Frequency Tracking Circuit for Fast Sweeping Signals Under Filter Delay
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Solution Overview
Problem
Existing frequency-locked loops (FLLs) fail to effectively track fast sweeping and weak signal components due to high sweeping rates and low Signal-to-Noise ratios, making it challenging to distinguish and eliminate such signals from received radio frequency signals.
Innovation Solution
A tracking circuit comprising a mixer, low-pass filter, discriminator circuit, loop filter, and replica signal generator circuit, which mixes the input signal with a replica signal, reduces noise through low-pass filtering, estimates frequency errors, and adjusts the replica signal to compensate for group delay, enabling accurate tracking of sweeping signal components even at high speeds.
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 which causes tracking lag for fast sweeping signals
Solution Approach 1:
The patent applies preliminary action by propagating the frequency estimation from a previous time unit to the current time unit. The replica signal generator creates a replica signal based on frequency information from time unit k-1, which is then used in the current time unit k. This anticipatory approach compensates for the delay introduced by the low-pass filter, allowing the system to maintain accurate tracking despite the filtering lag.
2Speed
If the sweeping rate of the interfering signal is increased, then the interference becomes more difficult to track and eliminate, but the signal may be drowned in noise making it even harder to detect
Solution Approach 1:
The patent implements feedback through the frequency-locked loop architecture. The discriminator circuit continuously monitors the frequency error between the input signal and the replica signal, and this error information is fed back to adjust the replica signal generation. This closed-loop feedback mechanism enables the system to dynamically track and eliminate interfering signals even at high sweeping rates, while the low-pass filter ensures that noise does not overwhelm the detection capability.
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 achieves reliable tracking and removal of fast sweeping signal components by compensating for group delay and improving Signal-to-Noise ratios, ensuring proper signal decoding and reducing interference in wireless communication systems.
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
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AI summary
In one embodiment a tracking circuit for tracking a frequency of a sweeping signal component in an input signal comprises an input (9) for receiving the input signal (Sin) comprising the sweeping signal component and a noise component, a mixer (10) coupled to the input and configured to mix the input signal (Sin) with a replica signal (Srep) and therefrom provide a residual input signal (Sinr), a low-pass filter (20) coupled downstream of the mixer (10), a discriminator circuit (30) coupled downstream of the low-pass filter (20), a loop filter (40) coupled downstream of the discriminator circuit (30) and configured to provide a frequency control value (Sfc), and a replica signal generator circuit (50) coupled downstream of the loop filter (40) and configured to provide the replica signal (Srep) with a frequency adjusted based on the frequency control value (Sfc), wherein the frequency of the replica signal (Srep) represents an estimation of a frequency of the sweeping signal component propagated to a current time unit of the input signal (Sin).