Bias current zeroing circuit for logarithmic and log ratio amplifiers LOG101/LOG1104

As shown in the figure, the bias current zeroing circuit of LOG101/104. The input current I1 and I2 of LOG101/104 are limited to the range of 100pA to 3.5mA. If the input current is greater than 3.5mA, the nonlinearity will increase; if the input current is less than 100pA, the input error will increase due to the input bias current (typical value 5pA). When the ±5V power supply is working, the current value of the input (I1 I2) is limited to 4.5mA. Two 10kΩ potentiometers R2 and R'2 are used in the circuit to zero the input bias current of the internal amplifiers A1 and A2. The internal amplifiers A1 and A2 are field effect transistor (FET) inputs, so they have FET input bias current characteristics, that is, the input bias current will double for every 10℃ increase in temperature.