DDS Frequency Source With Spur Filtering and Clock Selection
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Solution Overview
Problem
Direct digital synthesis (DDS) synthesizers in laboratory instruments suffer from high levels of spurious signals and moderate phase noise performance, making them uncompetitive for general laboratory use, despite being inexpensive and widely available.
Innovation Solution
A DDS frequency source with a DDS circuit and a filter system that includes a frequency tracking bandpass filter and a frequency divider, along with a controller to select clock inputs, reduces spurious signals and phase noise by attenuating high-level spurs and minimizing low-level spurs, achieving performance comparable to fractional-N synthesizers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If DDS synthesizers are used, then cost is reduced and availability is improved, but spurious signal levels increase and phase noise performance deteriorates
Solution Approach 1:
The patent extracts and removes high-level spurious signals from the DDS output using a notch filter tuned to the specific spur frequency, separating the harmful spurious components from the desired frequency signal
Solution Approach 2:
The patent introduces an intermediary filtering stage between the DDS circuit and the output, using a combination of notch filter and bandpass filter to mediate and clean the signal before delivery
2Ease of manufacture
If DDS synthesizers are used, then cost is reduced, but phase noise performance becomes moderate
Solution Approach 1:
The patent employs a feedback mechanism where the controller monitors the output spectrum and dynamically adjusts the notch filter frequency and Q-factor to continuously suppress spurious signals that may drift with temperature and frequency changes
Solution Approach 2:
The patent makes the filter characteristics dynamic by allowing the controller to adjust the notch filter parameters in real-time based on the operating conditions, adapting to temperature variations and frequency changes
3Object-generated harmful factors
If fractional-N synthesizers are used, then spurious signal levels are reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces the expensive and complex fractional-N synthesizer with a cheaper DDS circuit combined with simple filtering components, achieving comparable performance through a more economical architecture
Solution Approach 2:
The patent substitutes the complex analog fractional-N division mechanism with a digital DDS approach combined with electronic filtering, replacing mechanical/analog complexity with digital simplicity
Data Source
AI summary
A frequency source for providing a desired source frequency has a direct digital synthesis circuit having a DDS output including a desired DDS frequency, a plurality of low-level spur frequencies and a plurality of high-level spur frequencies; a first clock input for the direct digital synthesis circuit; a second clock input for the direct digital synthesis circuit; a DDS filter in communication with the DDS output; and a controller. The controller selects one of the clock inputs to avoid having a high-level spur in an output of the DDS filter. The source frequency is provided at the DDS filter output.