10000 100000 1000000 10000000 Gain (dB) Without Feedback
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Experiment 2 Group 5 Page 28 Part 3 – Measurements of Circuit with Feedback After completing the first section, I unsoldered the feedback resistor (R8), and replaced it with a 4.7 kOhm resistor. I then unsoldered the 1n4148 diodes (D1, D2), and replaced them with red LEDs. Figure 16 – The Schematic Output from the PCB Design Software The above schematic is as it was entered into the PCB design software, note that D1 and D2 have been replaced with RED LEDs, and that R8 is now 4.7 kOhm instead of 10 MEG Ohm. Reference Nominal Value Measured Value R1 82k 81.9k R2 47k 46.71k R3 33k 32.91k R4 100 100.9 R5 34k 33.96k R6 47k 46.96k R7 55k 54.69k R8 4.7k 4.73k R9 14k 13.98k R10 25k 24.83k C1 10uF 9.8uF C2 100uF 96uF C3 10uF 10.6uF C4 10uF 9.03uF Figure 17 – Table of Measured Values
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Experiment 2 Group 5 Page 29 Figure 17 shows the values of the components used to construct the current-shunt feedback amplifier after modifications. After modifying the circuit, I continued to take the measurements over frequency. I configured the function generator to a frequency of 1 kHz with a sine wave function. I set the offset to 0VDC, and configured the amplitude of the function generator to 20mV. Figure 18 – Scope Image of 1kHz input In Figure 10, we can see that the input amplitude is 48.8mV p-p, and the output is 0.114V p-p. The mid band gain can be calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 0.114 0.0488 ) = 7.370?? Next I began to sweep the frequency input until I noticed a 3dB decrease in gain. Assuming that the input voltage stays constant, the expected output voltage for the upper and lower cutoff frequencies would be: 0.0488 × 10 ( 7.37𝑑?−3𝑑? 20 ) = 𝑉 ??? = 0.0807𝑉
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Experiment 2 Group 5 Page 30 Figure 19 – Scope Image of Lower Cutoff Frequency In figure 19, we can see that at 46 Hz, we have an input voltage of 50.4mV p-p, and an output voltage of 0.082V p-p. The gain is then calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 0.082 0.0504 ) = 4.227?? Next I continued to sweep above 1kHz to locate the upper cutoff frequency.
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Experiment 2 Group 5 Page 31 Figure 20 – Scope Image of Upper Cutoff Frequency In figure 30, we can see that at 955 kHz, we have an input voltage of 43.2mV p-p, and an output voltage of 0.072V p-p. The gain is then calculated as: ?𝑎𝑖? = 20 × 𝐿?? 10 ( 𝑉 ??? 𝑉 ?? ) = 20 × 𝐿?? 10 ( 0.072 0.0432 ) = 4.436?? Armed with the upper and lower cutoff frequencies, we are able to calculate the bandwidth as: ?𝑎??𝑤𝑖??ℎ = 𝑓 ? − 𝑓 𝐿 = 955000 − 46 ≅ 955 𝑘?𝑧 We can then find the Gain Bandwidth product as: ?𝑎𝑖? − ?𝑎??𝑤𝑖??ℎ ?𝑟????? = ?𝑎𝑖? × ?𝑎??𝑤𝑖??ℎ = 7.370 ?? × 955 𝑘?𝑧 ≅ 7.04?6
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Experiment 2 Group 5 Page 32 With Feedback Rf = 4.7kΩ and Cf = 10μF CH1 to CH2 Frequency (Hz) Vin (V p- p) Vout (V p- p) Vout/Vin Gain (dB) Phase Shift (Degrees) 10 0.0424 0.033 0.774 -2.230 108.30 12 0.0440 0.040 0.909 -0.828 110.50 14 0.0448 0.043 0.964 -0.316 105.00 25 0.0472 0.056 1.186 1.485 113.10 75 0.0540 0.098 1.815 5.177 32.57 100 0.0472 0.106 2.246 7.027 29.64 500 0.0472 0.114 2.415 7.659 -58.13 800 0.0472 0.114 2.415 7.659 -80.61 2000 0.0480 0.116 2.417 7.664 -19.05 5000 0.0464 0.114 2.457 7.808 -170.40 10000 0.0464 0.116 2.500 7.959 -171.80 15000 0.0464 0.116 2.500 7.959 -169.40 20000 0.0472 0.116 2.458 7.810 -169.00 25000 0.0464 0.114 2.457 7.808 -111.90 35000 0.0464 0.114 2.457 7.808 157.40 45000 0.0464 0.114 2.457 7.808 158.40 100000 0.0448 0.114 2.545 8.113 -170.90 600000 0.0432 0.090 2.083 6.375 -144.30 650000 0.0432 0.090 2.083 6.375 -144.30 10000000 0.0440 0.080 1.818 5.193 -137.20 Figure 21 – Frequency Response and Phase Shift Measurements Figure 21 is a table of measured frequencies to assess the frequency response and phase shift of the amplifier. After measuring each frequency and documenting the results, I then plotted the data into a scatter plot.
