Lab 6 – EE 420L
Authored by: Daniel Senda
Email: sendad1@unlv.nevada.edu
Spring 2019
Due: 03-27-2019

 

1) Introduction

This lab introduces students to the different types of amplifiers. The procedures have the student work with four different topologies that include: Source follower/ (Common Drain) amplifiers (NMOS and PMOS), Common source amplifiers (NMOS and PMOS), Common gate amplifiers (NMOS and PMOS), and Push-pull amplifiers.

2) Pre-Lab Description

The pre-lab required the student to complete the following before proceeding with lab:

-       Read through the datasheets of the N-Channel DMOSFET (ZVN3306A) and of the P-Channel DMOSFET (ZVP3306A) and become familiar with them.

-       Simulate the circuits given in the lab6_sims.zip file and understand operation and verify that the simulations reasonable model the behavior of the transistors.

-       Watch the single_stage_amps video and read single_stage_amps.pdf review.

3) Description of Lab Procedures

This lab utilizes the N-Channel DMOSFET and of the P-Channel DMOSFET mentioned above.

The lab had the student work with four circuit configurations which include:

-       Source follower/ (Common Drain) amplifiers (NMOS and PMOS)

-       Common source amplifiers (NMOS and PMOS)

-       Common gate amplifiers (NMOS and PMOS)

-       Push-pull amplifier

For the first three configurations listed, the student was instructed to hand calculate the gains, input resistances, and output resistances.

These circuits were built using electrolytic capacitors. An electrolytic capacitor has polarity; in simple terms it means that it has a positive and a negative side. These should not be put in backwards because it can cause harm to the capacitor making is useless. The positive side of the electrolytic capacitor should be connected to the higher DC potential (voltage) in the circuit. This will ensure proper operation.

The experimental gain of a circuit can found by taking the magnitude of the output (Vout) and dividing it by the magnitude of the input (Vin).

The experimental input resistance can be calculated by the following way:

-       First, the theoretical input resistance needs to be calculated. Once the theoretical resistance is calculated, a resistor of that value should be connected in series between the input voltage (Vin) and the AC coupling capacitor (input capacitor).

-       Second, calculate the AC current going through the added resistor. This can be accomplished by measuring the AC voltage (magnitude) on the Vin side of the resistor and measuring the AC voltage (magnitude) on the capacitor side of the resistor. Take the difference between these measurements and divide this difference by the value of the added resistor, thus resulting in the AC current (magnitude) value.

-       Third, find the amplifier’s input resistance. This can be accomplished by measuring the AC voltage (magnitude) at the input of the amplifier (the other side of the ac coupling capacitor not connected to the added resistor). Then divide this AC voltage (magnitude) by the AC current (magnitude) solved for previously, which results in the value of the amplifier’s input resistance.

The experimental output resistance can be calculated the following way:

-       First, the theoretical output resistance should be calculated. Once this value is obtained, a resistor of that value should be connected in series with big capacitor (to avoid messing up the DC biasing) and added between the output of the amplifier and ground.

-       Second, calculate the AC current flowing through this added resistor. This can be accomplished by measuring the AC voltage (magnitude) across the resistor and dividing that by the value of the added resistor.

-       Third, find the amplifier’s output resistance. This can be accomplished by measuring the AC voltage (magnitude) on the gate of the MOSFET and the AC voltage (magnitude) on the source of the MOSFET. Then take the difference of these two measurements and divide this value by the AC current value previously calculated, which results in the value of the amplifier’s output resistance.

The following sections discuss all of the listed circuits along with calculations, simulations, and experimental results.

NMOS and PMOS Source Follower (Common Drain) Amplifiers

These amplifiers are called source followers because the input and output closely resemble each other. The gain of this non-inverting topology is one, which explains the resemblance between the input and output. These tend to have a high input resistance and low output resistance.

LTspice circuit schematic:

NMOS Hand Calculations:

