Lab

Lab 6 - EE 420L

Authored by Iain Drews, drewsi2@unlv.nevada.edu

3/19/2015

Important charts

based on these charts it is safe to assume we are going to be operating near the threshold voltage because if VGS was even 3 volts in the nmos it would generate 500mA Drain Current and vs would become 500V in the first three schematics due to the 1k resistor placed there. therefor it is safe to estimate we will be operating around 1.8V VGS,VSG with a very small current and around 10ms

Below are schematics for NMOS and PMOS source followers amplifiers (also known as common-drain amplifiers).
In your lab report discuss the operation of these circuits.

these circuits work by generating a current in the mosfett which due to ohms law generate and output voltage

In your lab report discuss, in your own words, how to measure the input/output resistance.

to measure the input/output resistance we created a voltage divider at the nodes in question.
the simplest way to do this is to pick a resistor which is the same size as we estimated the input/output resistance to be at
it the voltage on positive end of the resistor is twice that as the negative end then the estimate was correct. if not caculate the resistance using the voltage divider formula.

	Gain: 0.92 hand calcualtions: id=gm(vin-vout) id=vout1k vout1k=gm(vin-vout) vout(gm+1k)=gm*vin vout/vin=1/(1+1k/gm) gm is about 10ms from above chart 1/(1+1k/10m) gain=1/10M hand calcualtions must be off
	Rin using a 33kohm Resistor Rin=33kohm Hand calcualtions 50k\|\|100K=33k
	Rout using 130ohm resistor Rout is about 130ohm
	Gain: 0.80 hand calcualtions: id=gm(vin-vout) id=vout1k vout1k=gm(vin-vout) vout(gm+1k)=gm*vin vout/vin=1/(1+1k/gm) gm is about 10ms from above chart 1/(1+1k/10m) gain=1/10M hand calcualtions must be off
	Rin using a 33kohm Resistor Rin=33kohm
	Rout is about 193ohm

	Gain: -5.4 hand calcualtions: gain= -RD/(1/gm+RS) -1k/(1/10m+100) -1k(200) -5
	Rin using a 33kohm Resistor Rin=33kohm
	Rout using a 1kohm Resistor Rout=1kohm
	Gain: -2.9 hand calcualtions: gain=- RD/(1/gm+RS) -1k/(1/10m+100) -1k(200) -5 gm must be greater for this pmos
	Rin using a 3.3kohm Resistor Rin=3.33kohm
	Rout using a 1kohm Resistor Rout=1kohm

	Gain: 4.9 hand calcualtions: gain=RD/(1/gm+RS) 1k/(1/10m+100) 1k(200) 5
	Rin using a 200ohm Resistor Rin=200ohm hand calculations 100+1/gm=200 gm=10ms
	Rout using a 1kohm Resistor Rin=1kohm
	Gain: 5.0 hand calcualtions: gain=RD/(1/gm+RS) 1k/(1/10m+100) 1k(200) 5
	Rin using a 330ohm Resistor Rin=200ohm hand calculations 100+1/gm=330 gm=23ms (see above results)
	Rout using a 1kohm Resistor Rin=1kohm

Below is a push-pull amplifier.
Discuss the operation of this amplifier in your lab report including both DC and AC operation.
Hand calculate the gain of this amplifier.

Do you expect this amplifier to be good at sourcing/sinking current? Why or why not?
What happens to the gain if the 100k resistor is replaced with a 510k resistor? Why?

Again compare your hand calculations to simulation and experimental results.

Note that the gain of this amplifier is large so the output may saturate at VDD and Ground. To avoid this saturation you can reduce the AC input voltage using a voltage divider.

	100k resistor 1/52 voltage divider: vin=2/52=0.038 2.5/0.038=65 gain=100k(gmn+gmp)
	150k resistor 1/52 voltage divider: vin=2/52=0.038 3.66/0.038=95 gain=150k(gmn+gmp)

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