7.1.4 Input Bias Current Cancellation

The input stage base current of the OPA177 is internally compensated with an equal and opposite cancellation

current. The resulting input bias current is the difference between the input stage base current and the

cancellation current. This residual input bias current can be positive or negative.

When the bias current is canceled in this manner, the input bias current and input offset current are

approximately the same magnitude. As a result, there is no need to balance the dc resistance seen at the two

input pins (Figure 7-2 and Figure 7-3). A resistor added to balance the input resistances can actually increase

offset and noise.

7.2 Typical Application

Trim range is approximately ±3.0 mV.

Figure 7-1. Optional Offset Nulling Circuit

Conventional op amp with external bias current cancellation

resistor.

Figure 7-2. Input Bias Current Cancellation With

Conventional Op Amp

OPA177 with no external bias current cancellation resistor.

Figure 7-3. Input Bias Current Cancellation With

OPA177

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OPA177

SBOS008A – SEPTEMBER 2000 – REVISED SEPTEMBER 2023

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Product Folder Links: OPA177