CNTFET-Based Sense Amplifier for Fast and Energy-Efficient SRAM

Abstract

CNTFET-Based Sense Amplifier for Fast and Energy-Efficient SRAM ABSTRACT This invention presents a novel design for sense amplifiers in Static Random Access Memory (SRAM) using Carbon Nanotube Field Effect Transistors (CNTFETs). The proposed sense amplifiers address limitations in traditional CMOS-based designs, including high sensing delay, increased power consumption, and reduced scalability at advanced technology nodes such as 32nm, 22nm, and 11nm. Leveraging the superior electrical properties of CNTFETs, the designs improve operational speed, energy efficiency, and noise margins, making them suitable for high-density and energy-efficient memory systems. The invention covers a variety of sense amplifier architectures, including voltage-mode, current-mode, clamped bit-line, hybrid, and deviating voltage detection amplifiers. These designs are tailored to specific requirements, ensuring versatility and robust performance across different operational scenarios. Simulation results, conducted using the Cadence Virtuoso tool, demonstrate significant improvements in read delay, power dissipation, and power delay product (PDP) compared to conventional designs. For example, the Full Complementary Positive Feedback amplifier achieves a PDP of 1.48fJ at 32nm, while the Hybrid Current Mode amplifier excels at 11nm with a PDP of 6.15fJ. These advancements position CNTFET-based sense amplifiers as a transformative technology for SRAM, enabling faster and more energy-efficient memory solutions in modern computing systems.

