Trans-Filter Circuit for In-Band Noise Cancellation in Signal Detection
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Solution Overview
Problem
Conventional FM detectors/demodulators suffer from a threshold phenomenon that limits detection sensitivity of exponentially modulated signals, introducing non-linearities and noise cross products, and fail to operate effectively below a certain carrier-to-noise ratio (CNR) threshold, preventing cascading of stages and resulting in pure noise output.
Innovation Solution
A system utilizing a trans-filter that splits the input signal into two paths to extract complimentary derivatives, cancels stationary in-band noise, and includes an auto-tuning circuit, phase modulator, and low pass filter to reduce phase noise, achieving a negative noise figure and maximizing detection sensitivity by transforming flat noise to a parabolic distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FM detectors/demodulators utilize diode rectifiers and matched filters, then the baseband information signals can be recovered, but non-linearities and noise cross products are introduced that cause the threshold phenomenon
Solution Approach 1:
The patent replaces the mechanical/electrical non-linear detection system (diode rectifiers and matched filters) with an optical system. The optical detector uses the optical equivalent of a first-order derivative operator to detect frequency deviations, avoiding the non-linearities inherent in conventional electrical diode-based detection while maintaining detection sensitivity.
Solution Approach 2:
The patent changes the detection parameter from direct amplitude detection (which causes threshold effects) to derivative-based frequency detection. By using an optical detector that implements a first-order derivative operator, the system transforms the detection mechanism to operate on frequency deviations rather than amplitude, eliminating the threshold phenomenon.
2Adaptability or versatility
If conventional demodulators operate below the CNR threshold, then detection is attempted, but the output becomes pure noise
Solution Approach 1:
The patent replaces the conventional electrical demodulation system with an optical detection system that uses optical equivalents of mathematical operators. This substitution enables the system to maintain reliable output signal quality below the CNR threshold by using the optical first-order derivative operator to extract frequency information even in high-noise conditions where conventional systems fail.
3Measurement precision
If conventional demodulators are used, then detection is achieved, but cascading of stages is prevented
Solution Approach 1:
The patent replaces conventional electrical demodulator stages with optical detection stages that use optical equivalents of mathematical operators. This substitution enables cascading of multiple stages because each optical detector is self-contained and processes signals independently through the optical domain, avoiding the complexity issues that prevent cascading in conventional electrical systems.
4Measurement precision
If matched filter is used for signal detection, then the output SNR equals the input CNR, but no improvement beyond this limit is achieved
Solution Approach 1:
The patent changes the detection parameter from direct signal correlation (matched filter approach) to derivative-based frequency detection. By using an optical detector that implements a first-order derivative operator, the system transforms the detection mechanism to operate on frequency deviations, achieving output SNR improvement beyond the matched filter ceiling by exploiting the statistical properties of frequency modulation in the presence of noise.
Data Source
AI summary
Trans-filter/Detectors are extremely sensitive circuits that recover exponentially modulated signals buried in noise. They can be used wherever Matched Filter/Coherent Detectors are used and operate at negative input signal-to-noise ratios to recover RADAR, SONAR, communications, or data signals, as well as reduce phase noise of precision oscillators. Input signal and noise is split into two paths where complementary derivatives are extracted. Outputs of the two paths are equal in amplitude and 180 degrees relative to each other at the band center frequency. The outputs are summed, causing stationary in-band noise to be reduced by cancellation while exponentially modulated signals are undiminished. Trans-filters are Linear Time Invariant circuits, have no noise x noise threshold and can be cascaded, increasing output signal-to-noise ratio prior to detection. Trans-filters are most sensitive to all types of digital modulation, producing easily detected polarized pulses synchronous with data transitions. Trans-filters do not require coherent conversion oscillators and complex synchronizing circuits.