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Experiment 2 Group 5 Page 33 Figure 22 – Plotted Measured Data from Figure 14 Figure 22 shows the measured gain in dB plotted over frequency. -4.000 -2.000 0.000 2.000 4.000 6.000 8.000 10.000 1 10 100 1000 10000 100000 1000000 10000000 Gain (dB) With Feedback
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Experiment 2 Group 5 Page 34 Figure 23 – Assembled PCB Figure 23 shows the PCB assembled with the modified components from the table in figure 17. We calculate the input impedance by measuring the voltage drop across the input capacitor and dividing by the current of the input signal. Calculating input impedance without feedback: 14.32?𝑉 − 14.31?𝑉 1.12𝜇? = 8.93Ω Calculating input impedance with feedback: 13.8?𝑉 − 13.78?𝑉 5.65𝜇? = 3.53Ω Without Feedback With Feedback Input Impedence at 1kHz 8.93 Ohm 3.53 Ohm Gain (Mid-Band) in dB 27.669 dB 7.370 dB Lower cut-off frequency (𝑓 𝐿 ) 80 Hz 46 Hz Higher cut-off frequency (𝑓 ? ) 63.3 kHz 955 kHz Bandwidth (𝑓 ? − 𝑓 𝐿 ) 63220 Hz 955 kHz Gain-Bandwidth Product 1.75E6 7.04E6 Figure 24 – Table of Simulated Values Summary The table in figure 24 summarizes the values encountered during the measurement process of the assembled PCB’s with and without feedback.
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Experiment 2 Group 5 Page 35 Part: D Voltage Shunt Feedback Amplifier Introduction Figure D1: AC Sweep Analysis of Voltage-Shunt Amplifier without Feedback Schematic Above in Figure D1 is a schematic of the Voltage-Shunt Amplifier without Feedback using ADS. As we can see in the schematic that in the feedback portion there is a drastically large resistor that is equal to 10MΩ. With such large resistance in the feedback, this limits the current going back into the base of the BJT. Therefore, it acts is if there is no feedback at all. We will test the Voltage-Shunt Amplifier with and without feedback in this portion of the experiment. What should we expect between the amplifier with feedback and the amplifier without feedback? The case without feedback should have a larger gain compared to the amplifier with feedback. Also, since this is a voltage-shunt amplifier, Rin and non-linearity should decrease when comparing the amplifier without feedback and the amplifier with feedback. Interestingly, we should also see an increase in bandwidth increase from the amplifier without the feedback to the amplifier with the feedback. Before we implement the circuit, we must test our circuit using software. We will be using ADS to analyze both cases of the Voltage-Shunt amplifier. Using ADS, we will look at an AC Sweep Response of the input resistance of the device and the gain bandwidth. We shall repeat to analyze both cases.
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Experiment 2 Group 5 Page 36 Proce dure and Simulations Before we start designing our schematic on ADS, we must first choose are values for all the components. Luckily, we are given our component values. Remember, there are two cases for this experiment, so we will have two separate tables to represent the values used for both cases. R2 & R3 → Base Resistors R4 → Feedback Resistor C1 → Feedback Capacitor R5 → Collector Resistor R6 → Emitter Resistor C2 → Emitter Capacitor R7 → Load Resistor C3 → Load Capacitor C4 → Input Capacitor Table D1: Simulation Component Values for Voltage-Shunt Amplifier without Feedback R2 R3 R4 R5 R6 R7 C1 C2 C3 C4 68K Ω 15K Ω 10M Ω 4.7K Ω 1.2K Ω 10K Ω 1nF 100uF 10uF 10uF Table D2: Simulation Component Values for Voltage-Shunt Amplifier with Feedback R2 R3 R4 R5 R6 R7 C1 C2 C3 C4 68K Ω 15K Ω 4.7K Ω 4.7K Ω 1.2K Ω 10K Ω 22uF 100uF 10uF 10uF The tables shown above are the values we will use to simulate our Voltage-Shunt Amplifier. The list above the tables shows the resistor names that correlates with the components in the Voltage-Shunt Amplifier. Now we can create our schematics and run an AC Sweep Analysis for both cases. Let’s have Case A be the Voltage -Shunt Amplifier without Feedback and Case B be the Voltage-Shunt Amplifier with Feedback.
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Experiment 2 Group 5 Page 37 Case A: Voltage-Shunt Amplifier without Feedback Figure D2: AC Sweep Analysis of Case A Schematic Table D3: Active Mode Table for AC Sweet Analysis of Case A BJT: Base Voltage: Junction: Bias Active mode? Q1 VB = 2.07V VC = 6.57V Reverse Yes Q1 VB = 2.07V VE = 1.4V Forward Yes Shown in Figure D2 is our schematic in ADS of the Voltage-Shunt Amplifier without Feedback. We can see in Table D3 that the BJT is in fact in active mode. We can now move on and simulate our circuit and see our bandwidth and input resistance of the circuit. We will conduct an AC Response from 1Hz to 100MHz.
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Experiment 2 Group 5 Page 38 Figure D3: AC Analysis Gain in dB of Case A In Figure D3 shows the bell-shape gain of the Voltage-Shunt Amplifier without Feedback. Looking at the figure we see that the lower cutoff frequency occurs at 72Hz and the higher cutoff frequency occurs at 18.27MHz. Also, at 1KHz, we have a mid-band gain of 42.56dB.