Specification

Description:CNTFET-Based Sense Amplifier for Fast and Energy-Efficient SRAM

FIELD OF THE INVENTION
The present invention relates to the field of semiconductor memory design, specifically focusing on Static Random Access Memory (SRAM). It addresses advancements in sense amplifier technology by employing Carbon Nanotube Field Effect Transistors (CNTFETs). The invention is designed to optimize memory read operations by improving sensing speed and energy efficiency, making it particularly suitable for high-density memory arrays and advanced technology nodes such as 32nm, 22nm, and 11nm. This innovation is relevant for applications in microprocessors, high-speed caches, and energy-efficient computing systems.
BACKGROUND OF THE INVENTION
Sense amplifiers are critical components in Static Random Access Memory (SRAM), which is widely used in various computing and electronic systems. SRAM is known for its fast access times and reliability, making it a preferred choice for cache memory in processors. However, with the scaling of technology nodes to smaller dimensions, such as 32nm, 22nm, and 11nm, the limitations of conventional sense amplifiers have become apparent. These limitations include increased sensing delay, high power consumption, reduced noise margins, and degraded overall performance.
The sense amplifier's primary function is to detect and amplify small voltage differences on the bit lines of an SRAM cell during read operations. It is a critical determinant of the memory's speed and energy efficiency. As memory capacity increases, the bit-line capacitance also rises, leading to slower sensing and higher power dissipation. Conventional sense amplifiers, predominantly designed using Complementary Metal-Oxide-Semiconductor (CMOS) technology, face challenges in maintaining high performance under these conditions. CMOS-based designs suffer from increased parasitics, leakage currents, and limited scalability at lower technology nodes.
Existing sense amplifier architectures, such as voltage-mode, current-mode, and hybrid designs, have been extensively studied. Each architecture offers specific advantages but is accompanied by trade-offs that limit its effectiveness in addressing the requirements of modern memory systems. Voltage-mode sense amplifiers, for example, are simple in design and effective at larger technology nodes, but their performance deteriorates due to smaller voltage swings and increased noise at scaled nodes. Current-mode sense amplifiers provide faster sensing due to their low input impedance but consume more power and are prone to crosstalk and substrate currents. Hybrid designs attempt to combine the advantages of both but often fail to achieve significant improvements due to inherent limitations in CMOS technology.
The emergence of Carbon Nanotube Field Effect Transistors (CNTFETs) offers a promising alternative to overcome these challenges. CNTFETs exhibit superior electrical properties, including high carrier mobility, excellent electrostatic control, and scalability to nanometer dimensions. These properties make CNTFETs well-suited for designing high-performance sense amplifiers. By replacing conventional CMOS transistors with CNTFETs, it becomes possible to reduce sensing delay, lower power dissipation, and enhance noise margins, all while maintaining scalability and reliability.
In this invention, a range of CNTFET-based sense amplifier architectures are proposed to address the limitations of traditional designs. These include voltage-mode, current-mode, clamped bit-line, hybrid, and deviating voltage detection amplifiers. Each design is optimized for specific operational parameters, such as sensing speed, power consumption, and energy efficiency, and is tailored for advanced technology nodes. The proposed designs are validated through simulation using Cadence Virtuoso, demonstrating significant improvements in performance compared to existing CMOS-based counterparts.
This invention not only addresses the performance bottlenecks of current SRAM sense amplifiers but also lays the foundation for future advancements in memory technology. The proposed CNTFET-based sense amplifiers are particularly relevant for applications in high-speed computing, energy-efficient devices, and emerging workloads in artificial intelligence and machine learning, where memory performance is critical. By leveraging the unique properties of CNTFETs, this invention represents a significant step forward in the field of semiconductor memory design.
SUMMARY OF THE INVENTION
The invention provides a novel approach to enhancing the performance and energy efficiency of Static Random Access Memory (SRAM) by leveraging Carbon Nanotube Field Effect Transistors (CNTFETs) in the design of sense amplifiers. The proposed sense amplifiers address critical challenges faced by conventional CMOS-based designs, including high power consumption, increased sensing delay, and limitations in scalability at advanced technology nodes like 32nm, 22nm, and 11nm. By utilizing CNTFETs, the invention enables faster sensing operations, reduces energy usage, and ensures robust functionality in high-density memory arrays.
Key Features of the Invention
The proposed sense amplifiers are designed to detect and amplify small voltage differences on the bit lines of an SRAM cell during read operations. These designs aim to achieve:
• High Speed: The architectures are optimized to reduce sensing delays, ensuring rapid memory access even at reduced technology nodes.
• Energy Efficiency: By exploiting the unique electrical properties of CNTFETs, the designs significantly lower power consumption during read operations.
• Scalability: The proposed amplifiers are tailored for operation at advanced technology nodes, making them suitable for modern, high-density memory systems.
• Versatility: The invention includes multiple architectures, each optimized for specific operational scenarios, including voltage-mode, current-mode, clamped bit-line, hybrid, and deviating voltage detection amplifiers.
Proposed Sense Amplifier Designs
1. Full Complementary Positive Feedback Sense Amplifier (FCPF):
 Utilizes dynamic positive feedback for rapid voltage sensing.
 Optimized for reduced read delay and low power dissipation.
 Achieves a Power Delay Product (PDP) of 1.48fJ at 32nm.
2. Conventional Current-Mode Sense Amplifier:
 Employs low input impedance to minimize sensing delay.
 Exhibits enhanced performance at advanced nodes, with a PDP improvement of 99% compared to CMOS-based designs.
3. Clamped Bit-Line Sense Amplifier:
 Features low resistance input terminals to minimize voltage swings on bit lines.
 Offers a rapid response and energy-efficient operation, achieving a PDP of 14.85fJ.
4. Simple Four-Transistor Sense Amplifier:
 Compact design eliminates the need for column-select devices, improving sensing speed.
 Provides a PDP of 62fJ at 32nm.
5. Hybrid Current-Mode Sense Amplifier:
 Combines current conveyor and regenerative latch designs for high-speed operation.
 Achieves superior performance at 11nm, with a PDP of 6.15fJ.
6. Deviating Voltage Detection Amplifier:
 Focused on precision voltage detection, suitable for applications requiring low common-mode interference.
 Demonstrates optimal performance at 22nm nodes with a PDP of 0.715fJ.
Advantages of the Invention
The invention offers significant improvements over traditional CMOS-based designs:
• Performance: Up to 99% reduction in sensing delay and power dissipation.
• Energy Efficiency: Substantial energy savings, crucial for high-speed computing and low-power devices.
• Noise Resilience: Enhanced noise margins ensure reliable operation in scaled nodes.
• Application Versatility: Suitable for use in microprocessor caches, artificial intelligence (AI), and machine learning (ML) workloads, where memory performance is critical.
Applications
The CNTFET-based sense amplifiers are ideal for integration into advanced SRAM systems, high-speed computing platforms, and energy-efficient memory designs. Their scalability and versatility make them a future-ready solution for the semiconductor industry.
In conclusion, this invention revolutionizes SRAM sense amplifier technology by addressing key performance bottlenecks and enabling robust, energy-efficient memory systems. Through innovative use of CNTFETs, the proposed designs represent a significant advancement in the field of semiconductor memory design.














