Cross-Coupled LO Buffer for High-Frequency IQ Mismatch Correction
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Solution Overview
Problem
Direct conversion RF transceivers face IQ mismatch issues due to gain and phase mismatches in local oscillator (LO) buffers, which degrade signal quality and communication performance, especially at high frequencies.
Innovation Solution
A cross-coupled LO buffer circuit comprising MOS or bipolar junction transistor differential input pairs with inductive loads, where each buffer receives output signals from the other to correct phase and amplitude mismatches, reducing quadrature mismatch without requiring calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional LO buffer circuits are used, then the circuit structure is simple, but phase and amplitude mismatches occur degrading signal quality
Solution Approach 1:
The patent implements a cross-coupled configuration where the output of one differential pair is fed back to the input of the other differential pair. This feedback mechanism automatically corrects phase and amplitude mismatches by utilizing the quadrature relationship between the two LO buffers, eliminating the need for external calibration circuits while achieving precise matching.
Solution Approach 2:
The patent employs asymmetric coupling between the two differential pairs, where each pair is configured with specific transistor sizing and loading conditions that create complementary characteristics. This asymmetric design enables one pair to compensate for the mismatches of the other, achieving precise quadrature generation without requiring symmetric identical circuits.
2Manufacturing precision
If calibration circuits are added to correct mismatches, then signal quality improves, but chip area and power consumption increase
Solution Approach 1:
The cross-coupled LO buffer circuit is self-correcting, where the two differential pairs automatically compensate for each other's mismatches through their mutual coupling. The circuit uses its own internal signals to correct phase and amplitude errors without requiring external calibration circuits, thereby minimizing chip area while achieving precise quadrature matching.
3Manufacturing precision
If conventional LO buffers are used, then power consumption is low, but phase and amplitude mismatches degrade communication performance
Solution Approach 1:
The patent merges the functions of two differential pairs into a single cross-coupled configuration, where both pairs work together to provide mismatch correction. By combining the functionality of multiple circuits into one integrated structure, the patent achieves precise phase and amplitude matching without proportionally increasing power consumption, as the two pairs share common biasing and loading structures.
4Speed
If high frequency operation is required, then communication performance improves, but mismatches become more significant
Solution Approach 1:
The cross-coupled configuration provides automatic feedback correction that becomes increasingly effective at higher frequencies. The quadrature relationship between the two differential pairs is maintained through their mutual coupling, and the feedback mechanism continuously corrects frequency-dependent mismatches, enabling high-frequency operation with preserved signal integrity.
Data Source
AI summary
A local oscillator (LO) buffer circuit comprises first and second LO buffers arranged in a cross coupled configuration. The first LO buffer generates in-phase output signals in response to in-phase input signals, and quadrature output signals from the second LO buffer. The second LO buffer generates the quadrature output signals in response to quadrature input signals and the in-phase output signals. The LO buffers may include inductive loads. The LO buffers may include MOS transistors or bipolar junction transistors.