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Experiment 2 Group 5 Page 39 Figure D4: AC Sweep Analysis Rin of Case A In Figure D4, we see that Rin is 2.715KΩ at 1KHz. This makes sense since we have a large 10MΩ resistor value as our feedback resistor. Therefore, we should see a less input resistance in Case B (with feedback) of the Voltage-Shunt Amplifier.
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Experiment 2 Group 5 Page 40 Case B: Voltage- Shunt Amplifier with Feedback Figure D5: AC Sweep Analysis of Voltage-Shunt Amplifier with Feedback Schematic Table D4: Active Mode Table for AC Sweet Analysis of Case B BJT: Base Voltage: Junction: Bias Active mode? Q1 VB = 2.07V VC = 6.57V Reverse Yes Q1 VB = 2.07V VE = 1.4V Forward Yes Similar to Case A, we see in Figure D5 that the amplifier has different values for the feedback resistor and feedback capacitor. Also shown in Table D4 above, we have a table showing the BJT in the ADS schematic is in fact in active mode. Moving forward, let’s simulate our schematic and prove our theory comparing the graphs of Case A to Case B.
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Experiment 2 Group 5 Page 41 Figure D6: AC Sweep Analysis Gain in dB for Case B In Figure D6 shows the bell-shape gain of the Voltage-Shunt Amplifier with Feedback. Looking at the figure we see that the lower cutoff frequency occurs at 316Hz and the higher cutoff frequency occurs at 32.86MHz. Also, at 1KHz, we have a mid-band gain of 37.69dB.
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Experiment 2 Group 5 Page 42 Figure D7: AC Sweep Analysis Rin of Case B In Figure D4, we see that Rin is 56.121Ω at 1KHz. As predicted, the input impedance is way smaller in Case B (with feedback) compared to Case A (without feedback).
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Experiment 2 Group 5 Page 43 Table D5: Voltage-Shunt Feedback Amplifier Simulation Summary Without Feedback With Feedback Input Impedance at 1KHz 2.715K Ω 56.12Ω Gain (Mid-Band) in dB 42.56dB 37.69dB Lower cut-off frequency ( 𝒇 𝑳 ) 72Hz 316Hz Higher cut-off frequency ( 𝒇 𝑯 ) 18.27MHz 32.86MHz Bandwidth ( 𝒇 𝑯 − 𝒇 𝑳 ) 18.27MHz 32.86MHz Gain-Bandwidth Product 7.78 × 10 8 1.24 × 10 9 Comparing the simulation results from Case A to Case B shown in Table D5, we can see that Case B (with feedback) has a larger bandwidth than Case A (without feedback. Also, the gain decreased from Case A to Case B proving that having feedback does affect our gain negatively. Input resistance also decreased from Case A to Case B, which makes sense since we have a smaller feedback resistor within Case B compared to the much larger feedback resistor in Case A. Now let’s move on and create our circuit.
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Experiment 2 Group 5 Page 44 Experimental Results The Voltage-Shunt Feedback Amplifier needed to be implemented on a PCB to achieve “cleaner” results. Thus, this amplifier was made on a breadboard as a prototype and then fully conducted on a PCB for both cases. Also, to minimize any parasitic interference we decided to use Surface Mount Devices instead of Through-Hole Devices. Pictures of the 4 circuits will be provided at the end of the experimental results. Therefore, all the measured component values are the values used for the PCB only. Before we test both cases of the Voltage-Shunt Feedback Amplifier, we must measure components using a digital multimeter (GW INSTEK GDM-8245). We will start with Case (without Feedback) first and then move on to Case B (with Feedback). Case A: Voltage-Shunt Feedback Amplifier without Feedback Table D6: Measured Component Values for Voltage-Shunt Amplifier without Feedback R2 R3 R4 R5 R6 R7 C1 C2 C3 C4 67.88K Ω 14.99 KΩ 10.03 MΩ 4.691 KΩ 1.198 KΩ 9.989 KΩ 0.956nF 104.1uF 9.76uF 10.23uF Now let’s measure BJT pin voltages by using a digital multimeter (GW INSTEK GDM- 8245) and setting the power supply (GW INSTEK GPS-3303) to 12V and compare them to our simulated results. Table D7: DC Voltage Levels at Transistor Pins for Case A Variable DC Voltage Simulated Operating Point Value Measured Operating Point Value V(Base) 2.07V 2.13V V(Collector) 6.57V 6.37V V(Emitter) 1.40V 1.47V Observing Table D7, we can see that the voltages at the transistor pins are relatively close from the simulation to the actual circuit (measured). Now we can input a sine wave, using a function generator (GW INSTEK GFG-3015), into our circuit and see how it behaves.
