High-Frequency Front End Circuit Filter Circuit for Intermodulation Distortion
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Solution Overview
Problem
High-frequency front end circuits face a reduction in receiver sensitivity due to the attenuation of receive signals by notch filters, which also reduce leakage components of transmit signals, leading to intermodulation distortion.
Innovation Solution
Incorporating a filter circuit, such as an LC series or parallel resonance circuit, between the receive filter and the low noise amplifier to attenuate the difference frequency between the transmit and receive frequency bands, thereby reducing intermodulation distortion and maintaining receiver sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a notch filter is disposed between the receive filter and the low noise amplifier to reduce transmit signal leakage, then isolation characteristics are improved, but the receive signal is attenuated resulting in reduction of receiver sensitivity
Solution Approach 1:
The patent applies local quality by designing a filter circuit with specific frequency selectivity that targets only the transmit frequency band while preserving the receive frequency band. The filter circuit is configured with resonant frequencies and impedance characteristics that create high attenuation specifically for transmit signal leakage components, while maintaining low insertion loss for receive signals, thus achieving localized filtering action rather than broad-spectrum attenuation.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the resonant frequency, quality factor, and impedance of the filter circuit components to optimize the attenuation of transmit leakage at specific frequencies while minimizing impact on receive signals. The filter circuit parameters are designed to create notching characteristics at transmit frequencies while maintaining passband characteristics for receive frequencies, resolving the contradiction through precise parameter control.
2Object-affected harmful factors
If a notch filter is used to reduce transmit signal leakage, then isolation between transmitter and receiver is improved, but intermodulation distortion occurs due to signal attenuation
Solution Approach 1:
The filter circuit implements local quality by creating frequency-selective attenuation that specifically targets transmit leakage components without broadly attenuating receive signals. The resonant circuit is designed with specific Q-factors and frequency responses that provide localized notching at transmit frequencies while maintaining signal integrity in the receive band, thereby preventing intermodulation distortion caused by excessive signal attenuation.
3Object-affected harmful factors
If isolation characteristics are achieved through filtering, then transmit signal leakage is reduced, but receiver sensitivity deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the filter circuit's resonant frequency, bandwidth, and impedance matching to achieve high attenuation of transmit leakage while maintaining minimal insertion loss for receive signals. The parameters are carefully selected and adjusted to create a frequency response that provides strong isolation at transmit frequencies while preserving receiver sensitivity in the receive band, thus resolving the contradiction through precise parameter control.
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
This configuration effectively suppresses the superimposition of intermodulation distortion on receive signals, thereby maintaining receiver sensitivity while achieving isolation characteristics.
Implementation Method 1
The filter circuit may be an LC series resonance circuit having a first inductor
Implementation Method 2
The filter circuit may be an LC parallel resonance circuit having a first inductor
Data Source
AI summary
A high-frequency front end circuit performs reception/transmission simultaneously, and includes a transmitter circuit and a receiver circuit. The transmitter circuit includes a transmit filter passing a signal in the transmit frequency band. The receiver circuit includes a receive filter, an LNA, and a filter circuit. The receive filter passes a signal in the receive frequency band different from the transmit frequency band. The LNA receives and amplifies a signal that has been output from the receive filter. The filter circuit is connected between the receive filter and the LNA. The filter circuit attenuates a component, which is included in the signal received by the LNA, of the frequency indicating the difference between the center frequency of the transmit frequency band and the center frequency of the receive frequency band.