Apparatus for ambient noise cancellation in PPG sensors
Disclosed is a PPG signal measurement apparatus comprising a light source for emitting light pulses; a light sensor for receiving reflected light from the light source and generating a sensor signal; an electronic unit including a transimpedance amplifier and an ambient light cancelation unit, a first switch in a front end portion of the light sensor, a second switch in the front end portion of the light sensor, a microcontroller in communication with the light source, the light sensor, and the ambient light cancellation unit.
1. A PPG signal measurement apparatus comprising:
a light source for emitting light pulses;
a light sensor for receiving reflected light from the light source and generating a sensor signal;
a combination unit electrically coupled to the light sensor, the combination unit including:
an ambient light signal cancelation unit including a first switch, and a second switch, and
a transimpedance amplifier; and
a microcontroller in communication with the light source, the light sensor, and the combination unit, the microcontroller being configured to switch on the first switch only during a first time period while the light source is switched off and switch on the second switch only during a second time period while the light source is switched on;
wherein the ambient light signal cancellation unit comprises a first capacitor and a voltage following amplifier configured to cancel an ambient light signal before the ambient light signal is processed by the transimpedance amplifier to provide an amplified analog sensor signal with an increased signal-to-noise ratio.
2. The PPG signal measurement apparatus of claim 1 , wherein the microcontroller includes additional instructions to control the light source and the ambient light cancelation unit such that the first time period is within 10 μs before the light source is switched on.
3. The PPG signal measurement apparatus of claim 1 , wherein the first switch is connected to an output side of the transimpedance amplifier and the second switch is connected to an input side of the transimpedance amplifier.
4. The PPG signal measurement apparatus of claim 3 , wherein a first pole of the first switch is connected between the output side of the transimpedance amplifier and a second pole of the first switch is connected in parallel to the first capacitor and an input side of the voltage following amplifier.
5. the PPG signal measurement apparatus of claim 4 , wherein a first pole of the second switch is connected to the input side of the transimpedance amplifier and a second pole of the second switch is connected to an output side of the voltage following amplifier.
6. A PPG signal measurement apparatus comprising:
a light source for emitting light pulses;
a light sensor for receiving reflected light from the light source and generating a sensor signal;
a combination unit electrically coupled to the light sensor, the combination unit including:
an ambient light signal cancelation unit including a first switch, and a second switch, and
a transimpedance amplifier; and
a microcontroller in communication with the light source, the light sensor, and the combination unit, the microcontroller being configured to switch on the first switch only during a first time period while the light source is switched off and switch on the second switch only during a second time period while the light source is switched on; wherein the ambient light signal cancellation unit comprises means for canceling an ambient light signal before the ambient light signal is processed by the transimpedance amplifier to provide an amplified analog sensor signal with an increased signal-to-noise ratio.