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Experiment 2 Group 5 Page 45 Figure D8: Mid-Band Gain for Voltage Shunt Amplifier without Feedback at f = 1KHz In Figure D8, we see the mid-band gain for Case A (without feedback) at a frequency of 1KHz. We see that it has a gain of 140.82 and a gain in dB of 42.97dB which is quite close to the simulated Case A mid-band gain of 42.56dB. Figure D9: Oscilloscope Image of the Higher Cut-off Frequency (f = 525KHz) of Voltage Shunt Feedback Amplifier without Feedback
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Experiment 2 Group 5 Page 46 Figure D10: Oscilloscope Image of the Lower Cut-off Frequency (f = 115Hz) of Voltage Shunt Feedback Amplifier without Feedback In Figure D9 and Figure D10, we see that the Lower Cut-off Frequency occurs at 115Hz and the Higher Cut-Off Frequency occurs at 525KHz. The Lower Cut-off Frequency is relatively close to the simulated results Lower Cut-off Frequency of 72Hz. But, with comparing the Higher Cut-off Frequency measured results and the simulated results, we see a drastic gap between the two. Recall that our simulated Higher Cut-off Frequency for Case A is 18.27MHz. This drastic difference could be due to several factors that we will discuss in the conclusion.
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Experiment 2 Group 5 Page 47 Table D8: AC Frequency Response of Voltage Shunt Feedback Amplifier without Feedback Frequency(Hz) Vin(Vp-p) Vout(Vp-p) Vout/Vin Gain (dB) Phase Shift 10 8mV 42mV 5.25 14.4 ? 12 10mV 176mV 17.6 24.91 ? 14 18mV 312mV 16.25 24.22 89° 25 19.2mV 584mV 30.42 29.66 99° 75 20mV 1.54V 77 37.73 120° 100 20mV 1.84V 92 39.28 126° 500 19.6mV 2.72V 138.78 42.85 158° 800 19.6mV 2.72V 138.78 42.85 163° 2000 20mV 2.80V 140 42.92 168° 5000 20mV 2.80V 140 42.92 171° 10000 20mV 2.84V 142 43.05 172° 15000 20mV 2.84V 142 43.05 172° 20000 20mV 2.84V 142 43.05 174° 25000 20mV 2.84V 142 43.05 173° 35000 20mV 2.80V 140 42.92 176° 45000 20mV 2.80V 140 42.92 176° 100000 20mV 2.76V 138 42.80 179° 600000 20mV 1.88V 94 39.46 138° 650000 20mV 1.76V 88 38.89 -135° 1000000 19.6mV 1.32V 67.35 36.57 -120° Figure D11: Excel Graph of AC Frequency Response of Voltage-Shunt Feedback Amplifier without Feedback 0 5 10 15 20 25 30 35 40 45 50 Gain (dB) Frequency (Hz) AC Frequency Response of Voltage-Shunt Feedback Amplifier without Feedback
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Experiment 2 Group 5 Page 48 As we view Table D8, we can see that the Cut-off Frequencies are confirmed with this table of measured gains at different frequencies. Also, with Figure D11, the excel graph gives us a similar shape like we had in our AC Sweep Analysis in ADS for our Voltage-Shunt Feedback Amplifier without Feedback. Case B: Voltage-Shunt Feedback Amplifier with Feedback Before we conduct our circuit for Case B, let’s measure our components and transistor pins. Table D9: Measured Component Values for Voltage-Shunt Amplifier with Feedback R2 R3 R4 R5 R6 R7 C1 C2 C3 C4 68.07 KΩ 14.93 KΩ 4.692K Ω 4.697 KΩ 1.196 KΩ 10.02 KΩ 1.036nF 95.1uF 10.44uF 9.77uF Table D10: DC Voltage Levels at Transistor Pins for Case B Variable DC Voltage Simulated Operating Point Value Measured Operating Point Value V(Base) 2.07V 2.09V V(Collector) 6.57V 6.60V V(Emitter) 1.40V 1.41V Based on Table D10, we were able to achieve a small gap between the simulated voltage and measure voltage at the transistor pins. Now we have our respective voltages and measured components for Case B, l et’s now conduct Case B and see if it matches our simulated results. Figure D12: Mid-Band Gain for Voltage Shunt Amplifier with Feedback at f = 1KHz
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Experiment 2 Group 5 Page 49 Analyzing the oscilloscope image in Figure D12, we can see that the mid-band gain of the Voltage-Shunt Feedback Amplifier with Feedback achieves a gain of 71.43 (or 37.08dB) at a frequency of 1KHz. This is relatively close to the mid-band gain we had in the simulate results of 37.69dB. Figure D 13: Oscilloscope Image of the Higher Cutoff Frequency (f = 815KHz) of Voltage Shunt Feedback Amplifier with Feedback Figure D14: Oscilloscope Image of the Lower Cutoff Frequency (f = 475Hz) of Voltage Shunt Feedback Amplifier with Feedback Observing both Figure D13 and Figure D14, we see that the Lower Cut-off Frequency is somewhat close to our simulated results. But our Higher Cut-off Frequency is very different from our simulated results.
