Analog Glossary

3G - The next generation of wireless technology beyond personal communications services. The World Administrative Conference assigned 230 megahertz of spectrum at 2 GHz for multimedia 3G networks. These networks must be able to transmit wireless data at 144 kilobits per second at mobile user speeds, 384 kilobits per second at pedestrian user speeds, and 2 megabits per second in fixed locations.

Adjacent Channel Interference - Signal impairment to one frequency due to the presence of another signal on a nearby frequency.

Analog Multiplier - A circuit that produces an output that is linearly proportional to the product of the two analog inputs.

Amplifier, Buffer, Closed Loop - An amplifier, usually configured for a gain of 1 or 2, with the feedback network on the IC saving board space. Used to drive a heavy capacitive or resistive load (cable).

Amplifier, Buffer, Open Loop - - A unity gain (gain = 1) amplifier not using a feedback network (loop). Thus it's "open loop" (see HA-5002, HA-5033, HA4600).

Amplifier, Buffer, Programmable Gain - An amplifier that can be used in a fixed number of user-selectable gains (typically +/-1 and 2). The feedback network is on the IC, thus saving board space.

Amplifier, Cable Driver - An amplifier, usually in a gain of 2, suitable for driving the low resistance of a double terminated cable (load resistance = 150 ohms for video, 100 ohms for instrumentation.

Amplifier, Current Feedback (CFA) - A newer, high performance architecture that delivers higher bandwidth and slew rates at much lower supply currents.

Amplifier, Differential - 1) Two transistors connected as a differential pair, with a third transistor (tail transistor) connected to the common emitters. 2) An op amp configured to amplify the difference between 2 input signals.

Amplifier, Operational (Op Amp) - A general purpose, closed loop amplifier used to implement linear functions. Its performance and function are defined by the external components (feedback network or loop) surrounding it.

Amplifier, Operational Transconductance (OTA) - A differential amplifier that converts the difference between the input voltages to a proportional output current.

Amplifier, with Output Disable - Also referred to as a "gated amp". An op amp whose output can be set to a high impedance state, so outputs from multiple amplifiers can be connected together (multiplexed).

Amplifier, with Output Limiting - An op amp with external pins (VH and VL) that define the maximum positive and negative output swing. Connecting reference voltages to these pins "limits" the output swing to this voltage range.

Amplifier, Precision - An op amp with very high open loop gain and common mode/power supply rejection ratios, and very low offset voltage and offset current. It is ideal for accurately amplifying signals, while introducing minimal error.

Amplifier, Sample and Hold - An op amp whose input may be turned on to sample a voltage, then turned off to hold the sampled voltage at the output, while an ADC converts the voltage to a digital number.

Amplifier, Single Supply - An op amp operating off a single supply voltage (typically +5V or +3V) vs. one requiring dual supplies (e.g., +/-5V or +/-15V).

Amplifier, Variable Gain (VGA) - An amplifier whose gain can be varied by an external analog or digital control signal. A VGA can be implemented with an OTA.

Amplifier, Voltage Feedback (VFA) - The original op amp architecture, especially useful for low noise and precision applications.

Analog - a representation of a signal that resembles the original; it implies a continuous, smoothly changing signal where any piece of information can take on any of an infinite set of values. Real-world phenomena, such as sound, heat, and pressure, are analog. For example, when someone says it is 55 degrees outside, it could really be 55.012492 degrees, or any value between that and 55.

Analog-to-Digital Converter (ADC) - A device that converts continuously varying analog input signals into a digital bit stream. The basic unit of all digital communications is the binary digit. A bit is a "1" or "0" in a binary language. Resolution is specified by number of bits (8 bit = 2⁸ = 256 discrete, non-continuous values). Conversion speed is specified in Mega Samples Per Second (MSPS). See A/D Converters

Asynchronous Transmission - Data transmission of one character at a time to the receiving device, with intervals of varying lengths between transmittals, and with start bits at the beginning and stop bits at the end of each character, to control the transmission.