Text Box: NMOS known values KP_n=0.1233 A/V^2 , V_THN=1.824V DC Analysis for NMOS V_G=VDD*R_3/(R_3+R_1 )=5*100k/(100k+50k)=3.33V V_s=I_D*R_2=I_D*1k V_GS=V_G-V_s I_D=(KP_n)/2 (W/L) (V_GS-V_THN )^2=0.1233/2 (1/1) (3.33-I_D*1k-1.824)^2 I_D=0.062*(1.506-I_D*1k)^2→Solving for I_D I_D=1.26mA V_GS=3.33-1.36=2.03V AC Analysis for NMOS gm_n=√(2*KP_n*I_D )=√(2*0.1233*1.26m)=18.3 mA/V 1/(gm_n )=1/18.3m=54.64Ω v_gs=v_in-v_out i_d=v_gs*gm_n v_out=i_d*R_2=i_d*1k |v_out/v_in |=(gm_n)/(1/R_2 +gm_n )=18.3m/(1/1k+18.3m)=0.948 NMOS Output Resistance R_in=R_1 ||R_3=(50k*100k)/(50k+100k)=33.3kΩ NMOS Input Resistance R_out=1/(gm_n )||R_2=(54.64*1K)/(54.64+1k)=52Ω  Text Box: PMOS known values KP_p=0.145 A/V^2 , V_THP=2.875V DC Analysis for PMOS V_G=VDD*R_5/(R_5+R_4 )=5*50k/(50k+100k)=1.66V V_S=〖(VDD-I〗_D)*R_6=〖(5-I〗_D)*1k V_SG=V_S-V_G I_D=(KP_p)/2 (W/L) (V_sg-V_THP )^2=0.145/2 (1/1) (5-1.66-I_D*1k-2.875)^2 I_D=0.073*(0.465-I_D*1k)^2→Solving for I_D I_D=433μA V_SG=5-0.39-1.66=2.95V AC Analysis for PMOS gm_p=√(2*KP_p*I_D )=√(2*0.145*433μ)=11.2 mA/V 1/(gm_p )=1/18.3m=89.29Ω v_sg=v_out-v_in i_d=v_sg*gm_p v_out=-i_d*R_6=〖-i〗_d*1k |v_out/v_in |=(gm_p)/(1/R_6 +gm_p )=11.2m/(1/1k+11.2m)=0.918 PMOS Output Resistance R_in=R_4 ||R_5=(50k*100k)/(50k+100k)=33.3kΩ PMOS Input Resistance R_out=1/(gm_p )||R_6=(89.29*1K)/(89.29+1k)=82Ω

NMOS and PMOS LTspice simulation results:

NMOS Experimental Results:

Shows gain of NMOS configuration which is essentially 1, no added resistor.

Shows input resistance results, with added resistor of 32.3k. The output is half the input.

Shows output resistance results, with added resistor of 50.56. The output is half the input.

The following table displays the theoretical and experimental results for the NMOS.

Data Type

Gain

Rin Ω

Rout Ω

Theoretical

0.948

33.3k

52

Experimental

1

31.7k

65.4

 

PMOS Experimental Results:

Shows gain of PMOS configuration which is about 0.78, no added resistor.

Show input resistance results, with added resistor of 32.2k. Output is half the input.

Shows output resistance results, with added resistor of 179. Output is half the input.

The following table displays the theoretical and experimental results for the PMOS.

Data Type

Gain

Rin Ω

Rout Ω

Theoretical

0.918

33.3k

82

Experimental

0.78

27.4k

170

 

NMOS and PMOS Common Source Amplifiers

These amplifiers are called common source amplifiers because Vin and Vout are common at the source.

LTspice circuit schematic:

NMOS and PMOS LTspice simulation results:

NMOS Experimental Results:

NMOS configuration shows a gain of 6 when Rsn it changed to 50 ohms instead of 100 ohms. 100 ohms created a gain of 4.5.

Shows input resistance results, added resistor of 32.3k.

Shows output resistance results, added resistor of 1k. Has expected gain of about 2.5.

PMOS Experimental Results:

PMOS configuration shows gain of about 2.7

Shows input resistance results, added resistor of 32.3k.

Shows output resistance results, added resistor of 1k. had an expected gain of about 1.3.

 

NMOS and PMOS Common Gate Amplifiers

LTspice circuit schematic:

NMOS and PMOS LTspice simulation results:

NMOS Experimental Results:

NMOS configuration shows a gain of about 4.39, no resistor added.

Shows input resistance results, added resistor of 198.7.

Shows output resistance results, added resistor of 1k.

PMOS Experimental Results:

PMOS configuration shows a gain of 2.42.

Shows input resistance results, added resistor of 413.

Shows output resistance results, added resistor of 1k. Has a gain of 0.84, slightly lower than expected. Theoretical gain is 1.21.

If Rsp is decreased to 50 ohms, the gain increases.

 

Push-Pull Amplifier

LTspice circuit schematic:

LTspice simulation results:

Experimental Results:

Gain with resistor of 100k:

Gain with resistor of 510k:

This concludes lab 6.

Additional Links

→ Return to listing of lab reports
→ Daniel’s CMOS homepage
→ Dr. Baker’s CMOS homepage