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Electronic Stuff - Glossary of Terms

This version was last updated around 2004. Many new terms (though very few basic concepts) have been introduced which are not covered. We don't do much in hardware these days (2011) so we have little incentive to keep it current. This stuff may be old but is still both highly relevant and absolutely fascinating.

With many thanks here for the original of this now much modified version. We would also suggest you look at this 6 volume series of books by Tony R Kuphaldt 'Lessons in Electric Circuits' published under the OpenBook initiative (means its free).

AC Alternating Current. In a time/voltage diagram, AC voltage represents a sine function (usually), or just any periodically alternating function. The mains voltage is AC voltage, for example.
Active high /
active low
Normally, signals are active high, which means a voltage level of 0V represents a logical 0 (LOW) and a voltage of above 5V represents a logical 1 (HIGH). If, for example, an IC pin is named "CS" (chip select), the chip is usually selected by pulling this line to HIGH (5V for TTL), and it gets deselected by pulling it to LOW (0V).
ADC Analog-Digital Converter.
Ammeter Device for measuring electric current. Usually part of a multi meter.
AND Logical function which is TRUE if all inputs are TRUE.
 A B | A AND B
-----+-------
 0 0 | 0
 0 1 | 0
 1 0 | 0
 1 1 | 1
Examples:
  7408: 4 AND gates with 2 inputs each
  7409: 4 AND gates with 2 inputs each, open collector
  4081: 4 CMOS AND gates with 2 inputs each
BGA Ball Grid Array. A type of chip package where the fixing method consists of a number of solder balls mounted under the chip and directly soldered onto a PCB.
Bread Board Board made of pertinax or other insulating material for building prototype circuits. It contains a matrix of holes. There are also types with soldering pads around the holes, these cost more but are easier to work with.
Buffer Same as driver.
Bus The name for a set of lines/signals fulfilling a common function, e.g. the address bus and the data bus. Examples include the PCI bus, H.100 and H.110 buses
Capacitance Electrical entity which describes the amount of charge a capacitor can store. Unit: farad (F).
Capacitor A capacitor is an electrical element which is capable of storing small amounts of electrical energy, just like an accumulator. The five most common capacitor types are:
Styroflex capacitor High quality, little tolerance. Mainly employed in high-end audio applications. Irrelevant for computer applications. Un-polarized.
Electrolytic capacitor High capacities, polarized, bigger tolerances. Typical application: filtering capacitor in power supplies. Typical capacity greater than 1uF.
Ceramic capacitor Un-polarized. Typical capacity smaller than 1uF. The Dielectric consists of ceramic layers. Widely used for all applications.
Film capacitor Like ceramic, self-healing, usually smaller tolerance range, as ceramic, this type is widely used in all applications. Un-polarized. Available for high voltages also (up to 1000V).
Tantalum (electrolytic) capacitor Like electrolytic, smaller tolerance range, particularly used in digital electronics. Polarized. Typical application: stabilizing. Rarely available for higher voltages (> 10V) and higher capacities (> 100uF) or at least very expensive then.

Since a simple capacitor only consists of two plates facing each other, you can imagine that even two wires lying in parallel have a certain capacitance. When you charge a capacitor by applying voltage to it, it first behaves like a shortcut, then its resistance increases until no current flows through it anymore. This shortcut period is also present in parallel wires (e.g. a cable), it drains lots of power from the chip the wires are connected to and the longer the cable, the higher its capacitance, the longer the shortcut period, the higher the current which the chip has to endure, and the shorter the chip's lifetime.

Chip

Generic Term. An IC in a housing or package. Package types may be Thru-Hole (THT), Surface Mount (SMT/SMD), Ball Grid Array (BGA) or Wafer-level Chip-scale Packaging (WLCSP).

chip packaging types

Dimensions and sizes for chips are defined by JEDEC.

