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Oct 14th, 2019, 2:00pm
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confusion about pss+pnoise result of simple sample/hold circuit (Read 3006 times)
maxswell
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confusion about pss+pnoise result of simple sample/hold circuit
Jan 18th, 2017, 5:47pm
 
    hi all,i recently use pss+pnoise (source method & time method) to analysis very simple sample/hold circuit. and get a confusion result.
    switch frequency is just 2.5MHz, sample/hold cap is just 2pf, switch mos is just nmos, input voltage is dc voltage。
    when i  include flicker noise of MOS,  and  plot  pnoise spectrum with source method, pnoise spectrum has very very high spur at 10MHz in surprise, and also has a high spur at 100MHz, when i disable flicker noise effect, these two  spur frequency  points disappea.
    when i plot  pnoise spectrum with  time method (enable  flicker noise effect), i also find 10MHz and 100MHz spur during mos switch disconnect phase, so i am  confused  by these spur, because when mos switch disconnect (that is to say hold phase), output voltage should appear no noise , at lease, switch mos flicke noise should have no effect on output voltage, and during hold phase, there is no current flow through mos switch and cap ,flicker noise should disappear? is it wrong?
    The same phenomenon appear in the paper 《SIMULATION  AND ANALYSIS OF  NOISE  IN  SWITCHED CAPACITOR AMPLIFIER CIRCUITS 》,but the author have no explain
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« Last Edit: Jan 19th, 2017, 5:43pm by Ken Kundert »  
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Ken Kundert
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Re: confusion about pss+pnoise result of simple sample/hold circuit
Reply #1 - Jan 19th, 2017, 5:46pm
 
This occurs in any periodically modulated system that has flicker noise. The flicker noise gets mixed up to all multiples of the clock frequency. However, flicker noise is very narrow band, so you often do not see it. In this case you happen to place analysis points very near to a clock harmonic and so you see the spike caused by the up-converted flicker noise.

-Ken
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davidshw
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Re: confusion about pss+pnoise result of simple sample/hold circuit
Reply #2 - Jan 19th, 2017, 6:11pm
 
here is some information from spectreRF mannual, maybe useful for you

Flicker Noise
To avoid inaccurate results with Pnoise analysis on a circuit that mixes flicker noise or 1/f
noise up to the carrier or its harmonics, place a cluster of frequencies near each harmonic to
resolve the noise peaks accurately, but do not put frequency points precisely on the
harmonics. In addition, choose Pnoise start and stop frequencies to avoid placing points
precisely on the harmonics of the periodic drive signal. Then use the values parameter to
specify a vector of additional frequency points near the harmonics. In the Analog Circuit
Design Environment, the values parameter is set in the Add Specific Points field in the
Choosing Analyses form.
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maxswell
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Re: confusion about pss+pnoise result of simple sample/hold circuit
Reply #3 - Jan 19th, 2017, 10:28pm
 
hi  ken & davidshw, thank you for your reply,
because sample frequency is 2.5MHz, why not see spur at 2.5MHz,5MHz,7.5MHz,12.5MHz,15MHz,17.5MHz,..,
i just see spur nearby 10MHz & 100MHz ? can you explain detailed? thank you.
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Ken Kundert
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Re: confusion about pss+pnoise result of simple sample/hold circuit
Reply #4 - Jan 20th, 2017, 11:23am
 
What frequencies are actually being used in the Pnoise analysis?
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Re: confusion about pss+pnoise result of simple sample/hold circuit
Reply #5 - Jan 23rd, 2017, 12:41am
 
hi ken, spectreRF can't perform at extract integer multiple frequencies of 2.5MHz, when perform at extract integer multiple frequencies of 2.5MHz, log file report " infinite flicker noise is ignored". and i see that 10MHz & 100MHz  analysis frequencies spur departure ideal 10MHz & 100MHz about 0.5MHz, other analysis frequencies  departure  further respective   integer multiple frequencies of 2.5MHz than 10MHz & 100MHz ,  
it seem to flicker noise cause frequency spur。and i will go hometown for Chinese New Year from tonight, can't reply you in time.  thank you for your help.
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