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Bias of folde cascode OP AMP

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wael_wael

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Hi friends
coulde you help me to find VB1, VB2 in the folded cascode OP AMP
untitled0la.png

regards
 

To maximize the output swing,
Vb1=vdd-(Veff4+Vt5+Veff5)----(=vdd-vt-2Veff, neglecting body effect and same veff)
Vb2=Veff10+Vt8+Veff8----(=Vt+2veff)

Here veff=Vgs-Vt

The output can swing 2 veff above ground and below Vdd.
 

The two things that determine the W/L are the bias current and Overdrive voltage(Vgs-Vt). You need to fix the overdrive voltage. Usually 100-200mV is a good number.

W/L=2Id/(uo*Cox*Vov²) for a long channel device.
 

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