A multichannel digital demodulator for LVDT/RVDT position sensors

The architecture, VLSI implementation, and test results for a mixed analog and digital multichannel demodulator used with linear/rotary-variable-differential-transformer (LVDT/RVDT) position sensors are presented. The monolithic multichannel demodulator has four regular demodulation channels and a fifth channel for system tests. Each channel has a first-order Sigma - Delta analog-to-digital converter implemented in switched-capacitor circuits, and a dedicated digital demodulator with a 32-b word length. The outputs of the analog-to-digital converters are digitally demodulated, down-sampled, and filtered. The digital demodulator uses an adaptive AM demodulation algorithm based on prediction techniques. Simulation of the digital circuitry as well as a placement and routing of the mixed signal circuitry was done using a bit-serial compiler. The design was fabricated in a 1.2- μm p-well bulk CMOS process and contains 83000 transistors in a die size of 325*330 mil². Test results show that absolute accuracies of +or-0.2% of full scale are achieved without calibration.