PLL A/D Converter Dithering to Reduce Spurious Noise
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Solution Overview
Problem
Spurious noise generation in digital processors due to malfunctions of A/D converters in PLL systems, particularly in frequency synthesizers, leads to performance deterioration, as high cyclic characteristics of analog signals cause repeated holding current fluctuations.
Innovation Solution
Incorporating a band noise generator that adds noise to the input signal of the A/D converter, with a frequency band not affecting digital signal processing, to reduce spurious generation by diffusing the cyclic characteristics of the holding charge current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If an A/D converter is used to convert analog signals to digital signals in a PLL system, then digital processing capability is improved, but spurious noise is generated due to cyclic holding current fluctuations
Solution Approach 1:
The invention applies preliminary action by adding dither noise to the analog input signal before it enters the A/D converter. This pre-processing step randomizes the cyclic holding current fluctuations that would otherwise cause spurious noise in the digital output, thereby preventing the harmful effect before it occurs.
Solution Approach 2:
The invention uses dither noise as an intermediary element between the analog input signal and the A/D converter. This intermediary noise signal interferes with the cyclic holding current fluctuations, converting deterministic spurious patterns into randomized noise that can be filtered more effectively in the digital domain.
2Object-generated harmful factors
If band noise is added to the A/D converter input to reduce spurious, then spurious noise is reduced, but the noise may affect digital signal processing
Solution Approach 1:
The invention applies local quality by carefully designing the dither noise to have specific frequency characteristics that target only the spurious components without affecting the signal band. The noise is localized in frequency domain to where it is most effective, leaving the useful signal frequencies untouched.
Solution Approach 2:
The invention uses parameter changes by adjusting the frequency spectrum of the added noise to match the characteristics of the spurious signals. By changing the noise parameters (frequency distribution, amplitude) to specifically counteract the cyclic holding current effects, the solution reduces spurious while maintaining signal integrity.
Data Source
AI summary
An object of the present invention is to reduce spurious generation due to a malfunction of an A/D converter in a device performing digital processing by converting an analog signal high in cyclic characteristics to a digital signal with the A/D converter.As a concrete solving means, for instance, in a frequency synthesizer of a certain system, the A/D converter is provided on an output side of a voltage controlled oscillator, and its output signal is given to a device performing digital processing to feed back the processing result to the voltage controlled oscillator through D/A conversion. In this case, the noise generated in the band noise generator is added to an input signal of the above-described analog/digital converter. This band noise is a band not affecting the digital signal processing performed by the device.