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2/21/2018 Willard Bachli, Christopher Soom, Bryant Forsythe, Kenny Atkinson, Angelo Lewis Experiment 3 Class C Power Amplifier & Colpitts Oscillator

Table of Contents Abstract .......................................................................................................................................... 2 Class C Power Amplifier ............................................................................................................... 3 ADS Simulations ...................................................................................................................................... 3 Laboratory Experiments .......................................................................................................................... 3 Open Loop Colpitts Oscillator ...................................................................................................... 4 ADS Simulations ...................................................................................................................................... 4 Laboratory Experiment ............................................................................................................................ 4 Closed Loop Colpitts Oscillator ................................................................................................... 5 ADS Simulations ...................................................................................................................................... 5 Laboratory Experiments .......................................................................................................................... 5 1

Abstract In this experiment, blah blah blah. 2

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Class C Power Amplifier ADS Simulations ALPHA Laboratory Experiments Bravo 3

Open Loop Colpitts Oscillator ADS Simulations Figure 1: ADS Schematic for the Open-Loop Colpitts Oscillator For this experiment, a schematic was developed in ADS circuit simulation software, and the following simulations were executed. First, we determined an open loop gain response of the system for a frequency span from 1- to 1Mhz. We will also look at the phase shift of the output across the same frequencies. 4

Figure 2 Open loop gain response of Colpitts oscillator. M1 = 11.18kHz, M2= 103.4kHz. Interpreting the results from the frequency sweep of the circuit, we notice a gain spike at 11.18kHz and 103.4kHz. These spikes indicate the resonant frequencies of the oscillator and we can infer that the higher frequency will dominate the system and be the frequency which the system will oscillate. Figure 3: Open loop phase shift for Colpitts oscillator Interpreting the simulation results, we note the two 180-degree phase shifts around the resonate frequencies of 12.31kHz and 102kHz. 5

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Laboratory Experiment Figure 4: Open loop Colpitts oscillator schematic Referring to the schematic in the above figure, we managed to layout the circuit on a bread board as seen in the figure below. This was accomplished without any additional wires or jumpers which should help to keep the unwanted noise to a minimum. Figure 5: Open loop Colpitts oscillator In preparation for taking measurements, the circuit was assembled using parts from the lab with component values as close to the schematic as was reasonably feasible. The following table shows a list of the components called for in the schematic, and the actual component values that were used in the construction of the circuit shown in the figure above. 6

Table 1: Table of Components used on Colpitts oscillator Component Schematic Value Measured Value C1 10uF 9.52uF C2 10nF 9.62uF C3 10nF 10.01nF C4 100nF 101nF C5 10uF 9.97uF L1 10mH 10.485mH L2 480uH 479.6uH R1 1.5k 1.498k R2 20k 19.69k R3 70k 67.9k V_DC 15V 15.196V Again, we found that some component values were not readily available in the lab and tried to get as close as we could with what was available. After assembling the circuit, we powered up the DC voltage supply and confirmed that the circuit was functioning and that the BJT was in active mode. The following tables shows the DC Bias measurements. Table 2: DC Bias points of the BJT in Colpitts oscillator DC Voltages Vcc (Source) 15.196 Vcollector 15.152 Vbase 3.278 Vemitter 2.597 Vcollector-emitter 12.557 Vbase-emitter 0.689 Following the assembly of the circuit, we began a bench top frequency sweep of the circuit. The results are shown in the following table 7

Table 3: Laboratorty Data Collection of Open-Loop Colpitts Oscillator Frequency Response Frequency (kHz) Vin (p-p) Vout Gain (vout/vin) Gain dB Phase 5.00 1.02 30.40 29.80 29.49 (45.00) 10.00 1.00 28.08 28.08 28.97 (150.00) 20.00 0.96 6.80 7.08 17.00 87.80 30.00 0.94 5.20 5.53 14.86 150.00 40.00 0.92 4.40 4.78 13.59 155.00 50.00 0.92 6.00 6.52 16.29 45.00 60.00 0.94 4.40 4.68 13.41 83.00 70.00 0.94 3.20 3.40 10.64 93.00 80.00 0.92 1.72 1.87 5.43 89.00 90.00 0.92 2.72 2.96 9.42 85.00 100.00 0.92 4.20 4.57 13.19 67.00 110.00 0.94 5.36 5.70 15.12 (52.00) 120.00 0.94 2.00 2.13 6.56 (70.00) 130.00 0.94 1.20 1.28 2.12 (72.00) 140.00 0.94 0.68 0.72 (2.81) (80.00) 150.00 0.94 0.46 0.49 (6.21) (80.00) 160.00 0.94 0.36 0.38 (8.34) (84.00) 170.00 0.93 0.30 0.32 (9.83) (77.00) 180.00 0.94 0.26 0.28 (11.03) (83.00) 190.00 0.94 0.18 0.20 (14.17) (82.00) 200.00 0.09 0.16 1.70 4.62 (85.00) The table developed allows for an organized flow of information and data measurements taken in laboratory. We took data points at 10kHz increments and anticipated gain spikes around 10kHz and 100kHz. We also noted the phase at all the points and generated two plots from this data. The first being Gain(dB) vs Frequency and the second plot is Phase vs frequency. 8

