In a mixed analog and digital integrated circuit for physiological signal instrumentation such as electrocardiographs, electromyographs, and electroencephalographs, an electronic differential amplifier comprises a chopper-stabilised first stage amplifier (402, 408, 412), a second stage amplifier (414) providing a negative output (418) and a positive output (416) to a chopper-stabilised feedback circuit (434-444), and a gain feedback circuit (420) which receives the negative output (418) and supplies a gain feedback voltage (24) to the first stage amplifier. The integrated circuit has five signal channels, each with analog amplification and analog to digital conversion. The channels can be configured for various combinations of input signal amplification, input signal summation, analog output driving, and AC impedance measurement. The integrated circuit has two digital serial input lines and two digital serial output lines, all designed for direct connection to optical couplers. Channel configuration, gain, and other parameters are externally controllable by a serial digital input signal. Up to six compatible devices can be serially connected in a chain. <IMAGE>
Biomedical amplifier circuit