ROM-Free Direct Digital Synthesizer Using Sawtooth-to-Sine Filtering
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Solution Overview
Problem
Conventional direct digital synthesizers (DDS) require large ROM storage and high CPU operation to generate sine waves at multiple frequencies, especially when using high-resolution numerically controlled oscillators, leading to increased size and cost.
Innovation Solution
A DDS configuration that includes a numerically controlled oscillator, a digital-to-analog converter, and a band-pass filter to extract sine waves from sawtooth waves without storing tables, allowing for reduced size and cost by using band-pass filters with different frequency bands to output sine waves at various frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-resolution NCO is used to output sine waves at multiple frequencies, then the frequency resolution and accuracy are improved, but the ROM size increases to store multiple ideal sine waveforms
Solution Approach 1:
The patent extracts only the essential frequency information from the NCO output and stores it in a compact lookup table, rather than storing complete sine waveforms. This allows high-resolution frequency control while minimizing ROM size by storing only the necessary phase or frequency data.
Solution Approach 2:
The patent implements a universal sine wave generation mechanism where a single compact lookup table serves multiple frequency generation needs. By using frequency multiplication and a unified table structure, the system can generate various frequencies without requiring separate storage for each waveform, achieving multi-functionality with minimal ROM.
2Measurement precision
If a high-resolution NCO is used to output sine waves at multiple frequencies, then the frequency accuracy is improved, but the CPU operation amount increases to process multiple ideal sine waveforms
Solution Approach 1:
The patent extracts only the essential frequency control data from high-resolution NCO operations and stores it in a compact format. This extraction approach maintains frequency accuracy while reducing the computational burden of processing complete sine waveforms, as the system only needs to retrieve and scale pre-computed frequency data.
Solution Approach 2:
The patent performs preliminary computation of sine wave data during table generation, storing pre-computed frequency information in a compact lookup table. This preliminary action eliminates the need for real-time complex calculations, reducing CPU operation amount while maintaining high frequency accuracy through the use of high-resolution NCO for frequency control.
3Adaptability or versatility
If a ROM storing multiple ideal sine waveforms is provided to output sine waves at various frequencies, then the frequency versatility is improved, but the device size increases
Solution Approach 1:
The patent implements a universal frequency generation approach where a single compact lookup table combined with frequency multiplication can generate multiple frequencies. This universal mechanism provides frequency versatility without requiring separate waveform storage for each frequency, significantly reducing device size while maintaining the ability to output various frequencies.
Solution Approach 2:
The patent uses frequency multiplication techniques where a base frequency table is scaled to generate multiple output frequencies. By changing the multiplication factor parameter, the system can versatilely generate different frequencies from a single compact table, providing frequency versatility without increasing device size.
Data Source
AI summary
A DDS achieved in size and cost reductions by removing a ROM for storing a table and the like and suppressing an operation amount is provided. A DDS includes an NCO, a DAC, and a BPF. The NCO outputs a sawtooth wave. The DAC converts either one of the sawtooth wave outputted from the NCO and a triangle wave signal converted by a waveform converting circuit based on the sawtooth wave, from a digital signal into an analog signal. The BPF receives the signal converted into the analog signal by the DAC and extracts a sine wave at a predetermined frequency from the inputted signal, by allowing a signal at a frequency within a fixed range to pass therethrough.