{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/29627"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/29627","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Emerging Power-Gating Techniques for Low Power Digital Circuits","abstract":"As transistor sizes scale down and levels of integration increase, leakage power has become a critical problem in modern low-power microprocessors. This is especially true for ultra-low-voltage (ULV) circuits, where high levels of leakage force designers to chose relatively high threshold voltages, which limits performance. In this thesis, an industry-standard technique known as power-gating is explored, whereby transistors are used to disconnect the power from idle portions of a chip. Present power-gating implementations suffer from limitations including non-zero off-state leakage, which can aggregate to a large amount of wasted energy during long idle periods, and high energy overhead, which limits its use to long-term system-wide sleep modes. As this thesis will show however, by vastly increasing the effectiveness of power-gating through the use of emerging technologies, and by implementing aggressive hardware-oriented power-gating policies, leakage in microprocessors can be eliminated to a large extent. This allows the threshold voltage to be lowered, leading to ULV microprocessors with both low switching energy and high performance. The first emerging technology investigated is the Nanoelectromechnical-Systems (NEMS) switch, which is a CMOS-compatible mechanical relay with near-infinite off-resistance and low on-resistance. When used for power-gating, this switch completely eliminates off-state leakage, yet is compact enough to be contained on die. This has tremendous benefits for applications with long sleep times. For example, a NEMS-power-gated architecture performing an FFT per hour consumes 30 times less power than a transistor-power-gated architecture. Additionally, the low on-resistance can lower power-gating area overhead by 36-83\\%. The second technology targets the high energy overhead associated with powering a circuit on and off. This thesis demonstrates that a new logic style specifically designed for ULV operation, Sense Amplifier Pass Transistor Logic (SAPTL), requires power-gates that are 8-10 times smaller, and consumes up to 15 times less boot-up energy, compared to static-CMOS. These abilities enable effective power-gating of an SAPTL circuit, even for very short idle periods. Microprocessor simulations demonstrate that a fine-grained power-gating policy, along with this drastically lower overhead, can result in up to a 44\\% drop in energy. Encompassing these investigations is an energy estimation framework built around a cycle-accurate microprocessor simulator, which allows a wide range of circuit and power-gating parameters to be optimized. This framework implements two hardware-based power-gating schedulers that are completely invisible to the OS, and have extremely low hardware overhead, allowing for a large number of power-gated regions. All together, this thesis represents the most complete and forward-looking study on power-gating in the ULV region. The results demonstrate that aggressive power-gating allows designers to leverage the very low switching energy of ULV operation, while achieving performance levels that can greatly expand the capabilities of energy-constrained systems.","abstract_html":"As transistor sizes scale down and levels of integration increase, leakage power has become a critical problem in modern low-power microprocessors. This is especially true for ultra-low-voltage (ULV) circuits, where high levels of leakage force designers to chose relatively high threshold voltages, which limits performance. In this thesis, an industry-standard technique known as power-gating is explored, whereby transistors are used to disconnect the power from idle portions of a chip. Present power-gating implementations suffer from limitations including non-zero off-state leakage, which can aggregate to a large amount of wasted energy during long idle periods, and high energy overhead, which limits its use to long-term system-wide sleep modes. As this thesis will show however, by vastly increasing the effectiveness of power-gating through the use of emerging technologies, and by implementing aggressive hardware-oriented power-gating policies, leakage in microprocessors can be eliminated to a large extent. This allows the threshold voltage to be lowered, leading to ULV microprocessors with both low switching energy and high performance. The first emerging technology investigated is the Nanoelectromechnical-Systems (NEMS) switch, which is a CMOS-compatible mechanical relay with near-infinite off-resistance and low on-resistance. When used for power-gating, this switch completely eliminates off-state leakage, yet is compact enough to be contained on die. This has tremendous benefits for applications with long sleep times. For example, a NEMS-power-gated architecture performing an FFT per hour consumes 30 times less power than a transistor-power-gated architecture. Additionally, the low on-resistance can lower power-gating area overhead by 36-83\\%. The second technology targets the high energy overhead associated with powering a circuit on and off. This thesis demonstrates that a new logic style specifically designed for ULV operation, Sense Amplifier Pass Transistor Logic (SAPTL), requires power-gates that are 8-10 times smaller, and consumes up to 15 times less boot-up energy, compared to static-CMOS. These abilities enable effective power-gating of an SAPTL circuit, even for very short idle periods. Microprocessor simulations demonstrate that a fine-grained power-gating policy, along with this drastically lower overhead, can result in up to a 44\\% drop in energy. Encompassing these investigations is an energy estimation framework built around a cycle-accurate microprocessor simulator, which allows a wide range of circuit and power-gating parameters to be optimized. This framework implements two hardware-based power-gating schedulers that are completely invisible to the OS, and have extremely low hardware overhead, allowing for a large number of power-gated regions. All together, this thesis represents the most complete and forward-looking study on power-gating in the ULV region. The results demonstrate that aggressive power-gating allows designers to leverage the very low switching energy of ULV operation, while achieving performance levels that can greatly expand the capabilities of energy-constrained systems.","abstract_has_math":false,"creators":["Henry, Michael B."],"institution":"Virginia Tech","degree_name":"Ph. 