noise in switch-capacitor circuit and noise peaking

[akbarza]

hi
i read the powerpoint filewith name switched capacitor.pptx.( more details:data converters eect 7327-Switched-Capacitor Circuits-Professor Y. Chiu
-2014)
in slide 24(title:in sampling(phi_1 active)-noise in sc circuit-cascaded stages) is written:
But parasitic loop delay may introduce peaking in freq. response, resulting in more integrated noise (noise peaking)
my questions:
what's the meaning parasitic loop delay?plz. explain.
what's the meaning of noise peaking?( i searched google and here but i didn't find anything).
how does parasitic loop delay cause noise peaking?
explain to me.thanks

 

[sutapanaki]

It means that you have parasitic caps that affect the loop gain of the feedback around amplifiers. Those parasitics will affect the non-dominant pole of the loop gain eventually bringing it closer to the unity cross-over frequency, which will reduce the phase margin of the loop. When this happens and when you close the loop, you will have a transfer function that exhibits peaking . If there is a peaking, it means the frequency components around the peak get boosted. Same is valid for noise in the frequency range of the peaking. Since that peaking usually happens at high frequencies around the corner frequency of the amplifier transfer function, when you integrate the noise, you will get an increase in the total integrated noise just from that specific area.