Attenuation - The factor by which a signal is made smaller.

Audio Crosspoint Switch - A crosspoint that isn't high performance, but is capable of handling the larger signals common to audio applications (typically requires power supplies of at least +/-10V.

Backlight - A light source typically placed behind a liquid-crystal display (LCD); several types of backlights are used including electroluminescent (EL) backlights, LED backlights, and cold-cathode fluorescent lamps (CCFLs); EL backlights are very thin, lightweight, and provide an even light; LED backlights consume more power, but offer a longer operating life and are brighter than ELs; CCFL backlights offer low power consumption and a very bright white light.

Bandwidth -The width measure of a signal or signal-carrying channel from the lowest to the highest frequency (or bit rate). For analog signals, the width is in the frequency domain, expressed in Hz. For digital signals, the width is in the time domain, expressed in bits per second. In semiconductor devices, the bandwidth is the range of frequency (or bit rate) in which the performance characteristics are within specified limits.

Base Station - A transmitter/receiver unit located in a fixed location which can talk directly to mobiles or portables.

Bipolar - One of two basic processes (MOS and bipolar) used to fabricate ICs, bipolar technology is based on transistors made from a sandwich of so-called n- and p-type semiconductor material, resulting in "npn" and "pnp transistors"; bipolar technology has more fabrication steps than CMOS technology, and therefore costs more. Bipolar circuits are often chosen for high-performance analog functions while CMOS circuits are often used for digital functions as well as analog functions (see CMOS).

Boost Converter - Or step-up converter, is a switching DC-DC converter that produces an output voltage greater than the source.

Broadband - A type of transmission that shares the bandwidth of a medium--such as copper or fiber optic cable--to carry more than one signal. Broadband facilities have a bandwidth (capacity) greater than a voice grade line of 3 kHz. Such a broadband facility--typically coaxial cable--may carry numerous voice, video and data channels simultaneously. Each "channel" will take up a different frequency on the cable. "Guardbands" (empty spaces) exist between the channels to make sure that each channel does not interfere with its neighbor. A coaxial CATV cable is the "classic" broadband channel. Simultaneously it carries many TV channels. Broadband cables are used in some office LANs. But more common are the baseband variety, which have the capacity for one channel only. Everything on that cable to be transmitted or received must use that one channel. That one channel is very fast, so each device needs only to use that high speed channel for only a little of the time.

Buck Converter - Or step-down converter, is a DC-DC converter that produces an output voltage less than the source.

Capacitor - A passive component that stores a charge, measured in Farads (F); capacitors resist changes in voltage, and are an essential component in (for example) power supplies for filtering out unwanted ac noise from a dc signal.

CMOS (Complementary Metal Oxide Semiconductor) - One of two basic processes (MOS and bipolar) used to fabricate ICs, CMOS uses MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) as the principal circuit element. Noted for having low power consumption (see bipolar).

Comparator, TTL (or CMOS, ECL, etc.) - A voltage comparator whose high and low output levels match the requirements for TTL (or CMOS, ECL, etc.) logic family input levels.

Comparator, Voltage - An amplifier that compares the magnitude of the voltages at its 2 inputs, and outputs a "high" level if +IN > -IN, or a "low" level if +IN < -IN. Basically a 1-bit ADC.

Crosspoint (or Matrix, M x N) Switch - A matrix of switches configured with M inputs and N outputs. Under digital control, any output may be connected to one of the inputs.

Data Acquisition - The process by which events in the real world are translated to machine-readable signals. The term usually refers to automated systems in which sensors are attached to machinery.

DC-DC Converter - An active device--similar to a switching power supply in its operation--that accepts a dc input and typically produces a different dc output voltage; sometimes the input and output are the same, in which case the converter is used for its noise isolation and/or regulation capabilities. Dc/dc converters are important for applications where electronic equipment must be operated from a battery or other dc source. Dc/dc converter modules typically offer full functionality, while dc/dc converter ICs usually require the addition of external components (like an inductor and capacitors) for complete operation.

