JFET input: why the 15 pA bias current matters
The 15 pA input bias current is the hallmark of a JFET amplifier. In a photodiode transimpedance amplifier, that bias current adds directly to the signal — 15 pA is negligible compared to the nanoamp-level photocurrent, so the error stays below 1%. For a precision integrator, the bias current charges the feedback capacitor and creates a voltage ramp; at 15 pA, that drift is small enough to allow integration times of several seconds before the output drifts appreciably. The 1 mV input offset voltage is typical for a trimmed JFET stage; if the application demands sub-millivolt accuracy, a nulling circuit or chopper-stabilized alternative would be needed.
Package and supply — board-fit constraints
The AD825ARZ comes in an 8-SOIC package (0.154" body width, 3.90 mm). Supply voltage range is 10 V to 36 V total.