Patent ID: 7988638

Claim:
A conditioning circuit for an external signal representative of a physiological quantity between an optical sensor and a processing unit, wherein the received external signal is broken down into a useful signal component and an ambient signal component, wherein said conditioning circuit includes: (a) a first stage including a transimpedance amplifier with an incorporated high pass filter using a feedback loop to subtract, at a stage input, the ambient signal component from the received external signal and to deliver, at a first output, an amplified useful signal; (b) a second stage including a blocker sampler circuit connected to demodulate said amplified useful signal and to deliver, at a second output, a demodulated useful signal; and (c) a third stage including a bandpass filter connected to filter said demodulated useful signal in a frequency band of the physiological quantity that is to be detected by the optical sensor, and the bandpass filter is connected to transmit a conditioned signal to said processing unit, wherein the bandpass filter is a 5 th order Bessel type filter comprising a switched capacitance circuit that includes a first 3 rd order bandpass filter in series with a 2 nd order low pass filter.