Decimation - Is reducing the output sampling rate by ignoring all but every Nth sample. When a digital filter reduces the bandwidth of a signal of interest so the filter output is over-sampled if the input sample rate is preserved. See appnote: AN9603

Demodulator - A device that extracts digital information from transmitted carrier waves.

Digital - A digital system is based around the idea of ON or OFF, so an electrical signal is either there or it isn't. This means that numbers have to be represented as a combination of 0 (OFF) or 1 (ON). This is a binary system, and the 1's and 0's are called bits.

Digital Integrated Circuits - A class of integrated circuits that process digital information (expressed in binary numbers). The processing operations are arithmetic (such as addition, subtraction, multiplication, and division) or logical (in which the circuit senses certain patterns of input binary information and indicates the presence or absence of those patterns by appropriate output binary signals).

Digital-to-Analog Converter (DAC) - Converts digital pulses into an analog output signal. The basic unit of all digital communications is the binary digit. A bit is a "1" or "0" in a binary language. Resolution is specified by number of bits (8 bit = 28 = 256 discrete, non-continuous values). Conversion speed is specified in Mega Hertz (MHz). See: D/A Converters

Digital Signal Processing (DSP) - Digital circuits designed to address a broad class of problems in signal reception and analysis that have traditionally been solved using analog components. DSP is rapidly replacing analog signal processing functions where requirements for stability over time and temperature variations are critical. DSP is used to enhance, analyze, filter, modulate, or otherwise manipulate standard real-world functions, such as images, sounds, radar pulses, and other such signals by analyzing and transforming wave-forms (e.g., transmitting data over phone lines via modem). Intersil offers building blocks and special function chips for DSP, including fast multipliers, multiplier accumulators, image processors, histogrammers, and digital filters. See: DSP Selection

Digital Subscriber Lines (DSL) - Technologies that allow telephone companies to use conventional phone lines to deliver data at rates far higher than today's traditional modems or even ISDN.

Digitally Controlled Potentiometer (DCP) - A digitally controlled potentiometer (DCP) is adjusted by giving it a digital value that it converts to a wiper position. In many applications, a processor or digital controller monitors the analog function's output and calculates the digital value that is applied to the DCP.

Diode - A two-terminal semiconductor device that allows current to flow in one direction only; an essential component used in power supplies to convert ac into dc (a process called rectification)

Discrete Device - A device that contains one active element, such as a transistor or diode, although a hybrid might contain more than one active element. In comparison, an integrated circuit could contain millions of active elements on a single chip.

Downconverter -A device that reduces the high-frequency signal to a lower, intermediate range. The three types od down conversion are signal, dual and block down conversion.

EEPROM - Electronically-Erasable Programmable Read-Only Memory

Field-Effect Transistor (FET) - A voltage-controlled semiconductor device having three terminals--a gate, drain, and source--whose control, or gate, signal creates an electromagnetic field that controls the flow of current through the device (see transistor and bipolar transistor).

Field-Programmable Gate Array (FPGA) - A high-density (that is, containing more than 1,000 gates) programmable-logic chip containing small logic cells interconnected through an array of programmable switches. FPGAs can implement thousands of gates of logic in a single IC and can be programmed by users at their site in a few seconds or less depending on the type of device used. FPGAs are popular for prototype development, custom computing, digital signal processing, and logic emulation.

Frequency - The number of times per second that a signal (or wave) alternates from positive to negative and back again, expressed in Hertz (Hz); the highest frequencies that a human ear can hear are those that oscillate at up to 15,000 to 20,000 times per second; the electromagnetic wave corresponding to the color red has a frequency of 428,570 GHz (pronounced gigahertz), which can also be stated as 428,570 billion cycles per second; when you look at red light, your eye receives over four hundred trillion waves every second.

General Purpose Timer - Usually an R-C oscillator providing a square wave output, with various control signals to perform Reset and gating (on/off) functions. Control signals allow generation of single pulses (monostable), continuous pulses (astable), or a burst of a fixed number of pulses at the output.