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Experiment 2 Group 5 Page 50 Table D11: AC Frequency Response of Voltage-Shunt Feedback Amplifier with Feedback Frequency(Hz) Vin(Vp-p) Vout(Vp-p) Vout/Vin Gain (dB) Phase Shift 10 15mV 26.0mV 1.733 4.778 86° 12 11.2mV 26.0mV 2.321 7.315 71° 14 14.0mV 66.0mV 4.714 13.47 78° 25 19.0mV 84mV 4.421 12.91 92° 75 19.6mV 244mV 12.45 21.90 99° 100 18.8mV 316mV 16.81 24.51 104° 500 16.4mV 600mV 36.59 31.27 127° 800 12.0mV 800mV 66.67 36.48 151° 2000 10.4mV 860mV 82.69 38.35 170° 5000 11.2mV 860mV 76.79 37.71 178° 10000 10.4mV 860mV 82.69 38.35 -177° 15000 10.4mV 860mV 82.69 38.35 -178° 20000 10.4mV 860mV 82.69 38.35 -178° 25000 10.4mV 860mV 82.69 38.35 -177° 35000 10.4mV 860mV 82.69 38.35 -176° 45000 10.4mV 860mV 82.69 38.35 -178° 100000 10.8mV 860mV 79.63 38.02 -173° 600000 12.0mV 820mV 68.33 36.69 -151° 650000 12.0mV 820mV 68.33 36.69 -144° 1000000 13.6mV 740mV 54.41 34.71 -129° Figure D15: Excel Graph of AC Frequency Response of Voltage-Shunt Feedback Amplifier with Feedback 0 5 10 15 20 25 30 35 40 45 Gain (dB) Frequency (Hz) AC Frequency Response of Voltage-Shunt Feedback Amplifier with Feedback
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Experiment 2 Group 5 Page 51 As we can see with Table D11, we were able to gather data like our AC Sweep Analysis in our simulations. Figure D15 has all the gains in dB graphed on a line plot that resembles the graphical shape we had in our AC Sweep Analysis of Case B (with Feedback). Table D12: Measured Voltage-Shunt Feedback Amplifier Summary Without Feedback With Feedback Gain (Mid-Band) in dB 42.97dB 37.08dB Lower cut-off frequency ( 𝒇 𝑳 ) 115Hz 475Hz Higher cut-off frequency ( 𝒇 𝑯 ) 525KHz 815KHz Bandwidth ( 𝒇 𝑯 − 𝒇 𝑳 ) 524.89KHz 814.53KHz Gain-Bandwidth Product 2.26 × 10 7 3.02 × 10 7 The data in Table D12 proves our theory that the Voltage-Shunt Feedback Amplifier decreases in gain from not having a feedback to having a feedback. But, the bandwidth of the amplifier with a feedback is larger than the amplifier without a feedback.
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Experiment 2 Group 5 Page 52 Images of all the board (PCBs and Breadboard) of the Voltage-Shunt Amplifier are provided below. Figure D16: Image of PCB; Voltage-Shunt Feedback Amplifier without Feedback (Case A)
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Experiment 2 Group 5 Page 53 Figure D17: Image of PCB; Voltage-Shunt Feedback Amplifier with Feedback (Case B)
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Experiment 2 Group 5 Page 54 Figure D18: Image of Breadboard; Voltage-Shunt Feedback Amplifier without Feedback (Case A)
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Experiment 2 Group 5 Page 55 Figure D19: Image of Breadboard; Voltage-Shunt Feedback Amplifier with Feedback (Case B)
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Experiment 2 Group 5 Page 56 Conclusion Using PCBs in this experiment did help by providing less interference and more consistent results than using a breadboard. However, the measured Voltage-Shunt Feedback Amplifier ’s bandwidth was a lot smaller than the simulations. What could cause the bandw idth to differ so much? There are lots of variables that could have affected our recorded data of the bandwidth. We could have used a better way to solder a more secure connection for all BNC connections and connections that lead to the power supply. Maybe there was too much interference in the labs during testing. Interference could be cell-phone signals and laptops that are connected to the internet via wi-fi. The main verdict of implementing the Voltage-Shunt Feedback Amplifier is to show that having a feedback will decrease the gain but give you a wider bandwidth in which we proved with our data.
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Experiment 2 Group 5 Page 57 Part E: Series-Shunt Feedback Amplifier ADS Simulations Figure E1: AC frequency between 1Hz and 100 MHz without feedback (10Mohm) For this part of the experiment, the Series Shunt Feedback Amplifier will be reconstructed exactly like the prior experiment except instead of using a breadboard to build the circuit, it will instead be soldered onto a through-hole board and reanalyzed to see if we yield more desirable result. The figure below shows the layout of the circuit.
