Due to CMOS technology scaling, devices are getting smaller, faster, and operating at lower suppl... more Due to CMOS technology scaling, devices are getting smaller, faster, and operating at lower supply voltages. The reduced capacitances and power supply voltages and the increased chip density to perform more functionality result in increasing the soft errors and making them one of the essential design constraints at the same level as delay and power. Even though the impact of process variations on the performance and the power consumption has been investigated by many researchers, its impact on soft errors has not been paid enough attention. This impact is investigated in this paper for 65-nm CMOS technology. The soft error yield is defined in this paper similar to the timing yield and the power yield. This paper shows that the soft error yield of the sense-amplifier based flip flop (SA-FF) is very poor. Therefore, soft error mitigation techniques are required when using this flip-flop topology. The semi-dynamic flip-flop (SD-FF) exhibits the best soft error yield behavior with a very high performance at the expense of large power requirement. Finally, some design insights are proposed to guide flip-flops designers to select the best flip-flop topology that satisfies their specific circuit soft error rate constraints.
In synchronous systems, any violation of the timing constraints of the flip-flops can cause the o... more In synchronous systems, any violation of the timing constraints of the flip-flops can cause the overall system to malfunction. Moreover, the process variations create a large variability in the flip-flop delay in scaled technologies impacting the timing yield. Overtime, many gate sizing algorithms have been introduced to improve the timing yield. This paper presents an analysis of timing yield improvement of four commonly used flip-flops under process variations. These flip-flops are designed using STMicroelectronics 65-nm CMOS technology. The analyzed flip-flops are compared for power and power-delay product (PDP) overheads to achieve this timing yield improvement. The analysis shows that the sense amplifier based flip flop (SA-FF) has a power overhead and PDP overhead of 1.7X and 2.8X, respectively, much higher than that of the transmission-gate master-slave flip flop(TG-MSFF) . The TG-MSFF exhibits the lowest relative power and PDP overheads of 30.87% and 9% ,respectively.
Dynamic logic circuits are considered the best choice for high performance applications due to th... more Dynamic logic circuits are considered the best choice for high performance applications due to their relatively high speed. These high performance applications have strict timing constraints. Moreover, process variations create a large variability in the dynamic circuit delay in scaled technologies impacting the timing yield. In this paper, the negative capacitance is adopted, for the first time, for statistical timing yield improvement under process variations. Simulation results show that the adoption of the negative capacitance at the output of a 16-input dynamic NOR gate improves the timing yield by reducing the dynamic circuit delay. In addition, the negative capacitance adoption results in power saving of 10% and reduces the delay variability by 57.6%.
In low power synchronous systems, sub-threshold flip-flops are used to reduce the total power dis... more In low power synchronous systems, sub-threshold flip-flops are used to reduce the total power dissipation. Moreover, process variations create a large variability in the flip-flop power in scaled technologies impacting the power yield, especially, for sub-threshold operation. This paper presents an analysis of power yield improvement of four commonly used flip-flops under process variations. These flip-flops are designed using STMicroelectronics 65-nm CMOS technology. The analyzed flip-flops are compared for delay, energy, and energy-delay product (EDP) overheads to achieve this power yield improvement. The analysis shows that the sense amplifier based flip flop (SA-FF) has the lowest overheads while the modified clocked CMOS master slave flip-flop (M-C2MOS-MSFF) exhibits the largest overheads, and correspondingly, it is not recommended for sub-threshold operation.
IEEE Transactions on Very Large Scale Integration Systems, 2012
An analog adaptive body bias (A-ABB) circuit is proposed in this paper. The A-ABB is used to comp... more An analog adaptive body bias (A-ABB) circuit is proposed in this paper. The A-ABB is used to compensate for die-to-die (D2D) and within-die (WID) parameter variations and accordingly, improves the circuit yield regarding the speed, the dynamic power, and the leakage power. The A-ABB consists of threshold voltage estimation circuits and analog control of the body bias performed by on-chip amplifier circuits. Circuit level simulation results of a circuit block case study, extracted from a real microprocessor critical path, referring to an industrial hardware-calibrated 65-nm CMOS technology transistor model, are demonstrated. This study shows that the proposed A-ABB reduces the standard deviations of the frequency, the dynamic power and the leakage power by factors of 6.6 X, 8.8 X, and 3.3 X, respectively, when both D2D and WID variations are considered. In addition, in this presented case study, initial total yields of 16.8% and 5.2% are improved to 99.9% and 84.1%, respectively. The advantage of the proposed A-ABB is its lower area overhead allowing it to be used at lower granularity level than that of the previously published ABB circuits.
