Output Driver Circuit With Two-Phase Slew Rate Compensation
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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 increases propagation delay, affecting speed performance.
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 activated at the beginning of the first edge of the driving signal to preemptively speed up transistor switching before the output signal edge transitions. This preliminary action reduces propagation delay at the critical moment when delay would most impact performance, while slew rate control remains active to manage EMI during the actual signal transition.
Solution Approach 2:
The compensation circuit operates periodically only during the initial phase of signal edges (rising or falling transitions) rather than continuously. It is enabled at the beginning of each signal edge and disabled when the output signal edge starts transitioning, providing speed enhancement only when needed while maintaining EMI control during the full transition period.
2Speed
If switching speed is increased to improve IC performance, then speed performance is improved, but SSO noise and crosstalk increase
Solution Approach 1:
The compensation circuit provides preliminary speed enhancement at the very beginning of signal edges by speeding up transistor switching. This allows the circuit to achieve fast switching performance when needed while the subsequent slew rate control manages the transition to prevent SSO noise and crosstalk during the actual signal level change.
Solution Approach 2:
The system dynamically adjusts switching behavior in two phases: first using the compensation circuit for rapid initial switching, then transitioning to slew rate control for managed signal transitions. This dynamic approach allows the circuit to optimize between speed performance and noise reduction based on the real-time state of signal transitions.
Data Source
AI summary
In a method of operating a circuit, at a beginning of a first edge of a driving signal, a first transistor is turned ON to pull, at a first changing rate, a voltage of the driving signal on the first edge from a first voltage toward a second voltage. Then, in response to the voltage of the driving signal on the first edge reaching a threshold voltage between the first voltage and the second voltage, the first transistor is turned OFF and an output circuit is caused to start a second edge of an output signal in response to the first edge of the driving signal. The second edge has a slew rate corresponding to a second changing rate of the voltage of the driving signal on the first edge from the threshold voltage toward the second voltage. The second changing rate is smaller than the first changing rate.