Fig. 8. N-Curve for stability analysis
Static Voltage Noise Margin (SVNM)
The SVNM refers to the maximum threshold of DC noise voltage that an
SRAM cell’s inverter input can endure without inducing any alteration in
its stored data. The simulation plot presented in Figure IV(e), the
voltage disparity between points A and B is depicted, showcasing the
maximum permissible DC noise voltage that the SRAM cell can endure while
preserving the integrity of its stored data. In simpler terms, SVNM
serves as a measure of the SRAM cell’s stability against external noise
disturbances.
SVNM = VB - VA
Static Current Noise Margin (SINM)
The SINM is an essential parameter that evaluates the stability of the
SRAM cell under the influence of external current disturbances. It
represents the maximum allowable DC current that can be injected into
the cell without causing any modification to its stored data. The
accompanying plot depicts the peak current positioned between points A
and B, providing insight into the SRAM cell’s ability to withstand
current interference while preserving data integrity. By measuring SINM,
we can ensure that the SRAM cell can withstand external current noise
and maintain its stored data, thus evaluating its stability.
Write Trip Voltage (WTV)
The WTV denotes the minimum voltage reduction required to switch the
internal node ”1” of the SRAM cell from one state to another, while both
bit lines are held at the Vdd voltage level. This value can be
determined by measuring the voltage discrepancy between points C and B
in the corresponding plot, as depicted in Figure IV(e). Through the
measurement of the WTV, we can evaluate the essential voltage required
for writing data into the SRAM cell. This information is crucial for
assessing the functionality and performance of the cell. The WTV serves
as a critical parameter in assessing the SRAM cell’s write ability,
ensuring accurate and reliable data storage operations. In other words,
WTV indicates the voltage threshold at which the SRAM cell can be
successfully programmed with a new data bit.
SVNM = VB – VC
Write Trip Current (WTI)
WTI refers to the minimum current level necessary to write data into the
SRAM cell without causing any undesired disruptions. It can be
determined by identifying the negative peak current between points C and
B in the N-curve illustrated in Figure IV(e). The overlapping of points
A and B, or B and C, can compromise the stability of the SRAM cell.
Hence, WTI serves as a crucial metric for evaluating the write
capability of the SRAM cell, ensuring accurate and reliable data writing
while preserving its stability. In essence, WTI specifies the minimum
current required to change the state of the SRAM cell without any
unwanted disturbances.
Power Dissipation for various Technologies