Comparative Study of Sense Amplifiers for SRAM
Abstract
This paper presents the comparative study of different type of sense amplifiers. These sense amplifiers are voltage-mode sense amplifier (VMSA) and Charge transfer sense amplifiers (CTSA). The first objective of this research work is to design the sense amplifier and the next objective is to compare and identify which design has better performance in term of power and speed. Sense amplifiers are one of the most essential circuits in the CMOS memories that plays an important role to reduce the overall sensing delay and voltage. Previous voltage mode sense amplifiers sense the voltage difference at bit and bit lines bar but as the memory size increase the capacitances of bit line and date line also increases. The tools used for simulation is TANNER EDA for layout using 90nm technology. The results show that the CTSA has higher speed with lower delay and low power dissipation than VMSA. But cell size of VMSA in comparison with CTMA is smaller. CTSA is more suitable for high speed performance and low power circuitry and VMSA is best suited for stability and smaller design.
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Introduction
SRAM stand for Static Random Access Memory, a nonvolatile memory that can store the information as long as the power is applied. The sense amplifier operated only when stored data is read from memory. Sense amplifier (SA) is used to detect the very small difference voltage at bit-lines and amplify the signals to its full digital voltage swing before the signals are fully charged or discharged. This situation causes the time taken to read the content of memory is shorten since the circuitry does not requires to wait until the signals getting fully charged or discharged to determine either it is '1' or '0'. The small spark or glitch at both bit-lines may determine its state. So the memory may take it quickly either as 'I' or '0' rather than trying to calculate or wait for its voltage full swing level, thus saves time in read operation into memory.
In this paper the sense amplifiers are selected is conventional voltage sense amplifiers and charge transfer sense amplifiers. These sense amplifiers are simulated at 90nm technology scale. At this technology sense amplifiers is compared on the basis of sensing delay and power consumption at different voltages.
The organization of this paper is done in following manner i.e. initially a brief explanation of 6T SRAM and conventional sense amplifiers are done. After that comparison of both the sense amplifiers is done with graph.
Conclusion
In this paper SRAM with both the sense amplifiers i.e. Voltage Sense amplifier & Charge Transfer sense amplifier is analyzed and discussed. The observation shows that the CTSA give best results in terms of power consumption and sensing delay in comparison to VMSA. Observation of the work shows that power consumption of the sense amplifier is increases with the increase in supply voltage whereas sensing delay is decreases with increase in supply voltage. In future scope more efficient sense amplifier can be realized by improving available sense amplifiers so that power consumption and delay can be reduced during sensing the data from memory cell.