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Figure 6: Open-Loop Colpitts Oscillator Gain vs. Frequency 5,00 0 25,000 45,000 65,000 85,000 105,00 0 125,00 0 145,00 0 165,00 0 185,00 0 (20) (10) - 10 20 30 40 Gain (dB) Frequency (Hz) Gain (dB) We found that the gain was high at the low end of the frequency spectrum (less than 10kHz). There also was a spike at around 100kHz, which was anticipated based on our earlier ADS simulation results. Figure 7: Open-Loop Colpitts Oscillator Phase vs. Frequency 5,000 25,000 45,000 65,000 85,000 105,000125,000145,000165,000185,000 (200) (150) (100) (50) - 50 100 150 200 Phase Frequency (Hz) Phase Similarly, we noted 180-degree phase shifts at the two points of 10kHz and 100kHz. 9

Figure 8: Oscilloscope Readings for Open-Loop Colpitts Oscillator @ 10kHz We noted an open loop gain of 28.08 dB at 10hHz input frequency, it should also be noted the output wave form is slightly distorted at this frequency. Figure 9: Oscilloscope Readings for Open-Loop Colpitts Oscillator @ 100kHz With an input frequency of 100kHz the gain was noted at 13dB and the output waveform was a clean sinusoidal function. 10

Closed Loop Colpitts Oscillator The next part of the experiment will be based on the closed-loop Colpitts oscillator circuit. We will be using the same circuit as in the previous open loop Colpitts Oscillator, but with a few minor changes. The voltage source will be removed, and the output will be tied directly back to the 10μF input capacitor, creating the closed-loop circuit. Figure 10: Colpitts Closed Loop Oscillator (PRE-DESIGNED EXAMPLE SCHEMATIC) ADS Simulations Figure 11: ADS Schematic of Colpitts Closed Loop Oscillator @480 uH The figure above shows the closed-loop Colpitts oscillator modeled by our team in ADS. 11 Figure 10 shows the closed loop Colpitts oscillator circuit we will be simulating, building and testing. The source has been removed from the previous open loop Colpitts setup we were testing. In place of the source, the output has been fed directly back to the input, creating the closed loop circuit.

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Figure 12: Transient Response @480uH Figure 13: Frequency Response @480 uH 12 The figure to the left shows the transient response of the closed- loop Colpitts oscillator circuit using a 480 uH inductor in series with the output. The figure to the left shows the frequency response of the closed- loop Colpitts oscillator circuit using a 480 uH inductor in series with the output. The simulated oscillation frequency is 115 kHz.

Figure 14: ADS Schematic of Colpitts Closed Loop Oscillator @50 uH The figure above shows the closed-loop Colpitts oscillator circuit with the output inductors value lowered to 50μH. Figure 15: Transient Response @ 50 uH The figure above shows the transient response of the closed-loop Colpitts oscillator with the updated inductance value of 50μH. From observation of the output waveform, we can see that the oscillations have increased in amplitude slightly. 13

Figure 16: Frequency Response @ 50 uH The figure above shows the simulated frequency response of the closed-loop Colpitts oscillator with the output inductor lowered to 50μH. Note that the oscillation frequency has increased to 330 kHz, double the previous frequency we found with the 480μH output inductance value. Laboratory Experiments Based on the simulations ran in ADS on the Colpitts oscillator circuit, we have a reasonable idea of what type of behavior to expect out of the circuit. The next step is to build the closed-loop Colpitts oscillator on a breadboard. Component values may vary slightly from the ADS model based on what was available in the laboratory. The team had previously built an open-loop Colpitts oscillator, so to achieve the closed-loop set up we simply disconnected the voltage source from the breadboard and connected the output back to the 10μF input capacitor. The photo in the following figure shows the completed closed-loop Colpitts oscillator with a 480μH inductor in series with the output. 14

