Dual-Mode Notch Filter for LO Spur Rejection in mmW Transmitters
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Solution Overview
Problem
Millimeter-wave (mmW) communication systems face challenges in minimizing unwanted spectral emissions from local oscillator (LO) signals, which can degrade communication signals by generating spurious tones that fall within communication bands, particularly in multi-band mmW transmitters.
Innovation Solution
A dual mode notch filter circuit is implemented, comprising a switch, center-tapped inductance, and capacitance, configured to provide two filter responses: one that reduces unwanted spectral emission of LO signals in a specific communication band while having a negligible effect on another band, and another mode that selectively filters spurious signals in different frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional filter is used to reduce unwanted spectral emission of LO signals, then spurious signal rejection is improved, but signal loss in the communication band increases
Solution Approach 1:
The filter employs a varactor diode that can dynamically change its capacitance value based on applied voltage, allowing the filter's resonant frequency and rejection characteristics to be tuned in real-time. This dynamic adjustment enables the filter to maintain optimal signal rejection while minimizing signal loss by adapting to different operating conditions and frequency bands.
Solution Approach 2:
The filter design incorporates variable capacitance through varactor diodes, allowing electrical tuning of the filter parameters (resonant frequency, Q-factor, rejection depth) without changing the physical structure. By changing electrical parameters rather than mechanical ones, the filter can be optimized for different communication bands while maintaining low signal loss.
2Object-affected harmful factors
If a fixed filter design is used for one communication band, then spurious signal rejection is improved for that band, but adaptability to other bands deteriorates
Solution Approach 1:
The filter is designed with variable capacitance elements that allow a single filter structure to serve multiple communication bands (e.g., 3.5 GHz, 5 GHz, 6 GHz). By electronically tuning the capacitance values, the same physical filter can provide spurious signal rejection for different LO frequencies and communication bands, eliminating the need for separate fixed filters for each band.
Solution Approach 2:
The filter's rejection characteristics can be dynamically adjusted to match different communication bands by changing the bias voltage on the varactor diodes. This allows the filter to adapt its resonant frequency and rejection depth to provide optimal spurious signal suppression for the currently active communication band.
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 dual mode notch filter effectively rejects spurious LO and 2LO signal energy, minimizing interference with communication signals in targeted bands while allowing passage of wide-bandwidth signals, thus meeting stringent RF energy emission standards.
Implementation Method 1
a center-tapped inductance having a first terminal coupled to the positive input terminal and a second terminal coupled to the negative input terminal
Implementation Method 2
a switch having a first terminal coupled to the first terminal of the center-tapped inductance and a second terminal coupled to the second terminal of the center-tapped inductance
Data Source
AI summary
A dual mode notch filter for use in a multi-band millimeter wave (mmW) transmitter includes a transmit filter circuit disposed between two amplifiers in a mmW transmit signal path, the transmit filter circuit formed by at least one switch, at least one capacitor, and a double-tuned transformer, the transmit filter circuit having at least two modes configured to selectively filter a spurious signal in at least a first communication band.