Concepts of Engineering and Technology Copyright © Texas Education Agency, All rights reserved.

Basic Electricity and Electronics Module Two Basic Electronics Copyright © Texas Education Agency, All rights reserved.

Transistor Basics A semiconductor device A semiconductor device Conductivity is controlled by current Conductivity is controlled by current An example of a voltage controlled device is a MOSFET An example of a voltage controlled device is a MOSFET Made from a silicon crystal Made from a silicon crystal Doped with impurities to allow conductivity to be controlled Doped with impurities to allow conductivity to be controlled N and P type doping use different conducting particles (electrons and holes) N and P type doping use different conducting particles (electrons and holes) Copyright © Texas Education Agency, All rights reserved.

Silicon Crystal Four valence electrons per atom Four valence electrons per atom Bonds with four more silicon atoms to create a stable molecule Bonds with four more silicon atoms to create a stable molecule Creates a solid three- dimensional structure Creates a solid three- dimensional structure Si Copyright © Texas Education Agency, All rights reserved.

The diamond unit cell is the basic crystal building block. An atom covalent bonds to four others, which in turn bond to four others, and so on. Copyright © Texas Education Agency, All rights reserved.

N-type Doping Adds arsenic, keeps the stable crystal structure Adds arsenic, keeps the stable crystal structure Has an extra electron Has an extra electron Negative charge carrier Negative charge carrier The extra electron becomes free to conduct current The extra electron becomes free to conduct current More arsenic atoms gives more conductivity More arsenic atoms gives more conductivity Si As Si Copyright © Texas Education Agency, All rights reserved.

P-type Doping Gallium has only three electrons Gallium has only three electrons Still keeps the stable crystal structure Still keeps the stable crystal structure Creates a hole where an electron is needed for a bond Creates a hole where an electron is needed for a bond The hole is a positive current carrying particle The hole is a positive current carrying particle Si Ga Si Copyright © Texas Education Agency, All rights reserved.

The simplest semiconductor device is a diode, which is half P material and half N material The simplest semiconductor device is a diode, which is half P material and half N material At the junction between the two regions, electrons from N combine with holes from P At the junction between the two regions, electrons from N combine with holes from P This creates a charged depletion region This creates a charged depletion region Copyright © Texas Education Agency, All rights reserved.

N P P N

Reverse bias creates a wider depletion region Reverse bias creates a wider depletion region No current flow (No Conduction) No current flow (No Conduction) Forward bias has opposite polarity, and when greater than.7 V eliminates the depletion region, allowing current to flow freely Forward bias has opposite polarity, and when greater than.7 V eliminates the depletion region, allowing current to flow freely Copyright © Texas Education Agency, All rights reserved.

A Transistor A transistor has 3 layers of semiconductor A transistor has 3 layers of semiconductor NPN or PNP NPN or PNP The regions are called the emitter, base, and collector The regions are called the emitter, base, and collector The key to how it works is that the base is THIN and LIGHTLY DOPED The key to how it works is that the base is THIN and LIGHTLY DOPED N N P Emitter Base Collector Copyright © Texas Education Agency, All rights reserved.

Turning a Transistor ON It takes two connections to the power supply It takes two connections to the power supply Forward Bias Reverse Bias Emitter (N)Collector (N) Base (P) Copyright © Texas Education Agency, All rights reserved.

The emitter-base forward bias overcomes the depletion region of the reverse biased base-collector junction, creating an electron flood that goes through the base and spills over into the collector. The emitter-base forward bias overcomes the depletion region of the reverse biased base-collector junction, creating an electron flood that goes through the base and spills over into the collector. Forward Bias Reverse Bias Copyright © Texas Education Agency, All rights reserved.

Current flows from Emitter to Collector (diffusion), negative to positive, while a smaller current flows from Emitter to Base (recombination). Current flows from Emitter to Collector (diffusion), negative to positive, while a smaller current flows from Emitter to Base (recombination). Forward Bias Reverse Bias Copyright © Texas Education Agency, All rights reserved.