Global System for Mobile Communications (GSM) - A digital cellular or PCS network used throughout the world.

Hot Swap - To remove and replace a system component while power is on and the system is functional (without first shutting the system down).

IGBT (insulated-gate bipolar transistor) - A power semiconductor device available for use in power conversion circuits; usually found in high-voltage circuits (above 300 V) because it has significantly lower values of on-resistance than a power MOSFET with the same die size.

Inductor - A coiled conductor that tends to oppose any change in the flow of current; usually has coils wrapped around a ferrous core; may be used in power supply filtering.

Interface - An IC that provides an interconnect to an interface standard such as; RS-232, RS-485, RS-422, USB, USB2, etc.).

Interpolation - Means increasing the sampling rate. It is often used when a narrowband signal will be combined with a signal that requires a higher sampling rate. See appnote: AN9603

IS-54 - The first generation of the digital standard time division multiple access technology.

IS-95 - The standard for code division multiple access.

IS-136 - The latest generation of the digital standard time division multiple access technology.

Joint Test Action Group (JTAG) - (1) Test standards group working on boundary scan and standard test interfaces. (2) Any of the standards approved by this group. Some Intersil design libraries provide cells to implement the chip-level standards, and design information is available for most other libraries.

Linear Power Supply - A power supply that uses a conventional 50- or 60-Hz power transformer followed by a diode rectifier, capacitor filter, and linear regulator; these supplies are about 40% to 55% efficient.

Linear Regulator - A stabilization circuit in which a control device--such as a power MOSFET or bipolar transistor--is placed in series or parallel with the load to deliver a constant voltage across the load.

Microcontroller - A highly integrated chip that contains all of the components needed--a central processing unit (CPU), random access memory (RAM), some form of read-only memory (ROM), input/output ports, and timers--to control a system. Unlike a general-purpose computer, which also includes all of these components, a microcontroller is designed for a very specific task-to control a particular system. As a result, the parts can be simplified and reduced, which cuts down on costs.

Microprocessor - (1) A central processing unit (CPU) fabricated on one or more chips, containing the basic arithmetic, logic, and control elements of a computer that are required for processing data; (2) An integrated circuit that accepts coded instructions, executes the instructions received, and delivers signals that describe its internal status. The instructions may be entered or stored internally. Also called "MPU" (microprocessor unit). Widely used as control devices for household appliances, business machines, toys, etc., as well as for microcomputers. Intersil is the industry leader in 16-bit CMOS microprocessors.

Metal-Oxide Varistor (MOV) - A voltage-sensitive breakdown device that is commonly used to limit overvoltage conditions (electrical surges) on power and data lines. When the applied voltage exceeds the breakdown point, the resistance of the MOV decreases from a very high level (thousands of ohms) to a very low level (a few ohms), shorting the voltage safely to ground.

Mixed Signal IC - An integrated circuit that has both digital and analog functions on the same semiconductor chip, permitting a high degree of system integration. Intersil mixed signal ICs are of three types: (1) In those optimized for analog, the major part of the design is analog with a small digital content; (2) In those optimized for power, the circuit has analog, digital and power functions; (3) In those optimized for digital, the major part of the design is digital with some analog content. Intersil recently introduced a cell library for mixed signal optimized for analog, called HBC2500. The library is supported by a double-metal, double-poly BiCMOS process with 3µm CMOS and 300-MHz bipolar transistors.

MOSFET (Metal Oxide Semiconductor Field Effect Transistor) - A device that does not require as much power as bipolar devices because of its insulation. The term can be applied either to transistors in an IC or to discrete power devices. MOSFETs are easier to manufacture than bipolar devices and are a building block in the fabrication of CMOS chips.

Multiplexer (MUX, M-Channel) - A device that combines several input signals into a single output signal in such a manner that each of the input signals subsequently can be recovered. At Intersil, an IC consisting of multiple analog CMOS switches and digital decoding, allowing one of many inputs to be passed to the output.

