P Raghavan | TU Delft Repository

Sense amplifier offset voltage analysis for both time-zero and time-dependent variability

Journal article (2019) - Innocent Agbo, Mottaqiallah Taouil, Daniël Kraak, Said Hamdioui, Pieter Weckx, Stefan Cosemans, Praveen Raghavan, Francky Catthoor, Wim Dehaene

This paper presents an accurate technique to extensively analyze the impact of time-zero (i.e., global and local variation) and time-dependent (i.e., voltage, temperature, workload, and aging) variation on the offset voltage specification of a memory sense amplifier design using 45 nm predictive technology model (PTM) high performance library. The results show that increasing the supply voltage both for time-zero and time-dependent reduces the offset voltage specification marginally, irrespective of the process corners. In contrast, the offset voltage specification is very sensitive to the temperature and the workload, i.e., the applied voltage patterns. The results also show that a balanced workload results in a significantly lower offset voltage specification. The above results can be used to estimate the required offset voltage accurately for a given lifetime, and operational conditions such as workload, temperature, and voltage; hence, enable the designer to take appropriate measures for a high quality, robust, optimal and reliable design. ...

Integral Impact of BTI, PVT Variation, and Workload on SRAM Sense Amplifier

Journal article (2017) - Innocent Agbo, Mottaqiallah Taouil, Daniël Kraak, Said Hamdioui, H. Kükner, Pieter Weckx, Praveen Raghavan, Francky Catthoor

The CMOS technology scaling faced over the past recent decades severe variability and reliability challenges. One of the major reliability challenges is bias temperature instability (BTI). This paper analyzes the impact of BTI on the sensing delay of standard latch-type sense amplifier (SA), which is one of the critical components of high performance memories; the analysis is done by incorporating the impact of process, voltage, and temperature variations (in order to investigate the severity of the integral impact) and by considering different workloads and four technology nodes (i.e., 45, 32, 22, and 16 nm). The results show the importance of taking the SA degradation into consideration for robust memory design; the SA degradation depends on the application and technology node, and the sensing delay can increase with 184.58% for the worst case conditions at 16 nm. The results also show that the BTI impact for nominal conditions at 16 nm reaches a 12.10% delay increment. On top of that, when extrinsic conditions are considered, the degradation can reach up to 168.45% at 398 K for 16 nm. ...

Comparative BTI Analysis for Various Sense Amplifier Designs

Conference paper (2016) - Innocent Agbo, Mottaqiallah Taouil, Said Hamdioui, Pieter Weckx, Stefan Cosemans, Praveen Raghavan, Francky Catthoor

With the continuous downscaling of CMOS technologies, ICs become more vulnerable to transistor aging mainly due to Bias Temperature Instability (BTI). This paper presents a comparative study of the BTI impact while considering varying supply voltages and temperatures for three memory sense amplifier (SA) designs: low power (LP), mid power/performance (MP), and high performance (HP). As an evaluation metric, the sensing delay (SD) of the three designs is analyzed for various workloads using 45nm technology. The results show that HP SA degrades faster than MP SA and LP SA irrespective of the workload, supply voltage, and temperature. At nominal supply voltage and temperature, HP degrades up to 1.62x faster than MP, and up to 1.94x faster than LP designs for the worst case workload. In addition, the results show that an increase of 10% in power supply has a marginal impact on the relative degradation. In contrast, the results show that a temperature increment significantly worsens the BTI impact. Finally, the results show that for 16nm technology, BTI impact becomes worse and even causes read failures. This clearly indicates that designing for reliability is not only strongly application dependent, but also technology node dependent. Hence, one has to carefully consider the targeted application, design, and technology node in order to provide appropriate solutions. ...

Quantification of Sense Amplifier Offset Voltage Degradation due to Zero-and Run-Time Variability

Conference paper (2016) - Innocent Agbo, Mottaqiallah Taouil, Said Hamdioui, Pieter Weckx, Stefan Cosemans, Praveen Raghavan, Francky Catthoor, Wim Dehaene

Nowadays, typical (memory) designers add design margins to compensate for uncertainties, however, this may be overestimated leading to yield loss, or underestimated leading to reduced reliability designs. Accurate quantification of all uncertainties is therefore critical to provide high quality and optimal designs. These uncertainties are caused by zero-time variability (due to process variability), and by run-time variability(due to environmental variabilities such as voltage and temperature, or due to temporal variability such as aging). This paper uses an accurate methodology to predict the impact of both zero-and run-time variability on the offset voltage of sense amplifiers while considering different workloads and PVT variations for a pre-defined failure rate. The results show a marginal impact of environmental run-time variability on the offset specification when considering zero-time variability only, while this becomes significant (up to 2X) when incorporating aging run-time variability. The results can be used to quantify whether the required offset voltage is met or not for the targeted lifetime, hence, enable the designer to take appropriate measures for an efficient and optimized design, depending on the targeted application lifetime. ...