VLSI Design - Dec 2012

Electronics & Telecomm. (Semester 6)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1(a) Write equation and draw the profile for diffusion from constant source and diffusion from instantaneous source. (5 marks) 1(b) Draw VTC of three CMOS inverter circuits (on same Plot) with K_R=1, K_R<1 and K_R>1. (5 marks) 1(c) Draw the profile indicating sub-threshold conduction in MOSFET and show ideal value of sub-threshold slope on it. (5 marks) 1(d) A microprocessor was fabricated in a 0.25μm technology and was able to operate at 1 MHz, consuming 10 watt using a 2.5v power supply.
i. Using fixed voltage scaling, what will the speed and power consumption of the same processor be if scaled to 0.1 μm technology?
ii. If the supply voltage on the 0.1 μm part were scaled to 1.0 v, what will the power consumption and speed be?
(5 marks) 2(a) With device cross section and band diagram, discuss accumulation, depletion and inversion in MOS capacitor. (10 marks) 2(b) Find the depletion layer with X_d the depletion region charge Q_BO, the threshold voltage with no source to body voltage V_Th0 and the body factor Y of a device with the following physical parameters :
T_OX=400^oA, N_A=1.5x10¹⁶ cm^-3
N_D=10¹⁸ cm^-3
Nss= (density of singly charged positive surface ions)=5 x 10¹⁰ cm^-2 (10 marks) 3(a) What is the necessity of design rules? Specify lambda based design rules? Draw CMOS inverter for (W/L)_p=3(W/L)_n with design rules(indicate scale in terms of lambda on layout). (10 marks) 3(b) What is latch-up in CMOS ? How to prevent latch-up in CMOS? (10 marks) 4(a) Calculate noise margin for the CMOS inverter with the following specifications V_DD = 5v,V_T0,n=1.0 v, V_T0,p=-1.2 v, K_n=100 μA/V₂, Kp=100 μA/V₂. (10 marks) 4(b) Derive an expression for calculation of VOL and VIL for CMOS inverter. (10 marks) 5(a) Design the circuit and draw layout for the function $$ Y={(D+E+A).(B+C)} $$
using CMOS logic. Also find equivalent CMOS inverter Circuit for Simultaneous switching of all inputs assuming that (W/L)_p = 15,for all PMOS and (W/L)_n =10 for all NMOS transistors. (10 marks) 5(b) Draw cross section diagrams and their corresponding masks for all important masking steps required for fabrication of CMOS inverter with n-well process. (10 marks) 6(a) Implement a 2:1 multiplexer circuit using CMOS transmission gates. Write a Verilog module for the circuit at switch level of abstraction. Write a test bench to check the functionality of the circuit. (10 marks)

Write short notes on any four.

7(a) Y-chart representation for VLSI design. (5 marks) 7(b) Dry and wet oxidation process. (5 marks) 7(c) Transistor sizing. (5 marks) 7(d) Butting and buried contact. (5 marks) 7(e) Short channel effects. (5 marks) b(b) Implement CMOS 1-bit full adder and write gate level verilog HDL module for it. (10 marks)