BRIEF DESCRIPTION OF THE DRAWINGS



Figure 1: Different sense amplifier types


Figure 2: CNTFET Based FCPF sense amplifier

Figure 3: CNTFET Based FCPF sense amplifier waveform.
Table 1: Full complementary positive feedback sense amplifier
Parameters 32nm 22nm 11nm
CNTFET CNTFET CNTFET
Read Delay in sec 21.03n 16.9p 21.03n
Dynamic Power in W 70.49n 296.07p 74.73n
Static Power dissipation in W 86.03p 125.37p 89.415p
Total Power Dissipation in W 70.58n 296.2n 74.82n
Power Delay Product in J 1.4817f 5.32a 1.57f


Table 2: Conventional Current mode sense amplifier
Parameters 32 CNTFET 22 CNTFET 11 CNTFET
Read Delay in sec 21.06n 52.07p 21.07n
Dynamic Power in W 0.285 μ 2.886μ 329n
Static Power in W 22.725 μ 20.394μ 33.4μ
Power Delay Product 6fJ 0.15fJ 6.93fJ


Figure 4: Circuit of CNTFET Conventional Current mode sense amplifier

Figure 5: Simulated waveform of Conventional current mode sense amplifier

Figure 6: Circuit of Clamped bit line sense amplifier.
Figure 7: Simulated waveform of CNTFET Clamped bit line sense amplifier.


Table 3: Clamped bit line sense amplifier

Parameters 32 CNTFET 22 CNTFET 11 CNTFET
Read Delay in sec 22.47n 19.86n 22.36n
Dynamic Power dissipation in W 660.82n 710.6n 726.45n
Static Power dissipation in W 0.18054n 188p 242.64p
Total Power dissipation in W 661n 710.8n 726.7p
Power Delay Product 14.85fJ 14.11fJ 16.3fJ


Table 4: CNTFET Simple Four Transistor sense amplifier.

Parameters 32 CNTFET 22 CNTFET 11 CNTFET
Read Delay in sec 21.57n 11.48n 21.58n
Dynamic Power in W 2.87 μ 2.99μ 13.79 μ
Static Power 26.77 μ 25.92μ 9.567 μ
Total power dissipation in W 30.64μ 28.92μ 23.357μ
Power Delay Product in J 62f 34.32f 296f



Figure 8: CNTFET Simple Four Transistor Sense Amplifier

Figure 9: Waveform of simple four transistor sense amplifier.Hybrid current sense amplifier



Figure 10: Circuit of CNTFET Based Hybrid current sense amplifier.


Figure 11: Hybrid current sense amplifier waveform

Table 5: Hybrid current sense amplifier

Parameters 32 CNTFET 22 CNTFET 11 CNTFET
Read Delay in sec 1.103n 523.0p 0.534n
Dynamic Power in W 12.78 μ 1.368μ 13.4 μ
Static Power 1.785 μ 24.37μ 1.787 μ
Total Power Dissipation 14.565μ 25.74μ 15.187μ
Power Delay Product in J 14.1f 0.715f 6.15f

A comparative analysis of various types of sense amplifiers presents simulated results in




Table 6. Furthermore, Figure 12 illustrates the graphical representation of the power delay product for different types of CNTFET-based sense amplifiers.





