Sweeping Signal Tracking Circuit With Low-Pass Delay Compensation
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Solution Overview
Problem
Existing frequency-locked loops (FLLs) struggle to effectively track fast-sweeping and weak signal components due to high interference and noise, leading to challenges in accurately identifying and following the frequency of such components in wireless communication systems.
Innovation Solution
A tracking circuit comprising a mixer, low-pass filter, discriminator circuit, loop filter, and replica signal generator is employed to estimate and compensate for the delay introduced by the low-pass filter, enabling fast and reliable tracking of sweeping signal components by mixing the input signal with a replica signal, reducing noise, and adjusting the frequency control value to match the current time unit of the input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is used to reduce noise from the residual input signal, then the signal-to-noise ratio is improved, but group delay is introduced that causes tracking lag for fast-sweeping signals
Solution Approach 1:
The patent performs preliminary frequency estimation using a coarse estimator before applying the low-pass filter. This preliminary action provides an advance indication of the sweeping signal's frequency trajectory, allowing the system to compensate for the delay introduced by subsequent filtering operations. The coarse estimator operates on a broader frequency range to predict future frequency positions, effectively preempting the tracking lag that would otherwise occur.
Solution Approach 2:
The patent implements a feedback mechanism where the output of the low-pass filter is fed back to adjust the replica signal frequency in real-time. This continuous feedback loop allows the system to correct for the group delay by constantly comparing the filtered signal characteristics with the original sweeping signal and making dynamic adjustments to maintain accurate frequency tracking despite the filtering-induced lag.
2Speed
If the sweeping rate is increased to handle faster frequency changes, then the tracking speed is improved, but the ability to track weak signals drowned in noise deteriorates
Solution Approach 1:
The patent segments the frequency estimation process into two distinct stages: a coarse estimation phase that operates over a broad frequency range to track fast-sweeping signals, and a fine estimation phase using a low-pass filter for precise frequency measurement. This segmentation allows each stage to be optimized for its specific function - the coarse estimator handles high sweeping rates while the fine estimator provides accurate frequency measurement when the signal is within the filter's passband.
Solution Approach 2:
The patent employs dynamic switching between different estimation strategies based on the current signal conditions and sweeping rate. When the sweeping rate is high, the system dynamically transitions to relying more on the coarse estimator; when the signal slows down and enters the filter's effective range, it dynamically shifts to the fine estimator. This dynamic adaptation allows the system to maintain reliable tracking across varying signal conditions.
3Measurement precision
If a frequency-locked loop is used for frequency tracking, then frequency estimation is achieved, but tracking of fast-sweeping weak signals fails due to high noise and rapid frequency changes
Solution Approach 1:
The patent introduces a replica signal as an intermediary element that mimics the characteristics of the sweeping signal. This replica signal serves as a mediator between the noisy input signal and the frequency estimation process. By mixing the input signal with the replica signal, the system creates a residual signal that contains frequency error information while suppressing the effects of rapid frequency changes and noise, enabling more reliable frequency tracking.
Solution Approach 2:
The patent creates a copy of the expected signal characteristics through the replica signal generator, which produces a signal that replicates the anticipated frequency and phase properties of the sweeping signal. This copying approach allows the system to compare the actual input signal against an idealized model, extracting frequency information more reliably even when the actual signal is distorted by noise or rapid frequency transitions.
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 allows for rapid tracking and subsequent removal of fast-sweeping signal components, even when they are drowned in noise, by compensating for the group delay of the low-pass filter, ensuring accurate frequency estimation and efficient filtering of the interference.
Implementation Method 1
The mixer is coupled to the input and is configured to mix the input signal with a replica signal and therefrom provide a residual input signal
Implementation Method 2
The low-pass filter is coupled downstream of the mixer and is configured to reduce the noise component from the residual input signal
Data Source
AI summary
In one embodiment a tracking circuit for tracking a frequency of a sweeping signal component in an input signal comprises an input for receiving the input signal (Sin) comprising the sweeping signal component and a noise component, a mixer coupled to the input and configured to mix the input signal with a replica signal and therefrom provide a residual input signal, a low-pass filter coupled downstream of the mixer, a discriminator circuit coupled downstream of the low-pass filter, a loop filter coupled downstream of the discriminator circuit and configured to provide a frequency control value, and a replica signal generator circuit coupled downstream of the loop filter and configured to provide the replica signal with a frequency adjusted based on the frequency control value, wherein the frequency of the replica signal represents an estimation of a frequency of the sweeping signal component propagated to a current time unit of the input signal.