Calibration of Delta Sigma Converters in Synchronous Demodulation Sensing Application

TITLE: Calibration of Delta Sigma Converters in Synchronous Demodulation Sensing Applications

Advisors: Sameer R Sonkusale (Tufts), John Lachapelle (Draper)

Researchers: Ashwin Duggal

Sponsor: Draper Labs

ABSTRACT:

In capacitive sensing applications like in accelerometers, tuning fork gyroscopes and broadband dielectric spectroscopy,  synchronous demodulation techniques are employed. Synchronous demodulation are a general class of measurement algorithms that resemble lock-in detection. In such systems, delta sigma converters are typically employed to provide digital representations of in-phase and out-of-phase signal information. However, the analog coefficient errors in the loop filter and the signal path, causes the noise transfer function to deviate from its expected value. This seriously degrades the overall resolution of the sensing front end containing the sigma delta modulator.

Exploring the apriori known nature of the input, and utilizing existing analog components on chip, we propose simple calibration techniques to correct for the errors introduced in the noise transfer function. The approach can be extended to calibration of any delta sigma converters.