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Bandwidth calculation of transimpedence amplifier (on a common source stage)

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sony019

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Bandwidth calculation of transimpedence amplifier(on common source stage)

Hello,
I want an equation to calculate the bandwidth/3db frequency of the circuit which is basically a transimpedence amplifier. Both the transistors are in saturation region.
Can you please help me out with some hints.
Thanks in advance.

Schematic.png
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

I can't recognize a transimpedance amplifier. Also, where's the amplifier output?
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

I can't recognize a transimpedance amplifier. Also, where's the amplifier output?
Output is in the drain of both nmos & pmos. Also this is an open loop configuration. I'm wondering how to approach first.
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

Hi,

this is an open loop configuration
I wonder if it is possible to build a transimpedance amplifier without feedback...

Klaus
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

There's a feedback resistance between gate and drain(output as well) of NMOS. I just omit it for simplicity.
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

Hi,

I just omit it for simplicity.
But you asked for bandwidth.... the feedback resistor will influence the bandwidth.
I may be wrong, but I think you can´t omit it for bandwidth calculations.

Klaus
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

Hello,
You're absolutely right. I need to calculate the bandwidth with and without the feedback resistor. So if I can find anyone of those I can do other one.
Thanks in advance.
 

Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

Sketch an equivalent circuit of the post #1 schematic. You'll see an input and output pole if Cdg is small. Cdg however acts as Miller capacitor and performs pole splitting. Derivation in profound analog design text books, e.g. Gray/Hurst/Lewis/Meyer.
 
Re: Bandwidth calculation of transimpedence amplifier(on common source stage)

Thanks FvM for your reply.
In my case both Cgd & Cgs are around 3fF which is quite small. And input frequency is just 1hz. So do I need to consider this capacitance.
Thanks in advance.
 

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