# US 9,775,528 B2 · Photoplethysmography sensor apparatus and method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,775,528 B2 - Document ID: US9775528B2 - Status: Granted - Kind: B2 - Application number: 14/912,418 - Filed: 2015-06-19 - Published: 2017-02-16 - Granted: 2017-10-03 - Earliest claimed: 2014-06-30 - Assignees: Koninklijke Philips N.V. - Applicants: Koninklijke Philips N.V. - Inventors: Olaf Thomas Johan Antonie Vermeulen; Koen Geenen - Web page: https://patentgrep.com/patent/US9775528B2 ## CPC - A61B 5/02416: {using photoplethysmograph signals, e.g. generated by infrared radiation (A61B5/14552 takes precedence)} - A61B 5/02427: {Details of sensor} - A61B 5/7203: {for noise prevention, reduction or removal} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract The present invention relates to a photoplethysmography sensor apparatus (200, 300), a photoplethysmography sensor method (400), and a photoplethysmography sensor computer program product. It is proposed to measure a photoplethysmographic signal without ambient light interference. Ambient light signals are rejected by subtraction of a compensation current at the input of a transimpedance amplifier (240, 340). The compensation current is controlled via a closed loop, without interfering with the low duty cycle operation of a photoplethysmography LED (210, 310). ## Claims ### Claim 1 A photoplethysmography sensor apparatus comprising: a light source unit configured to generate a first light signal; a photodetector unit configured to observe a second light signal, where said second light signal is indicative of an absorption of said first light signal in a target, wherein said photodetector unit is further configured to output a photodetector output signal in response to observing said second light signal; and an ambient light compensating feedback loop comprising a track-and-hold unit configured to receive said photodetector output signal; wherein said photoplethysmography sensor apparatus is configured to compare an output signal of said track-and-hold unit to a reference signal (VR), and wherein said ambient light compensating feedback loop comprises a first amplifying unit configured to provide a compensation current based on said comparison to the track-and-hold unit. ### Claim 2 (depends on 1) The photoplethysmography sensor apparatus of claim 1, further comprising a second amplifying unite for amplifying a sum of the compensation current and the photodetector output signal and for delivering an amplified signal to an input of the track-and-hold unit. ### Claim 3 (depends on 2) The photoplethysmography sensor apparatus of claim 2, wherein said second amplifying unit comprises a transimpedance amplifier. ### Claim 4 (depends on 1) The photoplethysmography sensor apparatus of claim 1, wherein said first amplifying unit comprises a trans-conductance amplifier, wherein said trans-conductance amplifier comprises a resistor and/or a voltage controlled current source. ### Claim 5 (depends on 1) The photoplethysmography sensor apparatus of claim 1, wherein said photoplethysmography sensor apparatus comprises an analog-to-digital converter configured to receive an output signal from said second amplifying unit. ### Claim 6 (depends on 1) The photoplethysmography sensor apparatus of claim 1, wherein said photoplethysmography sensor apparatus further comprises a light source driver unit configured to control said light source unit. ### Claim 7 (depends on 1) The photoplethysmography sensor apparatus of claim 1, wherein said photoplethysmography sensor apparatus further comprises a synchronous detector. ### Claim 8 (depends on 7) The photoplethysmography sensor apparatus of claim 7, wherein said photoplethysmography sensor apparatus further comprises a light source driver unit configured to control said light source unit and wherein said synchronous detector is configured to operate synchronously with said light source driver unit. ### Claim 9 (depends on 7) The photoplethysmography sensor apparatus of claim 7, wherein said photoplethysmography sensor apparatus comprises an analog-to-digital converter configured to receive the output signal from said synchronous detector. ### Claim 10 (depends on 7) The photoplethysmography sensor apparatus of claim 7, wherein said synchronous detector comprises a synchronous rectifier followed by a low pass filter. ### Claim 11 (depends on 10) The photoplethysmography sensor apparatus of claim 10, wherein said synchronous rectifier multiplies the signal with +1 or −1. ### Claim 12 (depends on 1) The photoplethysmography sensor apparatus of claim 1, wherein said photoplethysmography sensor apparatus further comprises a microcontroller configured to adjust said reference signal (VR). ### Claim 13 A photoplethysmography sensor method comprising the steps of: generating a first light signal by a light source unit; observing a second light signal by a photodetector unit, wherein said second light signal is indicative of an absorption of said first light signal in a target; receiving, in response to observing said second light signal, a photodetector output signal by an ambient light compensating feedback loop comprising a track-and-hold unit and an amplifying unit; comparing an output signal of the track-and-hold unit to a reference signal (VR), wherein said output signal of said track-and-hold unit is based on said photodetector output signal; and providing a compensation current by the amplifying unit to the track-and-hold unit based on said comparison. ### Claim 14 A photoplethysmography sensor computer program product comprising a computer readable memory storing computer program code means for causing a photoplethysmography sensor apparatus to carry out the following steps, when the program is run on a computer controlling the photoplethysmography sensor apparatus: generate a first light signal by a light source unit; observe a second light signal by a photodetector unit, wherein said second light signal is indicative of an absorption of said first light signal in a target; receive, in response to observing said second light signal, a photodetector output signal by an ambient light compensating feedback loop comprising a track-and-hold unit and an amplifying unit; compare an output signal of the track-and-hold unit to a reference signal (VR), wherein said output signal of said track-and-hold unit is based on said photodetector output signal; and provide a compensation current by the amplifying unit to the track-and-hold unit based on said comparison.