Ring Oscillator Cell Timing Characterization for IC Simulation
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Solution Overview
Problem
Existing integrated circuit design simulations rely on inaccurate timing characteristics, as they do not account for manufacturing variations, leading to potential functional issues in the final product.
Innovation Solution
An oscillating signal-generating assembly, comprising a ring oscillator and switching units, is used to estimate post-fabrication timing characteristics, allowing for more accurate delay time calculations and updates to the cell library, thereby improving simulation accuracy and quality control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard cell library timing characteristics are used for simulation, then simulation can be performed efficiently, but the timing characteristics are inaccurate due to not accounting for manufacturing variations
Solution Approach 1:
The patent applies preliminary action by pre-characterizing cells using ring oscillators that replicate the actual circuit paths during fabrication. The timing characteristics are measured and stored in lookup tables before final simulation, accounting for manufacturing variations in advance. This allows accurate timing data to be retrieved during simulation without performing complex real-time measurements, thus improving accuracy while maintaining simulation efficiency.
Solution Approach 2:
The patent uses ring oscillators as simplified copies of the actual logic cell paths to measure timing characteristics. Instead of measuring the complex actual circuit paths directly, the ring oscillators create equivalent test paths that replicate the same transistor and interconnect variations. These copied measurement paths provide accurate timing data that reflects real manufacturing variations without the complexity of measuring the actual functional paths during simulation.
2Measurement precision
If post-fabrication timing measurements are performed to account for manufacturing variations, then timing accuracy is improved, but measurement and implementation complexity increases
Solution Approach 1:
The patent applies self-service by having the ring oscillators automatically generate the necessary test signals and measure their own propagation delays through the characterized cell paths. The measurement system uses the oscillating signals from the ring oscillators to directly determine timing characteristics without requiring external complex measurement equipment. The cells essentially measure themselves through their inherent oscillating behavior, simplifying the measurement process while achieving high accuracy.
3Measurement precision
If ring oscillators are used to characterize cells, then realistic timing estimates are obtained, but the device area and complexity increase
Solution Approach 1:
The patent applies universality by designing ring oscillators that can characterize multiple different cell types and paths using a single standardized structure. The same ring oscillator architecture can be used to measure timing for various logic cells by configuring the oscillator to include different cell instances in its loop. This multi-functional approach allows one ring oscillator design to serve multiple characterization purposes, reducing the total area needed compared to having dedicated measurement structures for each cell type.
Solution Approach 2:
The patent uses parameter changes by varying the configuration of the ring oscillator (such as the number of cells in the loop, the types of cells included, and the oscillation frequency) to characterize different timing scenarios. Instead of building physically different measurement structures for each cell type, the same ring oscillator structure is reconfigured through parameter changes to match different characterization needs. This allows accurate timing estimation for various cells while maintaining a compact, reusable oscillator design that minimizes area overhead.
Data Source
AI summary
An integrated circuit includes a circuit unit and an oscillating signal-generating assembly. The circuit unit includes a plurality of first cells. The oscillating signal-generating assembly is configured to generate different oscillating signals and includes a ring oscillator, a signal line, and a switching unit. The ring oscillator includes a plurality of second cells, each of which has an output terminal. The second cells are of the same type as the first cells. The signal line is configured to receive the different oscillating signals. The switching unit is coupled between the ring oscillator and the signal line and is configured to selectively couple the output terminals of the second cells to the signal line. A timing characteristic of a cell of the same type as the first cells can be estimated from the different oscillating signals.