Difference Amplifier Design

amplifieroperational-amplifier

I have two signal voltages

V1 ranging from 100mv to 600mV and

V2 ranging from 100mv to 600mv.

I want to implement a difference amplifier using this opamp 601 which is a single supply CMOS. My Vdd is 5V and Vss is 0V.

When V1>V2; I am getting an voltage 'X' as per the TF (V1-V2)*R2/R1

However when V2>V1; I am getting 0V. Where in I am actually supposed to get -ve 'X'

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Please guide me here.

  • Am I supposed to use -Rail to Rail Voltage OpAmp ?
  • I'm using R1 and R2 = 5.6 KOhm. Therefore my gain in 1.Because, I just need the difference between the signals
  • Is it because of improper choice of resistors ?

Thank you

Best Answer

You need to have a negative supply voltage on the op-amp to get a negative voltage out of it. A rail-to-rail op-amp can, at best, approach the supply rails at the output. A non-rail-to-rail type might only get to +1.5V if the negative rail is 0V.

So, the supply voltage must exceed the voltage you need out of the amplifier. If you need +/-4.9V, a +/-5V supply may do with a rail-to-rail output amplifier. If you have an LM324 it might only get to +3.5/-4.5V with a load resistor to ground.