I B = V BB -.7 / R B I B = V BB -.7 / R B I C = V CC (- V CE ) / R C I C = V CC (- V CE ) / R C I E = I C + I B I B << I C I E = I C + I B I B << I C Here is the same circuit, shown using schematic symbols: Here is the same circuit, shown using schematic symbols: ICIC IBIB RBRB RCRC V BB V CC Copyright © Texas Education Agency, All rights reserved.

Here is the same circuit, shown slightly different: Here is the same circuit, shown slightly different: This is a standard transistor switch This is a standard transistor switch Used in computers and other electronic devices Used in computers and other electronic devices Signal In Power Supply (V CC ) Output RCRC Copyright © Texas Education Agency, All rights reserved.

Signal In = 0 Transistor Off V CC V O = V CC Signal In = 1 Transistor On V O = 0 V CC The two states of a switch – on and off This circuit is called an inverter: When the input is one the output is zero, when the input is zero the output is one Copyright © Texas Education Agency, All rights reserved.

Here is a better circuit: This circuit is called a Totem Pole, and produces better 1’s and 0’s Signal In Voltage Out V CC T1T1 T2T2 T3T3 Copyright © Texas Education Agency, All rights reserved.

The Truth Table A tool used to understand binary logic A tool used to understand binary logic Shows every possible input Shows every possible input Shows the output for each input Shows the output for each input InputAOutputX 0110 What circuit does this represent? An Inverter! Copyright © Texas Education Agency, All rights reserved.

Binary Logic A set of rules that applies to a digital circuit A set of rules that applies to a digital circuit Logic defines the way the circuit will act Logic defines the way the circuit will act Given a set of inputs, the output will produce a specific outcome Given a set of inputs, the output will produce a specific outcome Always acts exactly the same way Always acts exactly the same way We use a truth table to help us define how we want the logic circuit to act We use a truth table to help us define how we want the logic circuit to act Copyright © Texas Education Agency, All rights reserved.

We build the circuit to perform the logic We build the circuit to perform the logic Always does the same thing with the same inputs Always does the same thing with the same inputs We must define each possible input or input combination We must define each possible input or input combination We have to define exactly what output we want for a particular input We have to define exactly what output we want for a particular input Lets look at an example Lets look at an example Copyright © Texas Education Agency, All rights reserved.

Two Bit Binary Adder Adds two binary bits Adds two binary bits Binary can only have two values, 0 and 1 Binary can only have two values, 0 and = 2, which is not valid binary = 2, which is not valid binary Carry 1 Copyright © Texas Education Agency, All rights reserved.

Truth Table for Binary Addition We have two inputs We have two inputs We generate two outputs We generate two outputs InputAInputBOutput Σ (sum) Carry C o How do we do this? First, we have to understand binary! Copyright © Texas Education Agency, All rights reserved.

Binary Numbers Binary only has two values, 0 and 1 Binary only has two values, 0 and 1 The decimal number system has ten values, 0 through 9 The decimal number system has ten values, 0 through 9 How do we count higher than 9 in decimal? How do we count higher than 9 in decimal? We add decimal places We add decimal places How do we count higher than one in binary? How do we count higher than one in binary? We add binary bits We add binary bits Copyright © Texas Education Agency, All rights reserved.

Decimal places are each multiples of ten Decimal places are each multiples of ten Binary bits are each multiples of two Binary bits are each multiples of two 10 0 = 1 (ones) 10 1 = 10 (tens) 10 2 = 100 (hundreds) 10 3 = 1000 (thousands) 2 0 = 1 (ones) 2 1 = 2 (twos) 2 2 = 4 (fours) 2 3 = 8 (eights) Copyright © Texas Education Agency, All rights reserved.

