Ultra-Low Power Frequency and Duty-cycle Modulated Implantable Pressure-Temperature Sensor

An ultra-low power frequency and duty-cycle modulated pressure-temperature sensor for use in a novel congestive heart failure monitoring system is presented. The temperature reading is used to improve the accuracy of the pressure sensor. The sensor features a temperature accuracy of less than 0.06 degrees C over the range 20-50 degrees C, a 0.9fF capacitive accuracy after 3-point calibration, equivalent to 2.83 mmHg pressure accuracy and consumes 2.3 mu W. It frequency modulates pressure, and provides redundant measurements of temperature using independent frequency and duty-cycle modulation. It uses a proportional-to-absolute-temperature (PTAT) core to generate bias currents and voltages required for the modulation and bias references for the circuit. A micromachined capacitive sensor is integrated to obtain the pressure reading as a capacitance value. By combining frequency and duty-cycle data obtained from the sensor, both pressure and temperature can be reconstructed.