ECEN Lab 12: MOSFET Amplifier Design Solution

Objectives

The purpose of this experiment is to design a multi-stage MOSFET amplifier based on a list of specifications.

Introduction

Figure 1 shows a two-stage amplifier composed of a common-source gain stage and a source follower, where the small-signal gain can be calculated as


Assuming that one gain stage followed by a buffer is sufficient for the design requirements, the circuit in Fig. 1 can be used as a starting point. Typical specifications include, but not limited to:

0-to-peak output swing: ^ Vo

Gain: Av = Av1Av2

Input resistance: Ri

Load resistance: RL

Linearity: v^sg1     2Vov1


c    Department of Electrical and Computer Engineering, Texas A&M University

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Using the circuit in Fig. 1, the design procedure can be given as follows:

    • Use 2N7000G for the NMOS, and CD4007P for the PMOS device.

^
í Choose IX    Vo .

RL
í Since    , calculate    ,    ,    ,    , and ^ .
ID2 = ID3 = IX    Vov2  Vov3  gm2  Av2    Vd
    • Choose VRX    0.5V and VRS    0.5V , then choose the maximum possible value of VRD based on (2) and (3).
Note that you can substitute Vov1 =
2VRD
=
2VRD
Av2 in (2).


jAv1j

jAv j








    • Calculate Vov1 = 2VRD , then ID1. jAv1j

    • Calculate RD = VRD , RS = VRS , and RX = VRX .
ID1          ID1ID3

    • Find RG 1 and RG 2 such that VRG 2 = VRS +jVtpj+Vov1 and Rid = RG 1kRG 2, where Rid is the desired input resistance.

    • Find RG 3 and RG 4 such that VRG 4 = VRX +Vtn +Vov3.


Calculations

Design a MOSFET amplifier based on the specifications provided in the table below. Both the input and the output should be AC coupled as in Fig. 1.

Dual Supply Voltage
5V
Load Resistance, RL
100 
^
2V
0-to-Peak Output Swing, Vo

Voltage Gain, jAv j
50
Input Resistance, Ri
10k
THD for 5kHz 2V (0-to-peak) Sine Wave Output Voltage, Vo
8%


Simulations

For all simulations, provide screenshots showing the schematics and the plots with the simulated values prop-erly labeled.

    1. Draw the schematics of the amplifier you designed, and obtain the DC solution for all node voltages and branch currents using DC operating point or interactive simulation. Adjust your component values if the results are significantly different from your calculations.

    2. Obtain Av and Ri using AC simulation. If necessary, adjust the resistor values to satisfy the specifications.

    3. Apply a 5kHz 40mV sine-wave input and obtain the time-domain waveforms at the input and the output using transient simulation. If your output voltage is clipped or significantly distorted, adjust your design values until you have unclipped 2V (0-to-peak) output signal, while keeping Av and Ri requirements satisfied.

    4. With the 5kHz 40mV sine-wave input, obtain the total harmonic distortion (THD) on the output waveform using Fourier simulation.






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Measurements

For all measurements, provide screenshots showing the plots with the measured values properly labeled.

    1. Build your amplifier using the simulated component values, and measure DC voltages at all nodes using the voltmeter or scope.

    2. Measure Av and Ri using the network analyzer. If necessary, adjust the resistor values to satisfy the specifica-tions.

    3. Apply a 5kHz 40mV sine-wave input and obtain the time-domain waveforms at the input and the output using the scope. If your output voltage is clipped or significantly distorted, adjust your design values until you have unclipped 2V (0-to-peak) output signal, while keeping Av and Ri requirements satisfied.

    4. Apply a 5kHz 40mV sine-wave input and obtain the total harmonic distortion (THD) on the output waveform using the spectrum analyzer.

Report

    1. Include calculations, schematics, simulation plots, and measurement plots.

    2. Prepare a table showing calculated, simulated and measured results.

    3. Compare the results and comment on the differences.

Demonstration

    1. Build the two-stage amplifier you designed on your breadboard and bring it to your lab session.

    2. Your name and UIN must be written on the side of your breadboard.

    3. Submit your report to your TA at the beginning of your lab session.

    4. Measure Av and Ri of the amplifier using the network analyzer.

    5. Apply a 5kHz 40mV sine wave input and show the time-domain output voltage using the scope.

    6. With the 5kHz 40mV sine wave input, measure the THD at the output using the spectrum analyzer.




























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