Table 6: Comparative analysis of different types of sense amplifiers
Param eter FCPF CC Mode CBL SFT HC
/Sense Ampli
fier
type
Lg in 32 22 11 32 22 11 32 22 11 32 22 11 32 22 11
nm
Read 21n 18p 21n 21n 52p 21n 22.47 19.8 22.36 21.5 11.4 21.5 1.10 523 0.53
Delay n 6n n 7n 8n 8n 3n p 4n
in s
Pdyn 70.4 296.7 74.7 285 2.88 329 660.8 710. 727.4 287 2.99 137 127 1.36 134
in W 9n n 3n n 6μ n 2n 6n 5 n 0 n μ 9 n 8 n 8μ 0 n
Pstat 86.0 125.3 89.4 22. 20.3 33. 0.18n 188 242.6 26.7 25.9 9.57 1.79 24.3 1.79
in W 3p 7p 2p 73 9μ 4μ p 4p 7 μ 2μ μ μ 7μ μ
μ
PDP in 1.48 5.32a 1.57 6fJ 0.15 6.9 14.85 14.1 16.3f 62f 34.3 296f 14.1 0.71 6.15
J 17f f fJ 3f f 1f 2f f 5f f

Figure 12: PDP Graph of implemented Sense Amplifiers.





Figure 13: CNTFET Based Deviating Voltage Detection amplifier circuit.
Table 7: Deviating Voltage Detection amplifier
Parameters 22 CNTFET
Read Delay in sec 32.74p
Dynamic Power in W 4.674μ
Static Power in W 0.9176 nW
Total Power Dissipation 4.675μ
Power Delay Product in J 0.715fJ

Figure 14: Simulation waveform of Deviating Voltage Detection Amplifier





Table 8: Tabulation of FCPF Sense amplifier and DVD amplifier in 22nm
Parameters DVD amplifier FCPF sense amplifier
Read Delay in sec 32.74p 16.9E-12
Dynamic Power in W 4.674μ 296.07E-9
Static Power in W 0.9176 nW 125.37p
Total Power Dissipation 4.675μ 296.2E-9
Power Delay Product in J 0.715f 5.32aJ


Table 9: Comparison of Sense amplifiers with existing system
Parameter Conventional Current mode sense Amplifier Clamped bit line sense amplifier. The hybrid current sense amplifier
Lg Existin g System CNTFET Existin g System CNTFET Existin g System CNTFET in m
32n 22n 11n 32n 22n 11n 32n 22n 11n
Read Delay 47.4ns 21n 52p 21n 490n 23n 20n 22n 18.4n 1.1n 523p 0.5n
Delay reduction Improvement 56
% 99% 56% 95% 96% 95% 94% 97% 97%
Dynamic Power Dissipatio n 27μ 0.3μ 2.9μ 329n 6.49 μ 661n 711n 728n 27 μ 1.3μ 1.37
μ 1.34
μ
Dynamic Power Dissipation Reduction 99
% 89% 99% 90% 89% 89% 95% 95% 95%
PDP 1.28p 6f 0.15
f 6.93
f 3.18p 14.9
f 14.1
f 16.3
f 0.5p 14.1
f 0.72f 7.15f
PDP /Energy Consumption reduction 99
% 99% 99% 99% 99% 99% 97% 99% 99%




