Oversampled LO Harmonic Rejection Mixer for Cleaner Frequency Translation
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Solution Overview
Problem
Existing electronic mixers in communication systems suffer from signal degradation due to the introduction of undesired spectral components from harmonics of the local oscillation signal, which are not effectively filtered by conventional band pass filters, degrading the quality of the mixer output.
Innovation Solution
The harmonic rejection mixer employs up-conversion and down-conversion mixers using p-time and m-time oversampled sine waves as local oscillation signals, where p and m are integer numbers, to suppress harmonics except those with harmonic numbers (2*k*N ± 1, resulting in significant reduction of undesired spectral components, with the 1/n characteristic achieving 40-50 dB suppression in each mixer stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a square wave signal is used as the local oscillation signal, then the mixing operation can be performed, but undesired spectral components at odd harmonics are introduced, degrading signal quality
Solution Approach 1:
The patent changes the waveform parameter from square wave to sine wave for the local oscillation signal. This parameter change eliminates the harmonic distortion inherent in square waves, as sine waves contain only the fundamental frequency component, thereby preventing the introduction of undesired spectral components while maintaining the mixing function
Solution Approach 2:
The patent converts the harmful effect of harmonics by using oversampling techniques. By sampling the sine wave at a rate significantly higher than the Nyquist rate, the oversampling process effectively pushes harmonic components to higher frequencies where they can be easily filtered out, transforming the potential harm into a manageable characteristic
2Ease of manufacture
If conventional band pass filters are used before mixing, then filtering can be performed, but they cannot effectively filter out harmonics of the local oscillation signal
Solution Approach 1:
The patent applies preliminary filtering by using oversampled sine waves before the mixing operation. The oversampling process pre-establishes a spectral structure where harmonic components are positioned at predictable, higher frequencies, enabling more effective subsequent filtering and preventing harmonic contamination at the mixer output
Solution Approach 2:
The patent transitions from conventional single-rate sampling to oversampling, adding a temporal dimension to the filtering approach. By spreading the spectral content over a wider frequency range through high-rate sampling, the filter design operates in an expanded frequency domain, making it easier to separate desired signals from harmonic components
Data Source
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AI summary
A harmonic rejection mixer for carrying out a frequency translation of a mixer input signal having a mixer input frequency, the mixer including an up-conversion mixer for generating an intermediate signal by multiplying the mixer input signal with a first local oscillation signal having a first local oscillation frequency, and a down-conversion mixer for generating a mixer output signal by multiplying the intermediate signal with a second local oscillation signal having a second local oscillation frequency. The first local oscillation frequency and the second local oscillation frequency are greater than the mixer input frequency. The first local oscillation signal is an 1-time oversampled sine wave and the second local oscillation signal is an m-time oversampled sine wave.