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Fully differential OPAMP design for large input signal.

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ajaychowdharykr

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Hi guys,
I need to design a fully differential operational amplifier as an ADC driver. I will get +/- 0.5volt sinusoidal input signal and have to generate the differential signal with the DC shift(i.e 0.4-1.4 volt differential sinusoidal signal). The problem is that, if I can bias the input transistors with 0.9 volts and then apply my input signal, then my input transistor will be in the cutoff region when my input approach -0.5 volts.
do anyone have any clues, how should I start designing so that my linear range can be increased.
Any kind of support or material is appreciated.

Thanks.
 

It seems like your input pair is made of nMOS devices. If you sufficiently large Vdd, why not make your differential amplifier with pMOS input pairs?
 

A potentiometer. Send your signal at one end, say 5V at the other end. Take output at the wiper terminal. Dial it so the output is in your desired voltage range.

Your signal needs to sink a small amount of current for this method to work.
 

Input signal and amplifier input voltage are not the same. Please show the external circuit around your fully differential amplifier.

Amplifier input voltage can be shifted by using additional bias resistors. Or use bipolar supply voltage.

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Are you amplifying a single ended or differential input signal? What's the supported amplifier common mode input range?
 

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