Digital Frequency Generator Without Off-Chip Filter Artifacts
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Solution Overview
Problem
Existing direct digital synthesis methods require fast high-resolution DACs and multi-pole low-pass filters, leading to increased size and cost due to the need for external components, and suffer from reduced accuracy due to approximation in computing carry signal delays.
Innovation Solution
A digital frequency generator circuit that integrates onto a simple chip without off-chip filters, using an accumulator, selector, digital-to-analog converter, and comparator to generate a pulse stream with a desired frequency relative to a reference clock signal, leveraging modulo arithmetic and pseudo-random binary sequences to eliminate the need for external filters and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fast high-resolution DAC and multi-pole low-pass filter are used in direct digital synthesis, then signal generation accuracy is improved, but device size and cost increase due to external components
Solution Approach 1:
The patent combines the DAC and low-pass filter into a single integrated circuit device, eliminating the need for separate external components. The filter is implemented using digital signal processing within the same chip that contains the DAC, thereby reducing device size while maintaining signal generation accuracy.
Solution Approach 2:
The patent replaces the traditional analog low-pass filter (which requires physical discrete components) with a digital filter implementation. This substitution allows the filter to be integrated onto the same chip as the DAC, reducing the need for external analog components and simplifying the overall device architecture.
2Measurement precision
If a multi-pole low-pass filter with precision discrete components is used, then signal filtering performance is improved, but cost increases due to external components
Solution Approach 1:
The patent merges the filter functionality with the DAC into a single integrated device, eliminating the need for separate precision discrete components. This integration reduces manufacturing cost by reducing the bill of materials and assembly complexity, while maintaining filtering performance through digital implementation.
Solution Approach 2:
The patent substitutes analog discrete component filtering with digital filtering implemented in software or digital logic within the integrated circuit. This replacement eliminates the need for expensive precision discrete components while maintaining or improving filtering performance through programmable digital signal processing.
3Device complexity
If approximation is used in computing carry signal delay, then circuit complexity is reduced, but output frequency accuracy deteriorates
Solution Approach 1:
The patent replaces the approximate carry signal delay computation with an exact digital implementation. By using digital signal processing to precisely calculate and compensate for delay effects, the system achieves high output frequency accuracy without requiring complex analog delay circuits or approximation methods.
Solution Approach 2:
The patent employs feedback mechanisms to measure and compensate for delay effects in the signal path. By continuously monitoring the actual delay and adjusting the output frequency accordingly, the system maintains high accuracy while using straightforward digital circuitry rather than complex approximate methods.
Data Source
AI summary
An opportunity is apparent to develop alternative circuitry. Simplified circuitry without artifacts tied to the clock that drives a digital frequency generator (DFG) is useful in a variety of tunable electronic devices. The present invention relates to digital frequency generation. In particular, it relates to a method and apparatus for the digital generation of a pulse stream having a desired frequency relative to a reference clock signal and the ratio of two integers. The method applies generally to integers whose ratio is not an integer. The DFG as a device can be integrated onto a simple chip, without need for an off-chip filter.