Analog IC Ch113

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Soclof, S. “Analog Integrated Circuits”

The Engineering Handbook.

Ed. Richard C. Dorf

Boca Raton: CRC Press LLC, 2000

© 1998 by CRC PRESS LLC



113Analog Integrated Circuits

113.1 Operational Amplifiers

113.2 Voltage Comparators

113.3 Voltage Regulators

113.4 Power Amplifiers

113.5 Wide-Bandwidth (Video) Amplifiers

113.6 Modulators, Demodulators, and Phase Detectors

113.7 Voltage-Controlled Oscillators

113.8 Waveform Generators

113.9 Phase-Locked Loops

113.10 Digital-to-Analog and Analog-to-Digital Converters

113.11 Radio-Frequency Amplifiers

113.12 Integrated Circuit TransducersOptoelectronic Devices

Sidney Soclof California State University

An integrated circuit is an electronic device in which there is more than one circuit component in

the same package. Most integrated circuits contain many transistors, together with diodes, resistors,

and capacitors. Integrated circuits may contain tens, hundreds, or even many thousands of

transistors. Indeed, some integrated circuits for computer and image-sensing applications may have

millions of transistors or diodes on a single silicon chip.

A monolithic integrated circuit is one in which all of the components are contained on a

single-crystal chip of silicon. This silicon chip typically measures from 1 £ 1 £ 0:25 mm thick for

the smallest integrated circuits to 10 £ 10 £ 0:5 mm for the larger integrated circuits.

A hybrid integrated circuit has more than one chip in the package. The chips may be

monolithic integrated circuits and separate or "discrete" devices such as transistor or diode chips.

There can also be discrete passive components such as capacitor and resistor chips. The chips are

usually mounted on an insulating ceramic substrate, usually alumina (Al2 O3 ), and areinterconnected by a thin-film or thick-film conductor pattern that has been deposited on the

ceramic substrate. Thin-film patterns are deposited by vacuum evaporation techniques and are

usually about 1 micrometer in thickness, whereas thick-film patterns are pastes that are printed on

the substrate through a screen and usually range in thickness from 10 to 30 micrometers.

Integrated circuits can be classified according to function, the two principal categories being

digital and analog (also called linear ) integrated circuits. A digital integrated circuit is one in




which all of the transistors operate in the switching mode, being either off (in the cutoff mode of

operation) or on (in the saturation mode) to represent the high and low (1 and 0) digital logic

levels. The transistors during the switching transient pass very rapidly through the active region.

Virtually all digital integrated circuits are of the monolithic type and are composed almost entirely

of transistors, usually of the MOSFET type. Some digital integrated circuits contain more than onemillion transistors on a single silicon chip.

Analog or linear integrated circuits operate on signal voltages and currents that are in analog or

continuous form. The transistors operate mostly in the active (or linear) mode of operation. There

are many different types of analog integrated circuits, such as operational amplifiers, voltage

comparators, audio power amplifiers, voltage regulators, voltage references, video

(wide-bandwidth) amplifiers, radio-frequency amplifiers, modulators and demodulators for AM

and FM, logarithmic converters, function generators, voltage-controlled oscillators, phase-locked

loops, digital-to-analog and analog-to-digital converters, and other devices. The majority of analog

integrated circuits are of the monolithic type, although there are many hybrid integrated circuits of

importance.

In addition to the two basic functional categories of analog and digital integrated circuits, thereare many integrated circuits that have both analog and digital circuitry in the same integrated

circuit package, or even on the same chip. Some of the analog integrated circuits mentioned

previously, such as the digital-to-analog and analog-to-digital converters, contain both types of

circuitry.