DESCRIPTION OF THE INVENTION
The invention includes a series of figures and tables that illustrate the proposed CNTFET-based sense amplifiers, their circuit architectures, simulated waveforms, and comparative performance metrics. These visual representations provide insights into the design, functionality, and performance advantages of the invention.
Figure 1 provides an overview of the different sense amplifier types, including voltage-mode, current-mode, clamped bit-line, hybrid, and deviating voltage detection amplifiers, showcasing the versatility of the proposed architectures. Figure 2 illustrates the circuit of the Full Complementary Positive Feedback (FCPF) sense amplifier, highlighting its dynamic feedback mechanism for rapid sensing. The corresponding simulated output, shown in Figure 3, demonstrates the FCPF amplifier's operational speed and low power consumption.
Figure 4 depicts the circuit design of the Conventional Current Mode Sense Amplifier, optimized for low input impedance to achieve faster sensing. Its simulated output waveform, presented in Figure 5, confirms its performance in terms of reduced sensing delay and improved energy efficiency. Similarly, Figure 6 displays the circuit diagram of the Clamped Bit-Line Sense Amplifier, designed for low resistance and minimal voltage swings on high-capacitance bit lines. The simulation results, captured in Figure 7, illustrate its quick response and energy-efficient operation.
Figure 8 introduces the Simple Four-Transistor Sense Amplifier, a compact design that eliminates the need for column-select devices to enhance sensing speed. The corresponding waveform, shown in Figure 9, demonstrates the amplifier's ability to operate with high efficiency. Figure 10 presents the architecture of the Hybrid Current Mode Sense Amplifier, combining current conveyor and regenerative latch mechanisms to ensure rapid sensing. The simulation output in Figure 11 highlights the amplifier's low power delay product (PDP) and high-speed performance.
Figure 12 provides a comparative graphical representation of the power delay product for various sense amplifiers at different technology nodes (32nm, 22nm, and 11nm). This figure emphasizes the efficiency gains achieved by the CNTFET-based designs over traditional CMOS-based architectures. Figure 13 illustrates the Deviating Voltage Detection (DVD) amplifier circuit, focusing on precise voltage discrepancy detection. Its simulation results, shown in Figure 14, confirm its accuracy and minimal power dissipation, making it ideal for applications demanding precise operations.
The tables further elaborate on the performance metrics of each amplifier design. Table 1 summarizes the performance of the FCPF sense amplifier, detailing its read delay, dynamic power, static power, and PDP across different technology nodes. Similarly, Tables 2 to 5 provide comprehensive performance data for the Conventional Current Mode, Clamped Bit-Line, Simple Four-Transistor, and Hybrid Current Mode amplifiers, respectively. These tables highlight the substantial reductions in delay and power achieved by the proposed designs.
Table 6 presents a comparative analysis of all CNTFET-based sense amplifiers, offering a clear understanding of their respective strengths. Table 7 focuses on the DVD amplifier's performance, showcasing its precision and energy efficiency at the 22nm node. Table 8 compares the FCPF and DVD amplifiers at 22nm, highlighting their trade-offs in terms of delay and power. Lastly, Table 9 contrasts the performance of CMOS-based and CNTFET-based designs, demonstrating the superiority of CNTFET technology in achieving significant improvements in delay, power dissipation, and energy consumption.
These figures and tables collectively showcase the innovation, operational effectiveness, and performance enhancements of the CNTFET-based sense amplifiers, forming the basis for the claims of this invention.
, Claims:CLAIMS
1. A sense amplifier for SRAM memory cells comprising Carbon Nanotube Field Effect Transistors (CNTFETs), designed to reduce sensing delay, minimize power consumption, and enhance energy efficiency, optimized for advanced technology nodes including 32nm, 22nm, and 11nm.
2. The sense amplifier of claim 1, wherein the architecture includes at least one of the following configurations: voltage-mode sense amplifier, current-mode sense amplifier, clamped bit-line sense amplifier, hybrid current-mode sense amplifier, and deviating voltage detection amplifier.
3. The sense amplifier of claim 1, wherein the design achieves a reduced read delay and power delay product (PDP), offering up to 99% improvement in delay and energy efficiency compared to traditional CMOS-based sense amplifiers.
4. The sense amplifier of claim 1, capable of operating efficiently at various technology nodes by leveraging CNTFET properties such as high carrier mobility and enhanced electrostatic control.
5. The sense amplifier of claim 1, integrated into Double-Density Cell (DDCSRAM) memory arrays to improve memory performance, scalability, and energy efficiency in high-speed computing applications.
6. The sense amplifier of claim 1, designed to improve noise margins, ensuring reliable detection and amplification of small voltage differences on bit lines in scaled memory systems.

Documents