A Mixed-Voltage Sensor Readout Circuit With On-Chip Calibration and Built-In Self-Test

This paper reports a mixed-voltage mixed-signal chip for interfacing multiple capacitive transducers to embedded processors in integrated microsystems. A programmable switched-capacitor readout circuit accommodates capacitive sensors from 16 fF to 40 pF and allows self-test and online calibration. The 20 mm
²
chip has a sensitivity of 1.25 mV/fF and is realized in a 1 mum n-well BiCMOS 2 P/2 M process that permits high-voltage operation, large-value resistors, and nonvolatile on-chip memory. An on-chip charge pump generates voltages up to 30 V that permits transducer electrostatic self-test. In normal operation mode, the chip provides a fast sensor readout consuming only 90 nj of energy, making it suitable for portable applications.