Parallel Output Driver Timing for EMC and EMI Immunity
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Solution Overview
Problem
Weakly driven output driver circuits in integrated circuits are susceptible to electromagnetic interference (EMI) noise, leading to false output pulses or no output, while strongly driven circuits can generate radiated emissions, posing a source of EMI to other devices.
Innovation Solution
An output driver circuit with multiple individually controlled devices connected in parallel, allowing for programmable control of fall and rise times of output signals, reducing the likelihood of generating undesired emissions and enhancing immunity to EMI, by selectively activating devices to achieve various waveshapes and drive strengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the drive level of the output driver is reduced to decrease fall time and reduce radiated emissions, then the likelihood of generating undesired emissions is reduced, but the susceptibility to EMI noise increases
Solution Approach 1:
The output driver is divided into multiple individually controllable driver devices connected in parallel. Each device can be controlled independently to switch on at different times, allowing the total drive strength to be distributed across multiple devices rather than concentrated in a single device. This segmentation enables reduced peak current bursts while maintaining sufficient total drive capability.
Solution Approach 2:
The driver circuit implements dynamic control of driver device activation through a controller that selectively enables individual driver devices based on desired output characteristics. The system can dynamically adjust which devices are active and when they switch on, providing adaptable control over fall time and EMI characteristics while maintaining reliability.
2Reliability
If the drive level of the output driver is increased to improve signal strength and reduce susceptibility to EMI, then the immunity to noise is enhanced, but a burst of current occurs during switching that creates radiated emission problems
Solution Approach 1:
The total drive strength required for EMI immunity is segmented across multiple driver devices. Instead of one device switching on with a large current burst, multiple devices can switch on in sequence or in groups, distributing the current demand over time and reducing peak current bursts that cause radiated emissions.
Solution Approach 2:
The controller can preliminarily enable smaller driver devices before enabling larger driver devices. This preliminary action allows the output to begin changing state with minimal current demand, then progressively adds more drive strength as needed, avoiding sudden large current bursts while still achieving the desired output transition.
3Adaptability or versatility
If multiple individually controlled driver devices are used to provide programmable fall time control, then user-selectable output configurations are increased, but the device complexity increases
Solution Approach 1:
The multiple driver devices and controller structure serves multiple functions: it provides programmable fall time control, enables different output configurations, maintains EMI immunity, and reduces radiated emissions. This multi-functionality justifies the increased complexity by delivering comprehensive control capabilities from a single integrated structure.
Data Source
AI summary
An integrated circuit includes an output driver circuit having a plurality of output driver devices connected in a parallel arrangement and an output driver controller that is capable of individually controlling the conducting states of the output driver devices. In at least one embodiment, the controller is capable of achieving any of a plurality of different fall times (and/or rise times) in an output signal by appropriately controlling the conducting states of the output devices if a change in the state of the output signal is desired, in some implementations, the controller is capable of achieving different waveshapes during rising and/or failing edges of an output signal.