E 25 VIII SingleStage A mplifiers Lab 8 SingleStage Amplifiers In this lab we will investigate the gain properties of an emitterfollower and a commonemitter amplifier. VIII.1 PreLab Calculations All calculations go in your notebook. No writing equations on a piece of paper and then copying them down in your notebook. Create tables for the two amplifiers discussed in this lab. Your prelab consists of the data contained in the tables and the calculations that support those values. VIII.1.A CommonEmitter Amplifier We will use the current source of the previous lab to bias the commonemitter amplifier below: 91k Rc 7.5k C6 1U Q2N394 MPF12 47u.1u 1u.1u 1u Obtain a data sheet for the 2N394 transistor. Find maximum and minimum values for VBE. Make the following calculations using the maximum and minimum current for the current source, resistor tolerances, and tolerance in VBE. Do not use PSpice to make these calculations. Maximum and minimum values of the bias collector voltage (VC). Maximum and minimum values of the bias emitter voltage (VE). Maximum and minimum values of the gain VO/VIN if = 1 MΩ. Maximum and minimum values of the gain VO/VIN if = 7.5 kω. Create a table for prelab and laboratory results and record these values in the table. Run the PSpice simulations listed below. These simulations will yield typical values that should fall within the maximum and minimum values calculated above. Enter these values in your table and verify that they fall within the maximum and minimum values that you calculated. E25 Lab VIII Page 1 of 6
Run a Bias Point analysis and find the bias value of the collector voltage (VC). Run a Bias Point analysis and find the bias value of the emitter voltage (VE). Run an AC Sweep analysis and find the midband gain VO/VIN if = 1 MΩ. See Section 5.D of the PSpice manual for an example. Run an AC Sweep analysis and find the midband gain VO/VIN if = 7.5 kω. VIII.1.B EmitterFollower Amplifier We will use the current source of the previous lab to bias the emitterfollower amplifier below:.1u 1u Q2N394 47u 91K 92k MPF12.1u 1u Make the following calculations using the maximum and minimum current for the current source, resistor tolerances, and tolerance in VBE. Do not use PSpice to make these calculations. Maximum and minimum values of the bias collector voltage (VC). Maximum and minimum values of the bias emitter voltage (VE). Maximum and minimum values of the gain VO/VIN if = 1 MΩ. Maximum and minimum values of the gain VO/VIN if = 7.5 kω. Maximum and minimum values of the gain VO/VIN if = 1 kω. Create a table for prelab and laboratory calculations, and record these values in the table. Run the PSpice simulations listed below. These simulations will yield typical values that should fall within the maximum and minimum values calculated above. Enter these values in your table and verify that they fall within the maximum and minimum values that you calculated. Run a Bias Point analysis and find the bias value of the collector voltage (VC). Run a Bias Point analysis and find the bias value of the emitter voltage (VE). Run an AC Sweep analysis and find the midband gain VO/VIN if = 1 MΩ. See Section 5.D of the PSpice manual for an example. Run an AC Sweep analysis and find the midband gain VO/VIN if = 7.5 kω. E25 Lab VIII Page 2 of 6
Run an AC Sweep analysis and find the midband gain VO/VIN if = 1 kω. VIII.2 Laboratory Procedure CommonEmitter Amplifier VIII.2.A Parts Measurement Measure the values of all of your resistors. Record the values in a table and compare them with their ±5% limits. VIII.2.B Bias Verification The first thing we must do is check that the bias is correct. Wire the circuit below and verify that VC, VE, and IC are within the range you calculated in the Prelab. Enter the values in your table. Rc 7.5k.1u 1u Q2N394 91K 91k MPF12.1u 1u If your bias is correct, you can proceed to the next section. If the bias is not correct, you must have made a wiring error. Do not continue until the bias is correct. VIII.2.C Amplifier Gain Measurement If your bias is correct you can measure the gain characteristics of the amplifier. Wire the circuit below. Note that we have added a 1 to 1 voltage divider. This divider is not part of the amplifier. Since the gain of this amplifier is large, we need a small input so we do not saturate the amplifier. Measure the values of R4 and R5 and make sure that they are within ± 5% of their stated value. E25 Lab VIII Page 3 of 6
Vsig Vsig R4 1 R5 1 91k Rc 7.5k C6 1U Q2N394 MPF12 47u.1u 1u.1u 1u Note that Vsig and Vo will be large signals and easy to measure with the oscilloscope. VIN will be a small signal and hard to measure, but we do not need to measure it because we know the divider ratio of R4 and R5, and we are measuring Vsig. Measure Vo and Vsig using the scope, and then calculate the gain as: V o R5 R4 Vo Vo = 1 V in R5 Vsig Vsig Measure the gain for = 1 MΩ and = 7.5 kω and compare the values to your calculated values. Record the values in your table. When you measure the gain, make sure that the peaktopeak value of Vo is less that 1 V. Record a scope trace of the waveforms you use to measure the gain. VIII.2.D Amplifier Maximum Voltage Swing Start with a small value of Vsig so that the output is an undistorted sine wave. Slowly increase the input until either the top or the bottom of the sine wave clips. Reduce the input slightly so that the output waveform is not clipped. Record the scope waveform and then measure the peaktopeak swing of the output. Measure the maximum swing with no load on the output (remove C6 and and measure the output at the collector of ). VIII.3 Laboratory Procedure EmitterFollower Amplifier VIII.3.A Parts Measurement Measure the values of all of your resistors. Record the values in a table and compare them with their ±5% limits. VIII.3.B Bias Verification The first thing we must do is check that the bias is correct. Wire the circuit below and verify that VC, VE, and the current source drain current are within the range you calculated in the Prelab. Enter the values in your table. E25 Lab VIII Page 4 of 6
.1u 1u Q2N394 91K 92k MPF12.1u 1u If your bias is correct, you can proceed to the next section. If the bias is not correct, you must have made a wiring error. Do not continue until the bias is correct. VIII.3.C Amplifier Gain Measurement If your bias is correct, you can measure the gain characteristics of the amplifier. Wire the circuit below. Since the gain of this amplifier is close to 1, we do not need to use a voltage divider to reduce the input signal. E25 Lab VIII Page 5 of 6
.1u 1u Q2N394 47u 91K 92k MPF12.1u 1u Measure the gain for = 1 MΩ, 7.5 kω, and 1 kω, and compare the values to your calculated values. Record the values in your table. When you measure the gain, make sure that the peaktopeak value of Vo is less that 1 V. Record a scope trace of the waveforms you use to measure the gain. VIII.3.D Amplifier Maximum Voltage Swing Start with a small value of so that the output is an undistorted sine wave. Slowly increase the input until either the top or the bottom of the sine wave clips. Reduce the input slightly so that the output waveform is not clipped. Record the scope waveform and then measure the peaktopeak swing of the output. Measure the maximum swing with no load on the output (remove and and measure the output at the emitter of ). E25 Lab VIII Page 6 of 6