Monotonic Delay Line With Digital DLL for Precise Clock Edge Placement
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Solution Overview
Problem
Existing clock placement systems in I/O systems with forwarded clock architectures face challenges in achieving precise clock edge placement under varying environmental conditions, particularly in high-frequency operations, due to non-monotonic delay steps and power consumption issues with analog DLLs.
Innovation Solution
A monotonic delay line with phase interpolation and a digital DLL that uses a finite state machine to control rising and falling insertion delays independently, allowing for precise and wide-range clock edge placement with minimal power consumption, and the ability to continuously update clock placement without interfering with data transfers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog DLL is used for clock placement, then clock placement capability is provided, but power consumption increases
Solution Approach 1:
The patent replaces the analog DLL system with a digital delay-locked loop that uses digital delay elements and logic circuits. This substitution of analog components with digital components achieves the same clock placement function while significantly reducing power consumption, as digital circuits can operate at lower voltages and consume less dynamic power.
Solution Approach 2:
The patent changes the operating parameters by using digital control signals to adjust delay stages rather than analog voltage control. The digital DLL uses control words to selectively enable or disable delay elements, providing precise clock placement through discrete delay steps while maintaining low power consumption through efficient digital logic design.
2Measurement precision
If analog DLL is used for clock placement, then clock placement capability is provided, but start and re-start performance deteriorates
Solution Approach 1:
The patent implements a startup detection mechanism that identifies when the clock signal is initially present and immediately initiates the locking sequence. The digital DLL is designed to quickly acquire lock by detecting the first few clock cycles and beginning delay adjustment, eliminating the slow startup behavior of analog DLLs that require gradual warm-up and stabilization.
Solution Approach 2:
The patent employs a fast acquisition mode where the digital DLL rapidly adjusts delay stages to achieve lock within a minimal number of clock cycles. The control logic skips intermediate adjustment steps and directly configures delay elements to reach the locked state quickly, enabling fast restart capability after clock stop events.
3Measurement precision
If delay line in DLL is used, then clock placement is achieved, but delay steps become non-monotonic causing misalignment
Solution Approach 1:
The patent divides the delay line into multiple independent delay stages, each controlled by separate control signals. This segmentation allows each stage to contribute a fixed, monotonic delay amount, and the total delay is the sum of individual stage delays. By controlling each segment independently through digital logic, the system ensures that delay steps remain monotonic even as the total delay varies across the full range.
Solution Approach 2:
The patent implements a feedback mechanism where the actual delay output is monitored and compared against the desired delay value. The control logic adjusts the delay stage configurations to maintain monotonic progression, ensuring that each incremental change in control word produces a consistent, monotonic change in output delay, preventing misalignment issues.
4Productivity
If fine control steps are implemented for clock placement, then data transfer rate increases, but device complexity increases
Solution Approach 1:
The patent resolves the complexity issue by organizing delay stages in a two-dimensional array structure with rows and columns, where control words select specific combinations of stages. This dimensional organization allows fine-grained control of delay steps while maintaining regular, predictable circuit patterns that are easier to design and manufacture compared to purely sequential control mechanisms.
Data Source
AI summary
Described is an apparatus comprising: a delay line including at least four delay stages coupled together in a series; a first multiplexer having a first input coupled to an output of a first delay stage of the at least four delay stages, and a second input coupled to an output of a third delay stage of the at least four delay stages; a second multiplexer having a first input coupled to an output of a second delay stage of the at least four delay stages, and a second input coupled to an output of a fourth delay stage of the at least four delay stages; and a phase interpolator coupled to outputs of the first and second multiplexers, the phase interpolator having an output.