A 0.5-mW passive telemetry IC for biomedical applications

A low-power, single-chip, one-channel, fully implantable microtransponder system for low-frequency biomedical sensor applications is described. The circuit is powered by an external RF source at 27/40 MHz. No battery is required. Wireless communication with external monitoring units is realized by absorption modulation. As the radiated power received by a small coil can be as low as a few milliwatts, the data acquisition/transmission system has been optimized for low power consumption. The system has been integrated in a 2-μm 40-V BiCMOS technology. It includes a low-offset amplifier, a low-pass notch filter, an A/D converter, a voltage doubler/rectifier, as well as a low-power voltage regulator. The implemented switched-capacitor amplifier features 45-μV offset and an integrated noise of 21 μV for a bandwidth of 30 Hz while consuming less than 30 μW power. The digitized sensor data are transmitted as low duty-cycle PPM-AM signals with a rate of 1 kBd. The entire system, including the 1.6-kΩ bridge sensor, consumes only 520 μW, which makes it well suited for long-term monitoring of biomedical signals