Hi
We need to collect 0 to 5 volts from the external input. The test shows that when the input voltage is 0 volts, the voltage at the front end of the op amp is 0 volts, but the voltage at the back end of the op amp is about 0.05 to 0.06 volts, resulting in the voltage collected in the range of 0 to 5 volts is inconsistent with the input voltage.
Hello,
This is expected behavior from the amplifier.
All amplifiers have input and output swing limitations, and these limits will be mentioned in the datasheet with respect to the supply rails of the device.
In the case of the LMV321 we can see that the datasheet mentions that the output can typically swing within 60mV of the negative supply rail with RL =10kOhm terminated to mid-supply:
In your circuit, we are seeing the exact same performance: 50-60mV from the negative supply rail (ground).
The easiest way to solve this problem involves splitting the supply rail to give additional swing to voltages near ground.
If this is not possible, it may be necessary to change the scaling of the amplifier to ensure full linear operation.
Some newer amplifiers will be able to swing closer to the negative supply rail, but they will never truly get to the rail, just very close.
Is this ADC feeding into a microcontroller? Is this 50/60mV range or less needed in your sensing system?
Best,
Jacob
