Dual-Accumulator NCO for 1 Hz Fractional Frequency Resolution
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Solution Overview
Problem
Traditional numerically controlled oscillators (NCOs) have fixed frequency resolution that is a fraction of the reference clock frequency, limiting their ability to produce output frequencies that are integer multiples of 1 Hz, making it difficult to plot these frequencies on a grid with corresponding frequencies divisible by 1.
Innovation Solution
The implementation of a numerically controlled oscillator module with a first accumulator circuit for accumulating fractional portions of frequency control words and a second accumulator circuit for generating a trigger signal, allowing dynamic adjustment of the phase value and output frequency to achieve integer-valued output frequencies divisible by 1 Hz, independent of the reference clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional NCO with fixed frequency control words is used, then the device complexity is low, but the frequency resolution is fixed and cannot achieve integer multiples of 1 Hz
Solution Approach 1:
The frequency control word is segmented into two parts: an integer portion and a fractional portion. The integer portion is fed to a first accumulator circuit, while the fractional portion is fed to a second accumulator circuit. This segmentation allows independent processing of integer and fractional components, enabling precise frequency control with 1 Hz resolution while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
A second accumulator circuit is introduced as an intermediary component to accumulate the fractional portions of frequency control words and generate trigger signals. This intermediary mechanism bridges the gap between fixed traditional NCO architecture and the requirement for variable fractional frequency control, enabling integer-valued output frequencies without significantly increasing overall system complexity.
2Adaptability or versatility
If fractional frequency control words are implemented, then the adaptability to different frequency requirements is improved, but the device complexity increases due to additional accumulator circuits
Solution Approach 1:
The frequency control word is divided into integer and fractional segments that are processed by separate accumulator circuits. This segmentation enables the system to handle diverse frequency requirements (high adaptability) by independently adjusting each segment, while the modular separated architecture prevents excessive complexity increase by keeping each accumulator's function simple and well-defined.
Solution Approach 2:
The dual-accumulator architecture provides universal functionality by handling both integer and fractional frequency control words through a unified structure. The same basic accumulator circuit design is reused for both integer and fractional portions, allowing the system to adapt to various frequency requirements while maintaining consistent design patterns that limit complexity growth.
3Measurement precision
If the phase accumulator width M is increased to improve frequency resolution, then the frequency resolution improves, but the area of the phase-to-amplitude converter module increases
Solution Approach 1:
By segmenting the frequency control word into integer and fractional portions processed by separate accumulators, the system achieves fine frequency resolution without requiring a single large-phase accumulator. The trigger signal mechanism allows the main phase accumulator to operate with controlled width while still achieving 1 Hz resolution, thereby limiting the area requirement of the phase-to-amplitude converter module.
Solution Approach 2:
The system changes the operational parameters by introducing a trigger signal mechanism that allows the phase accumulator to reset or adjust its accumulation based on fractional portion overflow. This parameter change enables high frequency resolution through temporal modulation of the accumulation process rather than through increasing the static width M, thus reducing the phase-to-amplitude converter area.
Data Source
AI summary
A numerically controlled oscillator (NCO) module includes a first accumulator circuit, a second accumulator circuit, and a phase-to-amplitude converter module. The first accumulator circuit receives a clock signal and at least first portions of each of multiple frequency control words and accumulates the first portions to generate a phase value. Each of the frequency control words identifies a fractional value and includes a respective one of the first portions and a respective second portion. The second accumulator circuit accumulates the second portions and generates a trigger signal based on a result of the accumulated second portions. The first accumulator circuit is configured to adjust the phase value based on the trigger signal. The phase-to-amplitude converter module generates a digital signal based on the clock signal and the phase value. An output transmits an output signal from the NCO module based on the digital signal.