Signal conditioning circuit between an optical device and a processing unit

The invention concerns a conditioning circuit for an external signal (IN) representative of a physiological quantity, arranged between an optical sensor and a processing unit, the received external signal (IN) being broken down into a useful component and an ambient component, characterized in that the conditioning circuit includes a first stage including a transimpedance amplifier with an incorporated high pass filter using a feedback loop to subtract the ambient signal component from the received external signal, and to deliver at output an amplified useful signal (IN), a second stage including a blocker sampler circuit for demodulating the amplified useful signal and delivering at output a demodulated useful signal (IN), and a third stage including a bandpass filter for filtering the demodulated useful signal in the frequency band of the physiological quantity to be detected and for transmitting a conditioned signal (OUT) to the processing unit.