Almost all integrated circuits are fabricated from silicon. The principal exceptions are some very

high-speed digital integrated circuits that use gallium arsenide (GaAs) to take advantage of the

very high electron mobility in that material. Integrated circuits are fabricated using the same basic

processes as for other semiconductor devices. In integrated circuits the vast majority of devices are

transistors and diodes, with relatively few passive components such as resistors and capacitors. In

many cases no capacitors at all are used, and in some cases there are no resistors either. The active

devices contained in an integrated circuit are transistors, including bipolar junction transistors

(BJTs), junction field-effect transistors (JFETs), and metal-oxide silicon field-effect transistors

(MOSFETs). Digital integrated circuits are made up predominantly of MOSFETs, with generally

very few other types of components. Some analog integrated circuits use mostly, or even

exclusively, BJTs, although many integrated circuits use a mixture of BJTs and field-effect

transistors (either JFETs or MOSFETs), and some are even exclusively FETs, with no BJTs at all.

The sections that follow give very brief descriptions of some of the analog integrated circuits.

113.1 Operational Amplifiers

An operational amplifier is an integrated circuit that produces an output voltage, V O , that is anamplified replica of the difference between two input voltages, as given by the equation

V O = AOL (V 1 ¡ V 2 ) , where AOL is called the open-loop gain. The basic symbol for the

operational amplifier is shown in Fig. 113.1. Most operational amplifiers are of the monolithic

type, and there are hundreds of different types of operational amplifiers available from dozens of

different manufacturers.




Figure 113.1 Operational amplifier symbols: (a) basic operational amplifier symbol; (b) symbol with

input polarities indicated explicitly; (c) symbol with input polarities indicated explicitly. (Source: Soclof,S. 1991. Design and Applications of Analog Integrated Circuits. Prentice Hall, Englewood Cliffs, NJ. Withpermission.)

The operational amplifier was one of the first types of analog integrated circuits developed; the

term operational amplifier comes from one of the earliest uses of this type of circuit in analog

computers dating back to the early and middle 1960s. Operational amplifiers were used in

conjunction with other circuit components, principally resistors and capacitors, to perform various

mathematical operations, such as addition, subtraction, multiplication, integration, anddifferentiation hence the name "operational amplifier." The range of applications of operational

amplifiers has vastly expanded since these early beginnings; operational amplifiers are now used to

perform a multitude of tasks through the entire field of electronics.

Operational amplifiers are usually used in a feedback, or closed-loop, configuration, as shown in

Fig. 113.2. Under the assumption of a large open-loop gain, AOL , the output voltage is given by

V O = V 1[1 + (Z 2 =Z 1 )]¡ V 2 (Z 2 =Z 1 ) .

Figure 113.2 Closed-loop (negative feedback) operational-amplifier system. (Source: Soclof, S. 1991.

Design and Applications of Analog Integrated Circuits. Prentice Hall, Englewood Cliffs, NJ. Withpermission.)




The following is a list of some important applications of operational amplifiers:

Difference amplifier. This produces an output voltage proportional to the difference of two

input voltages.

Summing amplifier. This produces an output voltage that is a weighted summation of a

number of input voltages.

Current-to-voltage converter. This produces an output voltage that is proportional to an

input current.

Voltage-to-current converter. This produces an output current that is proportional to an input

voltage but is independent of the load being driven.

Active filters. This is a very broad category of operational amplifier circuit that can be

configured as low-pass, high-pass, band-pass, or band-stop filters.

Precision rectifiers and clipping circuits. This is a broad category of wave-shaping circuits

that can be used to clip off or remove various portions of a waveform.

Peak detectors. This produces an output voltage proportional to the positive or negative peak

value of an input voltage. Logarithmic converters. This produces an output voltage proportional to the logarithm of an

input voltage.

Exponential or antilogarithmic converters. This produces an output voltage that is an

exponential function of an input voltage.

Current integrator or charge amplifier. This produces an output voltage proportional to net

flow of charge in a circuit.

Voltage regulators. This produces an output voltage that is regulated to remain relatively

constant with respect to changes in the input or supply voltage and with respect to changes in

the output or load current.

Constant current sources. This produces an output current that is regulated to remain

relatively constant with respect to changes in the input or supply voltage and with respect tochanges in the output or load impedance or voltage.

Amplifiers with electronic gain control. These are amplifiers in which the gain can be

controlled over a wide range by the application of an external voltage.

Function generators. These are circuits that can be used to generate various types of

waveforms, including square waves and triangular waves.

