**VI Semester B.Tech Degree Examination - 2012**

**Model Question Paper**

**VLSI DESIGN**

**Time:3 hrs max.marks : 100**

**PART-A**

Answer all questions. Each question carries 2 marks

2. State Fick’s law of diffusion.

3. A proximity printer operates with a 20μm mask to wafer gap and a wavelength of 250nm.

Find the minimum linewidth that can be obtained.

4. Define threshold voltage. Write the expression for threshold voltage under body bias

condition.

5. Explain channel length modulation. How is it incorporated in the current relationship of

MOS transistor?

6. Explain the junction capacitances associated with a MOSFET.

7. Illustrate a case of progressive transistor sizing to reduce propagation delay in CMOS

design.

8. Pseudo NMOS is a ratioed logic. Justify.

9. How the test patterns are minimized by modeling the circuit with independent logic

paths.

10. Consider a DRAM cell with Cs=50fF and Cbit=8Cs. Assuming a maximum voltage of

Vs=Vmax=2.5V on the storage capacitor, what is the final voltage during a logic 1 read

operation. (2x10 = 20 marks)

**PART B**

**Answer one full question from each module**

**MODULE I**

b) With neat sketches, explain Czochralsky method of wafer processing. List the

advantages and disadvantages of the process. (8)

OR

12. a) Derive Deal Grove model of oxidation. (10)

b) With the aid of neat diagram explain ion implantation process (10)

**MODULE II**

13. a)Derive the current relationship in a MOS transistor in deep triode and saturation

regions. (12)b) Define flatband voltage. Obtain an expression for threshold voltage of a MOS

transistor in terms of flat band voltage and body effect parameter. (8)

OR

14. Elucidate the short channel effects in MOS with neat diagrams. (20)

**MODULE III**

inverter. (20)

OR

16. a) Design a 14 bit square root carry select adder. Calculate the worst case delay. (10)

b) Explain the function of a 4 bit multiplier with block diagram. Write down the

expression for maximum delay. (10)

**MODULE IV**

are as follows 1011, 1110, 1101 and 1001. (10)

b) Design a regular PLA structure using MOS to implement the function

Y1= X4, Y2=X1X3+X2 X4 and Y3=X1X2+X2X3 (10)

OR

18. a) Explain the working of a 1 transistor DRAM cell with the help of timing diagrams.(10)

b) Explain the methods of design for testability

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