A LOW-POWER DATA ACQUISITION IC FOR A MICROTRANSPONDER SYSTEM

M. Oberle¹, Q. Huang¹, P. A. Neukomm^2
1Integrated Systems Laboratory, ETH Zurich
²Laboratory of Electrical Engineering Design, ETH Zurich
Gloriastr. 35, CH-8092 Zurich

INTRODUCTION An implantable, fully-integrated, single-chip, one-channel microtransponder system for low-power biomedical data acquisition applications is reported. The energy and communication is provided using passive telemetry by absorption modulation. The microtransponder is part of an monitoring system which also includes an adapter unit and a standard stationary unit. The monitoring system allows long term recording of external blood pressure sensor signals. The microtransponder system is integrated in standard 3 m m high-voltage BiCMOS process.

METHOD The microtransponder incorporates a RF/DC converter for power conversion and data communication, a low drop-out, low-power 3V / 200 m A voltage regulator and a low-power data acquisition circuitry.

The blood pressure is measured through an external semiconductor strain gauge bridge. The resulting electrical signal is sampled, amplified and filtered by the analog part of the data acquisition circuit. Finally, it is transformed into a digital word through an integrated 9 bit dual-slope A/D converter. The output is a bit-serial pulse train transmitted through the RF/DC converter. A complete conversion cycle for one word is 10 ms long.

The digitized sensor data will be transmitted using a passive RF telemetry link by modulating the bit-serial pulse train onto a 40.68 Mhz RF carrier with a data rate of 1kBaud.

To reduce the average power consumption, a clock frequency of 1kHz and a duty cycle of 1:100 has been chosen for the sampling of the sensor signal. Amplification is achieved by a fully-differential switched-capacitor instrumentation amplifier, followed by a fully-differential switched-capacitor lowpass 50 Hz notch filter. Employing correlated-double sampling technique allows excellent DC offset and 1/f-noise reduction.

The clock signals for the switched capacitor circuitry will be generated by an internal 100 kHz clock oscillator. The overall power consumption of the data acquisition circuit is less than 400 m W.

RESULTS The switched-capacitor readout-amplifier of the data acquisition circuit has already been integrated and successfully tested. The amplifier features are listed in the following table. The complete microtransponder system is in fabrication. Final test results will be reported at the symposium.

Test results of the switched-capacitor readout-amplifier