Single-Stage MOSFET Amplifiers

Transcription

1 ECE 25 IX SingleStage MOSF ET A mplifiers Lab IX SingleStage MOSFET Amplifiers In this lab we will investigate the gain properties of a sourcefollower and a commonsource amplifier. IX.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. IX.1.A CommonSource Amplifier We will use the current source of the previous lab to bias the commonsource amplifier below: Rc 7.5k C6 1U ZVN336A.1u 1u MPF12 CE 47u.1u 1u Obtain a data sheet for the ZVN336A transistor. Make the following calculations using the maximum and minimum current for the current source, resistor tolerances, VTmin =.8 volts, VTmax = 2.4 volts, and Kmin= 15 ma/v 2 and Kmax= 3 ma/v 2 o not use PSpice to make these calculations. Maximum and minimum values of the bias drain voltage (V). Maximum and minimum values of the bias source voltage (VS). 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. ECE25 Lab IX Page 1 of 7

2 Create a table for prelab and laboratory results and record these values in the table. You may be chasing your tail for a long time while trying to figure out how to choose between using VTmin,VTmax, Kmin, and Kmax. If you remember, we have the following equations for the commonsource amplifier: 2 I = K V V ( ) gm = 2K( VGS VT ) vo = gm( RC ) vin The difficult equation to calculate with minimum and maximum values is the transconductance equation because K, VGS, and VT all have maximum and minimum values, and we are not sure how to plug them in to get maximum and minimum values for gm. We can avoid this problem by solving the top equation for VGS VT and then substituting the result into the center equation: I = K( V V ) 2 there fore ( V V ) Substituting this into our transconductance equation gives GS T GS T GS T = I gm = 2 K( VGS VT ) = 2K K which can be rewritten as gm = 2 K I In this form it is easy to calculate max and min values of gm because, for our circuit, I is determined by the current source and K is determined by the MOSFET. Even though K has max and min values, and I has max and min values, they are both completely independent of one another and can be easily chosen so maximize or minimize gm. IX.1.B SourceFollower Amplifier We will use the current source of the previous lab to bias the sourcefollower amplifier below: I K ECE25 Lab IX Page 2 of 7

3 .1u 1u ZVN336A Cs 47u MPF12.1u 1u Make the following calculations using the maximum and minimum current for the current source, resistor tolerances, VTmin =.8 volts, VTmax = 2.4 volts, and Kmin= 15 ma/v 2 and Kmax= 3 ma/v 2 o not use PSpice to make these calculations. Maximum and minimum values of the bias drain voltage (V). Maximum and minimum values of the bias source voltage (VS). 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. IX.2 Laboratory Procedure CommonSource Amplifier IX.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. IX.2.B Bias Verification The first thing we must do is check that the bias is correct. Wire the circuit below and verify that V, VS, and I are within the range you calculated in the Prelab. Enter the values in your table. ECE25 Lab IX Page 3 of 7

4 Rc 7.5k.1u 1u ZVN336A 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. o not continue until the bias is correct. IX.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. ECE25 Lab IX Page 4 of 7

5 Vsig 7.5k C6 1U ZVN336A Rc R4 1 R5 1.1u 1u MPF12 CE 47u.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. IX.2. 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 drain of ) IX.3 Laboratory Procedure SourceFollower Amplifier IX.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. ECE25 Lab IX Page 5 of 7

6 IX.3.B Bias Verification The first thing we must do is check that the bias is correct. Wire the circuit below and verify that V, VS, and the current source drain current are within the range you calculated in the Prelab. Enter the values in your table..1u 1u ZVN336A 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. o not continue until the bias is correct. IX.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. ECE25 Lab IX Page 6 of 7

7 .1u 1u ZVN336A Cs 47u 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. IX.3. 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 CS and and measure the output at the source of ). ECE25 Lab IX Page 7 of 7