A difference amplifier question

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SUMMARY

The discussion clarifies the role of resistor R4 in a differential amplifier circuit. R4 is essential for forming a voltage divider network with R2, enabling the circuit to achieve a gain of +1 when V2 is driven. The gain of the non-inverting amplifier is calculated using the formula R3/(R1 + 1). This configuration allows for precise control of the output voltage based on the input signals.

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perplexabot
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Hi. I am trying to find out what R4 is for or what its job is. Can anyone help? Thank you.
 

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This is a typical differential amp circuit that you have gain of -1 if you drive V1, gain of +1 if you drive V2. Remember the gain of the non inverted amp is R3/R1+1. In order to achieve gain of 1, you need to divid the V2 by 2 so when multiplied by 2, you get gain of 1. R4 form the divide network with R2.
 
yungman said:
This is a typical differential amp circuit that you have gain of -1 if you drive V1, gain of +1 if you drive V2. Remember the gain of the non inverted amp is R3/R1+1. In order to achieve gain of 1, you need to divid the V2 by 2 so when multiplied by 2, you get gain of 1. R4 form the divide network with R2.

I see, it is needed for a voltage divider. That makes sense. Thank you for your reply and sorry for my late reply.
 

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