Clamping circuits. These circuits produce an output voltage that has the same AC waveform

as the input signal, but the DC level is shifted by an amount controlled by a fixed reference

voltage.

Analog signal multiplexer. This circuit combines several input signals for transmission over

a single communications link by means of time-domain multiplexing.Sample-and-hold circuit. The input signal is sampled over a short period of time, and the

sampled value is then held at that value until the next sample is taken.

Analog multiplier. This produces an output voltage proportional to the product of two input

voltages.




113.2 Voltage Comparators

A voltage comparator is an integrated circuit as shown in Fig. 113.3 that is used to compare two

input voltages and produce an output voltage that is in the high (or "1") stage if V 1 > V 2 and in the

low (or "0") stage if V 1

< V 2

. It is essentially a one-bit analog-to-digital converter.

Figure 113.3 Voltage comparator. (Source: Soclof, S. 1991. Design and Applications of Analog

Integrated Circuits. Prentice Hall, Englewood Cliffs, NJ. With permission.)

In many respects, voltage comparators are similar to operational amplifiers, and, indeed,

operational amplifiers can be used as voltage comparators. A voltage comparator is, however,

designed specifically to be operated under open-loop conditions, basically as a switching device.

An operational amplifier, on the other hand, is almost always used in a closed-loop configuration

and is usually operated as a linear amplifier.

Being designed to be used in a closed-loop configuration, the frequency response characteristics

of an operational amplifier are generally designed to ensure an adequate measure of stability

against an oscillatory type of response. This results in a sacrifice being made in the bandwidth, rise

time, and slewing rate of the device. In contrast, since a voltage comparator operates as anopen-loop device, no sacrifices have to be made in the frequency response characteristics, so a

very fast response time can be obtained.

An operational amplifier is designed to produce a zero output voltage when the difference

between the two input signals is zero. A voltage comparator, in contrast, operates between two

fixed output voltage levels, so the output voltage is either in the high or low states.

The output voltage of an operational amplifier will saturate at levels that are generally about 1 or

2 V away from the positive and negative power supply voltage levels. The voltage comparator

output is often designed to provide some degree of flexibility in fixing the high- and low-state

output voltage levels and for ease in interfacing with digital logic

circuits.

There are many applications of voltage comparators. These include pulse generators,

square-wave and triangular-wave generators, pulse-width modulators, level and zero-crossing

detectors, pulse regenerators, line receivers, limit comparators, voltage-controlled oscillators,

analog-to-digital converters, and time-delay generators.




A voltage regulator is an electronic device that supplies a constant voltage to a circuit or load. The

output voltage of the voltage regulator is regulated by the internal circuitry of the device to be

relatively independent of the current drawn by the load, the supply or line voltage, and the ambient

temperature. A voltage regulator may be part of some larger electronic circuit but is often a

separate unit or module, usually in the form of an integrated circuit. A voltage regulator, as shownin Fig. 113.4, is composed of three basic parts:

1. A voltage reference circuit that produces a reference voltage that is independent of the

temperature and supply voltage

2. An amplifier to compare the reference voltage with the fraction of the output that is fed back

from the voltage regulator output to the inverting input terminal of the

amplifier

3. A series-pass transistor or combination of transistors to provide an adequate level of output

current to the load being driven

Figure 113.4 Voltage regulator: basic block diagram. (Source: Soclof, S. 1991. Design and Applications

of Analog Integrated Circuits. Prentice Hall, Englewood Cliffs, NJ. With permission.)

Voltage regulators usually include protection circuitry such as current limiting and thermal

limiting to protect the integrated circuit against overheating and possible damage.

113.3 Voltage Regulators




An important type of voltage regulator is the switching-mode regulator , in which the series-pass

transistors are not on continuously but, rather, are rapidly switched from being completely on to

completely off. The output voltage level is controlled by the fraction of time that the series-pass

transistors are on (i.e., the duty cycle). Switching-mode regulators are characterized by having very

high efficiencies, often above 90%.

