This circuit is design for bias current compensation circuit. This circuit uses pre-regulation to solve this problem. The added reference diode has a low breakdown so that the minimum operating voltage of the op amp is unrestricted. This is the figure of the circuit;
The fact that this reference can be used for other functions should not be overlooked because a regulated voltage is frequently required in designs using op amps. This circuit is a divider is used so that the resistor feeding the compensating current to the op amp can be reduced. There will be an error current developed for any offset voltage change across R6. This should not be a problem with the LM11 because of its low offset voltage. But for tight compensation, mismatch in the temperature characteristics of R4 and R5 must be considered.
[Schematic circuit source: National Semiconductor Notes]
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