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3db Bandwidth of diff amp

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anal0g

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Can someone please help me in calculating the 3db bandwidth of this diff amp ?
I am attaching the schematic.
Thanks

[/img]
 

PoojanWagh

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The nodes Vout have some capacitance. Let's call the total capacitance on each side (mostly due the the drain capacitance of the MOSFET's plus any load capacitance not shown in your circuit) as Co.

The 3-dB bandwidth is 1/(2*pi*R1*Co).
 

anal0g

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So R2 has no effect on the 3dB bandwidth ? I would imagine that it does ...
 

PoojanWagh

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R2 has no effect if you are driving the circuit differentially and looking at the differential output. I presumed this was the case, since you have a tail current source that greatly suppresses any common-mode gain.

The common-mode bandwidth is

1/(2*pi*(R1+R2/2)*2*Co)
 

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