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Noise analysis in cadence at input but low noise at output

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ICdesignerbeginner

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Hi

I am doing noise analysis in cadence of an OTA when I am running noise analysis the equivalent input noise is 400uV/sqrtHZ. And when selecting equivalent noise then output noise is 10uV/sqrtHZ. How output noise is less than input noise.

Can any one tell me what's the reason of getting low noise at output. According to my knowledge output noise should be high than input noise. When I am looking at noise summary it is, 2.6mV .

Thanks
 

The only way to get equivalent input noise lower than output noise is to have a gain below unity, which is of course possible. Or some kind of miscalculation, possible as well.
 
Thanks for your reply. I want to calculate input referred noise. Do I have to Chk equivalent input noise or equivalent output noise. Because IRN is noise decided by gain. Is it output noise divided by gain or input noise divided by gain
 

ICdesignerbeginner said:
According to my knowledge,
output noise should be high than input noise.
Click to expand...
It is not true.

Consider simple example.
Assume T or Pi attenuator using resistors.
Output noise power is k*T*B regardless of attenuation value.

Pn_in = k*T*B
Pn_out = k*T*B

|S21|^2 * (Pn_in + Pneq_in) has to be Pn_out.

Pneq_in = Pn_out * (1/|S21|^2 -1)
When |S21|^2 < 1.0, Pneq_in > Pn_out

So input equivalent noise power has to be larger than output noise power.

ICdesignerbeginner said:
Do I have to Chk equivalent input noise or equivalent output noise.
Click to expand...
It depends on your needs.

ICdesignerbeginner said:
Because IRN is noise decided by gain.
Is it output noise divided by gain or input noise divided by gain
Click to expand...
It is output noise divided by gain.

Show me noise contribution lists.
 

I want to plot input referred noise. In noise summary it just show IRN value not plot. Is IRN the equivalent input noise which we plot by going to print---equivalent noise given in v/sqrtHz.

In different research article noise spectral density is plot. How to plot noise spectral density?
 

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Attached is the noise contribution list.

Fot input referred noise I have to take equivalent output noise and divide by gain. For IRN I was check equivalent input noise.

noisecontribution.png
 

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