The invention provides a biopotential signal acquisition system, comprising at least two active electrodes (10,16) each for receiving a signal from an input, for example in the form of a respective patient contact. A unity gain buffer (32) is used to feed forward a signal from an associated input and provide the buffered output to the amplifiers of the active electrodes as a reference signal. The buffered signal is approximately equal to the input common mode signal so that the effective common mode input voltage appearing at the inputs of each amplifier is significantly reduced. This reduces the common mode gain of the active electrodes and thus improves their common mode rejection ratio while also avoiding saturation of the active electrodes.
