Self-Oscillating PWM Circuit Eliminates Ramp Generator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional pulse-width modulation (PWM) circuits in class-D amplifiers require a ramp signal generator, which occupies a large area on the chip, making it challenging to reduce the chip area and efficiently control the duty factor of the PWM signal.
Innovation Solution
A PWM circuit that integrates a feedback signal and an input signal to generate an integral signal, using a comparator unit to switch between source voltages based on reference voltages, eliminating the need for a ramp signal generator and allowing control of the duty factor without it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ramp signal generator is used to generate PWM signals, then the PWM signal can be generated with controlled duty factor, but the chip area occupied increases significantly
Solution Approach 1:
The invention extracts and eliminates the ramp signal generator from the PWM circuit, replacing it with a self-oscillation type PWM circuit that generates PWM signals through the interaction of an integrator and switching circuit without requiring an external ramp signal generator, thereby significantly reducing chip area
Solution Approach 2:
The PWM circuit is designed to be self-sufficient by using the output of the integrator directly to control the switching circuit, which in turn feeds back to the integrator, creating a self-oscillating system that generates PWM signals without external assistance from a ramp signal generator
2Reliability
If the switching frequency is increased to improve PWM signal quality, then electromagnetic interference increases
Solution Approach 1:
The invention employs dynamic switching frequency modulation where the switching frequency varies automatically with the input signal amplitude and characteristics, allowing the circuit to operate at lower frequencies for simple signals (reducing EMI) while maintaining high signal quality for complex inputs through increased frequency when needed
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
The solution reduces the chip area required for the PWM circuit, allows for efficient control of the duty factor based on input signal variations, and minimizes electromagnetic interference by varying the switching frequency, while maintaining effective PWM signal generation.
Implementation Method 1
an integrator configured to integrate a feedback signal and an input signal and to thereby generate an integral signal
Implementation Method 2
a comparator unit configured to compare the integral signal with a first reference voltage and to compare the integral signal with a second reference voltage
Implementation Method 3
a switching circuit configured to generate a PWM signal by switching an output node from a first source voltage to a second source voltage based upon comparing the integral signal with a first reference voltage
Data Source
AI summary
Pulse-width modulation (PWM) circuits and methods integrate a feedback signal and an input signal to generate an integral signal, and generate a PWM signal by switching an output node from a first source voltage to a second source voltage based upon comparing the integral signal with a first reference voltage, and switching the output node from the second source voltage to the first source voltage based upon comparing the integral signal with a second reference voltage. A comparator unit compares the integral signal with the first and second reference (threshold) voltages, and a drive circuit for buffering the comparator unit's output signals generates drive signals. A feedback circuit generates the feedback signal based on (e.g., proportional with) the PWM signal. The switching circuit may include a P-type switch (e.g., PMOS transistor) and a N-type switch (e.g., NMOS transistor). Associated class-D audio amplifiers and modulation methods are provided.