Baseband Image-Rejection Calibration Circuit for Low-Power Receivers
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Solution Overview
Problem
Conventional image rejection calibration circuits for RF receivers are power-hungry, complex, and prone to precision losses due to operating at RF frequencies, making them unsuitable for low-power and narrowband wireless communication applications.
Innovation Solution
A robust, low-cost, and low-power image-calibration circuit that operates entirely at baseband frequencies using an analog approach with only two multipliers, reducing power consumption and component precision requirements, and improving digital circuitry to control analog components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional image rejection calibration circuits operate at RF frequencies, then image rejection performance can be achieved, but power consumption increases significantly and design complexity increases
Solution Approach 1:
The patent replaces RF-frequency calibration circuits with baseband-frequency calibration circuits. By moving the calibration operation from RF domain to baseband domain, the system achieves the same image rejection function with significantly reduced power consumption and simplified design, as baseband circuits operate at lower frequencies and can use simpler analog components
Solution Approach 2:
The patent changes the operating frequency parameter of the calibration circuit from RF frequency to baseband frequency. This parameter change enables the use of analog multipliers instead of complex RF calibration circuits, reducing both power consumption and design complexity while maintaining image rejection performance
2Use of energy by moving object
If digital phase and gain adjust circuits are used at baseband, then power consumption is reduced, but at least four multipliers are required increasing area and complexity
Solution Approach 1:
The patent segments the calibration function into two separate analog circuits: one for gain adjustment and one for phase adjustment. Each circuit uses a single analog multiplier, totaling two multipliers instead of four. This segmentation allows independent optimization of each function with simpler hardware
Solution Approach 2:
The patent uses analog multipliers instead of digital multipliers for the calibration function. Analog multiplication can be achieved with simpler circuitry (such as Gilbert cell multipliers) compared to digital multipliers, reducing both area and power consumption while maintaining the required calibration precision
3Measurement precision
If RF band-select filter with sharp cutoff is used, then image rejection is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces the need for sharp RF band-select filters with baseband filtering. By performing image rejection calibration at baseband frequency, the system can use simpler, less expensive filters with more relaxed specifications, significantly reducing manufacturing complexity and cost
Data Source
AI summary
Embodiments of a system for calibrating the image rejection of a receiver include an image-rejection correction circuit that modifies the gain and phase of a first channel of a baseband image signal. The image-rejection correction circuit may include a summing circuit and first and second variable-gain elements. In one implementation, a filter receives a corrected first channel from the image-rejection correction circuit and an unmodified second channel of the image signal, while a controller analyzes power measured at the output of the filter, and adjusts the variable-gain elements to reduce the power of the image signal.