What value of compensating resistor is required for bias current, and where should the resistor be placed?...?

Question

A voltage-follower is driven by a voltage source wit a resistance of 75 ohms...

(a) What value of compensating resistor is required for bias current, and where should the resistor be placed?

(b) if the two input currents are compensation for 42 micro-amps & 40 micro-amps, what is the output error voltage??

Answer 1

a) Bias compensation is usually not used for a follower, as the part is chosen so that it's bias current introduces negligible error. That is because usually the value of the source resistance is unknown or is variable.

But if Rsource is known, you can put a resistor between the output and the - input to do compansation. Value is equal to the source resistance, 75 ohms in this case.

b)If you mean the two inputs have bias currents of 40 and 42ua, with compensation, then the error voltage is 2ua x 75 = 150uv

PS: next time mention the word "opamp" I thought this was about an emitter follower and spent a lot of time on that.

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