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This allows the threshold voltage to be lowered, leading to ULV microprocessors with both low switching energy and high performance. The first emerging technology investigated is the Nanoelectromechnical-Systems (NEMS) switch, which is a CMOS-compatible mechanical relay with near-infinite off-resistance and low on-resistance. When used for power-gating, this switch completely eliminates off-state leakage, yet is compact enough to be contained on die. This has tremendous benefits for applications with long sleep times. For example, a NEMS-power-gated architecture performing an FFT per hour consumes 30 times less power than a transistor-power-gated architecture. Additionally, the low on-resistance can lower power-gating area overhead by 36-83\\%. The second technology targets the high energy overhead associated with powering a circuit on and off. This thesis demonstrates that a new logic style specifically designed for ULV operation, Sense Amplifier Pass Transistor Logic (SAPTL), requires power-gates that are 8-10 times smaller, and consumes up to 15 times less boot-up energy, compared to static-CMOS. These abilities enable effective power-gating of an SAPTL circuit, even for very short idle periods. Microprocessor simulations demonstrate that a fine-grained power-gating policy, along with this drastically lower overhead, can result in up to a 44\\% drop in energy. Encompassing these investigations is an energy estimation framework built around a cycle-accurate microprocessor simulator, which allows a wide range of circuit and power-gating parameters to be optimized. This framework implements two hardware-based power-gating schedulers that are completely invisible to the OS, and have extremely low hardware overhead, allowing for a large number of power-gated regions. All together, this thesis represents the most complete and forward-looking study on power-gating in the ULV region. The results demonstrate that aggressive power-gating allows designers to leverage the very low switching energy of ULV operation, while achieving performance levels that can greatly expand the capabilities of energy-constrained systems."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph. 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In this thesis, an industry-standard technique known as power-gating is explored, whereby transistors are used to disconnect the power from idle portions of a chip. Present power-gating implementations suffer from limitations including non-zero off-state leakage, which can aggregate to a large amount of wasted energy during long idle periods, and high energy overhead, which limits its use to long-term system-wide sleep modes. As this thesis will show however, by vastly increasing the effectiveness of power-gating through the use of emerging technologies, and by implementing aggressive hardware-oriented power-gating policies, leakage in microprocessors can be eliminated to a large extent. This allows the threshold voltage to be lowered, leading to ULV microprocessors with both low switching energy and high performance. The first emerging technology investigated is the Nanoelectromechnical-Systems (NEMS) switch, which is a CMOS-compatible mechanical relay with near-infinite off-resistance and low on-resistance. When used for power-gating, this switch completely eliminates off-state leakage, yet is compact enough to be contained on die. This has tremendous benefits for applications with long sleep times. For example, a NEMS-power-gated architecture performing an FFT per hour consumes 30 times less power than a transistor-power-gated architecture. Additionally, the low on-resistance can lower power-gating area overhead by 36-83\\%. The second technology targets the high energy overhead associated with powering a circuit on and off. This thesis demonstrates that a new logic style specifically designed for ULV operation, Sense Amplifier Pass Transistor Logic (SAPTL), requires power-gates that are 8-10 times smaller, and consumes up to 15 times less boot-up energy, compared to static-CMOS. These abilities enable effective power-gating of an SAPTL circuit, even for very short idle periods. Microprocessor simulations demonstrate that a fine-grained power-gating policy, along with this drastically lower overhead, can result in up to a 44\\% drop in energy. Encompassing these investigations is an energy estimation framework built around a cycle-accurate microprocessor simulator, which allows a wide range of circuit and power-gating parameters to be optimized. This framework implements two hardware-based power-gating schedulers that are completely invisible to the OS, and have extremely low hardware overhead, allowing for a large number of power-gated regions. All together, this thesis represents the most complete and forward-looking study on power-gating in the ULV region. 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