Implementation of a Biopotential Amplifier with a Conventional and Current-Balancing Approach for Foetal ECG Monitoring

In a biopotential monitoring system, the sensors, the front end circuit, microprocessor, digital signal processor and transmitter are important blocks. The front end circuit is capable of amplifying and conditioning the biosignal. The power requirement of a biopotential monitoring system depends on the individual blocks present in the system. Direct reduction of the power is not possible in the conventional instrumentation amplifier. The conventional instrumentation amplifier is not suitable for portable applications because it consumes much power and has a low common mode rejection ratio (CMRR). To optimize the power consumption and simplify the system architecture, the front end system adopts two-stage amplifiers. A current-balancing instrumentation amplifier approach that amplifies a biosignal is proposed to improve the noise performance and CMRR and minimize the area, power consumption, and cost. In this CBIA design, passive component mismatch is minimized. To obtain an ECG signal, the output of an instrumentation amplifier signal is further processed by high pass, low pass and notch filters to eliminate muscular noise, motion artefacts and power line interference. The resultant signal is interfaced to a personal computer through a USB/SPI interface after the conversion of the analogue biosignal into digital signals.

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