VLSI Interview Questions
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Need to convert this VHDL code into VLSI verilog code? LIBRARY IEEE; USE IEEE.STD_LOGIC_1164.ALL; ----using all functions of specific package--- ENTITY tollbooth2 IS PORT (Clock,car_s,RE : IN STD_LOGIC; coin_s : IN STD_LOGIC_VECTOR(1 DOWNTO 0); r_light,g_light,alarm : OUT STD_LOGIC); END tollbooth2; ARCHITECTURE Behav OF tollbooth2 IS TYPE state_type IS (NO_CAR,GOTZERO,GOTFIV,GOTTEN,GOTFIF,GOTTWEN,CAR_PAID,CHEATE D); ------GOTZERO = PAID $0.00--------- ------GOTFIV = PAID $0.05---------- ------GOTTEN = PAID $0.10---------- ------GOTFIF = PAID $0.15---------- ------GOTTWEN = PAID $0.20--------- SIGNAL present_state,next_state : state_type; BEGIN -----Next state is identified using present state,car & coin sensors------ PROCESS(present_state,car_s,coin_s) BEGIN CASE present_state IS WHEN NO_CAR => IF (car_s = '1') THEN next_state <= GOTZERO; ELSE next_state <= NO_CAR; END IF; WHEN GOTZERO => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTZERO; ELSIF (coin_s = "01") THEN next_state <= GOTFIV; ELSIF (coin_s ="10") THEN next_state <= GOTTEN; END IF; WHEN GOTFIV=> IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTFIV; ELSIF (coin_s = "01") THEN next_state <= GOTTEN; ELSIF (coin_s <= "10") THEN next_state <= GOTFIV; END IF; WHEN GOTTEN => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s ="00") THEN next_state <= GOTTEN; ELSIF (coin_s="01") THEN next_state <= GOTFIV; ELSIF (coin_s="10") THEN next_state <= GOTTWEN; END IF; WHEN GOTFIF => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTFIF; ELSIF (coin_s ="01") THEN next_state <= GOTTWEN; ELSIF (coin_s = "10") THEN next_state <= GOTTWEN; END IF; WHEN GOTTWEN => next_state <= CAR_PAID; WHEN CAR_PAID => IF (car_s = '0') THEN next_state <= NO_CAR; ELSE next_state<= CAR_PAID; END IF; WHEN CHEATED => IF (car_s = '1') THEN next_state <= GOTZERO; ELSE next_state <= CHEATED; END IF; END CASE; END PROCESS;-----End of Process 1 -------PROCESS 2 for STATE REGISTER CLOCKING-------- PROCESS(Clock,RE) BEGIN IF RE = '1' THEN present_state <= GOTZERO; ----When the clock changes from low to high,the state of the system ----stored in next_state becomes the present state----- ELSIF Clock'EVENT AND Clock ='1' THEN present_state <= next_state; END IF; END PROCESS;-----End of Process 2------- --------------------------------------------------------- -----Conditional signal assignment statements---------- r_light <= '0' WHEN present_state = CAR_PAID ELSE '1'; g_light <= '1' WHEN present_state = CAR_PAID ELSE '0'; alarm <= '1' WHEN present_state = CHEATED ELSE '0'; END Behav;

4727

what is the difference between the testing and verification?

Intel,

1 5885

What is the mealy and moore machine's state diagram that can detect 3 consecutive heads of 3 coins ?

2 7124

Calculate rise delay of a 3-input NAND gate driving a 3-input NOR gate through a 6mm long and 0.45m wide metal wire with sheet resistance R = 0.065 / and Cpermicron= 0.25 fF/m. The resistance and capacitance of the unit NMOS are 6.5k and 2.5fF. Use a 3 segment -model for the wire. Consider PMOS and NMOS size of reference inverter as 2 and 1 respectively. Use appropriate sizing for the NAND and NOR gate.

3379

verify nmos passes good logic 0 and passes bad logic 1.also verify that pmos passes good logic 1 and passes bad logic 0.

Cosmic Circuits, HP,

2 30668

Help with VHDL programming. Write a VHDL code for a D-Latch with clear input ?? (Hint: Set up a “Process” with appropriate sensitivity list to get the desired D-Latch with Clr working.) Inputs AND OUTPUTS: entity Lab4b is Port ( Clr, Clk, D : in STD_LOGIC; Q : out STD_LOGIC); end Lab4b;

1050

Design an 8 is to 3 encoder using 4 is to encoder?

Intel,

861

Explain Basic Stuff related to Perl?

Intel,

604

Explain Cross section of a PMOS transistor?

Intel,

739

What are the Advantages and disadvantages of Mealy and Moore?

Intel,

698

Explain the working of Insights of an inverter ?

Intel,

695

Explain Process technology? What package was used and how did you model the package/system? What parasitic effects were considered?

Intel,

605

If the current through the poly is 20nA and the contact can take a max current of 10nA how would u overcome the problem?

Intel,

688

Explain about 6-T XOR gate?

Intel,

729

Explain Cross section of an NMOS transistor?

Intel,

563


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Un-Answered Questions { VLSI }

Explain the Charge Sharing problem while sampling data from a Bus?

4170


In vlsi chip 1000s of transistors are dropped, specifically categorized. Which method is used to achieve this & how it is done practically?

573


What is the function of tie-high and tie-low cells?

614


What is the difference between synchronous and asynchronous reset?

613


what is a sequential circuit?

600






Explain the three regions of operation of a mosfet.

620


Explain how Verilog is different to normal programming language?

675


What is threshold voltage?

677


How do you size NMOS and PMOS transistors to increase the threshold voltage?

2531


What transistor level design tools are you proficient with? What types of designs were they used on?

2867


In a SRAM layout, which metal layers would you prefer for Word Lines and Bit Lines? Why?

3587


Calculate rise delay of a 3-input NAND gate driving a 3-input NOR gate through a 6mm long and 0.45m wide metal wire with sheet resistance R = 0.065 / and Cpermicron= 0.25 fF/m. The resistance and capacitance of the unit NMOS are 6.5k and 2.5fF. Use a 3 segment -model for the wire. Consider PMOS and NMOS size of reference inverter as 2 and 1 respectively. Use appropriate sizing for the NAND and NOR gate.

3379


What is the difference between the mealy and moore state machine?

583


What types of I/O have you designed? What were their size? Speed? Configuration? Voltage requirements?

1999


Tell me how MOSFET works.

1928