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Doubt in Razavi's book

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leelamadhav

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Hi,

I have a doubt in razavi's book. It is in Switched capacitor chapter pg 425. Here he says if switch s1 is open then the voltage at Vp and Vx goes to infinity if the capacitance from node vx to gnd is zero.
Also he says if cx is the capacitance frm Vx to Gnd then both Ch and Cx will carry a charge equal to dq1. I did not understand both these statements. Any one please help me out.

Thanks
 

Any one plz tell me why the voltage jumps to infinity..
 

I belive it is because the charge injection from the switch flows into X. If there is no capacitance there then the only impedance is the input resistance of the amplifier which is ideally infinite. This small current from the charge injection is absorbed by the amplifier and the V=IR drop will be infinity.
 
"Ch and Cx will carry a charge equal to Dq1". This is because of total charge must be conserved, ie net charge before injection = net charge after injection
Qch + Qcx = (Qch + Dq1) + (Qcx - Dq1)
 

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