Image Rejection Calibration Passive Network
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Solution Overview
Problem
Low-IF receiver architectures face challenges in image rejection due to mismatches in in-phase and quadrature phase paths, leading to unacceptable reception quality from strong adjacent channels causing image interference.
Innovation Solution
An apparatus and method that utilize a programmable gain amplifier and an image rejection circuit with controllable admittance networks to orthogonally correct gain and phase errors in the signal paths, including phase and gain correction circuits, to improve image rejection by injecting a tone and iteratively updating settings until desired signal power levels are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical low-IF receiver architecture is used, then the receiver can process RF signals, but mismatch between in-phase and quadrature phase paths causes image interference cross-talk that makes reception unacceptable
Solution Approach 1:
The image rejection circuit is divided into separate controllable admittance networks for the in-phase and quadrature signal paths. Each path has its own adjustable admittance elements that can be independently controlled to correct phase and gain mismatches, allowing targeted correction without affecting the entire receiver architecture.
Solution Approach 2:
The patent employs controllable admittance networks with selectable switching elements that can dynamically adjust the admittance values in real-time. This dynamic adjustment capability allows the system to adapt to varying signal conditions and correct phase/gain mismatches on-the-fly, improving image rejection without requiring complex fixed correction circuits.
2Adaptability or versatility
If strong adjacent channels are present, then the receiver can operate in typical environments, but they become image interference that makes reception unacceptable
Solution Approach 1:
The patent implements a feedback mechanism where the receiver measures the actual image rejection performance and uses this information to adjust the controllable admittance networks. The feedback loop continuously monitors reception quality and automatically tunes the admittance elements to optimize image rejection, enabling the system to adapt to strong adjacent channels dynamically.
Solution Approach 2:
The system changes the admittance parameters of the correction circuits based on detected signal conditions. By adjusting the controllable admittance elements in response to the presence and strength of adjacent channels, the receiver optimizes its image rejection ratio dynamically, maintaining acceptable reception quality across varying environmental conditions.
3Reliability
If image rejection calibration is implemented with controllable admittance networks, then image rejection improves to approximately 65 dB, but the device complexity increases
Solution Approach 1:
The patent uses a simplified model of the signal paths with controllable admittance networks that replicate the essential correction functionality without requiring complex physical implementations. The controllable admittance networks provide a manageable complexity level while achieving the target 65 dB image rejection ratio, avoiding the need for overly complex calibration circuits.
Solution Approach 2:
Rather than using complex fixed correction circuits, the patent employs controllable admittance networks with adjustable parameters. This approach achieves the required image rejection ratio by dynamically tuning the admittance values, providing a more efficient solution that balances performance requirements with acceptable device complexity.
Data Source
AI summary
In one aspect, an apparatus includes: a mixer to receive a radio frequency (RF) signal and downconvert the RF signal into a second frequency signal; an amplifier coupled to the mixer to amplify the second frequency signal; an image rejection (IR) circuit coupled to the programmable gain amplifier (PGA) to orthogonally correct a gain and a phase of the amplified second frequency signal to output a corrected amplified second frequency signal; and a complex filter to filter the corrected amplified second frequency signal.