RF Duplex Filter With Tunable Notch and Bandpass Isolation
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Solution Overview
Problem
In RF communications systems with low duplex frequencies, existing RF bandpass filters are inadequate for effectively blocking transmit signals from the receive path without attenuating receive signals, particularly in full duplex and multimode systems with receiver diversity.
Innovation Solution
An RF duplex filter comprising a notch filter with series resonant elements and a bandpass filter with parallel resonant elements, optionally with tunable elements and calibration circuitry, is used to block transmit signals and enhance receive signals, which can be integrated into the receive path or low noise amplifier (LNA) and RF mixer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a notch filter with notch frequency at the transmit frequency is used to block unwanted signals, then the effectiveness at blocking transmit frequency signals is improved, but errors in the notch frequency reduce the effectiveness and may attenuate receive frequency signals
Solution Approach 1:
The filter is divided into two distinct functional sections: a notch filter section for blocking transmit frequency signals and a bandpass filter section for passing receive frequency signals. This segmentation allows each section to be optimized independently, with the notch filter targeting specific transmit frequencies and the bandpass filter ensuring receive signals pass through with minimal attenuation, thereby resolving the contradiction between blocking effectiveness and frequency accuracy.
Solution Approach 2:
The patent employs tunable resonant elements that allow dynamic adjustment of the notch frequency and bandpass filter characteristics. By changing the resonant parameters of the filter circuits, the system can adapt to different transmit and receive frequency pairs, maintaining high blocking effectiveness while ensuring accurate frequency selectivity and preventing attenuation of receive signals.
2Object-affected harmful factors
If RF bandpass filters are used to remove unwanted signals, then filtering is provided, but in systems with low duplex frequency, they are inadequate and may attenuate receive signals
Solution Approach 1:
The filter architecture segments the filtering function into two specialized components: a notch filter that aggressively attenuates transmit frequency signals without affecting receive frequencies, and a bandpass filter that selectively passes receive frequency signals while blocking other frequencies. This segmentation eliminates the energy loss problem of conventional bandpass filters by using a notch filter for the primary blocking function and a bandpass filter only for frequency selection.
Solution Approach 2:
The notch filter acts as an intermediary element between the antenna and the bandpass filter. It first removes the harmful transmit frequency signals from the received signal mixture, preventing them from reaching the bandpass filter. This intermediary approach allows the bandpass filter to operate only on the receive frequency signals, minimizing energy loss and maintaining signal strength.
3Adaptability or versatility
If multiple SAW filters are used in multimode systems with receiver diversity, then adequate filtering for multiple frequency bands is provided, but the device complexity and number of filters increase
Solution Approach 1:
The duplex filter design provides multi-functionality by enabling a single filter circuit to handle multiple frequency bands through tunable resonant elements. The filter can be reconfigured via software control to adapt to different transmit and receive frequency pairs, replacing the need for multiple dedicated SAW filters for different frequency bands and receiver diversity paths, thereby reducing device complexity while maintaining versatility.
Solution Approach 2:
The filter incorporates dynamically tunable resonant elements that can be adjusted in real-time through software control to match different operating frequencies. This dynamic capability allows a single physical filter circuit to perform the function of multiple fixed-frequency filters, reducing the overall number of filter components needed in multimode systems with receiver diversity while maintaining adequate filtering performance across all frequency bands.
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 RF duplex filter effectively removes transmit signals from the receive path with minimal attenuation of receive signals, potentially replacing SAW filters and improving filtering in systems with low duplex frequencies, including full duplex, half duplex, and multimode communications systems.
Implementation Method 1
The notch filter is formed with series resonant elements... series resonant elements for tuning the notch filter to a transmit frequency
Implementation Method 2
the bandpass filter is formed with parallel resonant elements... parallel resonant elements for tuning the bandpass filter to a receive frequency
Data Source
AI summary
The present invention is an RF duplex filter that is used to remove transmit signals from the receive path of a full duplex transceiver. The RF duplex filter includes a notch filter for blocking signals at a transmit frequency and a bandpass filter for enhancing signals at a receive frequency. The notch filter is formed with series resonant elements and the bandpass filter is formed with parallel resonant elements. One embodiment of the present invention may include tunable resonant elements for tuning the notch filter to a transmit frequency, tuning the bandpass filter to a receive frequency, or both. Calibration circuitry may be included in the full duplex receiver for adjusting the tunable resonant elements. The present invention includes a method for calibrating the tunable resonant elements.