A multichannel CMOS interface IC for recording car-crash conditions

This paper describes an interface IC that maintains the recording car-crash conditions, processes the crash-accident data, and provides the interface between the sensors and microcontroller. The monolithic multichannel Analog-to-Digital Converter (ADC) has four regular channels to monitor a dual axes acceleration sensor, an LC-oscillator based compass circuitry, and a speed signal detector. Each channel has a second-order Σ - Δ modulator implemented in switched-capacitor circuits and digitally implemented multi-stage filters with 3-dB bandwidth selectable of 100Hz and 360Hz. A fifth channel is used for system tests and for continuous calibration of temperature drift. Other circuits included are bandpass shock detectors, real time clock, battery check and emergency power management including high voltage MOS transistors. The circuits work in different modes to meet the low power requirement. This IC has been fabricated in a 0.7µm CMOS double poly double metal process and has an area of 32 mm². Experimental results of the complete system indicate proper operation over full temperature and supply voltage. The absolute achieved precision of the ADC channels are 12 bits of full scale from VSSto VDD. The power dissipations are 3µA@3.3V in stand-by mode, 500µA@5V in sleep mode and 12.5mA@5V in active mode.