Heart Rate Signal Conversion Circuit Using Two-Phase Differential Sensing
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Solution Overview
Problem
Current signal conversion circuits face challenges in effectively suppressing ambient interference, leading to a decrease in signal-to-noise ratio, particularly in heart rate acquisition systems, due to high output impedance and susceptibility to noise from human skin.
Innovation Solution
A signal conversion circuit comprising a photoelectric conversion circuit, differential signal conversion circuit, and subtraction amplifier, which converts optical signals into current signals and then into differential signals, allowing the suppression of common mode noise and amplifying the difference to improve the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-voltage (I-V) conversion circuit is employed to convert current signal into voltage signal, then the high output impedance of the sensor is matched, but the low input impedance of the conversion circuit allows ambient interference signals to easily enter and be converted into noise voltage
Solution Approach 1:
The patent divides the signal processing into two separate stages: first converting the current signal to voltage through an I-V conversion circuit, then converting the voltage signal back to current through a transimpedance amplifier. This segmentation allows the system to benefit from the high input impedance of the first stage (reducing ambient interference) while maintaining the high output impedance matching of the second stage.
Solution Approach 2:
The patent introduces an intermediate voltage signal as a mediator between the current signal from the sensor and the final processed current signal. This intermediate representation allows for better impedance matching and interference rejection by decoupling the high-impedance current source from the low-impedance processing stages.
2Object-affected harmful factors
If the distance between the human body and the circuit is increased to weaken the coupled path, then ambient interference is reduced, but the signal also decreases, causing the signal-to-noise ratio to decrease again
Solution Approach 1:
The patent employs dynamic signal processing with adjustable gain stages and adaptive filtering that can compensate for signal attenuation. The system dynamically adjusts its sensitivity and processing parameters to maintain optimal signal-to-noise ratio regardless of the distance between the sensor and the human body.
3Object-affected harmful factors
If a shielding case is added to the current-type sensor to suppress interference, then ambient interference is reduced, but light transmittance decreases and parasitic capacitors are generated that amplify noise
Solution Approach 1:
The patent replaces the mechanical shielding approach with an electrical solution using differential signaling and balanced circuit topologies. Instead of physically blocking interference with a shielding case, the system uses electrical differential processing to reject common-mode interference signals while preserving the useful signal.
4Reliability
If the input impedance of the conversion circuit is kept low for effective current-to-voltage conversion, then current signal conversion is effective, but ambient interference signals are easily coupled into the circuit
Solution Approach 1:
The patent segments the impedance transformation into two separate conversion stages rather than one direct conversion. The first stage converts current to voltage with appropriate impedance matching, and the second stage converts voltage back to current with interference rejection, allowing each stage to be optimized for its specific function.
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 proposed solution effectively suppresses ambient interference, enhancing the signal-to-noise ratio and improving the accuracy of signal detection by isolating the useful optical signal from background noise.
Implementation Method 1
a photoelectric conversion circuit, configured to convert an optical signal into a current signal
Data Source
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AI summary
A signal conversion circuit, a heart rate sensor, and an electronic device are provided, and the signal conversion circuit includes: a photoelectric conversion circuit, configured to convert an optical signal into a current signal, where the current signal in a first phase includes a signal converted from a useful optical signal, a modulated optical signal and a background optical signal in the optical signal, and the current signal in a second phase includes a signal converted from the background optical signal; a differential signal conversion circuit, connected to the photoelectric conversion circuit, and configured to convert the current signal into a first differential signal and a second differential signal, where the first differential signal is an integration signal of the current signal in the first phase, and the second differential signal is an integration signal of the current signal in the second phase; and a subtraction amplifier, connected to the differential signal conversion circuit, and configured to amplify a difference value between the first differential signal and the second differential signal, to generate a third differential signal. The signal conversion circuit of embodiments of the present invention can effectively suppress ambient interference.