Abstract
The impedance matrix of the n-channel FET as an active network device as well as the general matrix equation of performance of an FET cascode (ECG) bio-instrumentation pre-amplifier have been obtained. Further, an interesting design criterion for minimization of interfering noise voltage in the output of the said pre-amplifier circuit has been derived in the text. According to this criterion, the bias point of the pre-amplifier circuit is uniquely related to the active device parameters of a matched pair of FETs. The input to the said pre-amplifier may contain bio-signal source voltage along with the electrode artifacts and electrostatic and electromagnetic interfering voltages from the neighbouring electrical power networks. If the design criterion is fulfilled, there is automatic suppression of the said interfering voltages in the output of the pre-amplifier. The advantage of the present method of eliminating the interfering voltages in the recorded (ECG) bio-signal as compared to the usual frequency domain filtering techniques have been pointed out in the text.
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