VLSI Design Questions and Answers - Capacitive Loads and Wiring Capacitances Part-1

1. The active capacitance is also called as __________
a) Parasitic capacitance
b) Interconnect capacitance
c) Junction capacitance
d) Diffusion capacitance

Answer: d
Explanation: Diffusion capacitance is also called as active capacitance.

2. The value of diffusion capacitance in pF x 10-4/µm2 in 2 µm design is?
a) 1.75
b) 4
c) 8
d) 16

Answer: c
Explanation: Diffusion capacitance has a value of 8 pF x 10-4/µm2.

3. The value of standard unit of capacitance is?
a) 0.01pF
b) 0.0032pF
c) 0.0023pF
d) All of the mentioned

Answer: d
Explanation: The value of standard unit of capacitance depends on the design style used.

4. The standard unit of capacitance is defined as?
a) Capacitance of gate to channel of MOS transistor having W = L dimensions
b) Capacitance of gate to channel of n-MOS transistor having W = 3L dimensions
c) Capacitance of gate to channel of p-MOS transistor having 3W = L dimensions
d) Capacitance of gate to channel of n-MOS transistor having W = L dimensions and p-MOS having W=3L dimensions

Answer: a
Explanation: Standard capacitance is capacitance of gate to channel with standard area.

5. The capacitances in MOSFET occurs due to _____________
a) Interconnects
b) Difference in Doping concentration
c) Difference in dopant materials
d) All of the mentioned

Answer: d
Explanation: All of the mentioned

6. The parasitic capacitances found in MOSFET are ___________
a) Oxide related capacitances
b) Inter electrode capacitance
c) Electrolytic capacitance
d) All of the mentioned

Answer: a
Explanation: The parasitic device capacitances can be classified into two major groups: oxide-related capacitances and junction capacitances.

7. The capacitance that exist between Gate and Bulk is called as ___________
a) Oxide parasitic capacitance
b) Metal oxide capacitance
c) MOS capacitance
d) None of the mentioned

Answer: a
Explanation: The capacitance that exist between Gate and Bulk is called as an oxide parasitic capacitance

8. In Cut-off Mode, the capacitance Cgs will be equal to ___________
a) 2Cgd
b) 0
c) Cgb
d) All of the mentioned

Answer: b
Explanation: In cut-off mode, the conducting channel does not exist, so gate-to-source and the gate-to-drain capacitances are both equal to zero.

9. In cut-off mode, the value of gate to substrate capacitance is equal to ___________
a) Cox .(W- L)
b) Cox W/ L
c) Cox* W*L
d) 0

Answer: c
Explanation: In Cut-off mode, the conducting channel does not exist, so gate-to-source and the gate-to-drain capacitances are both equal to zero. Therefore, the gate to substrate capacitance is equal to Cox* W*L.

10. In linear mode operation, the parasitic capacitances that exists are ___________
a) Nonzero Gate to source capacitance
b) Nonzero Gate to drain capacitance
c) Zero gate to substrate capacitance
d) All of the mentioned

Answer: d
Explanation: In linear-mode operation, the conducting channel exists, therefore there will be a finite amount of gate to source and gate to drain capacitances. Since the conducting channel exists, gate to substrate capacitance is reduced to zero.