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Noise Simulation of Chopper Amplifier using PSS & Pnoise (Read 15770 times)
jdp
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Noise Simulation of Chopper Amplifier using PSS & Pnoise
Aug 29th, 2015, 2:32am
 
Hi.

I am trying to simulate a simple chopper stabilized op-amp in Cadence Virtuoso (PSS + Pnoise analyses), and seeing the output noise spectrum. So, it is expected that the chopping and anti-chopping will translate the 1/f-noise spectrum (of the op-amp) to the chopping freq.

PROBLEM: although it seems that the flicker noise has got shifted to the chopper freq (1 kHz), but, some Flicker-like noise seems to have got introduced at baseband

I am not sure if this is some kind of circuit phenomenon;  or simulator-settings issue (various permutations of which I have tried out, and also tried to follow whatever literature/tutorials available on internet)   Embarrassed

Any suggestion/help in this regard is highly sought.

Thanks and Regards,
Jay
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Ckt_sch_and_output_noise__ADE_settings.png

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Ken Kundert
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #1 - Aug 29th, 2015, 5:45am
 
I recommend creating the noise contribution summary to determine which devices are responsible for the low frequency noise.

-Ken
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jdp
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #2 - Sep 2nd, 2015, 3:39am
 
Hi Ken,

From Pnoise simulation Noise Summary, it seems that 4 MOSes in the op-amp are contributing most of the noise. Please see the attached figure.

Also, I am showing the noise spectrum before and after the anti-chopper, side by side (note the different y-axes scales) - it is evident that there is reduction in noise, but the additional 1/f-noise in the spectrum after the anti-chopping seems strange!...any idea if this is okay??

Regards.
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Ken Kundert
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #3 - Sep 5th, 2015, 7:22pm
 
Chopping will only cause the flicker noise to go away if the chopping is perfectly symmetric. Is it possible that the excess noise in your circuit is caused by an asymmetry in the chopping?

-Ken
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hiSkill_11
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #4 - Sep 7th, 2015, 12:17am
 
Did you make sure the chopping clock is nonoverlapping?

jdp wrote on Aug 29th, 2015, 2:32am:
Hi.

I am trying to simulate a simple chopper stabilized op-amp in Cadence Virtuoso (PSS + Pnoise analyses), and seeing the output noise spectrum. So, it is expected that the chopping and anti-chopping will translate the 1/f-noise spectrum (of the op-amp) to the chopping freq.

PROBLEM: although it seems that the flicker noise has got shifted to the chopper freq (1 kHz), but, some Flicker-like noise seems to have got introduced at baseband

I am not sure if this is some kind of circuit phenomenon;  or simulator-settings issue (various permutations of which I have tried out, and also tried to follow whatever literature/tutorials available on internet)   Embarrassed

Any suggestion/help in this regard is highly sought.

Thanks and Regards,
Jay

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jdp
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #5 - Sep 8th, 2015, 7:10pm
 
Hi hiSkill_11,

I have tried with both non-overlapping as well as normal complementary clocks for chopping - but same problem in both cases  :(

Hello Ken,

Regarding asymmetry in chopping - I am not able to find any myself (maybe I am overlooking something), like the duty cycle used is 50%, switches are ideal,...

I am sure I am doing something silly that I am not able to find on my own  :-[

Thanks...

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petitidiot
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #6 - Sep 16th, 2015, 4:24am
 
Is your chopping frequency too low?
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jdp
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #7 - Sep 16th, 2015, 5:38am
 
No.
I have tried with chopping freq of 1 kHz, 10 kHz, etc. Also, have ensured that this freq. is within the op-amp bandwidth.
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saqibshah
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #8 - Oct 8th, 2015, 6:00am
 
I think your circuit is behaving OK. If you take a look at your 1/f noise before anti-chopping it is in the mV range, but has decreased to the uV range after anti-chopping. Correct me if I am wrong.

Before anti- chopping : approx 80mV peak flicker noise
After anti- chopping : approx 800uV flicker noise.
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jdp
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #9 - Oct 10th, 2015, 7:42am
 
Yes, there has been reduction in flicker noise indeed...but the low freq. 1/f behavior still persisting is what is unexpected.
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #10 - Oct 15th, 2015, 3:08pm
 
I am also working on a chopping amplifier and am seeing a similar effect.

With the chopping switches enabled I do see a significant reduction in IRN and removal of DC offset, but there is still a 10dB/decade rolloff at low frequencies (like OP).  I have tried increasing my chopping frequency well beyond any flicker noise, but the 10dB/decade rolloff still remains.

Is this expected? Or do people see a flat curve even to sub-Hz frequencies when they have done chopper design.

If OP or anyone could resolve this, I would be much appreciated.
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Ken Kundert
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #11 - Oct 18th, 2015, 9:30am
 
The chopping is never perfect. There is always some asymmetry in the chopping or some feed through around the switches. You can never completely get rid of the 1/f noise.

-Ken
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Raghu9685
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #12 - Mar 16th, 2016, 10:31am
 
jdp wrote on Aug 29th, 2015, 2:32am:
Hi.

I am trying to simulate a simple chopper stabilized op-amp in Cadence Virtuoso (PSS + Pnoise analyses), and seeing the output noise spectrum. So, it is expected that the chopping and anti-chopping will translate the 1/f-noise spectrum (of the op-amp) to the chopping freq.

PROBLEM: although it seems that the flicker noise has got shifted to the chopper freq (1 kHz), but, some Flicker-like noise seems to have got introduced at baseband

I am not sure if this is some kind of circuit phenomenon;  or simulator-settings issue (various permutations of which I have tried out, and also tried to follow whatever literature/tutorials available on internet)   Embarrassed

Any suggestion/help in this regard is highly sought.

Thanks and Regards,
Jay


Hi Jay

I am trying similar  chopper amplifier for noise simulation but not able to see 1/f-noise shifting at chopper frequency  PSS & PNOISE simulation result. I have done similar setting of PSS & PNOISE as you mention .
please help me how to simulate this .....I don't what I am missing.

Thanks & Regards

Raghu
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ULPAnalog
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #13 - Mar 16th, 2016, 12:03pm
 
Hello Raghu

I have not followed this thread before, so here are some thoughts.

1. It is not entirely clear to me on how your output common mode is being set. Have you simulated the amplifier under nominal conditions without introducing chopping? Are the DC operating points as expected? You may want to do this, first to check if the amplifier is indeed working as an amplifier and secondly to see where the flicker noise corner lies.

2. Jay's simulation settings are all good as far as I know. But I would make refsideband parameter = 0 to use the correct conversion gain when the noise is referred back to input (Input referred noise is usually useful figure for amplifiers).

Thanks and regards

PS.  It would have been better if you had created a separate thread, with a link to this topic, to be compliant with the forum guidelines.
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Raghu9685
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Re: Noise Simulation of Chopper Amplifier using PSS & Pnoise
Reply #14 - Mar 16th, 2016, 12:45pm
 
Hi ULPAnalog

yes I have simulated amplifier with gain of 51 db & bandwidth of 3 Mhz .
and I am getting flicker noise corner frequency from noise simulation about 100 khz.

steps that I followed :-

1. Simulated  Folded-cascode ampifer and optimize aspect ratios (W/L) for low noise . Using spice2 model of flicker noise.
2. Simulated modulator and demodulator circuit for chopping .
3. Then simulated chopper amplifier in this I have done analysis are as    
followed :
a. DC
b. AC
C. PSS
d. PNOISE

I don't what I am missing ...
please help me out..

Thanks & Regards
Raghu
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