Bandpass Filter Selection for Tx-Rx Isolation in Wireless Receivers
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Solution Overview
Problem
Poor isolation between transmitter and receiver in wireless communication devices leads to signal leakage, causing saturation of the low noise amplifier and reduced sensitivity in detecting the intended received signal.
Innovation Solution
Implementing a filter selection technique using high-frequency and low-frequency bandpass filters in conjunction with switching devices to selectively couple transmit and receive paths, allowing channel assignment to minimize interference and potential damage to the low noise amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the LNA is lowered to prevent saturation from leaked transmit signal, then the reliability of the receiver is improved, but the sensitivity in detecting the intended received signal deteriorates
Solution Approach 1:
The patent introduces filters as intermediary components between the transmit and receive paths. These filters selectively pass desired frequency bands while attenuating unwanted frequencies, including leaked transmit signals. By placing filters in the signal path, the system can maintain high LNA gain for sensitivity while the filters prevent saturation from transmit leakage, thus resolving the contradiction between reliability and sensitivity.
2Object-affected harmful factors
If filters are added to improve isolation between transmitter and receiver, then the harmful factors affecting the receiver are reduced, but the device complexity increases
Solution Approach 1:
The patent implements dynamic filter selection where the system can switch between different filter configurations based on operating conditions. Multiple filters with different characteristics are provided, and switching mechanisms allow the system to select the most appropriate filter for current transmit and receive frequency bands. This dynamic approach enables effective isolation across multiple frequency bands without requiring a completely different filter design for each band, thus managing complexity while maintaining effectiveness.
Solution Approach 2:
The patent designs a filter selection mechanism that serves multiple functions: frequency selection, signal isolation, and interference rejection. The same filter bank and switching infrastructure handles both transmit path filtering and receive path filtering, allowing a single complex subsystem to perform multiple isolation functions rather than requiring separate dedicated filters for each function.
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
Enhances isolation between transmit and receive signals, reducing interference and potential damage to the low noise amplifier, thereby maintaining sensitivity and preventing saturation.
Implementation Method 1
Implementing a filter selection technique using high-frequency and low-frequency bandpass filters
Data Source
AI summary
In one implementation, a wireless communication device includes a first transceiver configured to generate a transmit signal and a band pass filter (BPF) select circuit configured to filter the transmit signal by a one of a first BPF with a relatively high-frequency passband or a second BPF with a relatively low-frequency passband. The wireless communication device includes a second transceiver configured to receive a received signal filtered by the other one of the first or second BPF. Having the transmit and received signals filtered by two different passband filters improves the isolation between the transmitter and receiver. Another implementation configures the first transceiver to include its own set of first and second BPFs, and the second transceiver to also include its own first and second BPFs.