Indirect Current Feedback Instrumentation Amplifier with a Common Mode Input Range That Includes the Negative Rail

An instrumentation amplifier is presented which can handle common-mode voltages that extend 200 mV below the negative supply. The extended range is combined with a good common-mode rejection (91 dB) and good accuracy (0.1%) without the need for on-chip trimming. This has been achieved by the use of a simple PNP input stage with indirect current feedback. The output voltage can reach the negative supply. The offset voltage is 0.3 mV, the noise voltage is 30 nV/√Hz. The circuit can work at a supply voltages down to 2.5 V and the quiescent current is 240 μA. The instrumentation amplifier has been integrated in a semi-custom bipolar process.