Optical Signal Conditioning Circuit for Portable Physiological Sensors
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Solution Overview
Problem
Existing portable instruments for measuring physiological quantities, such as heart rate, face challenges with non-optimal space usage and power consumption due to the need for multiple discrete components in the conditioning circuit, leading to suboptimal amplification and filtering capabilities.
Innovation Solution
A conditioning circuit with integrated elements and optimized energy consumption, featuring a transimpedance amplifier with a feedback loop for separating ambient and useful signal components, a locker sampling circuit for demodulation, and a bandpass filter to filter signals within the physiological frequency range, reducing noise and increasing usable gain without saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high pass filter is placed after the amplifier in series, then the ambient signal can be removed, but the amplifier gain range is limited and the noise over signal ratio deteriorates
Solution Approach 1:
The patent extracts the ambient signal component from the total received signal using a dedicated ambient signal detection path. A second photoreceptor detects only the ambient light component, which is then processed separately and subtracted from the main signal path, removing the harmful ambient component before amplification.
Solution Approach 2:
The patent introduces an intermediary ambient signal detection path that measures only the ambient component through a second photoreceptor. This intermediary path allows the ambient signal to be characterized and removed without affecting the amplification of the useful signal, thereby improving the noise over signal ratio.
2Adaptability or versatility
If multiple discrete components are used for amplification, filtering and detection, then the circuit can perform all required functions, but the occupied surface area increases and power consumption rises
Solution Approach 1:
The patent merges multiple discrete components into an integrated circuit structure. The first and second photoreceptors, amplifiers, high pass filter, and detection circuit are combined into a single integrated conditioning circuit, reducing the occupied surface area while maintaining all required signal processing functions.
Solution Approach 2:
The integrated conditioning circuit performs multiple functions simultaneously: the first photoreceptor detects the useful signal, the second photoreceptor detects the ambient signal, the amplifier amplifies the difference signal, and the high pass filter removes remaining ambient components. This multi-functional integration reduces the overall circuit footprint.
3Adaptability or versatility
If multiple discrete components are used for amplification, filtering and detection, then the circuit can perform all required functions, but the power consumption increases
Solution Approach 1:
The patent combines multiple power-consuming components into a single integrated circuit, reducing overall power consumption. The shared amplifier and filter circuitry processes both the useful signal from the first photoreceptor and the ambient signal from the second photoreceptor, eliminating redundant power consumption that would occur with separate discrete components.
Solution Approach 2:
The conditioning circuit uses the ambient signal detected by the second photoreceptor to automatically adjust and remove ambient interference from the useful signal. This self-service mechanism eliminates the need for external ambient light compensation circuits, reducing overall power consumption while maintaining signal processing capability.
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 enhances signal-to-noise ratio and reduces power consumption by integrating components, allowing for more efficient signal processing and improved performance in portable devices.
Implementation Method 1
a first stage including a transimpedance amplifier with an incorporated high pass filter
Implementation Method 2
using a feedback loop for subtracting, at the stage input, the ambient signal component from the received external signal
Implementation Method 3
a second stage comprising a locker sampling circuit for demodulating the amplified useful signal
Implementation Method 4
a third stage comprising a bandpass filter for filtering the demodulated useful signal in the frequency band of the physiological quantity to be detected
Data Source
AI summary
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.