Re: AD625 big problem
fala,
If I understand your description correctly, you have the amplifier set up for a gain of 50. With a 3.5 volt differential input, the input stage will saturate. Input resistance specs are valid only when the device is operating in its linear region. Also, input resistance measurements made with a multimeter are not valid, since th input R spec applies only with power applied, and the amplifier operating in its linear region. If you use a multimeter to measure input resistance with power applied to the device, the voltage that the multimeter (used as an Ohmmeter) will probably also cause the amplifier to saturate, so the reading will not be valid.
Regards,
Kral