Output Driver Circuit With Edge Compensation for Low EMI
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Faster switching speeds in integrated circuits lead to issues like SSO noise, crosstalk, and EMI, which are partially mitigated by slew rate control, but this approach often results in increased propagation delay.
Innovation Solution
A compensation circuit is enabled at the beginning of a driving signal's edge to speed up transistor switching in the output circuit, reducing propagation delay by controlling the slew rate of the output signal, and is disabled when the second edge of the output signal starts to rise or fall, allowing the slew rate to be controlled independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If slew rate control is applied to mitigate SSO noise, crosstalk, and EMI, then electromagnetic interference is reduced, but propagation delay increases
Solution Approach 1:
The compensation circuit is enabled at the beginning of a first edge of a driving signal to speed up switching of a transistor in the output circuit before the main slew rate control takes effect. This preliminary action reduces the propagation delay that would otherwise be introduced by slew rate control, while the subsequent disabling of the compensation circuit allows slew rate control to maintain its benefit in reducing electromagnetic interference.
Solution Approach 2:
The compensation circuit is dynamically enabled and disabled based on the switching state of the output circuit transistor. By enabling the compensation circuit only during the initial switching edge and then disabling it, the system dynamically adjusts the switching speed to minimize propagation delay while still achieving slew rate control for electromagnetic interference mitigation.
2Speed
If switching speed is increased to improve circuit performance, then speed performance is improved, but Simultaneous Switching Output noise, crosstalk, and EMI increase
Solution Approach 1:
The compensation circuit provides a preliminary speed-up action at the beginning of the switching edge, allowing the circuit to achieve fast switching performance. After this initial boost, the compensation circuit is disabled and slew rate control takes over to limit the switching speed, thereby reducing SSO noise, crosstalk, and EMI while maintaining overall fast switching performance.
Solution Approach 2:
The compensation circuit operates periodically only during the critical initial edge of the driving signal, providing speed enhancement when needed, while the slew rate control operates continuously to manage electromagnetic interference. This periodic activation pattern allows the system to achieve both fast switching and low interference.
Data Source
AI summary
A circuit includes first to third transistors. The first transistor includes a first terminal coupled to a first voltage, and a second terminal coupled to a connection. The second transistor includes a gate terminal coupled to the gate terminal of the first transistor, a first terminal coupled to a second voltage, and a second terminal coupled to the connection. The third transistor includes a first terminal coupled to the connection, a second terminal coupled to a node between the second terminals of the first and second transistors. The third transistor is controlled to be turned ON at a beginning of a first edge of a driving signal on the connection to pull a voltage of the driving signal on the first edge toward a threshold voltage, and be turned OFF in response to and after the voltage of the driving signal on the first edge reaching the threshold voltage.