Delay circuit for a radio signal with filter circuitry to linearize a phase shift of an output signal relative to an input
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Solution Overview
Problem
Existing radio communication systems, such as LTE and TETRAPOL, experience interference due to parasitic actions between transmission and reception antennas, leading to degraded communication quality, even when operating on different frequency bands, as wideband noise is amplified by non-linearities and desensitizes receivers.
Innovation Solution
A delay circuit with an all-pass filter and two antiresonant circuits is used to adjust phase, amplitude, and time offset of the compensation signal, allowing efficient interference removal across a wide frequency band by providing a constant delay and improved stability, enabling effective cancellation of interference between radio communication systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional delay circuit is used to cancel interference signals, then the phase and amplitude can be adjusted at a central frequency, but the time delay varies significantly across the frequency band, limiting the rejection to about 30 dB at 50 MHz offset
Solution Approach 1:
The patent applies dynamics by making the delay characteristic frequency-dependent through the all-pass filter design. The filter introduces a phase shift that varies with frequency, creating a frequency-dependent time delay that compensates for the varying delays across the frequency band, thereby extending effective interference cancellation from a narrow bandwidth to a wide bandwidth (e.g., 300-460 MHz).
Solution Approach 2:
The patent changes the delay parameter dynamically across frequency by using an all-pass filter with specific pole-zero configurations. The filter's transfer function is designed to introduce a phase shift θ(ω) that results in a time delay τ(ω) = -dθ(ω)/dω varying with frequency, allowing the system to maintain constant group delay characteristics across the operating bandwidth and achieve wideband interference rejection.
2Object-affected harmful factors
If transmission and reception are carried out on different frequency bands, then interference is reduced, but wideband noise from the transmitter still overlaps with the receiver frequency band and degrades reception quality
Solution Approach 1:
The patent converts the harmful wideband noise into a beneficial cancellation signal by sampling the transmitter output and processing it through the all-pass filter and variable delay circuit. The processed noise signal is then injected into the receiver input with adjusted phase and amplitude to destructively interfere with and cancel the original wideband noise, transforming the harmful interference into a useful cancellation mechanism.
Solution Approach 2:
The patent applies preliminary anti-action by pre-processing the transmitter signal through the all-pass filter and variable delay circuit before injection into the receiver. The phase and amplitude are adjusted in advance to create a compensation signal that will destructively interfere with the wideband noise at the receiver input, preventing the noise from degrading reception quality rather than merely mitigating it after the fact.
3Measurement precision
If a compensation signal is injected to cancel the direct signal, then interference cancellation is achieved at a central frequency, but time delay differences degrade performance at frequencies 50 MHz away, limiting rejection to about 30 dB
Solution Approach 1:
The patent applies dynamics by using an all-pass filter that introduces a frequency-dependent phase shift, making the time delay dynamic rather than fixed. This allows the system to adapt the delay characteristic to different frequency components, maintaining constant group delay across the bandwidth and achieving effective cancellation at frequencies 50 MHz away from the central frequency, not just at the central frequency itself.
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 solution effectively reduces interference on a wide frequency range, improving communication quality by accurately adjusting time offsets and phase shifts, thereby enhancing the performance of radio communication systems.
Implementation Method 1
an all-pass filter having a given central frequency configured to linearize the phase-shift of the output signal relative to the input signal as a function of the frequency on a first frequency range
Implementation Method 2
a first antiresonant circuit having a first central frequency and a second antiresonant circuit having a second central frequency, the all-pass filter and the two antiresonant circuits being configured and arranged to linearize the phase-shift
Data Source
AI summary
A delay circuit for time offsetting an input radiofrequency signal, includes an all-pass filter having a given central frequency to linearize a phase-shift of an output signal relative to the input signal as a function of the frequency on a first frequency range; and first and second antiresonant circuits having respectively first and second central frequencies, the all-pass filter and the antiresonant circuits configured to linearize the phase-shift of the output signal relative to the input signal as a function of the frequency on a second frequency range including the first range. The difference between first and second central frequencies is less than 30% of the value of one of both frequencies, the difference between the first central frequency and the given central frequency of the all-pass filter is less than 30% of the value of a highest frequency between the first central frequency and the given central frequency.