A Low Power, Low Voltage Current Read-Out Circuit for Implantable Electro-Chemical Sensors

A low power, low voltage current read-out circuit suitable for implantable electro-chemical sensors has been designed, fabricated and tested. The circuit converts a very low level current signal from a generic sensor into an ASK signal where the modulating signal frequency is proportional to the sensor output current, usually in the range of 0.2 muA to 2 muA. An on-chip potentiostat is also incorporated in the design to bias the sensor electrodes. A programmable frequency divider is integrated into the chip to set the ASK envelope frequency within the audio frequency range for ease of testing. This chip can operate with a supply voltage as low as 1.5 V and consumes only about 400 muW power. A second generation of the chip has been designed with FSK modulation scheme. FSK modulated signals offer better noise performance and higher power efficiency compare to ASK modulated signals.