I am building an ECG sensor based on the AD620 instrumentation amplifier.For the purposes of testing , i have built a simple AD620 circuit with pin 2(-) and pin 3(+) connected to a 2.82mV(peak to peak) sinusoidal signal generator. pin 7(+Vs) is connected to +4.5,pin 4(-Vs) is connected to -4.5. a 33k Ohm resistor is connected between pin 1 and pin 8 which theoretically should give a gain of around 2.5. Pin 5(Vref) is grounded and pin 6(output) is connected to an oscilloscope with ac coupling. 1)My first problem is the signal on the scope is 282mV peak to peak which implies a gain of 100, how can this be explained and solved? 2) if I change the gain resitor from 33k, to 37.7k, to 70.3k, I still get the same output. 3)if I change the input signal from 2.82mV peak to peak to 0.91mV I stil get the same output swing, however if i switch off the signal generator the output goes to zero. I have also tried to connect 33k resitors between each input and the ground but the result is the same.