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Noise analysis on dynamic comparator

minci

 Hi,there

I am using  cadence IC5141 usr6 and MMSIM72.

I want to know the noise performance of my circuit,a dynmic comparator contains a pre-amp followed by latch.

I select noise analysis in ADE,sweep the frequecny from 1 to 10G,output noise I choose voltage,and select Pos.&Neg. differential output respectively.Then I am confusing about Input noise.Since my input is differential also and there is only one selection,I dont know how to do and just select one vdc source out of two.

The result is so weried,the input-referred noise is so big that is 1.3e+13.

I believe I have made some falses but I dont know where.And I try to find the simulation method in spectre manual but only to find nothing valuable about noise analysis.

I wonder whether noise analysis could be used for dynamic comparator,or just for linear op-amp? If not,how to simulate the noise of dynamic comparator where there are some switches during its operation?

 

Best regards

urian

 

Parents
  • Hello Andrew,

    very nice tutorial, many thanks for the new link.

    I tried to apply a pss/pnoise Analysis in order to find out the noise of my Clocked Comparator following the instructions given
    at page 51 and following and it seemed to me that everything was quite clear.

    1. Apply a small DC input voltage to comparator (1mV differential) and clock the comparator
    2. Setup Shooting Newton analysis to calculate the periodic operating point
    3. Use sample periodic noise analysis with the sample point determined by the differential output levels (internal latching nodes) of the comparator
    4. Set the sampling point to where the comparator differential output levels are separated by about 50mV
    5. Integrate squared noise of sampler output and take square root to find rms noise on ideal sampler from DC to Nyquist frequency
    6. Divide noise by gain from input to sampler output (50mV/1mV)

    I selected in the pnoise form --> noise type ´´jitter´´ and threshold value 10m, crossing direction ´´rise´´.

    It is verified on simulation results that the noise Analysis is done at this crossing Point, so it seems everything coherent and clear.


    But...when I change the threshold value to 50m, 100m, 200m I obtain totally different values for the noise.

    I apply a differential Input of 1mV at the Input of the comparator and, at the end (like suggested in step 6) I divide the integrated squared noise by the gain factor of 10, 50, 100, 200. Results of rms noise for the different cases are:

    Threeshod voltage - rms noise
    10mV 3.2mV
    50mV 975uV
    100mV 399uV
    200mV 157uV

    I cannot understand this variation...
    Overmore, I simulated the comparator noise in the time Domain (transient+noise) obtaining a Sigma_rms_noise=350uV.
    I am pretty sure that this second Simulation is good, unlucky it requires a lot of time and I would prefer a faster way to Support Long and painful design sessions.

    So, how to get correct results from pss/pnoise Analysis (it is evident that I am doing something wrong) and I have no idea how to proceed.

    Many thanks in advance for your help.

    Mauro
  • in reply to maurocleris

    Hi,

    I have exactly the same problem.

    Any update on this post ?

    Thanks a lot,

    Antonio

Reply Children
  • in reply to antoniosouza

    Should normally work. I have tested it for my dynamic comparator and when I am simulating for different thresholds, I am getting the nearly the same input-referred noise. Probably a wrong setting? Without seeing your testbench and ADE L setup, I cannot help you except by saying: try to do the same as described in the workshop.

    Kind regards,

    Nicolas

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