Introduction to Integrated Circuits

• After completing this topic, students should be able to define the construction and operation of logic circuits, linear circuits and operational amplifiers.

Integrated Circuits Introduction

• Semiconductors, resistors and capacitors have been considered separately packaged components.
• Separately packaged components are called discrete components.
• Integrated circuits (ICs) contain complete circuits in a single package.
• Microelectronics broadly describes integrated circuits use.

Integrated Circuits Construction

• Discrete components include transistors, resistors, capacitors
• Integrated circuits are complete circuits packaged as single components
• Advantages of using integrated circuits include reduced size and weight, increased reliability, lower cost, and improved circuit performance.
• A disadvantage is that they can only be repaired by replacement and not individual component replacements
• Packaging provides connection to an external circuit and dissipates heat.
• Integrated circuits replaced discrete components onto a single silicon chip.
• The first IC was manufactured in 1960.
• The Intel 8088 processor had 29,000 transistors in 1978.
• Quad core i7 processor has 731,000,000 transistors on one piece of silicon.

Binary Codes

• Binary codes consist of only zeros and ones.
• A binary circuit uses only two states.
• Circuit design with binary quantities defines "on" and "off" which is true and false.
• ON is represented by 1.
• OFF is represented by 0 (zero).
• Logic circuits use Boolean algebra.
• Basic logic functions include: AND, OR, NAND, NOR, EXCLUSIVE OR, and NOT.

AND Gate

• Logic gates represent digitally controlled binary circuits and microprocessors.
• A gate symbol represents a transistorized circuit.
• Input signals are applied to the bases of the transistors.
• A digital input is nominally 5 volts DC
• 5 volts DC is ample voltage to turn on the transistor.
• Input A AND input B must be a 1 to get a 1 out.

OR Gate

• Both transistors are switched off (open) at rest and the light is off.
• The right transistor will turn on and the light will illuminate when a '1' is supplied to Input A
• The left transistor will turn on and the light will illuminate when a '1' is supplied to Input B
• If both input A and B are 1, the light is illuminated.
• The logic of this circuit is that input A 'OR' input B may be a 1 to illuminate the light.

Inverter

• An inverter changes a 1 to a zero (0), or a zero (0) to a 1.
• The transistor is a NPN, needs a positive voltage on the base to turn it on
• The transistor turns on pulling the collector voltage down to zero when +5 volts is applied to the input
• If a 1 is input, a 0 is output.
• If a 0 is input, a 1 is output.
• This is an Inverter or 'NOT' Gate.

Exclusive OR Gate

• Exclusive OR gates are similar to an OR gate except when both inputs are 1, the output is zero.

NAND Gate

• The AND Gate output is inverted.
• A NAND Gate is a NOT 'AND' Gate.

NOR Gate

• A NOR Gate shows an OR Gate connected to an inverter.
• The OR gate output will be a 1 when either of the inputs are 1's.
• The inverter outputs a zero, when the OR gate outputs a 1

Inverter Symbol

• An inverter symbol is used as required.
• A NOT symbol is commonly used on the leg of the device indicating the signal to be inverted.
• Inverted input on OR gate produces the truth table as shown.
• Inverted input and output on AND gate produces the truth table shown.
• Both truth tables are same - both circuits would be same.

IEEE Gate Symbols

• IEEE gate symbols are a standard set of logic symbols
• Institute of ANSI Electrical and Electronic Engineers (IEEE) developed the symbols.
• This set of symbols are being increasingly used as time progresses

Integrated Circuit – Logic Circuits

• An integrated circuit chip houses 4 'AND' Gates.
• This is a typical logic gate chip available.
• Same circuitry using discrete components requires 16 resistors and 8 transistors.
• The gates are printed on a Printed Circuit Board (PCB).

Linear Integrated Circuits

• A linear IC is an analogue circuit, opposite to digital circuits.
• An analogue function yields continuous values within a specified range.
• A digital function yields discrete values or steps.
• Linear circuits can be broken down into several categories which includes Operational Amplifiers, Voltage regulators, Communication circuits and Interface circuits

Linear IC Example – Voltage Regulator

• A linear IC can be a three terminal voltage regulator with various packages and several fixed output voltages.
• They consist of many miniature components
• Employs internal current limiting and thermal shut-down.
• Virtually indestructible if adequate heat sinking is provided.

Operational Amplifiers (OP Amps)

• An Op Amp symbol is a triangle, pointing in direction of signal flow.
• Typically symbolised with two inputs and one output
• One non-inverting input (+)
• One inverting input (-)
• Positive and negative supplies are required to operate Op Amps, though usually omitted.
• Voltage at output depends on the difference between +ve and –ve voltages.

Operational Amplifier

• The modern integrated circuit version typified by the famous 741 op-amp
• General characteristics of the IC version are:
• High gain, may be up to 1 million
• High input impedance and low output impedance
• Used with split supply, usually +/- 15V
• Used with feedback, with gain determined by feedback network

Operational Amplifier Outputs

• Differential input signals combine and common input signals cancel.

Basic Op Amp Function

• Input configuration is a differential amplifier.
• Both transistors are connected in a common emitter configuration.
• Transistors Q1 and Q2 are npn transistors
• Q2's base is held at Earth potential so with -ve on Q2 emitter it will conduct.
• Input signal on Q1 base goes positive turning Q1 on further thus lowering the collector voltage with normal common emitter operation.
• Output is inverse of input.
• Q1s base held at Earth potential (+ve wrt emitter) so Q1 is conducting.
• The signal at Q2s base goes positive and turns Q2 on harder, drawing more current through the emitter.
• Extra current provides a greater voltage drop across the lower resistor.
• The lower resistors sends Q1s emitter more positive (less -ve) sending Q1 toward cutt-off.
• Q1s collector voltage will rise as it gets closer to cutt-off.
• The output voltage follows the input voltage.

Operational Amplifier Characteristics

• Two transistors in an Op Amp must be exactly matched.
• Mismatch creates unwanted signals and interference on the output.
• Usually only 1 output provided.
• An OP Amp may be non-inverting (+) or inverting (–) inputs.
• Ideally, input impedance is high, output impedance is low, and gain is high.

Operational Amplifier

• There is more in a single op amp circuit expected, coming in various configurations and packaging.

Negative Feedback

• Negative feedback will control gain of amplifier.
• A fixed resistor will give fixed value of gain.

Variable Feedback

• Negative feedback will control gain of amplifier.
• A variable resistor will give variable value of gain.

Voltage Follower

• Feedback determines the gain of amplifier.
• 100% feedback gives amplifier of Unity Gain (or gain of 1).

Non-Inverting Amplifier

• Feedback determines the gain of amplifier.
• Output is not inverted and the gain is determined by ratio of R2 to R1.