Multiplexing - A process of transmitting more than one signal over a single link, route, or channel. Of the two methods in use, parallel processing frequency-shares the bandwidth of a channel in the same way hurdlers run and jump in their assigned lanes, thus permitting a number of contestants to compete simultaneously on the same track. The second method, called serial processing, time-shares multiple signals in the same way that pole vaulters vault over the same bar one after the other. Although serial processing may not seem simultaneous, the signal speed is so fast that it is possible to multiplex four different numbers through a single decoder-driver and have them appear on four different displays without a flicker.

Multiplier - A circuit whose output state is the arithmetic product of two input signals. Important in DSP (digital signal processing) technology for signal processing and power control applications. Intersil offers high-speed analog and digital multipliers.

Multiplier, 2 Quadrant, Analog - A multiplier where the control input must be a positive voltage.

Multiplier, 4 Quadrant, Analog - A multiplier where both inputs (signal and control) may be positive or negative.

Noise - A random unwanted signal that is imposed on the wanted output signal.

Polyphase - See appnote: AN9661

On-Resistance - The output resistance of a power switching device--typically a power MOSFET--when it is in its fully "on" or conducting state; especially important in high-current switches, where the voltage drop across the power device must be minimized.

Optoelectronics - A device that is responsive to or that emits or modifies light waves. Examples are LEDs, optical couplers, laser diodes, and photo detectors.

Oscillator - A timing device consisting of quartz crystal and an oscillation circuit to generate an output signal at a constant specified frequency.

Phase Locked Loop (PLL) - A circuit which synchronizes an adjustable oscillator with another oscillator by the comparison of phase between the two signals.

Pin Driver - A very high performance 2 channel mux used to switch between 2 voltages at a very high rate, and drive a test "pin" on automated test equipment (ATE).

Power - Electrical energy measured according to voltage and current; usually given in Watts (W).

Power Factor - The ratio of ac power actually used by a piece of electrical equipment compared to the total apparent ac power supplied; a high apparent power yields a low power factor--meaning the equipment is using a higher current than it actually needs to satisfy its real power requirement; dc circuits always exhibit a power factor of 1.00 (i.e., real input power equals apparent input power).

Power Factor Correction (PFC) - Increases the portion of the ac input energy that an ac-input power supply can use, thus increasing overall efficiency.

Power MOSFET - A power semiconductor device often used as a power switch in dc/dc converters; capable of handling currents of more than 1 Ampere.

Power Supply - An electrical device that provides a known voltage and current output. A power supply can be a standalone device--like a battery or a unit that plugs into a wall outlet--or a fundamental component of a larger electrical product.

Quadrature Amplitude Modulation (QAM) - Modulation standard used for cable transmission.

Quadrature Phase Shift Keying (QPSK) - Modulation standard used for satellite transmission.

Quadrature - (1) The state of being separated in phase by 90° (p/2 radians). (2) Pertaining to the phase relationship between two periodic quantities varying with the same period, that is, with the same frequency or repetition rate, when the phase difference between them is one-quarter of their period.

Real Time Clock - A circuit or device that generates a periodic signal used for timing or synchronizing signals.

Rectifier - A diode circuit that passes current in only the forward direction; is used to convert alternating current (ac) to direct current (dc).

RF - Radio Frequency. The range of electromagnetic frequencies above the audio range and below visible light. All broadcast transmission, from AM radio to satellites, falls into this range, between 30KHz to 300GHz.

Regulation - Maintains the output voltage of a power supply to a constant value, regardless of changes in the input voltage or the demands of the load to which the power is being supplied.

Resistor - A passive component, measured in Ohms, that "resists" the flow of current through it; permits a predetermined current to flow with a given applied voltage.

Ripple - Distinguished from noise by its periodic non-random nature, ripple is characterized by a series of small ac voltage or current peaks on a dc signal; it is typically a by-product of converting ac to dc.

