Important Short Questions and Answers: VLSI Design - CMOS Testing

1. Give the basic nMOS PLA structure.

The basic PLA structure consists of an AND plane driving an OR plane. The terminology corresponds to a sum of products (SOP) realization of the desired function. The SOP realization converts directly into a NAND-NAND implementation. When a product of sums (POS) realization is desired, it can be implemented in OR-AND or NOR-NOR logic. In either case, the first array is referred to as the AND plane, and the second array as the OR plane. The line connecting the AND plane to the OR plane are called the product lines.

2. What do you mean by CMOS PLA.

The basic CMOS PLA is obtained by providing a well and replacing the pull-up devices in the NAND-NAND array or in the NOR- NOR array with enhancement mode pMOS devices. The CMOS array can be precharged or not, and can be clocked 2 AND plane OR plane Register Register In puts Outputs 1 with the same two-phase clocking scheme as used for the MOS PLA. CMOS PLA design offers many more varieties of layout than does nMOS.

3. Define finite state machine.

When feedback is added to the AND OR PLA structure, the PLA becomes a finite state machine (FSM). An FSM can be designed as a Mealy Machine or a Moore Machine. The Mealy machine has outputs, which may change with input changes in an asynchronous manner and cause erroneous behavior. Hence, the Mealy machine should be avoided whenever possible. The Moore machine has outputs which depend upon and change only with state changes, since all the outputs of the Boolean-logic block go through a state register, and are synchronously clocked.

4. What are the importance of the PLA/FSM in VLSI?

(i)       Regularity : It has a standard, easily expandable layout.

(ii)    Convenience : Little design effort is required.

(iii)  Compacted : It is efficient for small circuits.

(iv)  Modularity : It makes it possible to design hierarchical PLAs and FSMs into large sequential systems.

(v)    Suitability to being computer generated.

5. Give the structure of a CPLD.

A CPLD comprises multiple circuit blocks on a single chip, with internal wiring resources to connect the circuit blocks. Each circuit block is similar to a PLA or a PAL.It includes four PAL like blocks that are connected to a set of interconnection wires. Each PAL like block is also connected to a sub circuit labeled I/O block, which is attached to a number of the chip’s input and output pins

6. Give the CPLD packages available.

a. PLCC package: The PLCC package has pins that “wrap around” the edges of the chipon all four of its sides. The socket that houses the PLCC is attached by solder to the circuit board, and the PLCC is held in the socket by friction.

b. quad flat pack package: The QFP package has pins on all four sides, and they extendoutward from the package, with a downward-wiring

shape. The QFP’s pins are much thinner than those on a PLCC, which means that the package can support a larger number of pins; QFPs are available with more than 200 pins.

7. Give the structure of MAX 7000 CPLD.

8. What is meant by FPGA?

A field programmable gate array (FPGA) is a programmable logic device that supports implementation of relatively large logic circuits. FPGAs can be used to implement a logic circuit with more than 20,000 gates whereas a CPLD can implement circuits of upto about 20,000 equivalent gates. FPGAs are quite different from CPLDs because FPGAs do not contain AND or OR planes. Instead, they provide logic blocks for implementation of the required functions.

9. Give the general structure of FPGA.

10.   What are the different commercial FPGA products?

Manufacturer FPGA products www Locator

Actel Act 1,2 and 3,MX,SX www.actel.com

Altera FLEX6000,8000 and 10k APEX 20kwww.altera.com

Atmel AT6000, AT40k www.ateml.com

Lucent ORCA 1,2 and 3 www.lucent.com

QuickLogic pASIC 1,2 and 3 www.quicklogic.com

Vantis VFI www.vantis.com

Xilinx XC3000,XC4000,XC5200,Virtexwww.xilinx.com

11.   What are the types of reprogrammable GA?

Ad-hoc Array and Structured Array are the two types of Reprogrammable Gate Array.

12.   What is the type’s o FPLA?

I.PROM [Programmed Read-Only Memory]

PAL [Programmed Array Logic]

13.   What are the applications of PAL?

i.          Control logic application

ii.        Input/Output

iii.     Data-path logic

15. What is finite state machine (FSM)?

When feedback is added to AND-OR PLA structure, then it becomes FSM.

16.   What are the characteristics of PLA/FSM?

i.          Regularity

ii.        Modularity

iii.     Suitability

iv.     Efficiency

17.   What is CLB?

CLB means Configurable Logic Block.

18. Define mealy machine?

In mealy machine, output may change with the change in the input asynchronously.

19. Define moore machine?

In moore machine, output can be changed when state is changed.

20. What is HDL?

VHSIC Hardware description Language.

21. What is VHSIC?

Very High Sped Integrated Circuits.

22.   What are the various operators in VHDL?

i.          Logical operators

ii.        Relational operators

iii.     Shift operators

iv.     Adding operators

v.        Multiplying operators

23.   What are the data types available in VHDL?

i.          Scalar type

ii.        Composite type

iii.     Access type

iv.     File type

24.   What are the types of subprograms?

Functions and Procedures are types of subprograms.

25. What is the use of actual?

Actual in a subprogram call is used to pass the values from and to a subprogram.