Dual-Switching Harmonic Rejection Mixer for Mismatch Tolerance
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Solution Overview
Problem
Conventional harmonic rejection mixers are sensitive to gain and phase mismatches, which limit their ability to effectively reject harmonics in RF signals, especially in broad-band systems like TV tuners and cable systems.
Innovation Solution
A dual-switching stage mixer design where the first stage switches at a higher rate of N times the local oscillator (LO) frequency, and the second stage uses N switches controlled by non-overlapping phases of the LO, minimizing phase and duty cycle errors and eliminating harmonics except those at (m*2N)±1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple mixing blocks are used to eliminate harmonic signals, then harmonic rejection capability is improved, but sensitivity to gain and phase mismatches increases
Solution Approach 1:
The mixer is divided into multiple mixing blocks (first mixing block, second mixing block, third mixing block, fourth mixing block) that process different phases of the RF signal. Each block is controlled by LO signals with specific phase relationships (0°, 90°, 180°, 270°), allowing harmonic rejection through constructive and destructive interference while distributing the sensitivity burden across independent blocks
Solution Approach 2:
The invention changes the LO signal parameters (frequency, phase) to achieve harmonic rejection. Specifically, the LO signal frequency is set to twice the intermediate frequency (2×IF), and different LO phases are applied to different mixing blocks. This parameter optimization reduces the impact of gain and phase mismatches on overall harmonic rejection performance
2Manufacturing precision
If square wave LO is used for mixing, then noise and linearity are improved, but harmonic aliasing into the desired signal band occurs
Solution Approach 1:
The invention converts the harmful effect of square wave LO harmonics into a beneficial filtering mechanism. By using a square wave LO at 2×IF frequency and combining outputs from multiple mixing blocks with specific phase relationships, the harmonic components that would normally alias into the signal band are instead canceled through destructive interference, while the desired signal components reinforce through constructive interference
3Manufacturing precision
If LO frequency is set to twice the intermediate frequency, then in-phase and quadrature-phase signals are improved, but circuit complexity increases
Solution Approach 1:
The invention merges the functionality of multiple mixers operating at different LO frequencies into a single integrated structure. The first, second, third, and fourth mixing blocks are combined in parallel, all driven by the same 2×IF LO signal source but with different phase shifts. This merging approach achieves I/Q signal quality improvement while sharing common LO generation circuitry, thereby managing complexity
Data Source
AI summary
A harmonic rejection mixer includes a first scaling circuit for scaling an RF signal to generate a plurality of scaled RF signals, a first switching stage for sampling the scaled RF signals using a first plurality of switching signals, and a second mixing stage for mixing the sampled RF signals with a second plurality of switching signals to generate a plurality of frequency translated signals having different phases. A combiner adds the frequency translated signals together to generate a first plurality of baseband versions of the RF signal. A first amplifier stage processes the first plurality of baseband versions to generate a second plurality of baseband versions. The mixer further includes a second scaling circuit for scaling the second plurality of baseband versions and a second amplifier stage to generate an in-phase baseband signal and a quadrature baseband signal from the scaled second plurality of baseband versions.