Spectre PSS Analysis

Hello Dear members,
I need one help regarding spectre pss analysis.the following points I
am looking to be answered.

1- How it is different from transient analysis.Can be achieve the same
results from both the analysis (if we try)
2- Actually I did not understand how PSS works on a circuit....If
anyone can elaborate on PSS methodology it will be really helpful.

currently I am designing a chopper amplifier for very low offset
voltage and by the literature it has been recommended to perform PSS
simulations for Input offset voltage.I wonder how PSS can provide
better results rather then normal transient sims?.

Thanks
Ankur

 

Dear Ankur,

1. You are designing a Chopper amplifier and a transient simulation is
not enough to measure the performance of it. You should be interested
in knowing the transfer function and the noise of this amplifier. But
how can you do it, at transistor level, for such a non-linear
circuit ? You need a DC operating point to run small signal AC/Noise
analyses. But since you've got a switching-mode design, then the idea
is to determine a steady state and run the AC/Noise analyses about a
periodic OP point. SpectreRF is capable of this by using tools like
PSS.

2. Bit from the Virtuoso Spectre Circuit Simulator RF Analysis Theory
(You should give a look at this doc, it is in your Cadence tree):
Periodic Steady-State (PSS) analysis is a large-signal analysis that
directly computes
the periodic steady-state response of a circuit with a simulation time
that is independent of
the time constants of the circuit. PSS quickly computes the steady-
state response of circuits
that exhibit extremely long time constants, such as high-Q filters and
oscillators.

Cadence has got loads of application notes about using SpectreRF and
PSS for VCOs, LNAs, Mixers, Power Amplifiers ...etc. It could be very
useful for you to have a look at those. Since you are designing a
Chopper Amplifier, I would rather advice the Ken Kundert's 'Simulating
Switched-Capacitor Filters with SpectreRF' which is the closest to
your application. You can find this document in:
http://www.designers-guide.org/Analysis/sc-filters.pdf

I used to run SpectreRF/PSS a while back when helping some RFIC
designers in debugging their simulations. I found a little document on
the Internet which was very helpful for my oscillator case. It might
help you as well. Just bear in mind to not tick 'oscillator' when
running PSS in your case.
http://ocw.mit.edu/NR/rdonlyres/Ele...4196-A616-34C4B5F328DA/0/spectre_tutorial.pdf

PSS analysis is very useful in RFIC design, it is quicker and more
accurate than the transient.

BTW, please give a look at the http://www.designers-guide.org/
documents. It's worth posting your question in that DG forum as well.
You are most likely to find IC design engineers over there.

Hope this help !
Riad.

 

Hello Riad,

The post was also helpful for me since I am also trying to simulate
the chopper stabalization schematic.

I went throgh the cadence tutorial..But still I need some help to
simulate the PSd of chopper opamp.

I just want to see the 1/f noise of opamp cancelled after the chopper
stabalization.

Do u have any example for this simulation?

Thanks

 

Hi There,

I'm happy it was usefull for you
the PSS/PNOISE will do the trick for you, did you try it ?
I haven't got any extra documentation for this I'm afraid. The
Cadence's SpectreRF docs I have mentioned above are good enough
though.

Cheers,
Riad.

 

Hi Riad,

I simulated the chopper amplifier with PSS/PNOISE analysis.

I can see that the 1/f noise at dc is gone. But I have high energy at
both sides of input signal frequency. But at signal frequency the
energy is less.
Energy at chopping frequency is also very less.
Is that right? I expect the large energy at the chopping frequency but
not at the sides of signal frequency.

Intention of my simulation is to find out the correct chopping
frequency which cancels the 1/f noise.
The signal frequency is 100Hz.The corner frequency of the opamp is
around 1KHz( I believe the simulation is correct!). Now I have
chopping frequency around 25Khz.
Do u have any idea, which is the best chopping frequency I can choose?

Thanks

 

Dear Naisar,

Your questions are a bit smart for me I'm afraid. I have no expertise
in chopper design I'm afraid. i can help you to set up the tools but I
don't want to confuse you with any wrong statement about your design
issue. I'm sorry about that. My design knowledge is very weak in this
area I'm afraid. I would advice you to search the Designer's Guide
Forum. There are plenty of references to your worries over there. I
did a little quick search for you an I found these comments from
Andrew :
http://www.designers-guide.org/Forum/YaBB.pl?num=1169037920/1#1
You will find more in this forum if you dig it well !

If you fancy some theory to understand your stuff, then it is worth
sparing some minutes on Chapter 5 of this book:
http://www.edacafe.com/books/phdThesis/Toc.php

I have borrowed this book from one of my colleagues here and I'm
really surprised it is available on the Web !! That's good for you !

Cheers,
Riad.

 

Hi Riad,

Thank you for ur effort in helping me!!..

I go through the links..

Thanks