PWM Reference Switching for High-Frequency Pulse Skipping Control
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Solution Overview
Problem
Conventional analog circuits struggle to meet the requirements of higher switching frequencies for class-D amplifiers, leading to limitations in slew rate and output power, and existing solutions for pulse skipping control and EMI management are inadequate at frequencies above 350 kHz.
Innovation Solution
A PWM circuit that combines analog and digital features, using a switching mechanism between different reference voltages to provide both pulse skipping control and inhibit functions, allowing for controlled EMI characteristics and improved performance at frequencies up to 2.4 MHz, while avoiding additional circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional analog circuits are used for pulse skipping control, then the circuit structure is simple, but the slew rate limitation prevents operation at high switching frequencies above 350 kHz
Solution Approach 1:
The patent combines analog integration with digital pulse generation in a hybrid architecture. The integrator circuit (analog) generates a ramp signal that is compared with the modulating signal, while digital logic circuits generate the actual PWM pulses. This merging allows the system to operate at high frequencies (up to 2.4 MHz) while maintaining controlled EMI characteristics, resolving the contradiction between speed improvement and circuit complexity.
Solution Approach 2:
The PWM generation circuit is designed to perform multiple functions: it generates carrier waves at variable frequencies, implements pulse skipping control, and provides pulse skipping inhibition for EMI control, all within a single integrated structure. The circuit can operate in different modes (normal PWM, pulse skipping, and EMI-controlled modes) without requiring separate dedicated circuits, thus achieving high switching frequencies while managing complexity through multi-functionality.
2Power
If pulse skipping control is implemented to increase output power, then the output power increases, but EMI spectrum emissions become uncontrolled and spread across unknown frequencies
Solution Approach 1:
The patent implements a feedback mechanism where the PWM output is monitored and fed back to the comparator input. This feedback loop allows the system to detect when pulse skipping is occurring and adjust the carrier wave generation accordingly. The feedback ensures that while pulse skipping can occur to maintain high output power, the EMI emissions remain contained within predictable frequency ranges, resolving the contradiction between power increase and EMI control.
Solution Approach 2:
The system dynamically changes the carrier wave parameters (frequency, amplitude, duty cycle) based on the modulating signal and feedback from the PWM output. By adjusting these parameters in real-time, the circuit can enable pulse skipping to increase output power while simultaneously controlling the EMI spectrum by modifying the carrier characteristics, thus containing emissions within known frequency ranges.
3Object-generated harmful factors
If pulse skipping inhibition is used to contain EMI spectrum around known frequencies, then EMI characteristics are controlled, but output power is reduced
Solution Approach 1:
The patent employs dynamic switching between different operational modes: normal PWM mode for high output power, pulse skipping mode for power enhancement, and EMI-controlled mode for spectral containment. The circuit dynamically transitions between these modes based on real-time conditions, allowing it to achieve high output power when needed while maintaining EMI control when required, thus resolving the static contradiction between power and EMI control.
Solution Approach 2:
The system changes operational parameters (carrier frequency, duty cycle, pulse width) dynamically based on the desired operating mode. When EMI control is prioritized, parameters are adjusted to contain the spectrum; when output power is prioritized, parameters allow pulse skipping. This dynamic parameter adjustment enables the circuit to achieve both high power and EMI control at different times, resolving the contradiction.
4Speed
If conventional analog circuits operate at seven times higher frequencies (2.4 MHz), then high-frequency performance is achieved, but slew rate limitations of operational amplifiers become critical
Solution Approach 1:
The patent replaces the traditional analog operational amplifier-based PWM generation with a hybrid architecture that uses digital logic circuits for pulse generation. This substitution eliminates the slew rate limitations of analog op-amps at high frequencies, as digital circuits can operate at 2.4 MHz and above without being constrained by analog bandwidth and slew rate issues, thus achieving high-frequency performance with improved reliability.
Data Source
AI summary
In an embodiment, a PWM modulation circuit includes a first circuit block configured to receive a square wave input signal and produce from the square wave input signal a triangular wave signal, a second circuit block configured to receive a modulating signal and produce a PWM signal by comparing the modulating signal with a carrier signal, a switching circuit block coupled between the first circuit block and the second circuit block and sensitive to reference signals having upper and lower reference values and selectively switchable between a carrier transfer setting in which the switching circuit block couples the first circuit block to the second circuit block to transfer the triangular wave signal as the carrier signal, and one or more carrier forcing settings for optimizing or inhibiting pulse skipping in the PWM signal, wherein the switching circuit block forces the carrier signal to the upper and lower reference values, respectively.