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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
The differences between a DRAM and SRAM stem fundamentally from different implementations of the memory cell. In an SRAM, the cell consists of a cross-coupled logic circuit built from four to six transistors; a SRAM memory cell will indefinitely remember the bit written to it as long as it is powered. In contrast, a DRAM cell is made from a single transistor and capacitor, and its memory is transient. The DRAM cell is written by charging its capacitor. This charge slowly leaks out of the device in the form of an electrical current so that without special intervention the information stored in the cell is irrevocably lost. As a consequence, DRAM cells need to be periodically refreshed every few milliseconds or so. To refresh a cell, its contents are read and then written back again, thereby replenishing the charge on the capacitor as needed. The need for refresh circuitry complicates the design and operation of the DRAM interface, and impacts its operating speed since some portion of the time is used by the chip for refresh. However, because of the small size of each cell, DRAM chips are much denser than SRAM and have four to six times the capacity. SRAM, by contrast, is much faster and consumes less power than the DRAM, but holds fewer bits per chip and is considerably more expensive than DRAM.
Computer memory systems
Published in Joseph D. Dumas, Computer Architecture, 2016
Although dynamic RAM offers relatively low-cost and high-density storage, in general it is not capable of keeping up with the full speed of today’s microprocessors. Capacitors can be made very small and are easy to fabricate on silicon, but they take time to charge and discharge; this affects the access time for the device. The highest-speed semiconductor read/write memory technology is referred to as static random access memory (SRAM). In a SRAM device, the binary information is stored as the states of latches or flip-flops rather than capacitors. (In other words, SRAM is built in a very similar way to the storage registers inside a CPU.) SRAM is less dense than DRAM (it takes more silicon “real estate” to build a static RAM cell than a capacitor) and therefore is more expensive per amount of storage. SRAM, like DRAM, is a volatile technology that requires continuous application of electrical power to maintain its contents. However, because the bits are statically stored in latches, SRAM does not require periodic refresh. Contents are maintained indefinitely as long as power is applied. Compared to DRAM, SRAM circuitry requires more power for read/write operation, but some SRAMs, such as the Complementary Metal Oxide Semiconductor (CMOS) static RAM devices sometimes used to retain system settings, require very little current in standby mode and thus can maintain stored information for years under battery power.
Advanced System Designs
Published in Wen-Long Chin, Principles of Verilog Digital Design, 2022
As an off-chip memory, DRAM has the lowest cost per bit. Due to higher capacity and lower cost, DRAMs are most often used as the main memory of computer systems. By contrast, the hard disk has a lower cost per bit than DRAM, its speed is too slow to be used as the main memory. Modern DRAM chips have a capacity of up to 8 Gb, where G=109, significantly higher than that can be realized on an SRAM chip. However, such a high capacity also leads to a high access latency.
Radiation study of TFET and JLFET-based devices and circuits: a comprehensive review on the device structure and sensitivity
Published in Radiation Effects and Defects in Solids, 2023
The memory cell covers the majority of the chip making the investigation of the memory cell against radiation to be the most important. SRAM is an important circuit with excellent performance in comparison to other memory circuits in terms of speed and power consumption. 6 T SRAM occupies a lesser area compared to 8 T SRAM with a very low write delay (114). The effect of radiation on 6 T SRAM cell based on JL-DGFET is analyzed (115). The structure of SRAM is shown in Figure 15(a). The ionizing particle is made to strike at the OFF state of nMOS transistor. The state of the device gets flipped when the logic of the cell is disturbed. The transient response and QC at different time instants for various LET are shown in Figure 15(b). It can be seen from Figure 15(b) that when LET increases, the peak of transient current increases, and QC gets increased.
A Novel Design of Low Power & High Speed FinFET Based Binary and Ternary SRAM and 4*4 SRAM Array
Published in IETE Journal of Research, 2023
N. Shylashree, M. S. Amulya, Gulur R. Disha, N. Praveena, Vijay Kumar Verma, S. Muthumanickam, V. Kannagi, K. Sivachandar, Vijay Nath
The SRAM cell can store 1 bit, and its internal structure is composed of 6 transistors (N1, N2, N3, N4, N5, and N6), where 4 of these (N1-N4) form 2 crossed inverters, which are responsible for keeping the data stored in the SRAM cell is powered. The other 2 transistors (N5 and N6) are controlled by the Word Line and provide bidirectional access between stored data and the bit lines. The basic cell is shown in Figure 1. To perform the read operation, precharge both bit lines before turning on the word line. One of the two-bit lines will be pulled down by the cell depending on the value present at the output. To perform a write operation, drive the one-bit line high and the other low. Then turn on the word line. Bit lines overwrite the cell with new values.