ECG Signal Acquisition

I am using AD620 instrumentation Amplifier to amplify the ECG signal. Here's the datasheet.
**broken link removed**

I am still in the initial stages of the signal acquisition process. Right now, I am trying to see if the AD620 can amplify the signal with a Gain of 13.4 approximately. I used a 3.98K Ohm resistor to get this gain.

However, I am not using electrodes to get the signal. I am just using a function generator to give me a sinusoidal signal at 70Hz and 50 mV pk-pk amplitude. I connected the positive end of the function generator to pin 3 of the amplifier and ground to pin 2.

I expect the pk-pk voltage to go up by a factor of 13.4 but I do not see a sinusoidal signal on the oscilloscope. I just see a DC output. Could someone tell me why this is happenning?

Thanks!

As a differential amp you need a reference. Put two 10K resistors, in series, across your function generator output. Connect your instrumentation amp's power supply common to the junction of the two 10K resistors.

The setup in figure 36 is better...referred to as "driven right leg"...to reduce noise and offset signals from the "patient".

Ken