Ambient Light Cancellation Circuit Using Multi-Order Sampling
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Solution Overview
Problem
Existing ambient light cancellation technologies for photoplethysmography (PPG) devices lack multi-order filtering capabilities to effectively eliminate ambient light signals, which can interfere with the accuracy of heartbeat and blood oxygen measurements.
Innovation Solution
A capacitive transimpedance amplifying circuit with a switch circuit and capacitor paths that sample the detection signal multiple times during a sampling period, functioning as a Kth-order filter to isolate and filter out ambient light signals, using a combination of capacitors and switches to differentiate between controllable and ambient light signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a hardware circuit is used to cancel ambient light, then ambient light cancellation capability is improved, but the filtering order and measurement precision are insufficient
Solution Approach 1:
The patent segments the sampling period into multiple time slots (first time slot, second time slot, third time slot, etc.) and performs separate sampling operations in each slot. By dividing the sampling process into discrete segments with different switch configurations, the circuit achieves multi-order filtering capability without requiring a complex monolithic filter structure. Each time slot contributes to the overall filtering order K through weighted summation of the segmented samples.
Solution Approach 2:
The patent employs dynamic switch configurations that change state across different time slots. The switches are controlled to connect different capacitor electrodes to different circuit nodes (inverting input node or output node) depending on the current time slot. This dynamic reconfiguration enables the circuit to adaptively implement Kth-order filtering with adjustable filter coefficients, resolving the contradiction between filtering order and device complexity.
2Measurement precision
If multiple sampling operations are performed during a sampling period, then filtering precision is improved, but circuit complexity increases
Solution Approach 1:
The patent designs a universal capacitive transimpedance amplifying circuit that performs multiple functions through temporal multiplexing. The same circuit components (amplifier, capacitors, switches) are reused across multiple time slots to achieve Kth-order filtering, ambient light cancellation, and signal integration. This multi-functional approach allows the circuit to perform complex multi-order filtering operations without proportionally increasing hardware complexity, as the same physical components serve multiple sampling and filtering purposes across different time slots.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate filtering of ambient light signals, enhancing the measurement accuracy of PPG devices by effectively distinguishing and canceling ambient light, thereby improving the reliability of heartbeat and blood oxygen measurements.
Implementation Method 1
The capacitor circuit includes: a first capacitive path including a first capacitor which includes a first electrode and a second electrode
Implementation Method 2
the detection signal is generated by a photoelectric device
Data Source
AI summary
An ambient light cancellation circuit functions as a Kth-order filter to filter out an ambient light signal of the detection signal, wherein the K is not fewer than two. The circuit includes a capacitive transimpedance amplifying circuit including an amplifier, a capacitor circuit, and a switch circuit. The capacitor circuit includes one or more capacitive paths coupled in parallel. The switch circuit couples the amplifier with the capacitor circuit in a non-cross manner or a cross manner. The non-cross manner is applied N times to let the capacitor circuit sample the detection signal N times while the detection signal includes a controllable-light signal and the ambient light signal; and the cross manner is applied M times to let the capacitor circuit sample the inversion of the detection signal M times while the detection signal includes the ambient light signal without the controllable-light signal, wherein (N+M) equals (K+1).