Switching Mixer Notch Filter Circuit for LO Harmonic Rejection
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Solution Overview
Problem
Modern wireless devices face co-existence issues due to spurious responses caused by harmonic frequencies in switching mixers, which contaminate desired signals and are difficult to filter effectively with existing technologies.
Innovation Solution
A circuit using a double-tuned transformer with series-connected notch filters tuned to specific harmonics of the local oscillator frequency, reducing noise and rejecting harmonic responses in switching mixers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional filtering methods are used to remove harmonic frequencies, then harmonic responses are reduced, but desired signals are also attenuated and noise is increased
Solution Approach 1:
The filtering function is segmented into multiple independent notch filters, each tuned to a specific harmonic frequency (2fLO, 3fLO, 4fLO). This segmentation allows selective rejection of individual harmonic frequencies without affecting the desired signal band, resolving the contradiction between harmonic rejection and signal quality preservation
Solution Approach 2:
Each notch filter is designed with specific local characteristics (tuned to specific harmonic frequencies with specific Q-factors) to provide targeted harmonic rejection. The different Q-factors (e.g., Q=10 for second harmonic, Q=5 for third harmonic) create local quality variations that optimize rejection at each harmonic frequency while maintaining signal integrity in the desired band
2Object-generated harmful factors
If multiple notch filters are added to reject multiple harmonics, then harmonic rejection is improved, but circuit complexity increases
Solution Approach 1:
Multiple notch filters targeting different harmonic frequencies are merged into a single integrated circuit block. The filters share common circuit elements and are designed to work together as a unified harmonic rejection system, reducing overall complexity compared to implementing separate filters for each harmonic
Solution Approach 2:
The notch filter circuit is designed with universal applicability to reject multiple harmonics (2nd, 3rd, 4th) of the local oscillator frequency simultaneously. The circuit structure allows it to perform multiple rejection functions through a single integrated design, improving harmonic rejection without proportionally increasing complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces harmonic responses in switching mixers with minimal noise penalty, improving signal purity and reducing interference in wireless devices.
Implementation Method 1
A circuit using a double-tuned transformer with series-connected notch filters tuned to specific harmonics of the local oscillator frequency, reducing noise and rejecting harmonic responses in switching mixers
Implementation Method 2
A circuit using a double-tuned transformer with series-connected notch filters
Data Source
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AI summary
An apparatus for reducing a harmonic response in an electronic circuit is provided. The apparatus includes an RF input configured to provide a first signal operating at a radio frequency. The apparatus includes a local oscillator configured to produce a second signal operating at a local oscillator (LO) frequency. The apparatus includes a switching mixer configured to mix the first and second signals. The apparatus includes a notch filter comprising an inductor and a capacitor connected in parallel. The notch filter is directly coupled to an input of the switching mixer in series. The notch filter is tuned such that its resonant frequency is a harmonic of the LO frequency signal. In an aspect, the apparatus also includes a transformer configured to provide the first signal. In an aspect the apparatus also includes a second notch filter comprising a second inductor and a second capacitor connected in parallel.