Harmonic Rejection Mixer Circuit for Fundamental LO Noise Cancellation
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Solution Overview
Problem
Traditional receivers face challenges in rejecting noise interference introduced by the fundamental local oscillator signal, which affects the signal-to-noise ratio.
Innovation Solution
A harmonic rejection mixing circuit device is designed with multiple mixers and a signal amplifying circuit, where each mixer samples and phase-inverts local oscillator signals, and their outputs are combined with capacitors to eliminate noise interference using double balance features, ensuring a high signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional mixer is used for down conversion, then the circuit structure is simple, but the fundamental LO signal noise cannot be rejected
Solution Approach 1:
The single mixer is segmented into multiple mixers (first mixer, second mixer, third mixer, fourth mixer, fifth mixer, sixth mixer) arranged in parallel. Each mixer handles specific harmonic components of the LO signal, allowing selective rejection of fundamental and harmonic noise while preserving the desired signal. This segmentation enables targeted noise rejection without requiring complete system redesign.
Solution Approach 2:
Multiple mixer outputs are merged through capacitors into a combined output signal. The capacitors act as impedance matching elements that combine the parallel mixer outputs while maintaining signal integrity. This merging approach consolidates the noise rejection benefits of multiple mixers into a single output channel, achieving high noise rejection without proportionally increasing output complexity.
2Reliability
If multiple mixers are used in parallel to reject fundamental LO noise, then the noise figure is reduced, but the device complexity increases
Solution Approach 1:
The mixers operate with phase-inverted LO signals at different phases (0°, 90°, 180°, 270°), creating periodic sampling of the LO signal harmonics. This periodic phase-inverted sampling allows constructive addition of desired signal components while destructive cancellation of noise components at specific frequencies. The periodic action enables efficient noise rejection using a manageable number of mixers rather than requiring continuous complex processing.
Solution Approach 2:
Different LO signal phases (0°, 90°, 180°, 270°) are applied to different mixer groups, changing the operating parameters of each mixer. This parameter variation allows each mixer to target specific harmonic components of the LO signal. By adjusting the phase parameters rather than changing the physical structure, the system achieves flexible noise rejection across different frequency components.
3Object-affected harmful factors
If phase-inverted sampling is implemented, then fundamental LO signal noise is eliminated, but the circuit configuration becomes more complex
Solution Approach 1:
The circuit uses asymmetric phase inversion where the fourth mixer receives phase-inverted LO signals relative to the first mixer, and similarly for the fifth and second mixers, and sixth and third mixers. This asymmetric phase relationship (180° phase difference) creates destructive interference for fundamental LO noise while preserving the desired signal. The asymmetry in phase configuration enables noise cancellation without requiring symmetric complex circuitry.
Data Source
AI summary
The present disclosure discloses a harmonic rejection mixing circuit device and a receiver. In the harmonic rejection mixing circuit device, outputs of first and fourth mixers are combined with the input terminal of the fourth mixer being connected to a capacitor, the first mixer samples a first group of local oscillator (LO) signals, and the fourth mixer phase-invertedly samples the first group of LO signals, thus the noise introduced by a fundamental LO signal input to the first mixer may be eliminated using the double balance feature of the fourth mixer core, thereby ensuring a high signal-to-noise ratio of the receiver. Similarly, the noises introduced by fundamental LO signals input to second and third mixers may be eliminated respectively using the double balance features of the fifth and sixth mixer cores, thereby lowering the noise figure to ensure a high signal-to-noise ratio of the receiver.