A functional monitoring system for electrical safety of biochips

A safe electrical connection between an integrated circuit and the human body is required for the recording of physiological signals such as ECG, ENG, or EMG. The recording chip is typically connected to the patient through a blocking capacitor, which prevents the flow of DC currents in the event of circuit failure. However, in systems with a high integration density blocking capacitors become inconvenient due to their large size and the effect on the signal transfer function. Therefore, a fully integratable functional monitoring scheme is proposed which involves applying a test signal to the amplifier input and detecting its presence at the output. In the event of failure the resulting change in the output voltage is detected and the chip can be switched into a safe state. Test signal addition and extraction circuits are proposed and analyzed. Simulated results are presented to confirm the correct operation in the context of a typical recording front-end.