SAW-LC coupled resonator wideband VCO for medical telemetry.

Abstract

Wireless links with implantable devices can help in real-time monitoring of symptoms, irregularities, implanted device efficacy and their reconfiguration. We present the design of a low-power wideband voltage controlled oscillator (VCO) to facilitate implantable wireless telemetry. A coupled SAW-LC resonator design combines high Q and spectral purity of a SAW element and tunability of an LC-tank. The designed 2.7 MHz bandwidth VCO is suitable for full duplex communication protocols in the MedRadio band with frequency agility and higher duty cycles, in conformance with FCC regulations. Output power at the fundamental frequency is above -7.5 dBm for a wide range of load impedances. Output power load insensitivity provides a wide margin for selection of communication system parameters, variability in device placement, temporal variation in tissue properties and flexibility for implants at different locations (e.g. heart, gastrointestinal tract, brain). The maximum output power variation in the entire 2.7 MHz band is limited to 1.3 dBm. Sensitivity of oscillation frequency to loading can be addressed by individual device calibration. The small size, component count and low DC power consumption (1.9 V, ~1.95 mW) is favorable for including in a miniaturized and integrated design assembly with a battery-powered implanted device.