AC coupling using NMOS and PMOS

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    Ac Coupling Pmos
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Discussion Overview

The discussion revolves around the concept of AC coupling using NMOS and PMOS transistors, focusing on the differences in circuit behavior and output waveforms between the two configurations. It includes elements of homework problem-solving and technical explanation.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant asks for clarification on what AC coupling using NMOS and PMOS means.
  • Another participant describes a circuit where the drain of M2 is AC coupled to drive a load, explaining the role of M1 in setting up current mirroring to M2.
  • A participant presents a homework statement indicating they have successfully implemented AC coupling with NMOS but encountered different results when using PMOS.
  • One participant questions why the output from the PMOS circuit should not match the NMOS output in waveform and value.
  • A later reply acknowledges the concern about the PMOS circuit's output waveform, indicating a realization of a previously unnoticed aspect.

Areas of Agreement / Disagreement

Participants express differing views on the expected behavior of the PMOS and NMOS circuits, with some uncertainty about the output waveforms and values. The discussion remains unresolved regarding the reasons for the differences observed.

Contextual Notes

There are limitations in the explanations provided, particularly regarding the assumptions made about circuit behavior and the specific conditions under which the outputs were measured. The discussion does not clarify the mathematical or theoretical basis for the differences in waveforms.

nobrainer612
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AC coupling using NMOS

Hello. What does AC coupling by using NMOS and PMOS actually means?
 
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The drain of M2 is AC coupled by C2 to drive the load R4.

The way the circuit work is M1 have the gate and drain shorted to set up the current which mirror to M2. The drain of M2 has positive voltage. So AC coupling is needed to bring it to ground reference level.
 

Homework Statement



The problem is to perform AC coupling by using NMOS and PMOS

Homework Equations


The Attempt at a Solution



AC coupling by using NMOS is solved. Then I tried to build one by using PMOS, but the result from these 2 are different.

This is the NMOS circuit:
jl03lz.jpg


This is the result waveform from this circuit:
fnfmea.jpg


This is the PMOS circuit:
33xbj4j.jpg


This is the result waveform from this circuit:
15mjzhh.jpg
 
Perhaps you'd better explain what you don't like about the second circuit. It seems to me that in both you achieved an output of 200mV p-p, so I don't see anything amiss.

(I won't be able to help you further, but if you explain this, someone may be able to.)
 
my question is, shouldn't the blue wave from the circuit built by PMOS has the same waveform and value as NMOS?
 
nobrainer612 said:
my question is, shouldn't the blue wave from the circuit built by PMOS has the same waveform and value as NMOS?
Oh! The invisible blue waveform. I had not noticed it!

I now understand your concern.
 

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