Reading Binary Numbers A decimal number like 9437 reads: A decimal number like 9437 reads: Nine thousand, four hundred, thirty, seven. Nine thousand, four hundred, thirty, seven. The binary number 1011 has values: The binary number 1011 has values: One eight, no fours, one two, one one. One eight, no fours, one two, one one has a decimal value of 11 (eleven) 1011 has a decimal value of 11 (eleven) How do read the binary 1111? How do read the binary 1111? Decimal Fifteen Decimal Fifteen How do you count higher than fifteen? How do you count higher than fifteen? Add more binary bits (decimal places) Add more binary bits (decimal places) Copyright © Texas Education Agency, All rights reserved.

Binary Bit Values To count up to 1000 (decimal) you need ten binary bits To count up to 1000 (decimal) you need ten binary bits To count higher, you need more binary bits To count higher, you need more binary bits Bit number Decimal value Copyright © Texas Education Agency, All rights reserved.

Binary to Decimal The binary number: The binary number: Has a decimal value: Has a decimal value: This process involves addition This process involves addition = Copyright © Texas Education Agency, All rights reserved.

Decimal to Binary Decimal to binary is a little harder Decimal to binary is a little harder The process involves subtraction The process involves subtraction For example, consider the decimal number: For example, consider the decimal number: Go back to the binary count: Go back to the binary count: Copyright © Texas Education Agency, All rights reserved.

equals equals equals equals equals equals Copyright © Texas Education Agency, All rights reserved.

Binary Count The easiest way to show all possible input values is a binary count The easiest way to show all possible input values is a binary count Keep adding one to the previous value Keep adding one to the previous value Everyone should be able to count in binary Everyone should be able to count in binary D = 1, C = 2, B = 4, A = 8 D = 1, C = 2, B = 4, A = 8 ABCDDeciHex ABCDEF Copyright © Texas Education Agency, All rights reserved.

ABCDDeciHex ABCDEF What happens if you have to keep counting? FFF Copyright © Texas Education Agency, All rights reserved.

Hexadecimal Computers and electronic devices communicate in binary Computers and electronic devices communicate in binary All those 1’s and 0’s are confusing All those 1’s and 0’s are confusing Is there an easy way to tell what the binary values are? Is there an easy way to tell what the binary values are? YES – it’s called Hexadecimal YES – it’s called Hexadecimal Hexadecimal is a base 16 number system Hexadecimal is a base 16 number system Hexadecimal exactly represents 4 binary bits Hexadecimal exactly represents 4 binary bits Copyright © Texas Education Agency, All rights reserved.

Using Hex To create hex, start with bit 0 and group the binary number into groups of 4 To create hex, start with bit 0 and group the binary number into groups of 4 For example, our decimal 601 would be: For example, our decimal 601 would be: or = = 2BDh Copyright © Texas Education Agency, All rights reserved.

Using Hex To create hex, start with bit 0 and group the binary number into groups of 4 To create hex, start with bit 0 and group the binary number into groups of 4 For example, our decimal 601 would be: For example, our decimal 601 would be: or = = 2BDh Copyright © Texas Education Agency, All rights reserved.

There are several ways to indicate the hex number system: Use the subscript 16 Use a lower case h right after the number Use a dollar sign, e.g. $2BD Hex is a shorthand way of representing binary The hex number always exactly represents 4 binary bits Copyright © Texas Education Agency, All rights reserved.

Back to Addition Add 2 4-bit binary numbers: Add 2 4-bit binary numbers: = 2, which is written 10 in binary = 2, which is written 10 in binary This 1 is a carry into the next bit Copyright © Texas Education Agency, All rights reserved.

2 Bit Binary Adder Lets go back to the truth table for a binary adder: Lets go back to the truth table for a binary adder: InputAInputBOutput Σ (sum) Carry C o Now that we understand binary, we can figure out how to do this! Copyright © Texas Education Agency, All rights reserved.

We Use Transistors All logic uses transistors All logic uses transistors We use voltage to represent binary We use voltage to represent binary TTL (transistor – transistor logic) is common: TTL (transistor – transistor logic) is common: + 5 V = binary V = binary 1 0 V = binary 0 0 V = binary 0 These voltages will turn on or off transistors These voltages will turn on or off transistors Copyright © Texas Education Agency, All rights reserved.