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Experiment 2 Group 5 Page 58 Table E1: Active Mode Chart for AC Frequency Response (10 Mohm) After doing an AC Sweep simulation on this schematic, we’re then able to observe what the output signal will look like with 10 MΩ resistor feedba ck resistor, which due to its high resistance, acts somewhat like an open circuit and thus would be like not having a feedback network. More specifically, the simulation will show the mid-band gain and the cutoff frequencies so that there is a reference value when testing the soldered version of the amplifier. The overall gain/output obtained from the AC Sweep is demonstrated in the figure below. Figure E2: Frequency Response to DC Shunt without Feedback BJT: Base Voltage: Junction: Bias Active mode? Q1 VB = 2.35 V VC = 1.65 V Reverse Yes Q1 VB = 2.35 V VE = 3.15 V Forward Yes Q2 VB = 3.15 V VC = 2.5 V Reverse Yes Q2 VB = 3.15 V VE = 11.5 V Forward Yes
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Experiment 2 Group 5 Page 59 Figure E3: AC frequency between 1Hz and 100 MHz with a feedback resistor of 10kohm Table E2: Active Mode Chart for AC Frequency Response (10 kohm) BJT: Base Voltage: Junction: Bias Active mode? Q1 VB = 2.36 V VC = 5.31 V Reverse Yes Q1 VB = 2.36 V VE = 1.67 V Forward Yes Q2 VB = 5.31 V VC = 10.2 V Reverse Yes Q2 VB = 5.31 V VE = 4.64 V Forward Yes
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Experiment 2 Group 5 Page 60 Figure E4: Frequency Response to DC Shunt Feedback Table E3: Series Shunt Feedback Amplifier Simulation Summary Without Feedback With Feedback Input Impedance at 1kHz 880 900 Gain (Mid-Band) in dB 73.022 73.776 Lower cut-off frequency (F L ) 186.9 Hz 995.0 Hz Higher cut-off frequency (F H ) 1.56M Hz 1.118 MHz Bandwidth (F H -F L ) 1.56M Hz 1.12M Hz Gain-Bandwidth Product 113MHz 82MHz
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Experiment 2 Group 5 Page 61 Table E4: Component values used in DC Simulation for (10 Mohm) Before constructing the circuit, each component that was used was measured in order to verify their values and ensure that the circuit performs like the ADS version of the amplifier. The table below shows the capacitors and resistors used in the feedback amplifier, as well as their ideal and measured value. Components Nominal Value Measured Value (10 M Ω ) R1 0.5 kΩ 0.489 Ω R2 2.7 kΩ 2.69 k Ω R3 1 kΩ 0.95 k Ω R4 4.7 kΩ 4.69 k Ω R5 3 kΩ 2.97 k Ω R6 12 kΩ 11.94 k Ω C1 100 uF 99.8 uF C2 100 uF 99.1 uF C3 100 𝜇? 99.3 uF R7=Rf 10 MΩ 10.2 M Ω
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Experiment 2 Group 5 Page 62 Table E4: Component values used in DC Simulation for (10 kohm) After verified and matching our nominal value to our measure values, we set up the circuit on the breadboard and made sure everything was properly connected (no short/open circuit, spacing the BJT’s, spacing components away from the collector of the BJT’s, cutting wires as short as possible, etc.), the completed circuit is shown below: Components Nominal Value Measured Values (10 k Ω ) R1 0.5 kΩ 0.489 Ω R2 2.7 kΩ 2.69 k Ω R3 1 kΩ 0.95 k Ω R4 4.7 kΩ 4.69 k Ω R5 3 kΩ 2.97 k Ω R6 12 kΩ 11.94 k Ω C1 100 uF 99.8 uF C2 100 uF 99.1 uF C3 100 𝜇? 99.3 uF R7=Rf 10 k Ω 10.24 k Ω
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Experiment 2 Group 5 Page 63 Figure E5: Breadboard with 10 Mohm Resistor Figure E6: Oscillation capture of clipping with Breadboard
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Experiment 2 Group 5 Page 64 Case (a): PCB Shunt feedback Amplifier without Feedback After assembling every component on the Printed Circuit Board without feedback (10 Mohm) and making sure everything was properly connected (no short/open circuit, spacing the BJT’s, spacing components away from the collector of the BJT’s, cutting wires as short as possible, etc.), the completed circuit when soldered onto a board is as shown: Figure E7: Photograph of PCB circuit without feedback (10 Mohm) In this PCB Design, we were not certain of the transistor necessary to use whether it would be the BCN549 or the Q2N3904 as a surface mount device to lessen the noise. With that being said, we designed this PCB to have the through-hole and surface mount option for the transistor.
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Experiment 2 Group 5 Page 65 Table E4: DC Values on Soldered Board without Feedback resistance (10M ohm) Variable DC Voltage (V) Simulated Operating Point Value (V) Measured Operating Point Value (V) V (Base 1) 2.35V 2.37 V V (Base 2) 3.15 V 3.03 V V (Collector 1) 3.15 V 3.03 V V (Collector 2) 11.5 V 11.56 V V (Emitter 1) 1.65 V 1.68 V V (Emitter 2) 2.5 V 2.41 V Table E4, shows us the voltages that were read using a digital multimeter on the right side and the actual theoretical/simulated voltages. Figure E8: Photograph of PCB circuit oscillation without feedback at Midband Gain (10 Mohm)
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Experiment 2 Group 5 Page 66 Figure E9: Photograph of PCB circuit oscillation without feedback at 50 Hz Gain (10 Mohm) Figure E10: Photograph of PCB circuit oscillation without feedback at 1 kHz Gain (10 Mohm)
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Experiment 2 Group 5 Page 67 Figure E11: Photograph of PCB circuit oscillation without feedback at 800 kHz Gain (10Mohm) Table E5: PCB Series Shunt Feedback Amplifier with Feedback Without Feedback (10 M Ω ) Gain (Mid-band) in dB 35.6 dB Lower cut-off frequency ( 𝑓 𝑙? ) 50 Hz Higher cut-off frequency ( 𝑓 ℎ? ) 800 kHz Bandwidth ( 𝑓 ℎ? − 𝑓 𝑙? ) 799.95 kHz Gain Bandwidth Product 28.4 MHz
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Experiment 2 Group 5 Page 68 Laboratory Measurements – No Feedback For the first set of measurements, we will be measuring the Feedback Amplifier without the frequency network. Albeit there’s technically a feedback network incorporated onto and within the circuit, sine the resistor used in this feedback network has such a high resistance, the lack of current flowing through this network makes is negligible. This, the amplifier “feels” no feedback effect with the given setup. After applying a function generator signal, the input and the output voltages were measured at different frequencies and recorded in the tale below. It is important to note that since the input signal being measured were week (small), the oscilloscope has difficult time displaying the signal properly at very low frequencies.
