Chapter Four Active Components & Integrated Circuits

Introduction Basic solid-state electronic devices are described, and some idea of the powerful uses of digital electronics is given.

Active Electrical Components Background  Passive vs. Active electrical components.  Active: require an external source of power in order to work.  Vacuum Tubes are an example of the early types of active components.  Many electronic functions were possible using tubes, but there were serious limitations, these are:

Vacuum tubes  Tubes require high voltages to operate (250 – 300V).  They dissipate large amounts of heat.  They wear themselves out and need to be periodically replaced.  They were expensive to produce and fragile.  Tubes still find their way in certain applications (microtubes in the military).

Transistors These replaced vacuum tubes in many applications, because:  They are small in size.  They require little power to operate.  They are mechanically very rugged.  They are operated on low voltages (12V or less).  They are extremely simple in structure.

What is a transistor?  A piece of semiconductor material chemically treated to have some desired electrical properties.  Semiconducting materials conduct electricity better than insulators but much poorer than conductors.  Typically it has three terminals (BJT: Emitter, Base, Collector; MOS: Drain, Gate, Source).  Current amplifier: allows small (base) current to control much larger current (collector).

What is a transistor?  Can be used as ON/OFF Switch (Electronic switch)  In order to operate the transistor it should be connected in a circuit with the proper components Bipolar junction transistor MOS transistor

Integrated Circuits  Transistors and their associated circuits are manufactured on the same piece of semiconductor material (chip or IC)  Microprocessors contain millions of transistors are fabricated on a single chip due to the development in IC technology.  ICs are used in both digital and analog applications, there are thousands of different chips in the market.  The operating parameters & schematic diagrams are provided in Data books put out by the manufacturing companies (TTL, Synertek, Intel, Motorola).

Digital Electronics Electronics can be divided into two areas:  Digital: based on the binary number system and the output can assume only two values (ON=1=+5V DC, OFF=0=0V DC).  Analog (amplifier output might be any voltage from say -5V to +5V).  Digital electronics is the basis of operation of computers.

The Binary Number System  Numbers are represented in computers using the binary number system.  The reason for using the binary system is that the transistors internal to the computer chip act as simple switches.  The decimal system can be converted to the binary system so the binary system does not limit the capability of a computer to make calculations.

Logic Families  Families differ in: the way the transistors are connected together, switching speeds, power consumption, operating voltage levels, and other electrical characteristics.  TTL: Transistor-Transistor Logic  CMOS: Complementary Metal Oxide Semiconductor  ECL: Emitter Coupled Logic  Applications determine which family to use.

Simple logic functions Inverter.  Symbol  Truth table B A BA 10 01

Simple logic functions AND Gate  Symbol  Truth table CBA

Simple logic functions  OR Gate  Symbol  Truth table CBA

Example 15 cents toll. Only nickels (5 cents) and dimes (10 cents) can be deposited. N= number of nickels deposited D= number of dimes deposited G= command to raise gate G=0 if 15 cents is not deposited G=1 if 15 cents is deposited

Circuit Implementation G=n1n2+n1d1, n1=1Nickel, n2=2Nickels,d=1 Dime

The truth table gd1n2n