RF Transceiver Circuit with Switchable Receive Filter Bandpass
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Solution Overview
Problem
In frequency division duplex (FDD) systems, especially in downlink carrier aggregation (DL CA), filters used only for reception cause significant attenuation of radio-frequency receive signals, which affects receiver sensitivity and signal quality.
Innovation Solution
A radio-frequency signal receiver/transmitter circuit incorporating a power amplifying circuit, duplexers with switchable bandpass filters, and a control circuit that adjusts the receive filter's bandpass characteristics to minimize attenuation when the transmit signal is not present, allowing for reduced signal loss and improved sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a receive filter is used to block transmit signals in FDD systems, then transmit signal leakage is suppressed, but receive signal attenuation increases
Solution Approach 1:
The receive filter's bandpass characteristics are made dynamically switchable between first characteristics (when transmit signal is detected) and second characteristics (when transmit signal is not detected). This dynamic adjustment allows the filter to adapt its blocking behavior based on real-time transmission conditions, resolving the contradiction between suppressing transmit leakage and maintaining receive signal strength.
Solution Approach 2:
The filter's bandpass characteristics are changed as a control parameter based on the detection of transmit signals. When transmit signals are detected, the filter switches to first bandpass characteristics with higher attenuation for transmit frequencies. When transmit signals are not detected, the filter switches to second bandpass characteristics with lower attenuation, thereby reducing receive signal loss while maintaining interference suppression capability.
2Object-generated harmful factors
If the receive filter maintains high attenuation characteristics continuously, then transmit signal interference is suppressed, but receiver sensitivity deteriorates
Solution Approach 1:
The filter transitions from a static high-attenuation state to a dynamic state that adjusts its characteristics based on transmission conditions. The control circuit continuously monitors for transmit signals and switches the filter's bandpass characteristics accordingly, ensuring high sensitivity when needed while maintaining interference suppression when transmit signals are present.
Solution Approach 2:
The control circuit detects the presence of transmit signals and uses this feedback information to switch the receive filter between different bandpass characteristics. This feedback mechanism ensures the filter only applies high attenuation when necessary (when transmit signals are detected), thereby maintaining receiver sensitivity during normal reception operations while suppressing interference during transmission.
3Adaptability or versatility
If the receive filter is designed for broad bandpass characteristics, then receive signal coverage is improved, but transmit signal blocking capability deteriorates
Solution Approach 1:
The filter's bandpass characteristics are dynamically adjusted based on transmission conditions. When transmit signals are detected, the filter switches to first bandpass characteristics that provide strong blocking capability for transmit frequencies. When transmit signals are not detected, the filter switches to second bandpass characteristics that provide broader receive signal coverage. This dynamic switching resolves the contradiction between broad coverage and effective blocking.
Solution Approach 2:
The filter's frequency response parameters are changed based on the detection of transmit signals. The control circuit switches between first and second bandpass characteristics, effectively changing the filter's passband and stopband characteristics. This parameter change allows the filter to provide broad receive coverage when needed while maintaining strong transmit blocking capability when transmit signals are present.
Data Source
AI summary
A radio-frequency signal receiver/transmitter circuit includes a power amplifying circuit that amplifies a radio-frequency transmit signal for output, at least one duplexer including a transmit filter for passing the radio-frequency transmit signal and a receive filter for passing a radio-frequency receive signal, a switch that electrically connects between the power amplifying circuit and the transmit filter, and a control circuit that controls enabling/disabling the power amplifying circuit, that controls connection of the switch, and that controls switching the receive filter between first bandpass characteristics and second bandpass characteristics. The receive filter switches between the first bandpass characteristics and the second bandpass characteristics, in which attenuation is relatively less than that in the first bandpass characteristics. The control circuit exerts such control that the receive filter in the duplexer, including the transmit filter through which the radio-frequency transmit signal does not pass, changes to the second bandpass characteristics.