Class D Audio Circuit With Supply-Scaled PWM Reference
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Solution Overview
Problem
Existing class D amplifiers are limited by the fixed amplitude of the periodic voltage, restricting the use of input signals with large amplitudes and requiring high gains that degrade noise characteristics when used with varying power supply voltages.
Innovation Solution
An audio circuit with a class D amplifier that includes a bias circuit to generate a variable second reference voltage, allowing the periodic voltage amplitude to adjust with the power supply, enabling flexible signal level design and maintaining constant gain or reducing noise characteristics based on power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the periodic voltage amplitude is fixed, then the circuit design is simple, but the maximum amplitude of the analog audio signal is restricted and cannot utilize large signal levels
Solution Approach 1:
The patent makes the periodic voltage amplitude dynamic by controlling it with the power supply voltage. The amplitude of the periodic voltage generated by the periodic voltage generating circuit is no longer fixed but varies according to the power supply voltage level, allowing the integrator output voltage range to adapt to different power supply conditions and enable full-scale output utilization.
Solution Approach 2:
The patent changes the amplitude parameter of the periodic voltage based on the power supply voltage. By making the periodic voltage amplitude proportional to the power supply voltage, the system can accommodate different signal levels and power supply conditions without requiring fixed amplitude design constraints.
2Power
If the gain is increased to provide full-scale output with fixed periodic voltage, then the output range is sufficient, but the noise characteristics are degraded
Solution Approach 1:
The patent changes the periodic voltage amplitude parameter to be proportional to the power supply voltage. This allows the system to achieve full-scale output with appropriate gain settings without requiring excessively high gain values that would degrade noise characteristics. The dynamic amplitude adjustment ensures optimal signal-to-noise ratio across different power supply conditions.
3Stability of the object's composition
If the periodic voltage amplitude is fixed at a small value, then the circuit is stable, but it cannot utilize input signals with large amplitudes
Solution Approach 1:
The patent makes the periodic voltage amplitude dynamic rather than fixed. The amplitude adjusts according to the power supply voltage, allowing the PWM comparator to maintain stable operation across different voltage conditions while simultaneously accommodating a wide range of input signal amplitudes. This dynamic adjustment preserves stability while enabling full utilization of available signal levels.
Data Source
AI summary
A class D amplifier circuit receives an analog audio signal with a first reference voltage as its center level, and outputs an output pulse signal having a duty cycle that corresponds to the analog audio signal. A bias circuit generates a second reference voltage having a voltage level obtained as a division of the first reference voltage and the power supply voltage. A periodic voltage generating circuit of the class D amplifier circuit generates a periodic voltage having a triangle waveform or otherwise a sawtooth waveform having an amplitude that corresponds to the second reference voltage.