113.4 Power Amplifiers

Although most integrated circuit amplifiers can deliver only small amounts of power to a load,

generally well under 1 watt, there are integrated circuits that are capable of supplying much larger

amounts of power, up in the range of several watts, or even several tens of watts. There are a

variety of integrated circuit audio power amplifiers available that are used in the range of

frequencies up to about 10 or 20 kHz for amplification of audio signal for delivery to loudspeakers.

These integrated circuit audio power amplifiers also are used for other applications, such as relay

drivers and motor controllers.

There are also available a variety of power operational amplifiers. The maximum currentavailable from most operational amplifiers is generally in the range of about 20 to 25 mA. The

maximum supply voltage rating is usually around 36 V with a single supply or +18 V and ¡18 V

when a split supply is used. For an operational amplifier with a 36 V total supply voltage, the

maximum peak-to-peak output voltage swing available will be around 30 V. With a maximum

output current rating of 20 mA, the maximum AC power that can be delivered to a load is

P L = 30 V £ 20 mA =4 = 150 mW. Although this level of output power is satisfactory for many

applications, a considerably larger power output is required for some applications.

Larger AC power outputs from operational amplifiers can be obtained by adding external

current boost power transistors that are driven by the operational amplifier to the circuit. There are

also available power operational amplifiers that are capable of operation with supply voltages ashigh as 200 V, and with peak output current swings as large as 20 A. With the proper heat sinking

for efficient transfer of heat from the integrated circuit to the ambient, the power operational

amplifiers can deliver output power up in the range of tens of watts to a load.

HOW A CHIP IS MADE

Semiconductor chips are made from silicon, an element found in ordinary beach sand. Silicon's

conductive properties allow for the creation of on/off switches that equal a one or zero in a

computer's binary language.Through hundreds of complex processing steps, the switches are built and connected into

circuits, millions of which can be placed on a single chip.The exact nature and number of steps needed to manufacture a semiconductor chip varies with

its design and complexity, but the basic process remains the same.Ultra-pure silicon is processed into cylinders that are sliced into thin, 5- to 8-inch diameter

wafers on which hundreds of individual computer chips can be made. The wafers are cleaned,

inspected, and placed in high temperature furnaces where they are coated with a non-conducting

oxide film.




A thin layer of light-sensitive plastic, called photoresist, is applied over the oxide. A glass

"mask," containing the chip's circuit pattern, is placed over the wafer and precisely aligned. In a

process called photolithography, which is similar to developing a photograph from a negative,

light or an X-ray beam is projected through the mask to print each chip's circuit pattern on the

wafer surface.The unexposed photoresist is washed away in solvent baths, etching the protective oxide layer

with the shape of the circuit pattern. Holes are also etched in the protective oxide layer.The wafer is then bombarded with ions, or charged particles, that penetrate the holes etched in

the oxide surface. The depth and concentration of these materials determine the specific electrical

characteristics of the chip. The process of oxidation, photolithography, etching, and ion implanting

are repeated to build transistors and other electronic circuitry that make up each chip.Once the electronic components have been implanted in the silicon, interconnecting wiring is

added to the chip by placing the wafer in a vacuum chamber and coating it with copper mixed

with aluminum or other metals. The aluminum is etched away, leaving the desired wiring.A thin layer of material is added to protect the wafer. The wafers are then cut into individual

chips by diamond-bladed saws and mounted in metal or plastic packages, called modules. Thesemodules are tested and plugged into printed circuit boards, which are eventually built into finished

computers.(Courtesy of IBM Microelectronics Division.)

113.5 Wide-Bandwidth (Video) Amplifiers

Video, or wide-bandwidth, amplifiers are designed to give a relatively flat gain versus frequency

response characteristic over the frequency range that is generally required to transmit video

information. This frequency range is from low frequencies, generally around 30 Hz, up to severalmegahertz. For standard television reception, the bandwidth required is around 4 MHz, but for

other video display applications the bandwidth requirement may be as high as 20 MHz, and for

some applications up in the range of 50 MHz.

In contrast, the bandwidths required for audio applications extend only over the frequency range

corresponding to the range of the human ear around 50 Hz to 15 kHz.

