I/O Driver Slew Rate Compensation Using DLL Phase Feedback
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Solution Overview
Problem
Current techniques for controlling driver output slew rate variation in I/O drivers are inadequate, particularly at high frequencies, as they rely on indirect compensation methods that fail to achieve the required accuracy and ignore variations across the chip and local power supply.
Innovation Solution
A design structure that includes a driver circuit with a delay circuit, comparators, and a phase detector to directly measure and control the slew rate of the output signal by aligning phases and adjusting the driver output slew rate based on accurate time references and transition rate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If indirect PVT correlation compensation techniques are used, then device complexity is reduced, but measurement precision and manufacturing precision of driver output slew rate deteriorate
Solution Approach 1:
The patent replaces indirect electrical correlation-based compensation with direct time-domain measurement using a delay-locked loop (DLL) and phase detector. The DLL provides a precise time reference that directly measures the driver output transition time, substituting the indirect PVT correlation method with a direct time measurement system that achieves the required precision without proportionally increasing complexity.
2Device complexity
If indirect PVT correlation compensation techniques are used, then device complexity is reduced, but manufacturing precision of driver output slew rate deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the phase detector compares the actual driver output transition time against the target time reference from the DLL. The output of the phase detector feeds back to adjust the driver circuit, creating a closed-loop control system that precisely controls the slew rate by continuously monitoring and correcting deviations from the target value.
Solution Approach 2:
The patent replaces indirect electrical correlation-based compensation with direct time-domain measurement using a delay-locked loop (DLL) and phase detector. The DLL provides a precise time reference that directly measures the driver output transition time, substituting the indirect PVT correlation method with a direct time measurement system that achieves the required precision without proportionally increasing complexity.
3Reliability
If tight slew rate variation specifications are enforced, then signal integrity improves, but device complexity increases
Solution Approach 1:
The patent replaces complex indirect PVT correlation compensation circuits with a more efficient direct time-domain measurement system using DLL and phase detector. This substitution achieves the required signal integrity through direct feedback control of transition time, reducing the overall complexity compared to maintaining tight specifications through indirect correlation methods.
Data Source
AI summary
A design structure and more particularly to a design structure to minimize driver output slew rate variation. The design structure is embodied in a machine readable medium for designing, manufacturing, or testing an integrated circuit. The design structure includes a driver circuit having an input signal and an output signal, where the driver circuit is structured and arranged to control the slew rate of the output signal. A delay circuit is coupled to an output of the driver circuit, where the delay circuit has a delay proportional to a desired target slew rate of the driver output signal. A first comparator for detecting when the driver output signal rises through a specified level, and a second comparator for detecting when the driver output falls through a second specified level are included. A phase detector is coupled to outputs of the first and second comparators and an output of the delay circuit for aligning the phases (voltage-time relationships) of the comparator outputs and the delayed comparator outputs by adjusting the driver output slew rate.