Standard Cell Characterization With Adaptive Body Biasing
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Solution Overview
Problem
The characterization of standard cells in digital circuits without considering adaptive body biasing leads to high pessimism values, resulting in performance loss, increased area consumption, and higher power consumption due to the inability to accurately predict delay times and power dissipation, especially under varying fabrication, supply voltage, and temperature conditions.
Innovation Solution
A method for characterizing standard cells with adaptive body biasing, involving simulation and data-set generation for performance and hardware performance monitor values, followed by virtual regulation of body bias voltages to compensate for static deviations in supply voltage and temperature, and providing these results in optimized library files for reduced pessimism and improved design efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard cells are characterized without adaptive body biasing, then the characterization process is simpler, but high pessimism values are required leading to performance loss and increased power consumption
Solution Approach 1:
The patent applies parameter changes by introducing body bias voltage as an additional controllable parameter. Instead of characterizing cells with fixed body bias, the method varies body bias voltage to compensate for PVT variations, transforming the characterization from static to dynamic parameter adjustment. This resolves the contradiction by maintaining simplicity through systematic parameter variation while achieving accurate timing prediction without excessive pessimism.
Solution Approach 2:
The patent implements dynamics by enabling adaptive body biasing that adjusts cell characteristics in real-time based on operating conditions. The characterization process captures dynamic behavior of cells under varying body bias voltages, allowing the design tools to predict timing accurately without requiring high pessimism margins. This dynamic approach eliminates the trade-off between simplicity and accuracy.
2Reliability
If high pessimism values are used to guarantee timing criteria in worst cases, then timing reliability is improved, but performance is reduced and area consumption increases
Solution Approach 1:
The patent employs feedback through adaptive body biasing mechanisms that monitor actual cell performance and adjust bias voltages accordingly. The characterization process incorporates feedback loops that measure timing deviations and compensate them through body bias adjustment. This eliminates the need for high pessimism values while maintaining timing reliability, thereby preserving circuit performance without area overhead.
Solution Approach 2:
The patent uses parameter changes by adjusting body bias voltage to compensate for timing variations. Instead of using fixed pessimism margins that degrade performance, the method dynamically changes the body bias parameter to achieve accurate timing prediction. This allows the circuit to operate at optimal performance while meeting timing criteria without requiring area-consuming safety margins.
3Measurement precision
If adaptive body biasing is considered in characterization, then timing and power prediction accuracy is improved, but the characterization process becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the characterization process into distinct stages: initial characterization without body bias, followed by separate body bias adjustment stages. Each stage focuses on specific parameters, breaking down the complex adaptive characterization into manageable segments. This reduces overall process complexity while maintaining high prediction accuracy through systematic step-by-step characterization.
Solution Approach 2:
The patent uses preliminary action by performing baseline characterization of standard cells before introducing adaptive body biasing. The initial characterization establishes reference data that simplifies subsequent adaptive characterization steps. This preliminary work reduces the complexity of the full adaptive process while ensuring accurate timing and power prediction through pre-established cell parameters.
4Use of energy by moving object
If body bias voltages are adjusted during operation, then power dissipation is reduced and performance is optimized, but control complexity increases
Solution Approach 1:
The patent implements self-service through adaptive body biasing circuits that automatically adjust bias voltages based on cell performance requirements. The characterization process captures self-regulating behavior where cells adjust their own operating points through body bias feedback mechanisms. This eliminates the need for complex external control systems while achieving power optimization and performance enhancement automatically.
Solution Approach 2:
The patent merges the body bias control function with the standard cell structure itself, integrating control mechanisms directly into the cell design. The characterization process captures this merged structure where power optimization and performance control are inherent to the cell operation rather than separate control systems. This reduces overall control complexity while maintaining power efficiency and performance optimization.
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 reduces the need for high pessimism values, allowing for more precise timing and power management, leading to smaller design models with better performance and reduced power consumption by considering adaptive body biasing during the design process.
Implementation Method 1
The silicon-on-insulator (SOI) CMOS technologies allow the adaptation of the threshold voltage of transistors by adjusting the body bias (back-gate) voltage
Implementation Method 2
In the fully depleted SOI (FD-SOI) technology there is a very thin isolating layer between the transistor and the bulk substrate. Since there is no leakage from source and drain of a transistor to the bulk substrate, less power is lost
Data Source
AI summary
A method for an improved characterization of standard cells in a circuit design process is disclosed. Adaptive body biasing is considered during the design process by using simulation results of a cell set, a data-set for performance of the cell set, and a data-set for a hardware performance for a slow, typical and fast circuit property. Static deviations in a supply voltage are considered by determining a reference performance of a cell and a reference hardware performance monitor value at a PVT corner. A virtual regulation and adapting of body bias voltages of the cell set is performed such that the reference performance of the cell or the reference hardware performance monitor value will be reached at each PVT corner and for compensating the static deviation in the supply voltage. The results are provided in a library file.