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Experiment 2 Group 5 Page 69 Table E6: Measure Frequency response with without feedback (10M ohm) Without Feedback R f = 10 M Ω and C f = 100 𝜇? CH1 to CH2 frequency (HZ) Vin(mV p-p) Vout (V p-p) Vout/Vin gain(dB) Phase shift (Degree) 10 2.40 0.160 66.67 36.5 ? 12 2.80 0.240 85.7 38.7 ? 14 2.80 0.240 85.7 38.7 ? 25 2.40 0.160 66.67 36.5 ? 75 21.2 0.900 42.5 32.6 5.96 100 20.4 0.880 43.1 32.7 5.04 500 21.2 0.900 42.5 32.6 4.78 800 20.4 0.900 44.1 32.9 -1.86 2000 21.6 0. 900 41.67 32.4 -2.17 5000 21.2 0. 900 42.5 32.6 -1.80 10000 20.8 0. 900 43.3 32.7 -4.30 15000 21.2 0. 900 42.5 32.6 -3.23 20000 21.6 0. 900 42.5 32.6 -3.95 25000 21.2 0. 900 42.5 32.6 -4.20 35000 21.2 0.880 41.5 32.4 -13.9 45000 21.2 0.860 40.6 32.2 -18.7 100000 21.6 0.880 40.7 32.2 -17.3 600000 20.8 0.740 35.6 31.0 -45.0 650000 20.8 0.720 34.6 30.8 -49.6 1000000 19.2 0.580 30.2 29.6 -67.5
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Experiment 2 Group 5 Page 70 Case (b): PCB Shunt feedback Amplifier with Feedback After assembling every component on the Printed Circuit Board with feedback (10 kohm) and making sure everything was properly connected (no short/open circuit, spacing the BJT’s, spacing components away from the collector of the BJT’s, cutting wires as sho rt as possible, etc.), the completed circuit when soldered onto a board is as shown: Figure E11: Photograph of PCB circuit with feedback (10 kohm) With all the components measured, a voltage source of 12V was applied to the circuit and the voltage at the collector, base and emitter were measured on both the BJT in order to verify that they’re in active mode and to verify if it matches with the ADS Bias Point values.
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Experiment 2 Group 5 Page 71 Table E7: DC Values on Soldered Board with Feedback resistance (10k ohm) Variable DC Voltage (V) Simulated Operating Point Value (V) Measured Operating Point Value (V) V (Base 1) 2.36 V 2.40 V V (Base 2) 5.31 V 4.80 V V (Collector 1) 5.31 V 4.80 V V (Collector 2) 10.2 V 10.2 V V (Emitter 1) 1.67 V 1.7 V V (Emitter 2) 4.64 V 4.19 V Figure E11: Photograph of PCB circuit oscillation with feedback at 200 Hz (10 kohm)
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Experiment 2 Group 5 Page 72 Figure E12: Photograph of PCB circuit oscillation with feedback at 1 kHz (10 kohm) Figure E13: Photograph of PCB circuit oscillation with feedback at 900 kHz (10 kohm)
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Experiment 2 Group 5 Page 73 Table E8: PCB Series Shunt Feedback Amplifier with Feedback (10 kΩ) With Feedback (10 k Ω ) Gain (Mid-band) in dB 32.3 dB Lower cut-off frequency ( 𝑓 𝑙? ) 200 Hz Higher cut-off frequency ( 𝑓 ℎ? ) 900 kHz Bandwidth ( 𝑓 ℎ? − 𝑓 𝑙? ) 899.80 kHz Gain Bandwidth Product 29 MHz For the second set of measurement, the 1 M ohm resistor will be disconnected and replaced with a 10k ohm resistor which will make up the feedback network for this amplifier.
