For example, when analysing CPU malfunction, the cause of defect is often found to be low device input voltage and timing margin, etc. In order to avoid such malfunction, a margin analysis by means of a Shmoo Plot is highly recommended.
A Shmoo Plot is a graph with two axes which plots the magnitude of the dependency on each other as responding to constantly varied correlated parameters such as input timing and supply voltage -- a means of visualization of measurement results.
Figure 1 and 2 show a Shmoo Plot obtained by measuring the margin against device high (VIH) and low (VIL) level input supply voltages (VCC), while a Shmoo Plot obtained by measuring the margin against supply voltage of input timing (IN1) is shown in figure 3.
From figure 3 we understand that there is a margin of 5ns against an input value of 20ns, demonstrating that a Shmoo Plot, by which we can visualize measurement results, is an effective technique of margin analysis.
Figure 1: SHM • SHEET Input Voltage Characteristics Shmoo (VIL) | |||
---|---|---|---|
Item | Start | Stop | Step |
Inout voltage X: (VIL_1) |
1.5V | 0.0V | Auto |
Supply voltage Y: (VCC) | 3.0V | 3.0V | - |
Figure 1 SHM • SHEET Input Voltage Characteristics Shmoo (VIL)
Figure 2: SHM • SHEET Input Voltage Characteristics Shmoo (VIH) | |||
---|---|---|---|
Item | Start | Stop | Step |
Input voltage X: (VIH_1) |
2.5V | 1.0V | Auto |
Supply voltage Y: (VCC) | 3.0V | 3.0V | - |
Figure 2 SHM • SHEET Input Voltage Characteristics Shmoo (VIH)
Figure 3: SHM • SHEET AC Timing Characteristics Shmoo (Input) | |||
---|---|---|---|
Item | Start | Stop | Step |
Input timing X: (IN1) |
0.0ns | 40ns | 0.05ns |
Supply voltage Y: (VCC) | 3.6V | 3.0V | -0.1V |
Figure 3: SHM • SHEET AC Timing Characteristics Shmoo (Input)