Frequency Synthesizer Attenuator Control for Spurious Suppression
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Solution Overview
Problem
Frequency synthesizers experience spurious noise due to pulse-like voltage changes in D/A converters, leading to deterioration in radio characteristics and potential disturbances in systems like terrestrial digital broadcasting.
Innovation Solution
Incorporating a low-pass filter between the digital/analog converter and the variable attenuator, with a control unit that outputs control voltages at a time interval longer than the low-pass filter's time constant, and using a comparator or differential voltage adjustments to suppress overshoot and spurious noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a D/A converter is used to generate control voltage for the variable attenuator, then the signal level can be automatically adjusted, but pulse-like voltage changes occur causing spurious noise and deterioration in radio characteristics
Solution Approach 1:
A low-pass filter is introduced as an intermediary component between the D/A converter and the variable attenuator. This filter mediates the control voltage signal by removing high-frequency pulse components while preserving the DC control level, thereby eliminating spurious noise without compromising automatic signal level adjustment functionality
Solution Approach 2:
The harmful pulse-like voltage changes are extracted and removed from the control voltage signal using the low-pass filter. The filter separates the useful DC control component from the harmful AC pulse components, allowing only the desired control signal to reach the variable attenuator
2Stability of the object's composition
If the control voltage is changed frequently to maintain constant signal level, then the signal level stability is improved, but spurious noise increases due to pulse-like changes
Solution Approach 1:
The low-pass filter acts as a mediator that allows frequent control voltage updates for signal level stability while simultaneously filtering out the harmful pulse components. It passes the necessary control information (DC level) while blocking the spurious high-frequency content
3Ease of operation
If the attenuation amount is adjusted by changing the control voltage, then the signal level can be controlled, but overshoot occurs causing frequency components to be superimposed on the high-frequency signal
Solution Approach 1:
The low-pass filter provides beforehand cushioning by preemptively removing high-frequency components from the control voltage before they can cause overshoot. This prevents the harmful frequency components from being superimposed on the high-frequency signal path in the first place
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 spurious noise in the output of frequency synthesizers, improving radio characteristics and preventing disturbances in digital broadcasting systems.
Implementation Method 1
a low-pass filter provided between an output side of the digital/analog converter and the variable attenuator
Data Source
AI summary
To provide, in a frequency synthesizer including: a variable attenuator provided at a subsequent stage of a voltage controlled oscillator; a detector; and a control unit outputting a control voltage for adjusting an attenuation amount of the variable attenuator via a digital/analog converter in accordance with a detection voltage, a technology with which a spurious due to a change in an output of the digital/analog converter can be suppressed. A low-pass filter is provided between an output side of a digital/analog converter and a variable attenuator to cut a frequency component corresponding to an overshoot generated when an output of the digital/analog converter is changed. Further, a period of time from when a control unit outputs a control voltage to when it reads a signal level detected by a detector is set to a period of time longer than a time constant of the low-pass filter determined by a cut-off frequency of the low-pass filter so that no influence is exerted on an operation of automatically controlling the signal level.