IEEE Transactions on Circuits and Systems I-regular Papers, 2011
Reliability and variability have become big design challenges facing submicrometer SRAM designers... more Reliability and variability have become big design challenges facing submicrometer SRAM designers. A low area overhead adaptive body bias (ABB) circuit is proposed in this paper to compensate for NBTI aging and process variations to improve the SRAM reliability and yield. The proposed ABB circuit consists of a threshold voltage sensing circuit and an on-chip analog controller. Postlayout simulation results, referring to an industrial hardware-calibrated STMicroelectronics 65 nm CMOS technology transistor model, are presented. The transistor model contains process variations and NBTI aging model cards, which are declared by STMicroelectronics to be silicon verified. Cadence RelXpert, Virtuoso Spectre, and Virtuoso UltraSim tools are used to estimate the NBTI aging and process variations impacts on the SRAM array. These results show that the proposed ABB compensates effectively for NBTI aging and process variations. For example, the proposed ABB reduces the read failure probability from 0.32% to 0.05% and the SNM degradation from 10.9% to 2.6% at 10 years aging time. In addition, the proposed ABB enhances the soft errors immunity of the SRAM cell by reducing the critical charge degradation from 12.7% to 3.4% at 10 years aging time.
IEEE Transactions on Circuits and Systems I-regular Papers, 2011
Dynamic gates are preferred in the design of high-performance modules in modern microprocessors d... more Dynamic gates are preferred in the design of high-performance modules in modern microprocessors due to the relatively high speed of dynamic gates compared with that of standard CMOS gates. These high performance modules have strict timing constraints. Due to the increased process variations in scaled technologies, the dynamic circuit delay exhibits a substantial variability around its nominal value. This delay variability results in violating the timing constraints, and correspondingly, causes a timing yield loss. In this paper, novel negative capacitance circuits are developed, for the first time, to statistically improve the timing yield under process variations. Post layout simulation results, referring to an industrial hardware-calibrated TSMC 65 nm CMOS technology, show that the adoption of the negative capacitance circuit to a 64-input wide dynamic OR gate is capable of improving the timing yield from 50% to 100%. Moreover, the negative capacitance circuit adoption results in reducing the delay variability at the expense of excess power overhead.
Due to CMOS technology scaling, devices are getting smaller, faster, and operating at lower suppl... more Due to CMOS technology scaling, devices are getting smaller, faster, and operating at lower supply voltages. The reduced capacitances and power supply voltages and the increased chip density to perform more functionality result in increasing the soft errors and making them one of the essential design constraints at the same level as delay and power. Even though the impact of process variations on the performance and the power consumption has been investigated by many researchers, its impact on soft errors has not been paid enough attention. This impact is investigated in this paper for 65-nm CMOS technology. The soft error yield is defined in this paper similar to the timing yield and the power yield. This paper shows that the soft error yield of the sense-amplifier based flip flop (SA-FF) is very poor. Therefore, soft error mitigation techniques are required when using this flip-flop topology. The semi-dynamic flip-flop (SD-FF) exhibits the best soft error yield behavior with a very high performance at the expense of large power requirement. Finally, some design insights are proposed to guide flip-flops designers to select the best flip-flop topology that satisfies their specific circuit soft error rate constraints.
In synchronous systems, any violation of the timing constraints of the flip-flops can cause the o... more In synchronous systems, any violation of the timing constraints of the flip-flops can cause the overall system to malfunction. Moreover, the process variations create a large variability in the flip-flop delay in scaled technologies impacting the timing yield. Overtime, many gate sizing algorithms have been introduced to improve the timing yield. This paper presents an analysis of timing yield improvement of four commonly used flip-flops under process variations. These flip-flops are designed using STMicroelectronics 65-nm CMOS technology. The analyzed flip-flops are compared for power and power-delay product (PDP) overheads to achieve this timing yield improvement. The analysis shows that the sense amplifier based flip flop (SA-FF) has a power overhead and PDP overhead of 1.7X and 2.8X, respectively, much higher than that of the transmission-gate master-slave flip flop(TG-MSFF) . The TG-MSFF exhibits the lowest relative power and PDP overheads of 30.87% and 9% ,respectively.
Dynamic logic circuits are considered the best choice for high performance applications due to th... more Dynamic logic circuits are considered the best choice for high performance applications due to their relatively high speed. These high performance applications have strict timing constraints. Moreover, process variations create a large variability in the dynamic circuit delay in scaled technologies impacting the timing yield. In this paper, the negative capacitance is adopted, for the first time, for statistical timing yield improvement under process variations. Simulation results show that the adoption of the negative capacitance at the output of a 16-input dynamic NOR gate improves the timing yield by reducing the dynamic circuit delay. In addition, the negative capacitance adoption results in power saving of 10% and reduces the delay variability by 57.6%.
