Active Mixer Bias Feedback for High Image Rejection
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Solution Overview
Problem
Wireless communication devices operating at millimeter-wave and sub-terahertz frequencies face challenges in achieving desired image rejection ratios (IRR) due to IQ errors in mixers and local oscillator generation circuitry, particularly in zero intermediate frequency architectures, which degrade signal quality and error vector magnitude.
Innovation Solution
A communication system with passive quadrature generators and independent LO amplitude detect circuits generates DC bias voltages to bias I and Q mixers, improving the image rejection ratio by detecting and compensating for LO amplitudes in I and Q mixers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a ZIF architecture is used at mmWave and sub-THz frequencies, then spectral efficiency and direct frequency conversion are improved, but image rejection ratio degrades due to IQ errors in mixer and LO generation circuitry
Solution Approach 1:
The patent implements feedback circuits that detect the actual I and Q LO amplitudes and use this information to dynamically adjust mixer bias voltages. The feedback mechanism continuously monitors LO amplitude imbalance and compensates for it by adjusting the bias voltages applied to the I and Q mixers, thereby maintaining high image rejection ratio despite variations in LO generation
Solution Approach 2:
The patent changes the bias voltage parameters of the I and Q mixers based on detected LO amplitude conditions. By dynamically adjusting the bias voltages rather than using fixed values, the system adapts to LO amplitude variations and maintains optimal image rejection performance across different operating conditions at mmWave and sub-THz frequencies
2Measurement precision
If high IRR specifications are achieved through calibration, then signal quality is improved, but device complexity and calibration requirements increase
Solution Approach 1:
The patent implements self-service mechanisms where the system automatically detects its own LO amplitude imbalance and compensates for it without external calibration. The feedback circuits and automatic bias adjustment enable the mixer to self-correct IQ errors, eliminating the need for complex external calibration procedures while maintaining high IRR specifications
3Device complexity
If LO amplitude imbalance is present in I and Q mixers, then circuit simplicity is maintained, but image rejection ratio and signal quality deteriorate
Solution Approach 1:
The patent introduces intermediary feedback circuits and bias adjustment mechanisms that mediate between the simple mixer structure and the requirement for high image rejection. These intermediary components detect LO amplitude conditions and translate them into appropriate bias voltage adjustments, allowing the simple mixer circuit to achieve high IRR performance through intelligent bias control
Data Source
AI summary
A communication system includes a passive quadrature generator connected directly to an in-phase (I) mixer and a quadrature (Q) mixer, an I LO amplitude detect circuit connected to the passive quadrature generator and connected to the I mixer, and a Q LO amplitude detect circuit connected to the passive quadrature generator and connected to the Q mixer, the I LO amplitude detect circuit configured to detect an I LO amplitude and the Q LO amplitude detect circuit configured to detect a Q LO amplitude, and a combining and integrating circuit configured to receive the detected I LO amplitude and the detected Q LO amplitude and generate an I LO DC bias voltage to bias the I mixer and a Q LO DC bias voltage to bias the Q mixer.