A Current-Feedback Instrumentation Amplifier With 5 $\mu{\hbox{V}}$ Offset for Bidirectional High-Side Current-Sensing

This paper describes an instrumentation amplifier for bidirectional high-side current-sensing applications. It uses a multipath indirect current-feedback topology. To achieve low offset, the amplifier employs a combination of chopping and auto-zeroing in a low frequency path to cancel the offset of a wide-band amplifier in a high frequency path. With a 60 kHz chopper clock and a 30 kHz auto-zero clock, this offset-stabilization scheme results in an offset voltage of less than 5 muV , a CMRR of 143 dB and a common-mode input voltage range from 1.9 to 30 V. The input voltage-to-current (
V-I
) converters required by the current-feedback topology are implemented with composite transistors, whose transconductance is determined by laser-trimmed resistors. This results in a less than 0.1% gain inaccuracy. The instrumentation amplifier was realized in a 0.8 mum BiCMOS process with high voltage transistors, and has an effective chip area of 2.5 mm
²
.