1.0 INTRODUCTION Characteristics of the active electronic components that determine the internal construction and operation of electronic circuitry

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1.0 INTRODUCTION

Characteristics of the active electronic components that determine the internal construction and operation of electronic circuitry of a logic gate.

Y = 0

+5V

A = 1 10k

1k

UNIT 1 – CONSTRUCTION OF LOGIC GATES

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1.1 Types of logic gatesNOTANDORXOR


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1.1 Types of logic gates (cont.)NANDNORXOR


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1.2 Diode as a voltage controlled switchp-n junction componentTwo type material: p-type & n-typeOperation: forward biased & reverse biasedKnee voltage: 0.7V (Si) n 0.3V (Ge)


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1.2 Diode as a voltage controlled switch (cont.)

Operation 0V – knee voltage

Small current’s flow Beyond knee voltage Negative voltage

Leakage current More negative voltage

Zener voltage


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1.2 Diode as a voltage controlled switch (cont.)Forward biased vs. reverse biased


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1.2 Diode as a voltage controlled switch (cont.)Diode works as a logic ON/OFF switch


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1.2 Diode as a voltage controlled switch (cont.)Voltage range of logic level for TTL digital IC


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1.2 Diode as a voltage controlled switch (cont.)Simple 2-input OR gate


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1.3 Transistor as a voltage controlled switchp-n junction componentTwo type: PNP & NPN


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1.3 Transistor as a voltage controlled switch (cont.)B-E junction as switch


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1.3 Transistor as a voltage controlled switch (cont.)Not gate


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1.4 Diode controls switching speedSpeed limitation when switching diode from ON to

OFF and vice versa Minority-carrier density


Reverse biased (OFF)

Forward biased (ON)

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1.5 Switching timeRise and fall time

Time taken for a signal to go from LOW to HIGH and vice versa.

Tr and Tf


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1.5 Switching time (cont.)Storage time


(a)Circuit(b)Input waveform(c) Diode current(d)Diode voltage(e)Minority carrier

(c)

(d)

(e)

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1.5 Switching time (cont.)Propagation delay

Time interval between the application of an input pulse and the occurrence of the resulting output pulse.

Cumulative time delay when gates are cascaded.

Limits the max freq at which a gate can operate.For propagation delay of 40ns; max freq operation is

25MHzFor propagation delay of 25ns; max freq operation

is ???


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1.5 Switching time (cont.)Propagation delay (cont.)

Two types: TPLH

- delay time from

logic 0 to logic 1.TPHL - delay time from

logic 1 to logic 0.Measured at 50% on rising

and falling edges of the input and output.

Total propagation delay?


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1.6 TTL familyTTL Series:

74 Series – First line of standard TTL ICs 74L Series – low-power version 74H Series - high-speed version 74S Series – Schottky TTL, reduce storage time delay 74LS Series – Low-Power Schottky TTL 74AS Series – Advanced Schottky TTL 74ALS Series – Advanced Low-Power Schottky TTL 74F Series – Fast TTL


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1.6 TTL family (cont.)TTL NAND Gate OperationSchottky TTL 74SLow-Power Schottky TTLAdvanced Schottky TTL,

74AS Series (AS-TTL)Current-Sourcing and

Current-Sinking ActionTotem Pole TTLTristate (Three-state) TTL

UNIT 1 – CONSTRUCTION OF LOGIC GATESTUGASAN

1 :PETA

MINDA.TARIKH AKHIR

HANTAR : 12 FEB 2010NO

PLAGIARSM!!!

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1.7 CMOS familyCMOS INVERTER GATE


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1.7 CMOS familyCMOS NAND GATE


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1.7 CMOS familyCMOS TRANSMISSION GATE

Pass signal in both direction. Useful for digital and analog application.


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1.8 Comparison of CMOS and TTL


TTL CMOS

Noise Margin 0.4V (standard) 1.5V (30% of VDD)Typically 45%

Power dissipation

mW nW

Propagation delay

TPLH is 11ns – 22nsTPHL is 7ns – 15 ns

30 - 50ns

Fan-in Depends on number of unit loads it can

handle. Usually 3.

Depends on number of unit loads it can

handle

Fan-out Typically 10 Typically 50

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1.9 Interfacing TTL and CMOS ICsConnecting the output(s) of one circuit of system to

the input(s) of another circuit that has different electrical characteristics.

Why? Utilize strong points of different logic families. Ex: 74AS used in parts need for highest frequency

741 used in slower parts NMOS for LSI parts of the system.

Two things to consider: Voltage Current

Where? – device data sheets


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1.9 Interfacing TTL and CMOS ICs (cont.)CMOS driving TTL

Input current for CMOS arelow compared to output current TTL no prob.

Input voltage for CMOS arehigher than output voltage

TTL pull-up resistor.


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1.0 INTRODUCTION Characteristics of the active electronic components that determine the internal construction and operation of electronic circuitry