Triangular-Wave Generator Circuit for Stable Class-D PWM
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Solution Overview
Problem
Class-D amplifier circuits face challenges in maintaining a stable gain bandwidth product due to process and temperature variations, leading to performance issues such as noise, offset, and harmonic distortion, particularly in the generation of triangular voltages used for pulse width modulation.
Innovation Solution
A triangular-voltage generator with an operational amplifier in integrator configuration, utilizing a voltage divider and switches to alternately connect the input terminal to the power supply and ground, ensuring the amplitude of the triangular voltage is proportional to the power supply voltage and independent of resistor and capacitor values, thereby reducing noise and offset contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain bandwidth product is increased to improve amplifier performance, then the stability margin decreases and the system becomes unstable
Solution Approach 1:
The patent implements dynamic adjustment of the triangular wave amplitude based on the operating point of the amplifier. The amplitude is modulated according to the signal amplitude to maintain optimal loop gain across different operating conditions, allowing the system to achieve high gain bandwidth product while maintaining stability through adaptive control
Solution Approach 2:
The patent changes the amplitude parameter of the triangular wave dynamically. By adjusting the triangular wave amplitude according to the signal amplitude and operating point, the system optimizes the loop gain to achieve high gain bandwidth product while maintaining stability margin through parameter adaptation
2Device complexity
If fixed resistor and capacitor values are used in the integrator circuit, then the design is simplified, but the gain bandwidth product becomes sensitive to process and temperature variations
Solution Approach 1:
The patent implements feedback control where the triangular wave amplitude is adjusted based on the operating point detection. This feedback mechanism compensates for process and temperature variations, maintaining stable gain bandwidth product performance without requiring complex temperature compensation circuits or precision components
Solution Approach 2:
The system automatically adjusts the triangular wave amplitude based on its own operating conditions. The operating point detection and amplitude modulation work together to self-correct for environmental variations, eliminating the need for external compensation mechanisms while maintaining reliability
3Measurement precision
If the triangular wave amplitude is increased to improve signal-to-noise ratio, then the dynamic range increases, but the linearity deteriorates due to comparator saturation
Solution Approach 1:
The patent dynamically adjusts the triangular wave amplitude to match the signal amplitude and operating point. This dynamic adaptation ensures the triangular wave充分利用 the comparator's dynamic range without causing saturation, maintaining both high signal-to-noise ratio and linearity through real-time optimization
Solution Approach 2:
The patent changes the triangular wave amplitude parameter dynamically based on operating conditions. By adapting the amplitude to the signal level and operating point, the system achieves optimal signal-to-noise ratio while preventing comparator saturation that would degrade linearity
Data Source
AI summary
A triangular-voltage generator has an input terminal that receives a power supply voltage and an output terminal that supplies a triangular-wave voltage having a repetition period. An operational amplifier in an integrator configuration has a first input, a second input and an output coupled to the output terminal. The second input receives a reference voltage as a function of the power supply voltage. The first input is selectively and alternately connected to the input terminal during a first half-period of the repetition period and to a reference terminal during a second half-period of the repetition period.