Conditional Pulse Stretching for Cross-Domain Level Shifting
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Solution Overview
Problem
Existing systems-on-a-chip face challenges in reliably transferring control signals between digital domains with different power supply voltages and operating frequencies, particularly due to asynchronous external resets that can cause pulse shortening and prevent signals from passing through voltage level-shifting circuits.
Innovation Solution
A system-on-a-chip is designed with a conditional pulse-stretching circuit that lengthens the duration of control signals to a nominal duration adapted to the level-shifting circuit, ensuring that signals are effectively communicated across digital domains even if they are shortened by asynchronous resets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pulse-stretching circuit is used to generate a pulse long enough to pass through the voltage level-shifting circuit, then the control signal can be communicated to the second domain, but an asynchronous external reset can interrupt the pulse generation, causing the pulse to be too short to pass through the level-shifting circuit
Solution Approach 1:
The patent introduces a conditional pulse-stretching circuit as an intermediary component between the control circuit and the voltage level-shifting circuit. This mediator detects whether an asynchronous reset occurred during pulse generation and conditionally stretches the pulse duration to ensure it meets the minimum requirements of the level-shifting circuit, thereby resolving the contradiction between reliability and complexity by adding a targeted intermediate component rather than redesigning the entire control system
Solution Approach 2:
The conditional pulse-stretching circuit performs preliminary detection of reset conditions before the pulse fails to pass through the level-shifting circuit. By monitoring the generation process and proactively extending the pulse duration when needed, the system prevents transmission failure rather than reacting after the fact, thus improving reliability without requiring excessive complexity in the control logic
2Adaptability or versatility
If the control circuit is reset by an asynchronous external reset signal, then the system can be reset, but the pulse generation is interrupted causing the control signal to be ineffective
Solution Approach 1:
The patent converts the harmful effect of asynchronous reset interruption into a beneficial condition for pulse stretching. When the reset signal interrupts pulse generation, the conditional pulse-stretching circuit detects this interruption and uses it as the triggering condition to extend the pulse duration, thereby transforming the harmful reset interruption into an opportunity to ensure the pulse meets transmission requirements
Solution Approach 2:
The system implements feedback by monitoring the pulse generation process and detecting whether an asynchronous reset occurred. The conditional pulse-stretching circuit receives feedback about the reset condition and adjusts the pulse duration accordingly, creating a closed-loop control mechanism that ensures control signal effectiveness regardless of reset timing
Data Source
AI summary
A system-on-a-chip includes a first digital domain and a second digital domain. An interface circuit includes a level-shifting circuit for converting a signal between the first digital domain and the second digital domain. The first digital domain includes a control circuit configured to generate a control signal for transmission to the second digital domain. The control signal includes a pulse having a nominal duration adapted to the level-shifting circuit. At the input of the level-shifting circuit, the interface circuit includes, in the first domain, a conditional pulse-stretching circuit that lengthens a duration of the pulse of the control signal to at least the nominal duration when a duration of the pulse of the control signal is shorter than the nominal duration and non-zero.