I am using the AD620 as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of \$G_d = 1000\$.
The datasheet has this formula: \$ G_d = 1 + \frac{49.4 \: \text{k}\Omega}{R_G}\$, so using two resistors of \$27 \: \Omega\$ gives me a gain of \$916 \$ which is good enough.
I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -
simulate this circuit – Schematic created using CircuitLab
My instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -
Question: Why is the second setup needed to generate a differential signal? What does the second setup do that the first one doesn't?