ethan
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hi there,
I got problem with PSS, PAC, and PNOISE simulaion for my fold-cascode OTA with SC CMFB. have read Ken's paper and tried again, but I still couldn't get the appropriate results, I think.
Hence I still would like to ask some body whether he or she would like to look into this problem further if doesn't mind. I appreciate your help.
I am new here and don't know how to attach my netlist in this forum. I can send it to your email if you are interested.
The brief description about my circuit and setup is following:
1. for the two diff-pair inputs, one input with 2.5v vdc ("V4") as common mode. another input is vsin ("V3"). four clock signals for SC CMFB (clk1 and clk1_b, clk2 and clk2_b) for transimission gate switches with all 200kHz. I didn't use "psin" as port, I only use vsin.
2. Since I followed Ken's paper on page 4 "First make sure the input signal is disabled", I didn't specify the frequency value and transient amplitude in vsin, am I right?
3. In PNOISE setup, for input part, I don't know how to choose, to choose "none",or "voltage source", or something. for output part, I chose "voltage", not port, not instance. Am I right?
4. For the waveform of PNOISE, its shape is still like the shape of open-loop gain plot. for PAC, I got 10dB gain, which just like the results when I use common AC analysis, 10dB gain. However, when I use equvilant circuit for SC CMFB, I can achieve 70dB; without CMFB for open-loop, I can achieve above 60dB.
5. When I setup PSS and PNOISE, I found I need "port" for the inputs of diff-pair. So I found port "psin" in my library, but how can I specify the certain amount resistance (by default is 50ohms) in psin for diff-pair inputs? I attach the psin properties in this email. Which is the correct way to setup psin? Or I totally don't need to psin, just to work with vsin?
6. I notice in PNOISE, there are two ways to simulate noise, one is in frequency domain with port "psin" inserted, another is in timedomain with "vsin" inserted as source. I have done two ways (I know what I did was not 60% right). My noise waveforms' shape just looks like open-loop gain waveform shape, there is no flicker noise corner frequency. It also is in same shape with what I did by using simple "noise" simulation in spectre. Can anybody tell me why?
7. for PSS, I doubt my results.
8. I am using TSMC0.35um technology and I think I only have spectre in our designkit in this school. We got spectre_RF in our 0.18 um technology designkit. Can I still apply them to spectre?
Thank you for your time and consideration.
Ethan
ps. I can email your my waveforms and netlist.
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