Operational Amplifier balanced Resistance

When the input is equal to zero, the output end is not equal to zero because of the imbalance between the two inputs.
When there is a signal input, the original output will also be superimposed on the correct output signal, so that the output produces a deviation.
This principle is like a common voltmeter without zero adjustment before use (when the voltage is zero, the pointer does not mean zero ).

The balanced resistance of the operational amplifier is used to balance the offset current of the two input terminals of the operational amplifier, so that the voltage of the two terminals is balanced. Generally, the input level of an operational amplifier adopts a differential pair structure, and the difference requires strict symmetry of the circuit. However, the actual situation is that the Beta values of the two tubes cannot be completely consistent, which leads to an out-of-band voltage at the output end, therefore, to reduce the voltage imbalance, in the design, the balanced resistance is added to adjust the current of the two tubes and the balance resistance is used to adjust the offset voltage. This is only effective when a large Feedback resistance RF and a large offset current are used, otherwise, the offset resistance has little effect.

Calculation Formula of the balanced resistance: parallel resistance on the reverse arm = resistance of the same phase arm