Local Oscillator Filtering Circuit for VCO Pulling and Harmonics
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Solution Overview
Problem
Conventional local oscillator (LO) generation systems in wireless networks face issues with the VCO pulling phenomenon and high harmonic components, even when using active or passive mixers.
Innovation Solution
A local oscillator generation system and method that incorporates a band-pass filter with a base band-pass filter circuit, resonant frequency setting, and a bandwidth adjusting circuit to filter and narrow the passband, utilizing transistors and a varactor to increase transimpedance and eliminate harmonic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a VCO operates at the same frequency or harmonic frequency of the transmitter, then frequency generation is simplified, but the VCO pulling phenomenon occurs causing frequency instability
Solution Approach 1:
The patent divides the frequency generation process into separate stages: a frequency synthesizer generates the base frequency, and then a mixer combines this with a reference signal to produce the final transmitter frequency. This segmentation prevents the VCO from being directly exposed to high-power transmitter signals, thereby eliminating the pulling phenomenon while maintaining frequency generation capability.
Solution Approach 2:
The patent introduces a mixer as an intermediary component between the frequency synthesizer and the transmitter output. This mediator allows frequency multiplication through mixing operations without exposing the VCO to harmful power levels, thus preserving frequency stability while achieving the desired frequency multiplication.
2Ease of operation
If an active mixer or passive mixer is used in the LO generation system, then frequency mixing is achieved, but harmonic components remain high
Solution Approach 1:
The patent extracts and removes harmful harmonic components from the mixed signal using a band-pass filter. The filter is specifically designed to pass only the desired local oscillator frequency while attenuating harmonic frequencies, thereby eliminating the harmful effects of high harmonic content while preserving the frequency mixing function.
Solution Approach 2:
The patent changes the frequency domain characteristics of the mixed signal by applying band-pass filtering. This parameter change in the frequency spectrum selectively passes the desired frequency component while rejecting harmonics, thus transforming the signal quality from high harmonic content to clean spectral content.
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
Effectively eliminates the VCO pulling phenomenon and harmonic components, improving frequency stability and noise performance by filtering and amplifying signals through a combination of frequency division, mixing, and band-pass filtering.
Implementation Method 1
a base band-pass filter circuit configured to filter signals and output differential signals via a first filter output node and a second filter output node
Implementation Method 2
a resonant frequency setting circuit connected between the first filter output node and the second filter output node to set a resonant frequency
Implementation Method 3
the resonant frequency adjusting circuit includes a varactor
Implementation Method 4
the bandwidth adjusting circuit is configured to increase a transimpedance component of the base band-pass filter circuit
Data Source
AI summary
A local oscillator generation system includes a first frequency divider configured to divide frequencies of a first voltage controlled oscillator signal and a second voltage controlled oscillator signal by 2, and output a first divided signal and a second divided signal; a mixer configured to mix the first voltage controlled oscillator signal, the second voltage controlled oscillator signal, the first divided signal, and the second divided signal, and output a first frequency mixed signal and a second frequency mixed signal; a transimpedance amplifier configured to amplify the first frequency mixed signal and the second frequency mixed signal, and output a first amplified signal and a second amplified signal; and a band-pass filter configured to filter the first amplified signal and the second amplified signal, and output a first filtered signal and a second amplified signal.