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Chopper-CDS Amplifier

Jihyun Cho, Jaeyoung Kim and Inhee Lee

Abstract

µV-level signals from sensors are amplified by many instrumentation amplifiers, which require high gain, low offset, and low input noise. µW-level power is also needed for portable applications. The paper proposes a low power spur-free precision amplifier using two offset cancellation technique, chopper stabilization and correlated double sampling (CDS). CDS cancels its offset and low frequency noise by 1-z-1 while the combination method processes input signals by 1+z-1. The amplifier has low DC gain to prevent output saturation but high gain at the chopping frequency for high input gain. Noise characteristics are analyzed for the amplifier itself and offset cancellation method. A temperature-compensated oscillator is included to avoid temperature variation and the effect of clock accuracy is also discussed. The proposed circuit, designed in 0.13µm CMOS process, consumes 50µA with 1.2V supply voltage and achieves the offset voltage with 5µV standard deviation and the input noise density of 100nV/√Hz.

1. M. Belloni, E. Bonizzoni, A. Fornasari, and F. Maloberti, “A Micropower Chopper—CDS Operational Amplifier,” IEEE J. Solid-State Circuits, vol.45, no.12, pp.2521-2529, Dec. 2010.

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