The principal technique that is used to obtain the large bandwidths that are required for video

amplifiers is the trading off of reduced gain in each amplifier stage for increased bandwidth. This

trade-off is accomplished by the use of reduced load resistances for the various gain stages of the

amplifier and by the use of negative feedback. In many video amplifiers both techniques are

employed. The reduction in the gain of the individual stages can be compensated for by addingadditional gain stages.

Included in the category of video amplifiers are the very wide-bandwidth operational amplifiers.

Most operational amplifiers are limited to a bandwidth of around 1 to 10 MHz, but there are

wide-bandwidth operational amplifiers available that can be used up in the range of 100 to 200

MHz.




113.6 Modulators, Demodulators, and Phase Detectors

This is a category of integrated circuit that can be used to produce amplitude-modulated (AM) and

frequency-modulated (FM) signals. These same integrated circuits can also be used for the

demodulation, or detection, of AM and FM signals. In the AM case these integrated circuits can be

used to generate and to demodulate double-sideband/suppressed carrier (DSB/SC) and

single-sideband/suppressed carrier (SSB/SC) signals. Another application of this type of

integrated circuit is as a phase detector , in which an output voltage proportional to the phase

difference of two input signals is produced.

113.7 Voltage-Controlled Oscillators

A voltage-controlled oscillator (VCO) is an oscillator circuit in which the frequency of oscillation

can be controlled by an externally applied voltage. VCOs are generally designed to operate over a

wide frequency range, often with a frequency ratio of 100:1. One important feature that is often

required for VCOs is a linear relationship between the oscillation frequency and the controlvoltage. Many VCOs have a maximum frequency of operation of around 1 MHz, but there are

some emitter-coupled VCOs that can operate up to 50 MHz.

113.8 Waveform Generators

A waveform generator is an integrated circuit that generates the following three types of voltage

waveforms: square waves, triangular waves, and sinusoidal waves. The square and triangular

waves can be generated by the same type of circuits as used for VCOs.

For the generation of a sinusoidal waveform a feedback amplifier using an LC tuned circuit or an

RC phase shift network in the feedback loop can be used. These feedback oscillators can produce a

very low-distortion sine wave, but it is difficult to modulate the oscillation frequency over a very

wide range by means of a control voltage. The VCO, on the other hand, is capable of a frequency

sweep ratio as large as 100:1, with very good linearity between the frequency and the control

voltage. A sinusoidal waveform can be obtained from a VCO by using a waveshaping network to

convert the triangular wave output to a sine wave.

113.9 Phase-Locked Loops

A phase-locked loop (PLL) is a feedback loop comprising a phase detector, low-pass filter, and a

voltage-controlled oscillator (VCO) as shown in Fig. 113.5. When the PLL has locked in on a

signal, the frequency of the VCO will exactly follow the signal frequency.




The PLL can be used as an FM demodulator or detector. In this case the VCO control voltage is

proportional to the frequency deviation of the FM signal and represents the demodulated output

voltage. Another closely related application is the demodulation of frequency-shift keying (FSK)

signals, a process that is similar to FM except that the signal frequency is shifted between just two

values.

One important application of PLLs is in frequency synthesis, in which a precise series of

frequencies is produced, all derived from a stable crystal-controlled oscillator. In Fig. 113.6, a PLL

frequency synthesizer circuit is shown.

Figure 113.6 PLL frequency synthesizer. (Source: Soclof, S. 1991. Design and Applications of Analog


Figure 113.5 Phase-locked loop. (Source: Soclof, S. 1991. Design and Applications of Analog





113.10 Digital-to-Analog and Analog-to-Digital

Converters

A digital-to-analog converter (D/A or DAC) is an integrated circuit that converts a digital input

signal to an analog output voltage (or current) that is proportional to the digital signal. DACs vary

in resolution from 4 to 16 bits.

An analog-to-digital converter (A/D or ADC) is an integrated circuit that converts an analoginput signal to a digital output. ADCs vary in resolution from a simple voltage comparator used as

a 1-bit ADC to 16-bit ADCs.

For some applications, such as storing entire frames of video information in one-thirtieth of a

second, very high conversion rates are required. For these applications parallel comparator (or

"flash") ADCs are used with conversion rates as high as 500 MHz for an 8-bit ADC.

