Cross-Coupled Capacitor Cell Structure for IC Power Noise
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Solution Overview
Problem
Integrated circuits (ICs) face significant challenges due to voltage noise in power supply lines, which can lead to degradation of noise margins, reduced circuit reliability, and potential malfunction, especially at high operational frequencies.
Innovation Solution
The implementation of a capacitor cell with a cross-coupled de-coupling structure formed by PMOS and NMOS transistors, which provides MOS capacitance with series channel-resistance to enhance electrostatic discharge (ESD) protection and reduce gate leakage current, while also forming low resistance paths to improve latch-up immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filtering or de-coupling capacitors are used to reduce voltage fluctuations, then power supply noise is reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple capacitor units with different capacitance values into a single integrated capacitor structure. The first capacitor unit has a first capacitance value and the second capacitor unit has a second capacitance value, where the ratio between them falls within a specific range. This merging approach provides comprehensive noise filtering across multiple frequency ranges while avoiding the need for separate discrete capacitor components, thus reducing overall device complexity.
Solution Approach 2:
The capacitor structure serves multiple functions simultaneously: it acts as a de-coupling capacitor for high-frequency noise, a filtering capacitor for low-frequency noise, and an ESD protection element. The specific capacitance ratio design enables the same structure to handle different types of power supply noise and transient events, replacing what would traditionally require multiple separate components.
2Speed
If transient currents with high intensity are supplied to circuits, then circuit operation speed is improved, but voltage noise in power supply lines increases
Solution Approach 1:
The patent changes the electrical parameters of the power supply system by introducing capacitors with specific capacitance values and ratios. The first capacitance value and second capacitance value are designed with a specific ratio relationship to optimize the frequency response of the power supply network. This parameter optimization allows high-intensity transient currents to be supplied quickly while the capacitor structure simultaneously filters the resulting voltage noise, thus resolving the trade-off between speed and noise.
3Reliability
If de-coupling capacitors are used as charge reservoirs, then momentary voltage drops are prevented, but manufacturing complexity increases
Solution Approach 1:
The patent segments the capacitor structure into two distinct capacitor units with different capacitance values, where the ratio between them is controlled within a specific range. This segmentation allows each unit to be optimized for different functions (one for high-frequency response, one for low-frequency filtering) while maintaining a unified manufacturing process. The segmented design simplifies fabrication compared to creating a single complex capacitor with multiple functions, as each unit can be formed using standard capacitor fabrication techniques.
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 solution effectively reduces power supply noise, enhances ESD protection, decreases gate leakage current, and improves latch-up immunity, thereby increasing the reliability and stability of ICs operating at high frequencies.
Implementation Method 1
De-coupling capacitors act as charge reservoirs that additionally supply currents to circuits to prevent momentary drops in supply voltage
Implementation Method 2
voltage fluctuations in the supply line may be very large
Data Source
AI summary
Capacitor cells are provided. A first PMOS transistor has a source connected to a power supply and a drain connected to a first node. A first NMOS transistor has a source connected to a ground and a drain connected to a second node. A second PMOS transistor has a source connected to the second node and a drain connected to the first node. A second NMOS transistor has a source connected to the ground and a drain connected to the first node. A first P+ doped region is shared by drains of the first and second PMOS transistors. A first gate metal is between the first P+ doped region and a second P+ doped region. A first N+ doped region is shared by sources of the first and second NMOS transistors. A second gate metal is between the first N+ doped region and a second N+ doped region.