Low-IF Receiver Calibration Using Simulated Image Signals
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Solution Overview
Problem
Existing low IF type receiver systems face challenges in maintaining a high image rejection ratio due to mismatches in circuit elements, particularly in quadrature mixers, which are difficult to compensate for using existing methods that require high-frequency calibration signals, increasing system size and cost.
Innovation Solution
A receiver apparatus that utilizes IF band simulated image signals as calibration signals to adjust the attenuance of image signals, allowing for improved image rejection ratio without the need for high-frequency signal sources, by incorporating an IF band simulated image signal generating unit, a path switch, and a complex filter that adjusts element values to compensate for IQ mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-frequency calibration signals are used to compensate for IQ mismatches in quadrature mixers, then the image rejection ratio can be improved, but the system size and cost increase due to requiring high-frequency signal sources
Solution Approach 1:
The patent generates simulated image signals at the IF band that replicate the characteristics of actual image signals without requiring high-frequency sources. These simulated signals are copies of the problematic components that can be used for calibration, eliminating the need for complex high-frequency signal generation hardware while maintaining calibration effectiveness
Solution Approach 2:
The patent introduces an intermediary approach by using IF band signals as a medium to represent and calibrate the effects of RF band mismatches. Instead of directly using high-frequency calibration signals, the system uses lower-frequency simulated signals that mediate the calibration process, achieving the same compensation effect without the hardware complexity
2Measurement precision
If existing calibration methods are used to compensate for IQ mismatches, then the image rejection ratio can be improved, but the system requires additional high-frequency signal sources that increase cost
Solution Approach 1:
The patent creates simulated image signals that are copies of actual image signals but generated at a lower IF frequency. These simulated copies allow calibration to proceed without expensive high-frequency signal sources, reducing manufacturing costs while maintaining the ability to compensate for IQ mismatches in the quadrature mixers
Solution Approach 2:
The patent changes the frequency parameter of the calibration signals from RF band to IF band. This parameter change allows the use of lower-frequency signal generation which is less costly and simpler to implement, while the simulated signals maintain the necessary characteristics to effectively calibrate the quadrature mixer mismatches
3Measurement precision
If complex filters are used to remove image signals, then the image rejection ratio can be improved, but the filter requires precise amplitude and phase matching that is difficult to maintain due to circuit mismatches
Solution Approach 1:
The patent performs preliminary calibration by generating simulated image signals and adjusting the complex filter coefficients before actual signal processing. This preliminary action compensates for IQ mismatches in advance, ensuring that the filter maintains proper amplitude and phase relationships even when circuit elements have variations, thereby improving reliability
Solution Approach 2:
The patent implements a feedback mechanism where simulated image signals are processed through the complex filter, the output is analyzed, and the filter coefficients are adjusted accordingly. This feedback loop continuously optimizes the filter performance to maintain stable amplitude and phase matching despite circuit mismatches, improving the reliability of image rejection
Data Source
AI summary
To improve the degree of removal of unwanted component signals with a small area while eliminating the need for a high-frequency signal source. IF band simulated image signals IM-I, IM-Q output from an IF band simulated image signal generating unit (12) are input to a quadrature mixer (14) through a path switch (13). The signals IM-I and IM-Q which are fed through and output from the quadrature mixer (14) are output from a complex filter (16), and the amplitudes of the signals IM-I and IM-Q are detected by an amplitude detecting unit (17). Based on the detected amplitudes, an element value control unit (18) controls element values of constituent elements of the complex filter (16) so as to decrease the amplitudes.