Output Driver Transistor Leg Cycling for Electromigration Relief
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Solution Overview
Problem
Integrated circuit output driver circuits face challenges in reducing electromigration-induced wear on conductors due to high current congestion, particularly in fast process corner ICs, where excessive transistor activation leads to conductor degradation, and existing solutions like increasing conductor width or number result in excessive capacitance, degrading performance.
Innovation Solution
The output driver circuit employs a control circuit to periodically enable and disable subsets of transistor legs in a repeating cycle, reducing overall current in conductors and distributing the workload, thereby minimizing wear and extending conductor lifetime without compromising output signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all transistor legs are continuously enabled to maintain output signal quality, then output drive capability is improved, but conductor wear from electromigration increases
Solution Approach 1:
The patent implements periodic enabling and disabling of transistor legs in a repeating cycle. The control circuit selectively enables different subsets of transistor legs during different time periods, allowing conductors to rest periodically and reducing cumulative electromigration wear while maintaining adequate output drive capability through temporal distribution of workload.
Solution Approach 2:
The patent dynamically adjusts which transistor legs are enabled based on operational requirements. The control circuit switches between different configurations of enabled transistor legs, creating a dynamic system that adapts conductor usage patterns to balance reliability and performance needs.
2Reliability
If conductor width or number is increased to reduce current density, then electromigration effects are reduced, but circuit capacitance increases and performance degrades
Solution Approach 1:
The patent segments the transistor legs into multiple groups that are enabled selectively over time. Instead of having all transistor legs continuously active, the control circuit divides them into subsets that are activated in different time periods, distributing the current load across segments and reducing electromigration without modifying conductor physical dimensions.
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3E
AI summary
An output driver circuit includes a control circuit and first and second transistor legs that are coupled to an output pad. Each of the first and second transistor legs includes a pull-up transistor and a pull-down transistor. The control circuit is coupled to the first and second transistor legs. The control circuit enables the first transistor leg to generate an output signal at the output pad and disables the second transistor leg during a first phase of a cycle. The control circuit enables the second transistor leg to generate the output signal at the output pad and disables the first transistor leg during a second phase of the cycle. The control circuit repeats the first and the second phases of the cycle.