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input-referred noise measurement issue

engmsalik321

I’m facing an issue with the input-referred noise in a circuit I’m simulating in Cadence Virtuoso Spectre (maestro). The input noise I’m getting is significantly different from what I expected.

To elaborate, according to Chapter 4 of Dr. Behzad’s book, the output and input-referred noise of a resistance-based Transimpedance Amplifier (TIA) should be as follows:


However, when I simulate this circuit in Cadence and perform the noise analysis, I get the following results:

Interestingly, the output noise from the simulation aligns approximately with the formula. However, the input noise is completely different.

I’m unsure why this discrepancy exists and would appreciate any insights or suggestions.  I am calculating the total noise by integrating the I**2/Hz and V**2/Hz curves, as shown below. ( A form also discusses this method of noise measurement in cadence.)  


Thank you in advance for your help!

Update:  I have figured out from a circuit that the input noise is constant throughout the whole frequency band and is the thermal noise of the resistor, which is equal to 4kTR. (Where T=300k)
However, my method of integrating the input-noise is wrong. The integration method works for the output-referred noise because the output-noise curve decays and does not explode.  What will be the right way to find the input-referred noise?

Update2:
I tried to find the input-referred noise by dividing the Output Refereed Noise by the Gain, as shown below.

Now, I get the value of 346.8p, which is still not equal to the value given by the formula. What is the thing that I am missing?

  • I’m facing an issue with the input-referred noise in a circuit I’m simulating in Cadence Virtuoso Spectre (maestro). The input noise I’m getting is significantly different from what I expected.

    To elaborate, according to Chapter 4 of Dr. Behzad’s book, the output and input-referred noise of a resistance-based Transimpedance Amplifier (TIA) should be as follows:


    However, when I simulate this circuit in Cadence and perform the noise analysis, I get the following results:

    Interestingly, the output noise from the simulation aligns approximately with the formula. However, the input noise is completely different.

    I’m unsure why this discrepancy exists and would appreciate any insights or suggestions.  I am calculating the total noise by integrating the I**2/Hz and V**2/Hz curves, as shown below. ( A form also discusses this method of noise measurement in cadence.)  


    Thank you in advance for your help!



    Update:  I have figured out from a the circuit that the input noise is constant throughout the whole frequency band and is the thermal noise of the resistor which is equal to 4kTR. (Where T=300k)
    However my method of integrating the input-noise is wrong. The integration method works for the output-referred noise because the output-noise curve decays and does not explode.  What will be right way to find the input referred noise?

    Update2:
    I tried to find the input referred noise by dividing the Output Refereed Noise by the Gain as shown below.

    Now, I get the value of 346.8p, which is still not equal to the value given by the formula. What is the thing that I am missing?

  • in reply to engmsalik321

    Please do not post the same question in more than one forum - see the Guidelines for the Custom IC Design Forum.

    I was hoping to answer this (maybe somebody else will) but I haven't had time due to other commitments. However, posting the question multiple times just annoys people and won't necessarily get it answered any quicker.

    Andrew

  • in reply to Andrew Beckett

    Sorry for the trouble. Should I delete this, or it will automatically be deleted? 

  • in reply to engmsalik321
    engmsalik321 said:
    Sorry for the trouble. Should I delete this, or it will automatically be deleted? 

    No need; I merged the two threads.

    Andrew

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