Ring Oscillator Frequency Synchronization for LED PWM Dimming
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Solution Overview
Problem
In systems involving multiple semiconductor devices, variations in clock signal frequencies can lead to loss of synchronization, particularly in LED driving applications, which can result in defects in the image formed by PWM dimming, and using crystal oscillators to suppress these variations is costly.
Innovation Solution
A semiconductor device with an oscillator, counter, and controller that adjusts the clock signal frequency based on a comparison with an expected value, along with a frequency divider and selector to synchronize clock signals across multiple devices, and includes self-diagnosis circuits for fine-tuning and ensuring synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crystal oscillators are used to suppress variation among clock signal frequencies, then synchronization among multiple semiconductor devices is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the operating parameters of a ring oscillator by adjusting its oscillation period through a counter and controller. The controller counts clock signals and adjusts the oscillation period based on the count value, thereby changing the frequency parameter to achieve synchronization without using expensive crystal oscillators.
Solution Approach 2:
Instead of using expensive crystal oscillators in each device, the patent uses a ring oscillator that can be controlled to copy or match the clock signal frequency from another device. The counter measures the frequency and the controller adjusts the ring oscillator to replicate the desired frequency characteristics.
2Ease of manufacture
If ring oscillators are used instead of crystal oscillators, then manufacturing cost is reduced, but frequency stability and synchronization deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where a counter measures the oscillation period of the ring oscillator and feeds this information back to a controller. The controller then adjusts the oscillation period based on the measured value, creating a closed-loop system that stabilizes the frequency despite using a less stable ring oscillator instead of a crystal oscillator.
Solution Approach 2:
The patent makes the ring oscillator dynamic by allowing its oscillation period to be adjusted in real-time based on feedback from the counter. This dynamic adjustment capability enables the system to compensate for inherent instabilities in ring oscillators and maintain frequency stability.
3Productivity
If multiple semiconductor devices are used to drive large numbers of LEDs, then productivity and coverage are improved, but synchronization among devices becomes difficult to maintain
Solution Approach 1:
The patent creates a universal synchronization mechanism that can be applied to multiple semiconductor devices. The frequency measurement and adjustment circuitry can be used across different devices to ensure they all operate at the same clock frequency, enabling synchronized operation of multiple LED driving devices.
Solution Approach 2:
The patent uses the counter and controller as intermediary components that mediate between the clock signal source and the LED driving circuits. These intermediaries measure and regulate the clock frequency, ensuring that multiple devices remain synchronized even when driving large numbers of LEDs.
Data Source
AI summary
A semiconductor device includes an oscillator configured to generate a first clock signal, a first terminal via which an input clock signal is fed in from the outside, a first counter configured to count a clock signal based on the first clock signal between edges in the input clock signal, and a controller configured to send to the oscillator an instruction to adjust the frequency of the first clock signal based on the result of comparison of the count value by the first counter with an expected value.