In low power synchronous systems, sub-threshold flip-flops are used to reduce the total power dis... more In low power synchronous systems, sub-threshold flip-flops are used to reduce the total power dissipation. Moreover, process variations create a large variability in the flip-flop power in scaled technologies impacting the power yield, especially, for sub-threshold operation. This paper presents an analysis of power yield improvement of four commonly used flip-flops under process variations. These flip-flops are designed using STMicroelectronics 65-nm CMOS technology. The analyzed flip-flops are compared for delay, energy, and energy-delay product (EDP) overheads to achieve this power yield improvement. The analysis shows that the sense amplifier based flip flop (SA-FF) has the lowest overheads while the modified clocked CMOS master slave flip-flop (M-C2MOS-MSFF) exhibits the largest overheads, and correspondingly, it is not recommended for sub-threshold operation.
IEEE Transactions on Very Large Scale Integration Systems, 2012
An analog adaptive body bias (A-ABB) circuit is proposed in this paper. The A-ABB is used to comp... more An analog adaptive body bias (A-ABB) circuit is proposed in this paper. The A-ABB is used to compensate for die-to-die (D2D) and within-die (WID) parameter variations and accordingly, improves the circuit yield regarding the speed, the dynamic power, and the leakage power. The A-ABB consists of threshold voltage estimation circuits and analog control of the body bias performed by on-chip amplifier circuits. Circuit level simulation results of a circuit block case study, extracted from a real microprocessor critical path, referring to an industrial hardware-calibrated 65-nm CMOS technology transistor model, are demonstrated. This study shows that the proposed A-ABB reduces the standard deviations of the frequency, the dynamic power and the leakage power by factors of 6.6 X, 8.8 X, and 3.3 X, respectively, when both D2D and WID variations are considered. In addition, in this presented case study, initial total yields of 16.8% and 5.2% are improved to 99.9% and 84.1%, respectively. The advantage of the proposed A-ABB is its lower area overhead allowing it to be used at lower granularity level than that of the previously published ABB circuits.
IEEE Transactions on Circuits and Systems I-regular Papers, 2011
Reliability and variability have become big design challenges facing submicrometer SRAM designers... more Reliability and variability have become big design challenges facing submicrometer SRAM designers. A low area overhead adaptive body bias (ABB) circuit is proposed in this paper to compensate for NBTI aging and process variations to improve the SRAM reliability and yield. The proposed ABB circuit consists of a threshold voltage sensing circuit and an on-chip analog controller. Postlayout simulation results, referring to an industrial hardware-calibrated STMicroelectronics 65 nm CMOS technology transistor model, are presented. The transistor model contains process variations and NBTI aging model cards, which are declared by STMicroelectronics to be silicon verified. Cadence RelXpert, Virtuoso Spectre, and Virtuoso UltraSim tools are used to estimate the NBTI aging and process variations impacts on the SRAM array. These results show that the proposed ABB compensates effectively for NBTI aging and process variations. For example, the proposed ABB reduces the read failure probability from 0.32% to 0.05% and the SNM degradation from 10.9% to 2.6% at 10 years aging time. In addition, the proposed ABB enhances the soft errors immunity of the SRAM cell by reducing the critical charge degradation from 12.7% to 3.4% at 10 years aging time.
IEEE Transactions on Circuits and Systems I-regular Papers, 2011
Dynamic gates are preferred in the design of high-performance modules in modern microprocessors d... more Dynamic gates are preferred in the design of high-performance modules in modern microprocessors due to the relatively high speed of dynamic gates compared with that of standard CMOS gates. These high performance modules have strict timing constraints. Due to the increased process variations in scaled technologies, the dynamic circuit delay exhibits a substantial variability around its nominal value. This delay variability results in violating the timing constraints, and correspondingly, causes a timing yield loss. In this paper, novel negative capacitance circuits are developed, for the first time, to statistically improve the timing yield under process variations. Post layout simulation results, referring to an industrial hardware-calibrated TSMC 65 nm CMOS technology, show that the adoption of the negative capacitance circuit to a 64-input wide dynamic OR gate is capable of improving the timing yield from 50% to 100%. Moreover, the negative capacitance circuit adoption results in reducing the delay variability at the expense of excess power overhead.
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Papers by Hassan Mostafa