A digitally controllable current readout circuit and modulator unit for remote monitoring and biotelemetry applications

Healthcare providers are depending on remote patient monitoring system more and more to treat a patient before the conditions become acute. Low-power electronics is an integral part of the remote patient monitoring system which is required for data acquisition, signal processing and data transmission. This work reports a low-power digitally controllable current readout circuit and a modulator unit designed for remote patient monitoring system. The current readout block converts current (0.2 μA to 5 μA) from biosensors to a data signal whose frequency is proportional to the sensor current. A switched capacitor based modulator is realized which modulates the data using a low-power digital modulation scheme. The current readout and the modulator units are digitally controllable to save power and to provide either ASK or FSK modulated output signal. The circuit is simulated using a 0.35-μm standard CMOS process and it occupies less than 0.053 mm² of chip area. Power consumption of the circuit varies from 44 μW to 57 μW for 0.2 μA to 5 μA input current with 1.5 V supply, which is very attractive for biosensor applications.