VLSI Questions and Answers – Rules for Proper Design

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This set of VLSI Multiple Choice Questions & Answers (MCQs) focuses on “Rules for Proper Design”.

1. The Zp.u./Zp.d. ratio for nMOS inverter is
a) 4:1
b) 3:1
c) 1:4
d) 1:3
View Answer

Answer: a
Explanation: For nMOS inverters the Zp.u./Zp.d. ratio is 4:1 when driven from another inverter and 8:1 when driven through one or more pass transistors.
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2. The impedance ratio for pseudo-nMOS is
a) 4:1
b) 3:1
c) 1:4
d) 1:3
View Answer

Answer: b
Explanation: For pseudo-nMOS, the Zp.u./Zp.d. ratio is 3:1 and for CMOS 1:1 ratio is required for minimum area.

3. What is the value for peripheral capacitance for 5 micron technology?
a) 4 x 10(-4) pf/µm2
b) 5 x 10(-4) pf/µm2
c) 8 x 10(-4) pf/µm2
d) 12 x 10(-4) pf/µm2
View Answer

Answer: c
Explanation: Peripheral capacitance is the side wall capacitance. Peripheral capacitance of 5 micron technology is 8 x 10(-4) pf/µm2.

4. 1 square Cg is ______ of MOS transistor
a) gate to source capacitance
b) gate to drain capacitance
c) source to drain capacitance
d) gate to channel capacitance
View Answer

Answer: d
Explanation: 1 square Cg is defined as the gate to channel capacitance of a MOS transistor having standard feature size (W=L).

5. What is the delay value Ʈ for 1.2 micron technology?
a) 0.1 nsec
b) 0.12 nsec
c) 0.046 nsec
d) 0.064 nsec
View Answer

Answer: c
Explanation: The delay Ʈ is the time constant and for 1.2 micron technology its value is 0.046 nsec.
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6. Which is used to increase Ʈ?
a) parasitic capacitance
b) peripheral capacitance
c) area capacitance
d) load capacitance
View Answer

Answer: a
Explanation: Circuit wiring and parasitic capacitance must be allowed to increase the value of Ʈ by the factor of 2 or 3.

7. The inverter pair delay is given by
a) (Zp.u./Zp.d.)Ʈ
b) (1+ Zp.u./Zp.d.)Ʈ
c) (1+ Zp.u./Zp.d.)Ʈ
d) (1+ Ʈ)Zp.u./Zp.d.
View Answer

Answer: b
Explanation: The inverter delay is given by (1+ Zp.u./Zp.d.)Ʈ. The inverter pair delay for CMOS is 7Ʈ.

8. The number of stages N is given by
a) ln(y)/ln(f)
b) ln(f)/ln(y)
c) ln(2y)/ln(f)
d) ln(y)/ln(2f)
View Answer

Answer: a
Explanation: To calculate the value for N, where N inverters are cascaded, each one of which is larger than the preceding stage by a width factor f the formula used is ln(y)/ln(f).

9. If f assumes the value e then delay is
a) maximized
b) minimized
c) does not change
d) doubled
View Answer

Answer: b
Explanation: Total delay is minimized if f assumes the value of e which is the base of the natural logarithm. This applies to both nMOS and CMOS.

10. Propogation delay is given by
a) nrcƮ
b) n2rcƮ
c) nr2
d) n2
View Answer

Answer: b
Explanation: Propogation delay through cascaded pass transistors or transmission gate can be given as n2rcƮ.
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11. Using _____ long wires are possible
a) silicide
b) metal
c) polysilicon
d) diffusion
View Answer

Answer: a
Explanation: Using silicide, reasonable long wires are possible. It is a modest RC product. Silicides are used in place of polysilicon in some nMOS processes.

12. One pass transistor can be driven through output of another.
a) true
b) false
View Answer

Answer: b
Explanation: No pass transistor gate must be driven through the output of one or more pass transistors since logic 1 levels are degraded by threshold voltage.

13. Pass transistors are allowed to be constructed under
a) diffusion layer
b) polysilicon layer
c) metal layer
d) silicon layer
View Answer

Answer: c
Explanation: Pass transistors are allowed to be constructed under metal layers to save space and is more convenient.

14. Maximum allowable current density in aluminium is
a) 0.1 mA/µm2
b) 0.5 mA/µm2
c) 2 mA/µm2
d) 1 mA/µm2
View Answer

Answer: d
Explanation: The maximum allowable current density in aluminium wire is 1 mA/µm2. Otherwise metal migration may occur.

Sanfoundry Global Education & Learning Series – VLSI.
To practice all areas of VLSI, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn