Variable VLIF Receiver Tuning for Image Rejection and Sensitivity
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Solution Overview
Problem
RF receivers face challenges in effectively rejecting image signals, particularly when signal strengths vary, leading to reduced receiver sensitivity and image rejection, especially in systems with tight channel spacing and low intermediate frequencies.
Innovation Solution
An RF receiver that dynamically adjusts its very low intermediate frequency (VLIF) based on signal strength, using a quadrature RF mixer and polyphase filters to improve image rejection, and employs quadrature gain and phase correction circuitry to match in-phase and quadrature-phase signal processing, allowing for digital conversion and filtering to remove interfering signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a lower VLIF frequency is used, then image rejection is improved, but receiver sensitivity deteriorates due to increased 1/f noise, DC offsets, and inter-modulation effects
Solution Approach 1:
The patent implements dynamic VLIF frequency selection that adapts to signal conditions. The system switches between different VLIF frequencies (e.g., 120 kHz and 175 kHz) based on received signal strength, allowing optimization of both image rejection and sensitivity for different operating conditions
Solution Approach 2:
The patent changes the VLIF frequency parameter dynamically based on signal strength measurements. When signal strength exceeds a threshold, a lower VLIF frequency is selected for better image rejection; when signal strength is below the threshold, a higher VLIF frequency is selected for better sensitivity
2Object-affected harmful factors
If complex filtering methods are used to remove blocking image signals, then image rejection is improved, but device complexity increases
Solution Approach 1:
The patent dynamically adjusts the VLIF frequency to move blocking image signals away from the desired signal frequency. This dynamic frequency selection simplifies the filtering requirements compared to static systems that would need complex fixed filtering for all possible image frequencies
Solution Approach 2:
By changing the VLIF frequency parameter, the system moves image frequencies to different positions in the spectrum. This parameter change enables simpler filtering approaches since the image signals are dynamically positioned away from the desired signal band
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 enhances receiver sensitivity by adjusting VLIF frequency according to signal strength, reducing noise and inter-modulation effects, and improves image rejection by moving blocking image signals away from the desired frequency, thereby optimizing filtering and reducing the dynamic range requirements of analog-to-digital converters.
Implementation Method 1
when a received RF input signal FR mixes with a local oscillator signal FLO, the mixer produces an output signal with sums and differences of FR and FLO
Implementation Method 2
two different local oscillator signals that are equal in frequency and phase-shifted from each other by 90 degrees
Implementation Method 3
quadrature polyphase filters to reject image interfering signals
Implementation Method 4
quadrature gain correction circuitry, quadrature phase correction circuitry, or both to match the circuitry processing the in-phase signals and the quadrature-phase signals
Implementation Method 5
quadrature gain correction circuitry, quadrature phase correction circuitry, or both to match the circuitry processing the in-phase signals and the quadrature-phase signals
Data Source
AI summary
The present invention is a radio frequency (RF) receiver that uses an RF mixer for tuning to desired frequency bands. The RF receiver down converts a received RF signal into a very low intermediate frequency (VLIF) signal. When receiving a desired RF signal, the frequency of the resulting VLIF signal is called the desired VLIF frequency, and is based on the signal strength of the received RF signal. In one embodiment of the present invention, the desired VLIF frequency is selected to be one of two VLIF frequencies, and is inversely related to the signal strength of the received RF signal. For example, a higher desired VLIF frequency is selected when receiving lower signal strength RF signals to increase effective receiver sensitivity. A lower desired VLIF frequency is selected when receiving higher signal strength RF signals to improve image rejection.