Hi, We are using a AD8421 as the front end for some general purpose data acquisition. It is being driven by a signal generator (with grounded negative side). If we put a 10k resistor (R10 in the schematic below) across the AD8421 inputs, the output hits the negative rail, without the resistor it is OK (the output follows the input properly). Power supplies are +-5V and the signal is well inside them. It makes no sense to me.