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how does the feedback affect the circuit noise performance?

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robicyang

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In Gray's book, the feedback has no effect on the circuit equivalent input noise. But my question is, does the feedback have no effect on the circuit equivalent input noise rms value or the equivalent input noise spectral density? i.e. for a circuit with the feedback, does the equivalent input noise rms value not change or the equivalent input noise spectral density not change comparing without the feedback? thanks.
 

surianova

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Re: how does the feedback affect the circuit noise performan

robicyang said:
In Gray's book, the feedback has no effect on the circuit equivalent input noise. But my question is, does the feedback have no effect on the circuit equivalent input noise rms value or the equivalent input noise spectral density? i.e. for a circuit with the feedback, does the equivalent input noise rms value not change or the equivalent input noise spectral density not change comparing without the feedback? thanks.

it shd effect the RMS noise bcoz feedbk will increase the bandwidth. More noise will be inside the circuit.
 

robicyang

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Re: how does the feedback affect the circuit noise performan

you mean that the equivalent input noise spectral density does not change?[/quote]

Added after 1 minutes:

it shd effect the RMS noise bcoz feedbk will increase the bandwidth. More noise will be inside the circuit.[/quote]

you mean that the equivalent input noise spectral density does not change?
 

hhplay

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Re: how does the feedback affect the circuit noise performan

I believe feedback system will reshape your noise. In fact, PLL is a feedback system which changes your input noise.
 

surianova

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Re: how does the feedback affect the circuit noise performan

robicyang said:
you mean that the equivalent input noise spectral density does not change?
Added after 1 minutes:

equivalent input noise spectral density will change bcoz in closed loop, the gain become lower .
 

rajanarender_suram

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Actually effective output SNR doesnot change with the feed-back. hence your noise performance of the ckt doesnt get better
 

robicyang

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Re: how does the feedback affect the circuit noise performan

surianova said:
robicyang said:
you mean that the equivalent input noise spectral density does not change?
Added after 1 minutes:

equivalent input noise spectral density will change bcoz in closed loop, the gain become lower .
please tell me, how do the output noise rms value and the output noise spectral density and the equivalent input noise rms value and the equivalent input noise spectral density change in closed loop comparing in open loop?
 

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