Gate Level Diagrams of Latch

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DIGITAL ELECTRONICS COURSE, SPRING 2008 1

  Abstract—This report consider logic of some gates like NOR,

NAND, XOR, INVERTER (NOT), MUX 2 to 1 and also D-

LATCH and D-FLIPFLOP constructed from above gates.

I.  INTRODUCTION 

ost important subject in of digital electronic components

is that the component work true functionally and other

parameters are in lowers degree of importance.Here we’ll

simulate functionally some logical components with CMOS

technology in VERILOG language.

We’ll consider NOR, NAND, XOR, INVERTER (NOT),MUX 2 to 1 in A section and D-LATCH and D-FLIPFLOP

in B section and results will be available in appendix part.

II.  SOME NOTES 

 A.  Sections

NOR Logic Gate:

In boolean logic, logical nor or  joint denial is a truth-

functional operator which produces a result that is the inverse

of logical or. That is, a sentence of the form (A NOR B) is true

precisely when neither A nor B is true.

Fig. 1. NOR symbol [1].

XOR Logic gate

The XOR gate (sometimes EOR gate) is a digital logic

gate that implements exclusive disjunction. A HIGH output (1)

results if one, and only one, of the inputs to the gate is HIGH

(1). If both inputs are LOW (0) or both are HIGH (1), a LOW

output (0) results [1].

Fig. 2. XOR symbol [1].

NAND Logic gate:

The NAND operation is a logical operation on two logical

values, typically the values of two propositions, that produces

a value of  false if and only if both of its operands are true. In

Submitted May 3, 2008.

other words, it produces a value of  true if and only if at leastone of its operands is false.

Fig. 3. NAND symbol [1].

INVERTER:

In digital logic, an inverter is a logic gate which inverts the

digital signal driven on its input. It is also called NOT gate [1].

Fig. 4. NOT symbol [1].

MUX 2 to 1:

In electronics, a multiplexer is a device that performs

multiplexing; it selects one of many analog or digital input

signals and outputs that into a single line [1].

Fig. 5. MUX 2 to 1 symbol [1].

 B.  Section

D-LATCH:

It is also known as transparent latch, data latch, or simply

gated latch. It has a data input and an enable signal

(sometimes named clock , or control). The word transparent  

comes from the fact that, when the enable input is on, the

signal would propagate directly through the circuit, from the

input D to the output Q.

Fig. 6. D-LATCH symbol [1].

Switch Level Simulation

Mohammad Reza Najafi 810184285

M

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 Fig. 7. D-LATCH structure [1].

Master-slave D flip-flop:

The Q output always takes on the state of the D input at the

moment of a rising clock edge, and never at any other time.[4]

It is called the D flip-flop for this reason, since the output

takes the value of the D input or Data input, and Delays it by

one clock count. The D flip-flop can be interpreted as a

primitive memory cell, zero-order hold, or delay line.

Fig. 8. D-FlipFlop symbol [1].

Fig. 9. Master-slave D flip-flop [1].

Edge-triggered D flip-flop:

Fig. 10. Edge-triggered D flip-flop [1].

III.  METHODOLOGY 

Basic of this report is on gate level architecture but here is

some transistor designs too. In prior reports we worked on

transistor level with more depth.

IV.  RESULTS 

NOR gate result:

Input A Input B Output

0 0 1

0 1 0

1 0 0

1 1 0Fig. 11. Truth table of NOR [1].

Fig. 12.NOR architecture [3].

NAND gate result:

Fig. 13. Truth table of NAND [1].

Fig. 14. NAND architecture [1].

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NOT gate result:

Fig. 15. Truth table of NOT [1].

Fig. 16. NOT architecture [1].

XOR gate result:

Fig. 17. Truth table of XOR [1].

MUX gate result:

Input c Output

0 Input d0

1 Input d1

Fig. 18. Truth table of MUX 2 to 1 [1].

Fig. 19. NAND architecture [1].

D-latch result:

Fig. 20. Truth table of D-LATCH [1].

D flip-flop result:

Fig. 21. Truth table of D flip-flop [1].

V.  SUMMARY AND CONCLUSION 

The basic concept from this report was design of logic

circuit independent of electronic challenges. We should

remember in stages of design a component put the complexity

of every stage on its place, in this way there will be a clear

steps for design.

REFERENCES [1]  http://en.wikipedia.org.

[2]  www.sccs.swarthmore.edu/.../engin/e77vlsi/lab3/  

[3]  www.cs.uiowa.edu/~jones/assem/notes/08arith.shtml 

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APPENDIX