There are three ways to amplify a signal close to the GND level with an op-amp:
- Applying positive and negative voltages to VDD and VSS respectively and treating GND as the midpoint potential (Figure 1)
- Dividing the supply voltage with a resistor divider and applying the divided voltage to the noninverting input, IN(+), of a single-supply op-amp (Figure 2)
- Using an Input and Output (I/O) rail-to-rail op-amp
The first method requires a negative power supply, and the second method requires additional external components.
An I/O rail-to-rail op-amp can amplify an input signal that swings from GND to VDD without using either a negative power supply or external components.
However, the I/O rail-to-rail op-amp cannot provide an output signal exceeding the GND-VDD range.