A multi-channel digital demodulator for LVDT and RVDT position sensors

The authors present the architecture, VLSI implementation and test results of a mixed analog-digital multichannel digital demodulator for a linear-variable-differential-transformer (LVDT) position sensor. The monolithic multichannel demodulator has four signal channels for demodulation and a built-in-test (BIT) channel. Each channel has a 12-bit Δ-Σ oversampled analog-to-digital converter (ADC) implemented with switched-capacitor circuits, and a dedicated digital demodulator with a 32-bit wordlength. The outputs from the ADCs are processed by digital processors. The digital demodulator uses a novel adaptive AM demodulation algorithm based on prediction techniques. A bit-serial silicon compiler is used to complete the design. The design was fabricated in a 1.2-μm bulk CMOS process and contains 85000 transistors in a die size of 325×330 mils². Test results show that absolute accuracies of ±0.2% were achieved without the need for calibration