A differential switched-capacitor amplifier with programmable gain and output offset voltage

ABSTRACT

The design of a low-power differential Switched-Capacitor (SC) amplifier for processing a fully-differential input signal coming from a pressure sensor interface is reported. The circuit is intended to amplify the input signal, convert it to single ended mode and shift its output by an offset voltage; gain and output offset voltage are digitally programmable. The differential SC amplifier employs an Operational Transconductance Amplifier (OTA) error cancellation technique without requiring its output to slew to analog ground each cycle. Circuit topology is very insensitive to low OTA gain and allows attaining 9-bit linearity. A SC Common-Mode Feedback (CMFB) configuration with symmetric loading of the differential mode loop has been adopted to reduce charge injection and leakage current errors, as well as to settle faster than traditional CMFB circuits. The circuit has been successfully integrated into a SoC device which measures pressure sensor pre-processed signal with a 10-bit Analog-to-Digital Converter (ADC). Implemented in a standard 4-metal single-poly 0.25um CMOS process, the module occupies a silicon area of 0.115 mm², operates down to 1.8V and its 3-V typical current consumption is 40uA.

REFERENCES

• 1: Martin, K., Ozcolak, L., Lee, Y. S. and Temes, G. C. A Differential Switched-Capacitor Amplifier. IEEE Journal of Solid-State Circuits, 22, 1 (Feb. 1987), 104--106.
• 2: Enz, C. C. and Temes, G. C. Circuit Techniques for Reducing the Effects of Op-Amp Imperfections: Autozeroing, Correlated Double Sampling, and Chopper Stabilization. Proceedings of the IEEE, 84, 11 (Nov. 1996), 1584--1614.
• 3: Choksi, O. and Carley, L. R. Analysis of Switched-Capacitor Common-Mode Feedback Circuit. IEEE Transactions on Circuits and Systems II, 50, 12 (Dec. 2003), 906--917.

INDEX TERMS

Primary Classification:
  B. Hardware
  B.7 INTEGRATED CIRCUITS
      B.7.m Miscellaneous

General Terms:
Design, Experimentation, Performance

Keywords:
analog integrated circuits, differential to single ended, switched capacitor stage