Johan F. Witte

A Current-Feedback Instrumentation Amplifier With 5

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 mm2 .

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In this paper, a current-feedback instrumentation amplifier for bidirectional high-side current-sensing is proposed. The current sense amplifier was fabricated in a 0.8mum BICMOS process with high-voltage transistors and laser-trimmed thin-film resistors. It is concluded that these amplifiers offer a new level of precision in current sensing.

Offset for Bidirectional High-Side Current-Sensing

In this paper we introduce an offset-stabilized operational amplifier that uses a chopper amplifier in a low frequency path to cancel the offset of a wide-bandwidth amplifier. A sample-and-hold circuit is used to reduce the chopper ripple, and the low frequency path is also offset-stabilized to further reduce the residual offset. The amplifier has 1muV offset at a 4 kHz chopper frequency, and a unity gain frequency of 1.3MHz with a 50pF load. The amplifier was realized in a 0.7mum CMOS process, and has an effective chip area of 3.6mm2