Dual-Output DDS Synthesizer for Phase-Coherent Fast Tuning
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Solution Overview
Problem
Existing synthesizers face challenges in achieving high spur suppression/phase noise performance while maintaining high tuning speed, with direct digital synthesizers (DDS) experiencing issues due to imperfect digital-to-analog converters and requiring additional phase calibration steps.
Innovation Solution
A phase coherent synthesizer is designed with a digital direct synthesizer (DDS) module, a frequency multiplier, an oscillator, and a mixing stage, where the DDS module has two outputs for fine and coarse resolution synthesis, and a phase detector module synchronizes the signals to ensure phase coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct digital synthesizer (DDS) is used to generate signals with fixed phase relation, then phase coherence is achieved, but spurious responses and phase noise performance deteriorate due to digital-to-analog converter imperfections and truncation effects
Solution Approach 1:
The DDS module is divided into two independent output channels: a first output for fine resolution synthesis and a second output for step synthesis. This segmentation allows each channel to be optimized for different functions, with the fine resolution channel maintaining phase coherence and the step channel providing frequency stepping without degrading overall phase noise performance.
Solution Approach 2:
The harmful truncation effects and spurious responses are extracted and isolated to the second output channel dedicated to step synthesis. By separating the step synthesis function from the fine resolution synthesis, the detrimental effects are confined to a specific channel that can be processed differently (e.g., through the frequency multiplier and mixing stage) without affecting the overall phase coherence of the system.
2Object-generated harmful factors
If synthesizer with better spur/phase noise performance is used, then spurious responses are suppressed, but tuning speed deteriorates due to required phase calibration steps
Solution Approach 1:
Phase coherence is established in advance through the synchronized dual-output DDS architecture and phase detector configuration. By pre-configuring the phase relationships between the two output channels and the reference signal, the system eliminates the need for real-time phase calibration during frequency tuning, thereby maintaining high tuning speed while suppressing spurious responses.
Solution Approach 2:
A phase detector is implemented to monitor and maintain phase coherence between the DDS outputs and the reference signal. This feedback mechanism continuously adjusts the phase relationships, ensuring that spurious responses are suppressed while the system can rapidly switch between frequencies without requiring manual or iterative phase calibration.
3Device complexity
If single output DDS module is used, then device complexity is reduced, but synthesis resolution deteriorates due to inability to provide both fine resolution and step synthesis
Solution Approach 1:
The dual-output DDS module provides multi-functionality by simultaneously delivering fine resolution synthesis through the first output and step synthesis through the second output. This universal design allows a single DDS module to perform multiple synthesis functions that would otherwise require separate devices, maintaining low complexity while achieving high synthesis resolution across different operating modes.
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 phase coherent synthesizer achieves good phase noise and spurious performance while enabling high tuning speed, as the dual-output DDS module and phase detector ensure synchronized and coherent output signals.
Implementation Method 1
The mixing stage is configured to mix the multiplied output signal and an oscillator output signal of the oscillator, thereby generating an intermediate frequency (IF) signal
Implementation Method 2
a phase detector module synchronizes the signals to ensure phase coherence
Data Source
AI summary
A phase coherent synthesizer with good phase noise and spurious performance is described. The phase coherent synthesizer includes digital direct synthesizer (DDS) circuitry, frequency multiplier circuitry, an oscillator, and a mixing stage. The digital direct synthesizer (DDS) circuitry has a first output and a second output. The first output is associated with a fine resolution synthesis. The second output is associated with a step synthesis. A second output signal provided via the second output has a higher frequency compared with a first output signal provided via the first output. The frequency multiplier circuitry is connected with the second output. The frequency multiplier circuitry is configured to multiply the second output signal received via the second output, thereby generating a multiplied output signal. The mixing stage has two input ports connected with the frequency multiplier circuitry and the oscillator respectively. The mixing stage includes, for example, circuitry configured to mix the multiplied output signal and an oscillator output signal of the oscillator, thereby generating an intermediate frequency signal. The first output signal and the intermediate frequency signal are synchronized with each other.