Noise analysis of Sampling Mixer
I was studying sampling mixer and I have encountered a problem. There is noise formula which I do not understand where it comes from.
Can u help me with this ?
Very very easy.
About first equation.
This is derived from trasfer function which constitues RC LPF.
About Second equation.
This is derived from convolution.
Multiplication in time domain corresponds to Convolution in frequency domain.
See http://www.designers-guide.org/Analysis/sc-filters.pdf
For first one i dont understand how that transfer function is written? Isnt it a voltagr division zc/zc+ron
And second one i know its the convolution. It must be f-flo insteed of only f
? it should be like this
Simply, you can not understand convolution at all.
X(f) * delta(f-flo) = X(f-flo)
No.
You have to consider all contributions from delta(f+flo), delta(f-flo), delta(f+3*flo), delta(f-3*flo), ......
This is a noise folding.
I know what are u talking about, but we have f in noise function it should change to f-flo and f-3flo
Simply, wrong.
Surely see http://www.designers-guide.org/Analysis/sc-filters.pdf
Yeah i think i should read this all. I am getting the point now.
So what about transfer function ? I still dont know how its written like that ?
oh i understood now, i was making a silly mistake. Thank you very much it was so helpfull.