113.11 Radio-Frequency Amplifiers

There are radio-frequency (R-F) integrated circuits that use tuned circuits and operate as band-pass

amplifiers. These are used in communications circuits, such as AM and FM radio, and in television

for signal amplification and mixing.

113.12 Integrated Circuit Transducers

This is a broad category of integrated circuits that are used for the conversion of various physical

inputs to an electrical signal. These circuits include the magnetic field sensor, based on the Hall

effect, which produces an output voltage proportional to the magnetic field strength. There are also

temperature sensor integrated circuits that can produce a voltage or current output that is

proportional to the temperature. There are electromechanical integrated circuit transducers such as

pressure sensors that produce an output voltage proportional to pressure. Miniature solid-state

accelerometers based on integrated circuit sensors are also available.

Optoelectronic Devices

A very important category of integrated circuit transducers is that of the optoelectronic devices.

These devices range from photodiode or phototransistor-amplifier modules to image sensors

containing in the range of one million individual photodiode image-sensing elements. These

image-sensing integrated circuit chips also include additional circuitry to properly transfer out (line

by line, in a serial output) the information from the two-dimensional array of the image sensor.

There are also integrated circuits used with light emitting diodes (LEDs) and laser diodes for the

generation of light pulses for optoelectronic communications systems, including fiber optic

systems.In the case of a fiber optic communications system, a small diameter glass fiber is used as a

conduit or waveguide to guide a beam of light from transmitter to receiver. Optoelectronicintegrated circuits are used at the transmitting end with LEDs or laser diodes for the generation and

emission of the optical signal. Optoelectronic integrated circuits are used at the receiving end with

photodiodes or phototransistors for the detection, amplification, and processing of the received

signal.




MINIATURIZED ELECTRONIC CIRCUITS

Jack S. KilbyPatented June 23, 1964#3,138,743An excerpt:

In contrast to the approaches to miniaturization that have been made in the past, the present

invention has resulted from a new and totally different concept for miniaturization. Radically

departing from the teachings of the art, it is proposed by the invention that miniaturization can best

be attained by use of as few materials and operations as possible. In accordance with the principles

of the invention, the ultimate in circuit miniaturization is attained by using only one material for allcircuit elements and a limited number of compatible process steps for the production thereof.

Kilby patented what we now call the Integrated Circuit. He made whole circuits (with

transistors, resistors, and capacitors) using a single semiconductor substrate and diffusing opposing

materials onto it to form the circuit elements. This fundamental process has advanced to the point

that now millions of transistors are put on a single "chip." (© 1992, DewRay Products, Inc. Used

with permission.)




Defining Terms

Hybrid integrated circuit: An electronic circuit package that contains more than one chip. These

chips can be a mixture of monolithic ICs, diodes, transistors, capacitors, and resistors.

Integrated circuit: An electronic circuit package that contains more than one circuit element.

Monolithic integrated circuit: A single-crystal chip of a semiconductor, generally silicon, thatcontains a complete electronic circuit.

References

Franco, S. 1988. Design with Operational Amplifiers and Analog Integrated Circuits.

McGraw-Hill, New York.

Gray, P. R. and Meyer, R. G. 1992. Analysis and Design of Analog Integrated Circuits. John

Wiley & Sons, New York.

Irvine, R. G. 1987. Operational Amplifiers Characteristics and Applications. Prentice Hall,

Englewood Cliffs, NJ.

Kennedy, E. J. 1988. Operational Amplifier Circuits. Holt, Rinehart and Winston, New York.

McMenamin, J. M. 1985. Linear Integrated Circuits, Operation and Applications. Prentice Hall,

Englewood Cliffs, NJ.

Sedra, A. S. and Smith, K. C. 1982. Microelectronic Circuits. Holt, Rinehart and Winston, New

York.

Seippel, R. G. 1983. Operational Amplifiers. Prentice Hall, Englewood Cliffs, NJ.

Soclof, S. 1991. Design and Applications of Analog Integrated Circuits. Prentice Hall, Englewood

Cliffs, NJ.

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Analog IC Ch113