Programmable Clock Distribution for Deep-Submicron Skew Tuning
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Solution Overview
Problem
In high-speed synchronous deep submicron integrated circuits, variations in metal and semiconductor trace resistance and capacitance due to fabrication processes lead to significant clock tuning challenges, requiring precise adjustments on a flip-flop or register basis to optimize performance.
Innovation Solution
The implementation of tunable clock distribution structures using antifuse or phase change memory elements, with programmable inverters that adjust capacitance or resistance to fine-tune clock signals, and diagnostic methods to determine and program delays across the IC, ensuring accurate clock frequency and minimizing clock skew.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional clock distribution structures are used in deep submicron ICs, then manufacturing is simpler, but fabrication process variations cause large resistance and capacitance variations leading to poor performance
Solution Approach 1:
The clock distribution structure is made dynamically adjustable through tunable inverters whose delay characteristics can be modified after fabrication. Each inverter includes variable capacitance and resistance elements that can be programmed to compensate for fabrication variations, transforming a static structure into a dynamically可调 system that adapts to specific chip characteristics.
Solution Approach 2:
The invention changes the electrical parameters (capacitance and resistance) of the clock distribution network by introducing variable capacitance elements and resistance control mechanisms. These parameter changes allow precise adjustment of clock signal delay and frequency to compensate for fabrication process variations in deep submicron technologies.
2Measurement precision
If clock tuning is performed on a flip-flop basis to compensate for fabrication variations, then clock frequency accuracy improves, but device complexity increases
Solution Approach 1:
The clock distribution network is segmented into multiple independent tunable inverters, each controlling the clock signal to a specific flip-flop or group of flip-flops. This segmentation allows localized tuning without affecting the entire clock network, reducing the overall complexity compared to a fully centralized tuning mechanism while achieving flip-flop-level precision.
Solution Approach 2:
The system incorporates self-calibration capabilities where the tunable inverters automatically adjust their delay characteristics based on measured performance. Diagnostic circuits measure the actual clock timing at each flip-flop and automatically program the appropriate delay values, eliminating the need for manual tuning and reducing operational complexity.
3Manufacturing precision
If antifuse or phase change memory elements are used for tuning, then clock tuning precision improves, but manufacturing complexity increases
Solution Approach 1:
The tuning parameters are determined and programmed into the antifuse or phase change memory elements during the manufacturing process before the chips are shipped to customers. This preliminary action ensures that each chip is pre-configured with the optimal delay values needed to compensate for its specific fabrication variations, eliminating the need for post-fabrication tuning and simplifying the overall manufacturing workflow.
4Measurement precision
If diagnostic testing and path simulation are performed to determine optimal delays, then clock distribution accuracy improves, but testing time and complexity increase
Solution Approach 1:
Comprehensive diagnostic testing and path simulation are performed during the manufacturing process to determine the optimal delay values for each chip before it leaves the factory. This preliminary characterization captures the fabrication variations and programs the appropriate compensation values into the tunable elements, so that when the chip is deployed, no additional tuning time is required and the system operates at optimal performance immediately.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise tuning of clock frequencies, improving IC performance by averaging out variations in combinatorial logic paths and reducing errors, while maintaining minimal clock skew between master and slave latches.
Implementation Method 1
each branch of the clock distribution structure may contain tunable inverters, which may be tuned by varying either the capacitance or the resistance on the output of the inverter
Implementation Method 2
the variable capacitances and resistances may form a programmable memory where variable resistors may be programmed to vary the delay of the clock signals
Implementation Method 3
clock distribution structures using antifuse or phase change memory elements
Data Source
AI summary
A memory-like structure composed of variable resistor elements for use in tuning respective branches and leaves of a clock distribution structure, which may be used to compensate for chip-by-chip and/or combinatorial logic path-by-path delay variations, which may be due, for example, to physical variations in deep submicron devices and interconnections, is presented. A single system clocked scan flip-flop with the capability to perform delay test measurements is also presented. Methods for measuring combinatorial logic path delays to determine the maximum clock frequency and delays to program the variable resistors, as well as methods for calibrating and measuring the programmed variable resistors, are also presented.