Deberjeet Usham
2K21/VLS/05
Exp No. 2
EXPERIMENT No. 2
AIM:
Analysis of short-circuit current variation with respect to:
1. Variation in output load capacitance
2. Variation of Input transition
3. Variation in temperature
4. Variation in Power supply
THEORY:
In practice, finite rise and fall times results in a direct current path between the supply and ground, GND,
this exists for a short period of time during switching. During switching both NMOS and PMOS
transistors in the circuit conduct simultaneously for a short amount of time. Specifically, when the
condition, VTn (lesser than) Vin (lesser than) Vdd - |VTp| holds for the input voltage, where VTn and
VTp are NMOS and PMOS thresholds, there will be a conductive path open between Vdd and GND
because both the NMOS and PMOS devices will be simultaneously on (also known as slew ) . This forms
direct current path between the power supply and the ground. This current has no contribution towards
charging of the output capacitance of the logic gate. When the input rising voltage exceeds the threshold
voltage of NMOS transistor, it starts conducting. Similarly until input voltage reaches Vdd-|Vt,p| PMOS
transistor remains ON. Thus for some time both transistors are ON. Similar event causes short circuit
current to flow when signal is falling. Short circuit current terminates when transition is completed.
Fig 2.1 : Short circuit current
Short circuit currents are significant when the rise/fall time at the input of a gate is much larger than the
output rise/ fall time. This is because the short-circuit path will be active for a longer period of time. Short
circuit current also depends upon the load capacitance. In this experiment we analyze the short circuit
current variation with the respect to variation with output capacitance and input transition time.
1
Deberjeet Usham
2K21/VLS/05
CIRCUIT SCHEMATIC
Fig 2.2: Circuit Schematic of inverter
Analysis at Typical Corner:
1. Variation in short circuit current with output load variation
Fig 2.3: Short circuit current at different load capacitances
2
Exp No. 2
Deberjeet Usham
2K21/VLS/05
Exp No. 2
TABLE:
S.No.
1
2
3
Load Capacitance(fF)
10
60
100
Short Circuit Current (µA)
1.05
0.2
0.1
2. Variation in short circuit current with input Transition
Fig 2.4: Short circuit current at different input transitions
3. Variation in short circuit current with temperatures
Fig 2.5: Short circuit current at different temperatures
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Deberjeet Usham
2K21/VLS/05
4. Variation in Short circuit current with power supply
Fig 2.6: Short circuit current at different supply voltages
OBSERVATION:
1.
2.
3.
4.
4
As output load capacitance increases short circuit current decreases
As transition time of input increases short circuit current increases
As temperature increases short circuit current decreases
As power supply voltage increases short circuit current increases
Exp No. 2
Deberjeet Usham
2K21/VLS/05
Exp No. 2
Analysis at FF corner:
1. Variation in short circuit current with output load variation
Fig: Short circuit current at different load capacitance
Table:
S.No.
1
2
3
Load Capacitance(fF)
10
60
100
Short Circuit Current (µA)
3
0.9
0.55
Fig: Short circuit current at different input transition
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Deberjeet Usham
2K21/VLS/05
3. Variation in short circuit current with temperatures
Fig: Short circuit current at different temperatures
4. Variation in Short circuit current with power supply
Fig: Short circuit current at different voltages
OBSERVATION:
1.
2.
3.
4.
6
As output load capacitance increases short circuit current decreases
As transition time of input increases short circuit current increases
As temperature increases short circuit current decreases
As power supply voltage increases short circuit current increases
Exp No. 2
Deberjeet Usham
2K21/VLS/05
Exp No. 2
Analysis at FS corner:
1. Variation in short circuit current with output load variation
Fig: Short circuit current at different load capacitance
Table:
S.No.
1
2
3
Load Capacitance(fF)
10
60
100
Short Circuit Current (µA)
1.15
0.25
0.15
2. Variation in short circuit current with input Transition
Fig: Short circuit current at different input transition
3. Variation in short circuit current with temperatures
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Deberjeet Usham
2K21/VLS/05
Fig: Short circuit current at different temperature
4. Variation in Short circuit current with power supply
Fig: Short circuit current at different voltage
OBSERVATIONs:
1.
2.
3.
4.
As output load capacitance increases short circuit current decreases
As transition time of input increases short circuit current increases
As temperature increases short circuit current decreases
As power supply voltage increases short circuit current increases
Analysis at SF corner:
1. Variation in short circuit current with output load variation
8
Exp No. 2
Deberjeet Usham
2K21/VLS/05
Exp No. 2
Fig: Short circuit current at different load capacitance
Table:
S.No.
1
2
3
Load Capacitance(fF)
10
60
100
Short Circuit Current (µA)
1
0.2
0.1
2. Variation in short circuit current with input Transition
Fig: Short circuit current at different input transition
3. Variation in short circuit current with temperatures
9
Deberjeet Usham
2K21/VLS/05
Fig: Short circuit current at different temperature
4. Variation in Short circuit current with power supply
Fig: Short circuit current at different voltage
OBSERVATION:
1.
2.
3.
4.
As output load capacitance increases short circuit current decreases
As transition time of input increases short circuit current increases
As temperature increases short circuit current decreases
As power supply voltage increases short circuit current increases
Analysis at SS corner:
10
Exp No. 2
Deberjeet Usham
2K21/VLS/05
Exp No. 2
1. Variation in short circuit current with output load variation
Fig: Short circuit current at different load capacitance
Table:
S.No.
1
2
3
Load Capacitance(fF)
10
60
100
Short Circuit Current (µA)
0.28
0.02
-0.02
2. Variation in short circuit current with input Transition
Fig: Short circuit current at different input transition
3. Variation in short circuit current with temperatures
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Deberjeet Usham
2K21/VLS/05
Fig: Short circuit current at different temperature
4. Variation in Short circuit current with power supply
Fig: Short circuit current at different voltage
OBSERVATIONS:
1.
2.
3.
4.
12
As output load capacitance increases short circuit current decreases
As transition time of input increases short circuit current increases
As temperature increases short circuit current decreases
As power supply voltage increases short circuit current increases
Exp No. 2