SIGNAL CONDITIONING CIRCUIT BETWEEN AN OPTICAL DEVICE AND A PROCESSING UNIT

Abstract

The invention concerns a conditioning circuit (10) for an external signal (IN) representative of a physiological quantity, arranged between an optical sensor (11) and a processing unit (12), 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 (13) including a transimpedance amplifier with an incorporated high pass filter (15) using a feedback loop to subtract the ambient signal component from the received external signal, and to deliver at output an amplified useful signal (IN1), a second stage (16) including a blocker sampler circuit (17) for demodulating the amplified useful signal and delivering at output a demodulated useful signal (IN2), and a third stage (18) including a bandpass filter (19) 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear more clearly upon reading the following detailed description of embodiments of the invention given solely by way of non-limiting example and illustrated by the annexed drawings, in which:

FIG. 1 is an operational block diagram showing the whole of the conditioning circuit according to one embodiment of the invention;

FIG. 2 a is a flow chart of an advantageous embodiment of the first stage of the conditioning circuit according to the invention;

FIG. 2 b shows a preferred implementation example of the embodiment of the first stage of FIG. 2a;

FIG. 3 a is a flow chart according to one embodiment of the second stage of the conditioning circuit of the invention;

FIG. 3 b is a flow chart according to another embodiment of the second stage of the conditioning circuit according to the invention;

FIG. 3 c shows a preferred implementation example of the second stage of the conditioning circuit;

FIG. 3 d shows the control signals applied at the second stage according to the embodiments of FIGS. 3b and 3c;

FIG. 4 a is a flow chart according to one embodiment of the third stage of the conditioning circuit according to the invention;

FIG. 4 b shows the first section of a 5^th order bandpass filter of the third stage of the conditioning circuit;

FIG. 4 c shows the second section of a 5^th order bandpass filter of the third stage of the conditioning circuit;

FIG. 4 d shows a replacement circuit for each of the first four operational amplifiers of FIGS. 4b and 4c;

FIG. 5 is a cross-section of a portable electronic instrument comprising a conditioning circuit according to one embodiment of the invention;

FIG. 6, already described, is a block diagram illustrating various components of a portable instrument according to the prior art;

FIG. 7 is a flow chart of one embodiment of the first stage of the conditioning circuit.

Claims

1. A conditioning circuit for an external signal representative of a physiological quantity between an optical sensor and a processing unit, said received external signal being broken down into a useful component and an ambient component, wherein said conditioning circuit includes: a first stage including a transimpedance amplifier with an incorporated high pass filter using a feedback loop to subtract, at the stage input, the ambient signal component from the received external signal, and to deliver at output an amplified useful signal;a second stage including a blocker sampler circuit for demodulating said amplified useful signal and delivering at output a demodulated useful signal; anda third stage including a bandpass filter for filtering said demodulated useful signal in the frequency band of the physiological quantity to be detected and for transmitting a conditioned signal to said processing unit.

2. The conditioning circuit according to claim 1, wherein the first stage is made by means of a voltage current converter, the feedback loop including a low pass filter and a current voltage converter.

3. The conditioning circuit according to claim 1, wherein the blocker sampler circuit of the second stage includes correlated double sampling means for demodulating said amplified useful signal.

4. The conditioning circuit according to claim 3, wherein said correlated double sampling means are associated with a follower amplifier including a single active transistor.

5. The conditioning circuit according to claim 1, wherein said bandpass filter of said third stage is an N order bandpass filter, N being greater than or equal to 5.

6. The conditioning circuit according to claim 5, wherein said bandpass filter is a 5th order Bessel type filter made by means of a switched capacitance circuit including a first 3rd order bandpass filter in series with a 2nd order low pass filter.

7. The conditioning circuit according to claim 5, wherein each of the N−1 first stages of the bandpass filter uses a single active transistor.

8. The conditioning circuit according to claim 5, wherein the gain of said bandpass filter can be adjusted by altering at least one capacitance ratio.

9. The integrated circuit including a conditioning circuit for an external signal representative of a physiological quantity between an optical sensor and a processing unit, said received external signal being broken down into a useful component and an ambient component, wherein said conditioning circuit includes: a first stage including a transimpedance amplifier with an incorporated high pass filter using a feedback loop to subtract, at the stage input, the ambient signal component from the received external signal, and to deliver at output an amplified useful signal;a second stage including a blocker sampler circuit for demodulating said amplified useful signal and delivering at output a demodulated useful signal; anda third stage including a bandpass filter for filtering said demodulated useful signal in the frequency band of the physiological quantity to be detected and for transmitting a conditioned signal to said processing unit for receiving said external signal transmitted by said optical sensor and delivering a conditioned signal at output.

10. The integrated circuit according to claim 9, further including a processing unit connected to the conditioning circuit, receiving said conditioned signal and processing said signal to supply information relating to said conditioned signal.

11. The electronic instrument worn on the wrist including an integrated circuit according to claim 9, wherein it further includes: an optical device for measuring a physiological quantity, particularly the heart rate, said optical device including at least one light source for subjecting a portion of organic tissue to a light emission and at least one optical sensor for detecting the intensity of the light emission after propagation in said organic tissue;said integrated circuit arranged for processing the optical signals detected by said optical sensor;a display device for displaying information relating to the physiological quantity measurement, particularly the heart rate.

12. The conditioning circuit according to claim 2, wherein the blocker sampler circuit of the second stage includes correlated double sampling means for demodulating said amplified useful signal.

13. The conditioning circuit according to claim 6, wherein each of the N−1 first stages of the bandpass filter uses a single active transistor.

14. The electronic instrument worn on the wrist including an integrated circuit according to claim 10, wherein it further includes: an optical device for measuring a physiological quantity, particularly the heart rate, said optical device including at least one light source for subjecting a portion of organic tissue to a light emission and at least one optical sensor for detecting the intensity of the light emission after propagation in said organic tissue;said integrated circuit arranged for processing the optical signals detected by said optical sensor; a display device for displaying information relating to the physiological quantity measurement, particularly the heart rate.