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Experiment 2 Group 5 Page 74 Table E9: Measure Frequency response with Feedback (10K ohm) With Feedback R f = 10 k Ω and C f = 100 𝜇? CH1 to CH2 frequency (HZ) Vin(mV p-p) Vout (V p-p) Vout/Vin gain(dB) Phase shift (Degree) 10 21.6 0.080 3.7 11.37 ? 12 25.6 0.068 2.65 8.48 ? 14 22.0 0.060 2.71 8.71 ? 25 32.8 0.260 7.93 17.98 ? 75 21.6 1.16 53.7 34.6 55.6 100 20.8 1.18 56.73 35.07 48.6 500 21.6 1.26 58.3 35.32 30.6 800 20.8 1.26 60.57 35.6 28.2 2000 20.8 1.28 61.53 35.78 27.9 5000 20.8 1.28 61.53 35.78 25.9 10000 21.6 1.28 59.25 35.45 26.6 15000 21.6 1.28 59.25 35.45 25.4 20000 21.6 1.28 59.25 35.45 23.0 25000 21.6 1.28 59.25 35.45 25.1 35000 21.6 1.26 58.3 35.3 21.4 45000 21.8 1.26 57.79 35.2 21.1 100000 20.8 1.26 60.57 35.64 16.2 600000 21.6 1.08 50 33.97 -24.2 650000 22.4 1.06 47.3 33.5 -26.3 1000000 21.6 0.900 41.66 32.29 -46.0
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Experiment 2 Group 5 Page 75 Conclusion A final characteristic of this amplifier that is worth determining is its input impedance. To achieve this, the circuit must once again be modified so that a resistor could be placed in series with the capacitor that passes the input signal. Specifically, this resistor will be placed right after the capacitor, where the current probe is placed in the ADS schematic. Then, the resistance value of the resistor will be changed until the gain reaches half of its original mid-band gain. This concept will work as a voltage divider so when the input impedance of the amplifier equals the resistance of the resistor being added, the input signal will be half, and as a result, so will the output. This experiment helped us grow with a different mindset. We had many hours of trial and error until we finally achieved a sinusoidal output. We first achieved a clipping signal and slowly we had achieved out desires. Working with the surface mount devices is a great route to take. Unfortunately, we had tools that were not quite ideal that made the experiment very difficult. To conclude this, we learned that the circuit with feedback is more efficient and required less trouble shooting. The circuit without feedback had slight clipping that was not ideal.
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Experiment 2 Group 5 Page 76 Lab Report Questions Questions: 1. Complete the tables of gain-bandwidth products that you started with your simulation results. Compare the simulation results with the measured results and offer explanations for any discrepancies. 3. Which amplifier has the largest gain-bandwidth product referring to your table of gain bandwidth products? 4. On the basis of experimental results, state the effects of negative feedback on gain, and input resistance. 5. State the difference between current and voltage feedback Answers: 1. The results for the Voltage-Series feedback amplifier came close to the simulated values in gain. Despite the closeness however, there was a considerable difference in the bandwidth between the two methods of testing. The simulated amplifier had a much larger bandwidth than the amplifier that was built and tested. As a result, the gain- bandwidth product for the simulated results were larger than the actual results obtained due to experimenting. This was the case for both the case of having feedback and not having feedback. This discrepancy could be due to external factors that come into play, such noise in the equipment being used or due to slight inaccuracies in the capacitor and resistor values. Due to unknown oscillations in the circuit when the feedback loop was added in the current shunt feedback amplifier, the only comparisons that can be made for this amplifier are for the case without feedback.
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Experiment 2 Group 5 Page 77 I believe it’s safe to state that from our amplifier performed as we expected based off our ADS and actual breadboard stimulations and results. Comparing both gain values from ADS and our actual breadboard stimulations were that different in Case A which is without feedback and Case B which is with feedback. For the soldered and breadboarded, the gain-bandwidth products obtained from the experimental were smaller than that of the simulation results. The main reason is the bandwidth difference between the two sets of result. The gain in both results were identical between the two, however, the bandwidth shown in the simulation appeared to be larger than the experimental result and this could be due to the component values in the circuit, like the capacitors. The slight difference in values could have had a large effect on the amplifier at high and low frequencies. In addition, external disturbances such as cell phones and laptop could have influenced the measurements. 2. Referring to all the gain-bandwidth tables, for all of the amplifiers, the feedback that provided the largest gain-bandwidth product was the Series Shunt Feedback Amplifier. Due to its much larger bandwidth than the other amplifiers, the gain-bandwidth product for this amplifier feedback system was the largest. 3. When negative feedback is introduced to any of the amplifier the resulting max gain, or mid-band gain, is noticeably reduced. It does, however, expand the bandwidth of the amplifier significantly. Furthermore, including negative feedback causes the input impedance of the amplifier to increase, based on majority of the experimental and simulation result.
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Experiment 2 Group 5 Page 78 4. Voltage and current feedback mean that either a voltage or a current is taken from the output and mixed into the input. To take a voltage signal from the output, a shunt or parallel connection must be made with the output. To take a current signal from the output, a series connection must be made with the output. The difference lies in the connection that is made with the output. A series connection with the output will cause the output resistance to increase, like putting resistors in series. Therefore, current feedback will cause the output resistance to increase. A shunt connection with the output will make the output resistance decrease, like putting resistors in parallel. Therefore, voltage feedback will cause the output resistance to decrease.
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Experiment 2 Group 5 Page 79 Acknowledgements We would like to thank Dr. Peterson for his knowledge and expertise for taking the time to provide us with assistance and help in scrutinizing and verifying our circuits.
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