Digitally Controlled Oscillator With Wave Shaping for Low-Aliasing Audio
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Solution Overview
Problem
Existing digitally controlled oscillators face challenges in generating multiple independent waveforms with controlled frequencies while minimizing aliasing, which requires significant DSP resources and increases component count.
Innovation Solution
A digitally controlled oscillator comprising a microcontroller, summing circuit, and linear wave shaper, which generates pulse waves at multiple frequencies and integrates them to produce an electrical audio signal, using a summing circuit and linear wave shaper with active or passive filters to reduce aliasing and component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DDS method is used to generate multiple waveforms with independently controllable frequencies, then waveform generation capability is improved, but DSP resources and component count increase significantly
Solution Approach 1:
The patent combines multiple waveform generation functions into a single integrated circuit that uses a shared voltage-controlled oscillator core. Multiple output waveforms are generated by routing the same VCO output through different waveform shaping circuits (sawtooth, square, triangle generators) rather than using separate oscillators for each waveform type, thereby reducing component count while maintaining independent frequency control.
Solution Approach 2:
The VCO circuit is designed as a universal frequency generator that can produce multiple waveform types through a single device. The oscillator core serves multiple functions by feeding into different waveform transformation circuits, allowing one component to replace what would traditionally require multiple separate oscillator modules.
2Device complexity
If VCO based on relaxation oscillator is used, then circuit simplicity is improved, but frequency stability deteriorates
Solution Approach 1:
The patent introduces a phase-locked loop (PLL) as an intermediary mechanism between the simple relaxation oscillator and the final output. The PLL uses a stable reference frequency to lock and stabilize the VCO's output frequency, thereby maintaining the circuit simplicity of the relaxation oscillator while achieving high frequency stability through the feedback control mechanism.
Solution Approach 2:
The relaxation oscillator is incorporated into a feedback-based PLL architecture where the oscillator's output is compared against a stable reference frequency, and the difference is used to adjust the oscillator's frequency. This feedback mechanism preserves the simplicity of the relaxation oscillator design while ensuring accurate and stable frequency output.
3Measurement precision
If DCO replaces reset circuit with digitally controlled reset, then frequency control precision is improved, but aliasing increases requiring intensive DSP resources
Solution Approach 1:
The patent converts the potentially harmful aliasing effect into a beneficial feature by deliberately designing the sampling rate to be exactly twice the output frequency (Fs = 2f). This specific relationship causes higher harmonics to alias back to the fundamental frequency in a controlled manner, effectively synthesizing rich harmonic content (sawtooth and square waves) without requiring additional DSP processing for anti-aliasing filtration.
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
Enables the generation of multiple independent waveforms with high frequency resolution and low aliasing, reducing DSP requirements and component count, while maintaining audio quality similar to analog sound generation methods.
Implementation Method 1
The linear wave shaper is arranged to produce an output signal at the output of the oscillator based on modifying the resultant signal, wherein the modifying comprises at least integration of the resultant signal
Data Source
AI summary
A digitally controlled oscillator (100), a synthesizer module (200), a synthesizer (300), and a method for producing an electrical audio signal are presented. The oscillator (100) comprises a digital processing unit (10) configured to generate a first pulse wave at a first output (PulseUp) of the processing unit (10), wherein the first pulse wave is arranged to include pulses at at least two different frequencies. The oscillator (100) further comprises a summing circuit (30) and a linear wave shaper (20). The output (PulseUp) of the processing unit (10) is connected to the summing circuit (30) which is arranged to produce a resultant signal based on at least the first pulse wave. The resultant signal is arranged to be fed into the linear wave shaper (20) which is arranged to produce an output signal at the output (OUT) of the oscillator (100) based on modifying the resultant signal.