PCM-to-PWM Audio Modulation With Dynamic Sample-Rate Changes
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Solution Overview
Problem
Conventional PCM-PWM conversion methods are limited by the requirement that the PWM period must be an integer multiple of the master PWM clock period, restricting dynamic variation of the PWM clock rate and leading to wide-band noise when the period changes abruptly.
Innovation Solution
A circuit and method that dynamically adjusts the PWM period over a continuous range, aligning transition times with the PWM clock grid while using filter functions to suppress transients, allowing the PWM signal to be slaved to an input sample rate and operate from a fixed clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the PWM period is constrained to be an integer multiple of the master PWM clock period, then the PWM signal can be generated with proper clock alignment, but the PWM clock rate cannot be dynamically varied and the system lacks flexibility
Solution Approach 1:
The patent implements dynamic PWM period selection by allowing the PWM period to be any value within a continuous range rather than fixed to discrete clock multiples. The system dynamically adjusts the PWM period based on desired output frequency while maintaining synchronization through calculated transition times that map to the clock grid, enabling flexible adaptation without rigid constraints.
Solution Approach 2:
The invention changes the parameter of PWM period from a discrete set (integer multiples of clock period) to a continuous range of values. By calculating transition times based on the desired PWM frequency and mapping them to the clock grid, the system achieves continuous parameter adjustment while maintaining proper clock synchronization.
2Speed
If the PWM period changes abruptly, then the system can respond quickly to frequency changes, but wide-band noise and transients are generated in the output signal
Solution Approach 1:
The patent applies filter functions to the PWM period values before they are used to generate the PWM signal. This preliminary filtering action prepares the period transitions to be smoother, preventing abrupt changes that would generate wide-band noise and transients, while still allowing the system to respond to frequency changes.
Solution Approach 2:
The invention implements cushioning against harmful effects by pre-filtering PWM period transitions. The filter functions act as a cushion that smooths out abrupt period changes, reducing the generation of wide-band noise and transients in the output signal while maintaining the ability to change frequency when needed.
3Adaptability or versatility
If the PWM period is fixed, then the system is simpler to implement, but the system cannot reduce interference or implement spread-spectrum modulation
Solution Approach 1:
The patent implements dynamic PWM period adjustment that allows the system to vary the period continuously. This dynamic capability enables interference reduction by avoiding fixed frequency harmonics and allows spread-spectrum modulation by deliberately varying the PWM period according to a spreading code, providing adaptability without requiring complex additional hardware.
Solution Approach 2:
The invention creates a universal PWM generation system that can perform multiple functions: standard PWM generation, interference reduction by frequency avoidance, and spread-spectrum modulation. The same dynamic period adjustment mechanism serves all these purposes, making the system multi-functional without proportionally increasing complexity.
Data Source
AI summary
Digital audio circuitry including modulation circuitry (35; 135) for generating a pulse-width modulated (PWM) signal from processed pulse-code modulated (PCM) audio signals. The modulation circuitry includes a duration quantizer function (32) that generates a sequence of duration values d(k) from received PCM samples, quantized to integer multiples of periods of a master PWM clock (CLKpwm). The duration quantizer function also produces a feedback PCM value x(k) from each quantized duration value d(k) that is applied to a loop filter (36), the output of which modifies the received PCM sample stream to suppress quantization noise. Transient effects caused by modulation or abrupt changes in the desired PWM period are suppressed by digitally filtering (34; 134) the PWM period sample stream.