Single-Sideband Calibration Signal for Low-IF Image Rejection
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Solution Overview
Problem
Low-IF receivers face challenges in rejecting image responses due to phase and amplitude mismatches in in-quadrature signals, which are difficult to correct with limited ADC performance and complex filter architectures, leading to increased power consumption and complexity.
Innovation Solution
A calibration signal with high rejection of its own image component is generated using a single-sideband mixer and frequency dividers, operating on harmonic components within the transceiver system, such as tones with frequencies four times the intermediate frequency, to minimize image interference and correct phase and amplitude errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex filter architectures are used to reject image responses, then image rejection performance is improved, but device complexity increases
Solution Approach 1:
The system uses itself to generate the calibration signal needed for correction. The transmitter circuit generates a calibration signal that is processed through the receiver chain, allowing the system to self-calibrate without external equipment. This reduces the need for complex external calibration equipment while maintaining image rejection performance.
Solution Approach 2:
The system corrects phase and amplitude parameters of the in-quadrature signals by adjusting these parameters based on calibration measurements. By dynamically changing these parameters to optimize performance, the system achieves better image rejection without requiring permanently complex filter architectures.
2Measurement precision
If high-performance ADC is used to correct phase and amplitude mismatches, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The system performs self-calibration using internally generated calibration signals and existing ADC resources. By reusing the existing ADC and processing chain for calibration purposes, the system achieves precise phase and amplitude measurements without requiring additional high-performance ADC components.
Solution Approach 2:
The system performs calibration measurements in advance during dedicated calibration periods, storing the measured phase and amplitude corrections for use during normal operation. This preliminary action allows the system to achieve high measurement precision using the existing ADC, avoiding the need for continuously operating high-performance conversion equipment.
3Measurement precision
If external calibration equipment is used, then calibration accuracy is improved, but ease of operation deteriorates
Solution Approach 1:
The transceiver performs calibration autonomously using internally generated signals and existing circuitry. The control circuit automatically executes calibration sequences, measures phase and amplitude mismatches, and applies corrections without requiring external calibration equipment or manual intervention, significantly improving ease of operation while maintaining calibration accuracy.
Solution Approach 2:
The system implements a feedback loop where calibration measurements are continuously taken, corrections are applied to the in-quadrature signal generation, and performance is monitored. This automatic feedback mechanism maintains high calibration accuracy while eliminating the need for manual calibration operations with external equipment.
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 approach enables effective calibration of phase and amplitude errors with high spectral purity, reducing power consumption and complexity by utilizing internal signals for calibration, thereby improving image rejection and system performance.
Implementation Method 1
a single-sideband mixer for modulating the modulating signal on the carrier signal
Implementation Method 2
at least two frequency dividers by two connected in cascade, wherein the dividers receive at input the signal at output from the single-sideband mixer
Data Source
AI summary
A calibration signal is generated from a modulating signal having a first frequency and a carrier signal having a second frequency. A single-sideband mixer modulates the modulating signal on the carrier signal. At least two frequency dividers by two connected in cascade receive the modulating signal modulated on the carrier signal and generate an output of the calibration signal.