# Need help with threestage MOS Amplifiers design

Discussion in 'Homework Help' started by latete, Apr 8, 2012.

1. ### latete Thread Starter New Member

Apr 8, 2012
3
0
I need to design a threestage MOS amplifier that adheres to the following:

1) 1st stage should be a differential amplifier
2) 2nd stage should be common-emitter or common-source
3) 3rd stage Class AB

These specifications need to be observed:
Signal path = DC coupled, no series capacitors
Maximum transistor channel length = 12μm
Max number of independent sources for bias = 1
Power supply voltage = ±15V
Minimum output voltage at 1KHz = ±12 Vp-p across 100Ω load
minimum single-ended open-loop gain = 50 dB (20logAv0
Max offset voltage for 0V differential input = 20mV for ±15 V supplies
minimum gain-bandwidth product = 10 MHz with 45° phase margin
Max THD at 1kHz = 1% for ±12 Vp-p across 100Ω resistor
minimum CMRR at 1KHz = 70 dB
Max DC power consumption, load resistor = ∞, = 0.75W

If some one could walk me through the stages and help me understand this design process, I would definitely appreciate it very much.

2. ### panic mode Senior Member

Oct 10, 2011
1,664
474
i guess you need a little hint. here is comparable amp with BJTs from book "The Art of Electronics" 2nd Edition by Horowitz & Hill. this should get you started:

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3. ### panic mode Senior Member

Oct 10, 2011
1,664
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Jaeger - Blalock "Microelectronics Circuit Design 4th Ed" Chapter 15 has just about everything you need.

you need to design circuit stage by stage, calculate all components by working from output towards inputs.
Once you have every resistor and current source sized and you know Q points of each transistor, you design each transistor (W/L ratio).

4. ### latete Thread Starter New Member

Apr 8, 2012
3
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My biggest problem really is that I am not sure how to test the circuit. For example, I have built this one as my 1st stage. I do not know how to test it to see whether or not it is working?

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5. ### panic mode Senior Member

Oct 10, 2011
1,664
474
sounds like you need to go back to your book and learn how this supposedly works. all electrical circuits are something - a black box - that do things when stimulated in certain way. if you don't know this, you cannot tell if circuit behaves as expected. in case of amplifier, i'd expect to see amplitude change, hopefully proportional to input signal. i'd try bringing input signal, carefully change it's magnitude and record outputs

6. ### panic mode Senior Member

Oct 10, 2011
1,664
474
here are some figures from mentioned book, you can replace M4 in first image with output stage shown in second one.

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Apr 8, 2012
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Thanks guys!