Signal Extraction via Chopper Modulation and Subtraction
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Solution Overview
Problem
Existing methods fail to reliably extract weak desired signals overwhelmed by high-dynamic interference or ambient light, especially when the interference magnitude exceeds the desired signal by several orders, and often require expensive high-resolution analog-to-digital converters or large filtering devices.
Innovation Solution
A method and apparatus that store the combined signal's magnitude during periods where the desired signal is below a threshold, subtracting this value from the combined signal to extract the desired signal, using chopper modulation to keep the signal below the threshold and amplify it without exceeding supply voltage limits, and optionally using additional storage devices for transient component compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If filtering devices are used to extract desired signal from combined signal, then signal extraction capability is improved, but device size becomes mechanically large
Solution Approach 1:
The patent replaces mechanical filtering devices with electronic signal processing methods. Specifically, it uses a lock-in amplifier that employs electronic modulation and demodulation techniques to extract the desired signal from the combined signal, eliminating the need for large mechanical filters while achieving the same signal extraction capability.
Solution Approach 2:
The patent changes the frequency parameter of the desired signal through modulation before processing. By modulating the desired signal to a higher frequency range and then using synchronous detection, the system can extract the signal without requiring large physical filters, thus resolving the contradiction between extraction capability and device size.
2Measurement precision
If analog-to-digital converters with high resolution are used, then signal extraction accuracy is improved, but device cost increases
Solution Approach 1:
The patent applies preliminary signal conditioning and modulation before any conversion or processing. By pre-modulating the desired signal and using synchronous detection techniques, the system enhances the signal-to-noise ratio early in the processing chain, allowing for the use of lower-resolution, less expensive analog-to-digital converters while still achieving high extraction accuracy.
Solution Approach 2:
The patent introduces an intermediary modulation stage that translates the desired signal into a different domain (frequency domain) where it can be more easily separated from noise and interference. This intermediary step allows for more efficient signal extraction using simpler, lower-cost conversion equipment.
3Power
If amplification is applied to desired signal, then signal strength is improved, but supply voltage limits are exceeded
Solution Approach 1:
The patent uses periodic modulation of the desired signal at a specific frequency, followed by synchronous demodulation. This periodic action allows the signal to be amplified during specific phases while maintaining the average power within supply voltage limits. The lock-in amplifier technique exploits this periodicity to achieve high signal strength at the output without requiring continuous high-power amplification that would exceed supply limits.
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
A method and an apparatus for extracting a desired signal (118) from a combined signal (112) are disclosed, wherein the combined signal (112) exhibits a magnitude (110) which comprises a sum (154) of the magnitude (110) of the desired signal (118) and the magnitude (110) of an additional signal (122). Within at least one time interval (134, 134', 134"), wherein the magnitude (110) of the desired signal (118) remains below a threshold (136), at least one value of the magnitude (110) of the combined signal (112) within the time interval (134, 134', 134") is stored in a storage device (166) as at least one stored value (170, 170', 170"), followed by subtracting the stored value (170) from the magnitude (110) of the combined signal (112), by which difference (178) the magnitude (110) of the desired signal (118) is acquired in a period (138, 138', 138") outside the time interval (134, 134', 134"), wherein the magnitude (110) of the desired signal (118) stays at least partially above the threshold (136). Preferably used for acquiring a magnitude (110) of a desired signal (118) which comprises an electromagnetic signal, preferably a light signal, more preferably a fluorescence signal, wherein the desired signal (118) is superimposed by an additional signal (122), wherein the additional signal (122) is preferably influenced by ambient conditions, in particular by ambient light.