Shared Ring-Oscillator PWM Modulator With Built-In Deadtime
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Solution Overview
Problem
Existing digital pulse width and frequency modulators require external deadtime circuits and consume significant power, especially when generating high-resolution signals for multiple channels, which limits their efficiency and scalability in applications like switch-mode power supplies.
Innovation Solution
A multichannel digital pulse width/frequency modulator design that shares a single ring oscillator among channels, allowing independent generation of PWM and PFM signals with selectable deadtimes and reduced power consumption by triggering logic on both rising and falling edges, eliminating the need for external deadtime circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a single ring oscillator is shared by multiple channels, then power consumption is reduced, but the ability to generate independent PWM signals for each channel is compromised
Solution Approach 1:
The ring oscillator is designed to serve multiple functions: it generates the primary clock signal for synchronization and also provides tapped delay signals that serve as independent timing references for each channel's PWM generation. This multi-functionality allows the single oscillator to support independent PWM signals for multiple channels while consuming power equivalent to a single oscillator rather than multiple separate oscillators.
2Adaptability or versatility
If logic in channels is synchronized by ring clock, then channels can independently produce different frequency PWM signals, but the ring oscillator requires many delay cells increasing power consumption
Solution Approach 1:
The ring oscillator is segmented with taps at specific delay points along its path. These taps provide intermediate delay signals that are distributed to multiple channels. By segmenting the oscillator's output and distributing these segmented signals to different channels, each channel can independently generate PWM signals at different frequencies using the same physical oscillator infrastructure, thereby reducing the total number of delay cells needed compared to having separate oscillators for each channel.
3Reliability
If external deadtime circuit is used, then high side and low side switches are protected from simultaneous conduction, but hardware complexity and power consumption increase
Solution Approach 1:
The deadtime generation function is merged with the existing channel logic that generates PWM signals. The same finite state machine and counter structures used for PWM generation are extended to also generate the complementary signals with built-in deadtime. This merging eliminates the need for separate external deadtime circuits while maintaining switch protection, thereby reducing hardware complexity and power consumption.
4Measurement precision
If high-resolution PWM signals are generated for multiple channels, then power supply control precision is improved, but power consumption and hardware requirements increase
Solution Approach 1:
Instead of creating entirely separate signal generation paths for each channel, the design uses a single ring oscillator whose output is copied and distributed to multiple channels through taps. Each channel receives a copy of the fundamental clock signal and can independently generate its PWM output. This copying approach maintains high resolution for each channel while sharing the power-consuming oscillator infrastructure, thereby reducing overall power consumption compared to having separate high-resolution oscillators for each channel.
Data Source
AI summary
A multichannel digital pulse width modulator/digital pulse frequency modulator uses a single ring oscillator that is shared by multiple channels. The ring oscillator has taps that can be used for least significant bit (LSB) precision of the generated PWM signal. The ring oscillator also produces a ring clock that is used to synchronize logic in the channels. Since the logic in the channels are synchronized by the ring clock, the channels can each independently produce different frequency PWM (or PFM) signals and still share the same ring oscillator.