My input voltage range is from 0 to 200mV. The signal power supply is 5V. In order to avoid the rail-to rail effect, I will a REF3112 to generate 1.25V reference to the REF Pin of INA155, In theory, the output voltage is G(V+ - V-)+REF. But I have found that the output is 0 when the input is zero, the voltage amplify is 10 but not very linear when the input voltage changes. My question is why the output is not Vref when the input voltage is zero. I have tried to connect the REF pin to GND. The output is zero, but I could understand that. But why I connect the REF to the voltage reference, the minimum output is not VREF, but zero. Thanks!