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Figure 17: Photo of Closed Loop Colpitts Oscillator Circuit with 480μH inductor Using the circuit shown in the figure above, an oscilloscope was connected to the output of the circuit in order to inspect the waveform. The figure below shows the readings that registered on the oscilloscope. It is interesting to note that there is not a signal source hooked up to the circuit. The oscillations are generated by the charging and discharging of the capacitors in the circuit. With the 480μH inductor in the circuit, we are getting an oscillation frequency of 108.2 kHz with an amplitude of 7V peak-peak. Figure 18: Oscilloscope Readings for Closed-Loop Colpitts Oscillator @480 μH 15

Figure 19: Photo of Closed-Loop Colpitts Oscillator with 50μH Inductor Figure 20: Oscilloscope Reading for Closed-Loop Colpitts Oscillator @ 50μH The oscilloscope image in the figure above shows the oscillation waveform that results with the 50μH inductor in place. Compared to the first version of the circuit, this waveform looks much 16 In an attempt to understand the effect that the inductance value in series with the output has on the circuit, we removed the 480μH inductor and replaced it with a 50μH inductor. The updated circuit is pictured in the figure to the left.

cleaner and more stable. The oscillation frequency has nearly doubled to a value of 302.7 kHz, while the amplitude has increased by a little over 10% to a value of 7.9V peak-peak. 17

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Lab Report Questions KENNY 1. Comment on the efficiency of the Class A amplifier compared to the Class C Amplifier. 2. Where does the power delivered from the Class C Amplifier come from? (Explain) 3. If 40% of the D.C. power can be converted to output power, explain what happens to the remaining 60%. 4. Research the topic of “1 dB compression point” and explain how it applies to a power amplifier. 5. Provide a photo of your Colpitts Oscillator Breadboard Circuit. 6. Include a photo of your Q = 15 Class C Amplifier Breadboard Circuit. 7. Include a photo of your Q = 35 Class C Amplifier Breadboard Circuit. 18

Figure Index Figure 1: ADS Schematic for the Open-Loop Colpitts Oscillator ................................................... 4 Figure 2 Open loop gain response of Colpitts oscillator. M1 = 11.18kHz, M2= 103.4kHz ........... 5 Figure 3: Open loop phase shift for Colpitts oscillator .................................................................... 5 Figure 4: Open loop Colpitts oscillator schematic .......................................................................... 6 Figure 5: Open loop Colpitts oscillator ........................................................................................... 6 Figure 6: Open-Loop Colpitts Oscillator Gain vs. Frequency ......................................................... 9 Figure 7: Open-Loop Colpitts Oscillator Phase vs. Frequency ....................................................... 9 Figure 8: Oscilloscope Readings for Open-Loop Colpitts Oscillator @ 10kHz ........................... 10 Figure 9: Oscilloscope Readings for Open-Loop Colpitts Oscillator @ 100kHz ......................... 10 Figure 10: Colpitts Closed Loop Oscillator (PRE-DESIGNED EXAMPLE SCHEMATIC) ...... 11 Figure 11: ADS Schematic of Colpitts Closed Loop Oscillator @480 uH ................................... 11 Figure 12: Transient Response @480uH ....................................................................................... 12 Figure 13: Frequency Response @480 uH .................................................................................... 12 Figure 14: ADS Schematic of Colpitts Closed Loop Oscillator @50 uH ..................................... 13 Figure 15: Transient Response @ 50 uH ....................................................................................... 13 Figure 16: Frequency Response @ 50 uH ..................................................................................... 14 Figure 17: Photo of Closed Loop Colpitts Oscillator Circuit with 480μH inductor ...................... 15 Figure 18: Oscilloscope Readings for Closed-Loop Colpitts Oscillator @480 μH ....................... 15 Figure 19: Photo of Closed-Loop Colpitts Oscillator with 50μH Inductor ................................... 16 Figure 20: Oscilloscope Reading for Closed-Loop Colpitts Oscillator @ 50μH .......................... 16 Table Index Table 1 Table of Components used on colpitts oscillator ................................................................ 7 Table 2 DC Bias points of the BJT in Colpitts oscillator ................................................................ 7 Table 3 Laboratorty data collection of open loop colpitts oscillator ............................................... 8 19