Dual-Output DDS Synthesizer for Phase Coherence and Low Spurs
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Solution Overview
Problem
Existing synthesizers, such as direct digital synthesizers (DDS), suffer from poor spur/phase noise performance due to imperfections in digital-to-analog converters, leading to crossing spurs and noise floors, and lack phase coherence, resulting in slower frequency tuning.
Innovation Solution
A phase coherent synthesizer is designed with a digital direct synthesizer (DDS) module having two outputs for fine and coarse resolution, a frequency multiplier, and a mixing stage, along with a phase detector module and phase-locked loop, to synchronize and control the oscillator output signals, ensuring phase coherence and reduced spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct digital synthesizer (DDS) is used to generate signals with fixed phase relation, then phase coherence is achieved, but spur/phase noise performance deteriorates due to digital-to-analog converter imperfections
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. Each channel operates with different resolution characteristics, allowing the system to segment the frequency synthesis task to avoid spurs while maintaining phase coherence between both outputs
Solution Approach 2:
The system changes the resolution parameter between the two DDS outputs - the first output uses fine resolution for precise frequency control, while the second output uses step synthesis with coarser resolution. This parameter differentiation allows each channel to operate in its optimal range, reducing spurious responses while maintaining overall phase coherence
2Object-generated harmful factors
If synthesizers with better spur/phase noise performance are used, then spur suppression is improved, but phase coherence is lost, requiring additional phase calibration steps that slow down frequency tuning
Solution Approach 1:
A phase detector module continuously monitors the phase relationship between the first and second outputs of the DDS module and provides feedback to a phase calibration module. This automatic feedback mechanism maintains phase coherence without requiring manual intervention or slowing down the frequency tuning process
Solution Approach 2:
The phase calibration module automatically adjusts the phase of the second output to maintain coherence with the first output, enabling the system to self-correct phase errors without external intervention. This self-service capability eliminates the need for manual phase calibration steps, maintaining high tuning speed while ensuring spur suppression
3Device complexity
If a single DDS output is used for frequency synthesis, then device complexity is reduced, but the ability to provide both fine resolution and coarse step synthesis simultaneously is limited
Solution Approach 1:
The DDS module is designed with multi-functionality, providing two independent outputs that can simultaneously serve different synthesis requirements. The first output handles fine resolution applications while the second output handles step synthesis, making the single DDS module versatile enough to cover multiple operating modes without requiring separate synthesizer units
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 improved spur suppression and phase noise performance while maintaining high tuning speed, ensuring phase stability and accurate frequency setting with reduced spurious responses across a wide frequency range.
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 (42), particularly a digital phase detector, which is associated with the first output (20) and the mixing stage (28), so that respective signals received, namely the first output signal from the first output (20) as well as the intermediate frequency signal from the mixing stage (28), are compared with each other with respect to their phase
Implementation Method 3
The frequency multiplier is configured to multiply the second output signal received via the second output, thereby generating a multiplied output signal
Data Source
Figure 1
AI summary
The invention relates to a phase coherent synthesizer (10) with good phase noise and spurious performance. The phase coherent synthesizer (10) comprises a digital direct synthesizer (DDS) module (12), a frequency multiplier (24), an oscillator (32), and a mixing stage (28). The digital direct synthesizer (DDS) module (12) has a first output (20) and a second output (22). The first output (20) is associated with a fine resolution synthesis. The second output (22) is associated with a step synthesis. A second output signal provided via the second output (22) has a higher frequency compared with a first output signal provided via the first output (20). The frequency multiplier (24) is connected with the second output (22). The frequency multiplier (24) is configured to multiply the second output signal received via the second output (22), thereby generating a multiplied output signal. The mixing stage (28) has two input ports (38, 40) connected with the frequency multiplier (24) and the oscillator (32) respectively. The mixing stage (28) is configured to mix the multiplied output signal and an oscillator output signal of the oscillator (32), thereby generating an intermediate frequency signal. The first output signal and the intermediate frequency signal are synchronized with each other.