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Noise analysis SNR Signal amplitude [TINA]

bilgehan paray
Prodigy 10 points

I want to sweep a resistor value and calculate SNRs at a certain frequency and compare them to decide which one is the largest, in an opamp circuit.

Problem is that signal amplitude is constant in Noise analysis tool, set by user. I want it to change according to the resistor value. 

Currently what I am doing is that, I run AC transfer analysis and measure signal amplitude there, then come back to total noise voltage and measure noise from there(and convert it to db). Then subtract them to get the SNR. How can I automate this? Or can I?

  • 0
    TI__Mastermind 37790 points

    Bilgehan,

    The noise analysis tells you the noise floor introduced by your circuit. I think you are measuring the noise at the output. This is output-referred noise. You can refer the noise at the input as well, which is the total noise measured at the output divided by the gain of your circuit. Your SNR will be simply the ratio betwen the input signal amplitude and the input-referred noise. There's no need for a separate AC analysis.

    A detailed analysis can be found by searching slyt094 on www.ti.com.

    Thanks,
    JC

  • 0 in reply to JC Zhu
    Expert 2056 points

    JC Zhu - WEBENCH Design Center said:

    You can refer the noise at the input as well, which is the total noise measured at the output divided by the gain of your circuit. Your SNR will be simply the ratio betwen the input signal amplitude and the input-referred noise. There's no need for a separate AC analysis.

    This does not show SNR as a function of frequency, though, does it?  That would be an AC analysis divided by an output noise sweep.  What the SNR plot actually shows is the cumulative noise integrated over frequency, same as the Total Noise sweep?  So the SNR plot will always decrease with frequency, as it accumulates more noise?  There's no way to plot (gain / output noise) vs frequency?

    Edit: Actually as shown in it seems like the "Signal to Noise" measurement doesn't tell you anything more than the "Total Noise" measurement.