Superheterodyne Receiver Filtering for Wideband Image Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Super-heterodyne receivers face challenges in effectively rejecting image bands, leading to degraded signal-to-noise ratio due to the inability of existing methods to consistently achieve sufficient attenuation across a wide frequency range, especially with external filters imposing power penalties and requiring customized designs.
Innovation Solution
An apparatus comprising an image rejection filter, a local oscillator, a mixer, a frequency divider, and a translational filter with passive mixers and frequency-dependent impedances, which together provide a bandpass filter for selecting desired signals and a band-stop filter for suppressing image bands, enhancing image rejection across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an image rejection filter is placed in front of the mixer to attenuate image frequency components, then image band suppression is improved, but the filter requires customized design for each desired frequency and cannot achieve sufficient attenuation across the entire image band
Solution Approach 1:
The patent employs a band-stop filter with multiple notches that can suppress multiple image bands simultaneously across a wide frequency range. This universal filter design eliminates the need for customized filters for each operating frequency, as it can handle multiple image rejection requirements through its multi-notch structure
Solution Approach 2:
The filter is designed with multiple notches segmented at different frequency positions, allowing each notch to target specific image bands. This segmentation enables the filter to provide comprehensive suppression across the entire image band by dividing the rejection function into multiple specialized notches
2Object-affected harmful factors
If external surface acoustic wave (SAW) filters are used as bandpass filters to remove energy within the image band, then image band attenuation is improved, but power penalty increases due to impedance matching requirements and integration difficulty
Solution Approach 1:
The patent introduces a band-stop filter as an intermediary component that directly processes the RF signal to suppress image bands before mixing. This intermediary filter eliminates the need for complex impedance matching networks required by external SAW filters, thereby reducing power consumption and simplifying integration while maintaining effective image band attenuation
3Power
If tuned amplifiers are used before the mixer instead of filters, then gain is improved, but image rejection consistency deteriorates due to difficulty in tracking amplifier characteristics
Solution Approach 1:
The patent extracts the image rejection function from the amplifier path and implements it through a dedicated band-stop filter. This separation allows the amplifier to focus on providing consistent gain while the filter independently handles image suppression, eliminating the tracking problems that arise when both functions are combined in tuned amplifiers
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 effectively suppresses image bands, improving signal-to-noise ratio and receiver selectivity, while being cost-effective and adaptable for various frequency operations without the need for customized designs or external filters.
Implementation Method 1
an incoming radio frequency (RF) signal at a frequency f RF is mixed with a local oscillator (LO) signal by a non-linear device to produce a signal at a lower, intermediate frequency (IF)
Implementation Method 2
a frequency divider configured to generate a plurality of local oscillator signals in quadrature with each other
Implementation Method 3
a translational filter comprising a plurality of passive mixers configured to convert the first IF signal to a plurality of second intermediate frequency (IF) signals in quadrature with each other based on the plurality of quadrature local oscillator signals
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An apparatus for rejecting an image band in an RF signal includes: an image rejection filter; an oscillator to generate an oscillator signal; a mixer coupled to the image rejection filter and the oscillator, to convert a received input signal to a first intermediate frequency signal based on the oscillator signal; a frequency divider to generate a plurality of oscillator signals in quadrature with each other; and a translational filter including a plurality of passive mixers to convert the first intermediate frequency signal to a plurality of second intermediate frequency signals in quadrature with each other based on the plurality of quadrature oscillator signals; and a plurality of frequency dependent impedances each coupled as a load to an output of a respective one of the plurality of passive mixers, wherein: the image rejection filter and the translational filter combine to provide a bandpass filter for selecting a desired signal in the RF signal and a band stop filter for suppressing the image band in the RF signal.