Indirect current feedback instrumentation amplifier with a common-mode input range that includes the negative roll

Abstract

An instrumentation amplifier which can handle common-mode voltages that extend 200 mV below the negative supply is presented. The extended range is combined with a common-mode rejection of 92 dB and an accuracy of 0.1%, without the need for on-chip trimming. This has been achieved by the use of two p-n-p V-to-f converters in an indirect current feedback configuration. The output voltage can reach the negative supply. The offset voltage is 0.3 mV, and the noise voltage is 30 nV/ square root Hz. The circuit operates at supply voltages down to 2.5 V, and the quiescent current is 240 mu A. The instrumentation amplifier has been integrated in a semicustom bipolar process. >