A MULTICHANNEL DIGITAL DEMODULATOR FOR LVDT/RVDT POSITION SENSORS

The architecture, VLSI implementation, and test results are presented for a mixed analog and digital multichannel demodulator used with linear/rotary-variable-differential-transformer (LVDT/RVDT) postion sensors. The monolithic multichannel demodulator has four regular demodulation channels and a fifth channel for system tests. Each channel has a first-order Σ-Δ 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 a new adaptive AM demodulation algorithm based on prediction techniques. Simulation of the digital circuitry as well as 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 83 000 transistors in a die size of 325X330 mils2. Test results show that absolute accuracies of ±0.2% of full scale are achieved without calibration. 0018-9200/90/0400-0441$01.00 © 1990 IEEE