Silicon Controlled Rectifier (SCR) - Also known as a thyristor; like a diode it only allows electric current to flow through it in one direction, but in addition it can be controlled so that its "turn-on" can be delayed indefinitely.

Semiconductor - A solid crystalline material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber); the most common semiconductor material is silicon; examples of semiconductor devices include integrated circuits and discrete (non-integrated) semiconductors like transistors and diodes.

Sensor - An input device that sends information about its surroundings in the form of electronic signals, or data.

Signal - Any electronic visual, audible, or other indication used to convey information. In semiconductors, an electrical quantity (typically voltage, current, or light level) corresponding to some physical quantity. Signals are coded in frequency or amplitude to separate them from unwanted noise.

Signal Processing - Electronic functions that enhance the representations of physical or electrical phenomena. Temperature, pressure, vibration, acceleration and flow are examples of physical properties that rely on signal processing enhancements. The detection and conversion of RF, X-ray or ultrasonic energy into images and sound is another form of signal processing.

Switching Frequency - The rate at which dc voltage is switched in a switching power supply or DC/DC converter.

Switching Supply - Usually an off-line device, it first converts ac line voltage to crude dc voltage, then "switches" the resulting dc signal on and off at up to 500,000 times per second; this "chopped" ac signal is then converted to dc again; because of the high frequency, the transformer and capacitors required to convert the signal to a stable dc signal can be much smaller than their 50/60-Hz counterparts; switching supplies are 60% to 80% efficient.

Symbol - A modulation symbol is the interval of time during which the modulated parameter of the radio waveform is held (approximately) constant. For a system with one symbol per bit, such as GSM and related systems, the symbol duration is the same as one bit duration. For GSM and relatives, the frequency is held approximately constant for one bit interval.

Synchronous Transmission - Data transmission using synchronization bytes, instead of start/stop bits, to control the transmission.

Thyristor - (see also SCR) A component like a diode, but will not conduct until a voltage is applied to its third terminal known as the "gate."

Time Division Multiple Access (TDMA) - A process of sharing a cellular channel by sharing time slots or intervals between users. Each user is assigned a specific time interval.

Transceiver - Short for "transmitter-receiver"; a device that both transmits and receives signals.

Transformer - Passive electromagnetic component that transfers alternating-current (ac) power from one circuit to another; typically used to transform one ac voltage into another lesser or greater ac voltage.

Transistor - A three-terminal semiconductor device used for amplifying or switching signals. Today's microprocessor ICs contain tens of millions of microscopic transistors. Individually packaged discrete transistors are often used in power and control applications (see bipolar transistor and field-effect transistor).

Transistor, Bipolar - invented over 50 years ago, the bipolar transistor is a current-controlled device made from a sandwich of "n-" and "p-type" semiconductor material, resulting in "npn" and "pnp" transistors. The middle section of the transistor is known as the "base" and the other two sections as the "collector" and "emitter" (see transistor and field-effect transistor).

Transistor Array - Multiple discrete (usually unconnected) transistors on a single silicon chip.

Transistors, Differential Pair - Two transistors connected in a differential configuration (emitters connected together).

Transistors, Gilbert Cell - An analog multiplier configuration useful for implementing mixers, and up and down converters (see HFA3101).

Transistors, Matched Pair- Two very similar transistors, on a single silicon chip, with specified matching characteristics (usually Vbe and beta).

Voltage - The electrical "pressure" that causes current in a circuit.

Voltage Controlled Oscillator (VCO) - A circuit whose output is an AC signal (square wave or sine wave) at a fixed frequency (oscillation) determined by the voltage on a control input. Changing the voltage changes the output frequency.

Waveform - The pattern of a sound wave or other electronic signal in analog form.

Wavelength - Measured in meters, it is the length from the peak of one wave to the peak of the next (or the length of one oscillation); the higher the frequency of a wave, the shorter its wavelength. For example, visible red light has a wavelength of only 700 nanometers, which means that one wave spans only 7 ten millionths of a meter.