Lab_4_Report_Christian-323

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12/11/2023 CHRISTIAN M ANDRADE SAURABH SACHDEVA Operational Amplifier

Objective The purpose of this experiment is to design an operational amplifier. In order to achieve this design, we will divide the circuit into three stages, each of which we are already familiar with. The three stages, from the input to the output, are the differential amplifier, the common emitter amplifier, and the emitter follower. We have the input that goes into the differential amplifier, the common emitter stage has further amplification, and the emitter follower is where the output comes from. Prelab First, we started by performing the required calculations to meet the specifications of our design that are given in Table 1 below. Table I: OP-AMP Specifications with a 1k and 50pF load. Calculations We begin by determining R1, for this resistor we know the input bias from the table, we then find the value of ß from the CA3046 data sheet which comes out to be 100. We can also assume R2 and R4 from figure 1 to be negligible which allows us to easily calculate R1 below. IC2=β1B2=110*2u = 0.22mA IC4-IC3=2×1C2=2×0.22m = 0.44mA RI=VCC-VB4 IC4 = 6-(-5.3)0.44m = 25.7 KΩ So, we found that R1=25.7 KΩ

Now we move onto approximating R3. We know that the quiescent output voltage must be approximately 0. An approximate value for R3 can be found such that the voltage across it is 0.7 volts, which is the "turn on" voltage of Q7. R3=VCC-VC2/IC2=0.7 V/.22mA = 3.18 KΩ So, we found that R3=3.18 KΩ Now we can find our common mode voltage ranges, designated as Vcom+ and Vcom-. VCOM+=VCQ+0.5V=VCC-VR3+0.5V=6V-0.7V+0.5V = 5.8 V VCOM-=VE3, min+0.9V=VR4+VEE+0.9V=0V-6V+0.9V = -5.1V Now we move onto differential gain denoted as Ad. Since this amplifier consists of 3 stages, we can find the gain of each of the stages then multiply them together to obtain the overall gain. Ad=VB7/VIN*VB6/VB7×VOUT/VB6 VB7/VIN = R3/2re2=3.18 K/2*113.6 = 14 V/V VB6/VB 7=R5/re 7 =10 K/ 227.3 = 44 V/V VOUT/VB 6 = 1 VIV Ad = 14x44×1 = 615 V/V To determine Vout max and Vout min which are the maximum and minimum voltage. Output swings we need to look at which conditions the transistors Q6 and Q5 go into saturation. Vout max = VCC-VCE6 min = 6V-0.2V = 5.8 V Vout min=VCES min +VEE = 0.2V-6V = -5.8 V Now we will determine Icc, this current is simply the addition of the currents IQ4, IQ1, IQ2, IQ7 and IQ6. ICC = IQ4+ IQ1+IQ2+IQ7+IQ6 = 0.44m +0.22m+0.22m+0.11m+4m = 5mA Table 2 shows the theoretical results from hand calculations, these are the initial specifications of the design of the OP-Amp.

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Simulations To find the resistor value of R3 that yields a DC output of ~ 0V. A voltage range within - 0.5 < Vout < 0.5 is acceptable. The following figure shows the circuit simulation. A convenient way to perform this measurement is to use what's called parameter sweep, in which a circuit parameter is swept, while a measurement is being taken for each point. This will allow us to find a value easily and conveniently for R3 such that the requirement is fulfilled. The result of the simulation is shown in Figure 2 below.

We can conclude from the figure that the appropriate value for R3 is 3.47 KΩ, and it's when the value of the output voltage is 2.11mV. Next, we will find the value for R6 such that the current ICS is set to 4mA. The result of simulation can be seen in Figure. The plot of the data is.

Post Lab Quiescent Voltages We assembled the circuit on the breadboard and measured the quiescent voltages and compared it to the simulated values, the results are shown in table below. As seen from the table we got acceptable operating point value, and we can continue the lab. Input Offset Voltage Then, we measured input offset voltage. We set up the circuit from Figure 7 but this time we set. Ra = Rb = 1000Ω. The input voltage is then grounded. We then measure the voltage difference. from the input terminals, meaning the non-inverting input and the inverting input. We find that the input offset voltage is Vd = 0.1mV. This value is within acceptable limits, meaning under 20mV.

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Input bias Current Then, we measured input bias current. In order to make this measurement we will make use of the circuit from Figure 8, and we will ground the input. Next, we wish to measure the current that goes into the non-inverting input of our OP-AMP. An ideal OP-AMP should have a current of zero that goes into the non-inverting input and inverting input. When we take our measurement into the non-inverting input, we see a current of luA. This is within acceptable limits, the highest acceptable value for this current is 3uA. Output Voltage Swing We performed the measurement and got the following results shown in Figure below. The input waveform is shown on channel 1 and the output is shown on channel 2. We can see that the output voltage swing is between +6.80 V and -6.40 V, which fits our requirements. Slew Rate Slew rate is defined as the maximum rate of change of the output voltage of the OP- AMP. To make this measurement we make the circuit from figure and set Ra = 0Ω and Rb =∞Ω (open loop). Then we apply a voltage that has a fast rise time and fast fall time, in other words a square wave. The result is shown in the Figure below. We got a slew rate of 1.5V/us. Closed Loop Bandwidth The closed loop bandwidth. To measure this, we build the circuit and configure the feedback resistor to a fixed value and the input resistor to two different values. The table shows the values that have been measured and simulated. We see that there are some discrepancies in the values measured, specifically that of the 3dB BW. Measuring the 3dB bandwidth is a difficult task to begin with. One must adjust the frequency such that the gain of the system decreased to that which is 3dB less than the highest gain. The instruments make big leaps in the frequency range and voltage amplitude range. This can be a source of error in the measurement of this 3 dB frequency.

Open Loop Frequency Response We configured the circuit as shown in Figure below. We took the measurements over the frequency specified in the lab report. The results are shown Figure below.

Absolute Maximum Ratings Conclusion In this lab our OP-AMP experiment met our expectations although we were a bit off with the measurement that we got in the laboratory and the simulation. It was a big and complex circuit and there were a lot of components. It was a tough job to get the exact value for each part of the experiment, but we managed to get the values which were within the experiment range. So, it was an overall success, we managed to design the appropriate circuit and then build and test it and troubleshoot the OP-AMP as stated in the manual.

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