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# newbee need help for complimentary differntial cascode amplifier

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##### Newbie level 4
I have designed a complimentary differential cascode amplifier and the pmos and nmos both are in saturation but i am not getting the gain can u plz help me???????? i hav designed it in cadence.The power supply is 3.3V and resistances use are 1Kohm. The sources used at gate are sinusoidal and the amplitude is 1mv and -1mv. frequency is 500hz and dc voltage is 1.2V.

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I don't know of what use your circuit is. It has no common mode rejection since it has no tail current source.
And there are four possible outputs. Two from NMOS drains and Two from PMOS drains.

The gain would be gm * Ro. Where gm is the transconductance of your transistor and Ro is the effective output impedance.
In this case Ro = 1/(gds) || 1kΩ.

Most likely your rout(1/gds) of your transistor is in mega-ohms or atleast in teh 100s of kilo-ohms range. so in parallel with 1kΩ, the output impedance is just 1Ω.
And your gm is not likely to be greater than the 10s of mS range unless this is a power part. This is why you have no or little gain.

Perhaps if you give some more details on your circuit, we may be able to help more.

The gain would be gm * Ro. Where gm is the transconductance of your transistor and Ro is the effective output impedance.
In this case Ro = 1/(gds) || 1kΩ.

Most likely your rout(1/gds) of your transistor is in mega-ohms or at least in teh 100s of kilo-ohms range. so in parallel with 1kΩ, the output impedance is just 1Ω.
Should read 1kΩ , I think.

And your gm is not likely to be greater than the 10s of mS range unless this is a power part. This is why you have no or little gain.
So the gain could be of the order 10-2 * 103 = 10 , isn't it?

Gain would be 10 in the 'best' case. ( 'Best' applied loosely since I don't know any sizes/parameters here.)
For a differential amplifier, a gain of 10 is not that great.

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