Current DAC Circuit for Low-Frequency Noise Cancellation in Optical Measurements
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Solution Overview
Problem
Current optical measurement systems face challenges in reducing low-frequency noise, particularly in plethysmograph (PPG) signals, which limits the ability to accurately measure vital signs like blood oxygen saturation and heart rate, especially in wearable devices where power consumption is a concern.
Innovation Solution
A low-frequency noise cancellation method is introduced, which includes a current DAC circuit at the front of the receiver synchronized with the LED driver to cancel the DC portion of the received current, using a shared reference voltage and timing control to mitigate flicker noise, thereby enhancing the signal-to-noise ratio (SNR) without increasing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical measurement systems are used, then the system can detect light signals, but low-frequency noise (flicker noise) degrades the signal-to-noise ratio and measurement accuracy
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation current through the IDAC circuit that anticipates and counteracts the flicker noise before it degrades the measurement signal. The IDAC generates a compensation current based on the LED drive current that is subtracted from the photodetector signal, effectively pre-neutralizing the low-frequency noise component before it can affect the SNR
Solution Approach 2:
The patent uses an intermediary approach by introducing a current DAC (IDAC) circuit as a mediator between the LED driver and the signal processing chain. This IDAC circuit generates a compensation current that acts as an intermediary signal to cancel the flicker noise component, allowing the main measurement signal to pass through with improved quality
2Measurement precision
If noise reduction techniques are applied to improve measurement accuracy, then the signal-to-noise ratio improves, but power consumption increases
Solution Approach 1:
The patent applies self-service by designing the IDAC circuit to generate its compensation current autonomously based on the LED drive current signal. The IDAC uses the existing timing and control signals from the LED driver to automatically produce the appropriate compensation current without requiring additional power-intensive active noise cancellation algorithms or external calibration procedures
Solution Approach 2:
The patent changes the parameter approach by working in the current domain rather than converting to voltage domain for noise cancellation. By implementing the IDAC circuit that operates with current signals throughout the chain, the system achieves noise cancellation without the power consumption penalties associated with high-gain voltage amplifiers and complex analog-to-digital conversion procedures
3Productivity
If the LED driver generates pulse signals to drive the LED, then the system can perform optical measurements, but the LED driver generates DC portion in the received current that contributes to low-frequency noise
Solution Approach 1:
The patent applies the extraction principle by separating and removing the DC portion of the received current from the measurement signal. The IDAC circuit specifically extracts the DC component that originates from the LED drive pulses and generates an equal and opposite compensation current, effectively taking out this harmful DC portion before it can contribute to low-frequency noise in the measurement
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
This method effectively reduces low-frequency noise in optical measurement systems, improving the accuracy of vital sign monitoring and extending the battery life of wearable devices by maintaining high SNR with lower power consumption.
Implementation Method 1
producing light in response to the received signal waveform, illuminating an object with the light
Implementation Method 2
receiving the light at a photodetector
Data Source
AI summary
Low-frequency Noise Cancellation Method for Optical Measurement Systems. The present disclosure provides a low frequency noise cancellation method for optical measurement system, An optical measurement system has a transmitter to drive an LED and a receiver connected to a photodiode. The LED driver will generate a pulse signal to drive the LED and act as the radiation source for the optical measurement. Consequently, the receiver will convert the received photo-diode current to a voltage signal. The signal will then be digitized by an ADC for further processing. A current DAC circuit IDAC is added at the front of the receiver and has the same timing control with the LED driver to cancel the DC portion of the received current.