Bias Current Compensation Circuit Using LM11

This is design circuit of bias current compensation circuit. This circuit can operate from MW source resistances with little increase in the equivalent offset voltage. This circuit is based on LM11. This is the figure of the circuit.

This is impressive considering the low initial offset voltage. The situation is much improved if the design can be configured so that the op amp sees equal resistance on the two inputs. However, this cannot be done with all circuits. Examples are integrators, sample and holds, logarithmic converters and signal-conditioning amplifiers. And even though the LM11 bias current is low, there will be those applications where it needs to be lower.

[Circuit source: National Semiconductor Notes]

Bias Current Compensation Circuit for Use with Unregulated Supplies

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]

Low Impedance Loads Circuit Using LT1210

This is a circuit for impedance load of voltage. This circuit is work using transformer coupling that is frequently used to step up transmission line signals. This circuit is based on LT1210 IC. This IC is fast and capable of delivering high levels of current. They can be readily compensated for reactive loads and are fully protected against thermal and short-circuit faults. This is the figure of the circuit.


The operation of this circuit is begun from a transformer-coupled application for ADSL in which an LT1210 drives a 100W twisted pair. The 1:3 transformer turns ratio allows just over 1W to reach the load at full output. Resistor RT acts as a primary side back termination and also prevents large DC currents from flowing in the coil. The overall frequency response is flat to within 1dB from 500Hz to 2MHz. Distortion products at 1MHz are below – 70dBc at a total output power of 0.56W (load plus termination), rising to –56dBc at 2.25W. If RT is removed, the amplifier will see a load of about 11W and the maximum output power will increase to 5W. A DC blocking capacitor should be used in this case. [Schematic source: Linear Technology Corporation, Inc].