The following types are some examples:

DIL/DIP Dual In Line (THT). This is the most widely used IC housing. The pins come out on both sides of the chip. When the notch on the case points to the top, pin 1 is in the upper left corner, the other pin numbers are counted counter-clockwise. Also used in 'DIP switch', a set of small switches in a chip like case.
SIL/SIP Single In Line (THT). They have pins on only one side of the case. SILs are used on SIMMs (Single In line Memory Module) and SIPs (Single In line Peripheral Package).
SOP, SOT, SOIC, TSOP etc. Examples of surface mount package (SMT) types. May be Dual-in-line or have pins on all four sides.
BGA, FBGA etc Examples of Ball Grid Array types.
CMOS Complementary Metal Oxide Semiconductor. TTL uses bipolar transistors, while CMOS chips use uni-polar transistors (FETs) which are connected complementarily (one p-mos, one n-mos), thus consuming virtually no power and staying much cooler than appropriate TTL chips. Alas, CMOS chips are not suitable for very high frequencies: when the input level changes, the supply voltage pin and GROUND get quickly short-circuited. The higher the switch frequency, the higher the shortcut time. If you run CMOS chips at high frequencies, most of the switching time there is a shortcut, resulting in high power consumption and heat generation.
The switching thresholds are less than 30% (LOW) and greater than 70% (HIGH) of the supply voltage.

As opposed to the TTL series (74xx), CMOS family chips are not bound to 5V supply voltage. Vcc ranges from 3 to 18V (for the 4000 family). There are also TTL compatible CMOS families available, e.g. the widely used 74HCxx series (voltage range 4-6V), where HC stands for High speed Cmos.

Composite video Video signal which comprises of color and brightness information as well as horizontal and vertical synchronization information. Since the video chip's output signals are mixed into one signal (the composite video signal) and then must be split again in the monitor, losses occur and deteriorate the display quality, often resulting in color streaks. If possible, use the computer's Chroma/Luma output, which carries brightness and sync information on one line, but color information on another line, which eliminates the color streaking. The best result is achieved by using an RGB output.
Conductor A material is called a conductor if electrons can move through it, in other words, if it allows flow of electrical current. How well current can flow through the conductor is determined by its resistance. If the resistance is very high, the material is called an insulator.
Connector Many types of connectors are used the following list indicates some of the most common:
BNC Bayonet Nut Connector (you may also see it spelled as Bajonett if you are German, Bayonette if you are French or Bayonett if you are Spanish - so now you know). Used for video connections, Ethernet (10base2)/arcnet, and for high frequencies e.g. measuring equipment (oscilloscope, etc. and RF applications).
DB-xx Used for: RS232C (DB9 or DB25 male), parallel port (DB25 female). For some Pinouts.
DIN Deutsches Institut für Normung. Used for AT style PC keyboards (5-pin), PS/2 mice (6-Pin mini-DIN) ATX sytle keyboards (6-pin mini-DIN) and for MIDI connections. For pinouts here.
RCA [Cinch] Radio Company of America. Used for audio and video connections. In Germany and probably other countries, too, this connector is also known as 'cinch'.
SMA/SMB RF Co-ax connector.
TNC RF Co-ax connector. May have standard or reverse polarity (mandated by FCC for use with ISM band radios e.g. 802.11).
                  TNC Connector Polarity
                   Jack | Plug
                   -----------
Standard         female | male
Reverse-polarity   male | female
N-Type RF Co-ax connector.
Continuity A cable (or other conducting material) has continuity when it has a low resistance, when it therefore constitutes a shortcut.
Continuity tester Device for checking for continuity. It reacts to a resistance below ~100ohm, normally acoustically; some devices have a selectable threshold. Usually part of a multimeter.
Counter Counters are elements counting the number of clock signals and outputting them as binary or decimal representation on the output pins.
Examples

4060: 14-step CMOS binary counter with internal oscillator circuit 7468: 2 asynchronous decimal counters

Current Electrical entity which is defined by the amount of charge flow in Coulomb per second. Unit:=Ampere (A). 1 A = 1 C / 1 sec. Symbol:=I In electrical equations
DC Direct current. DC voltage is linear and constant, and either positive or negative. The same applies to direct current. See also AC.
DAC Digital-Analog Converter.
Diode Semiconductor element which lets current flow in only one direction (forward direction). Current flows if a positive voltage greater than the forward voltage is applied to the anode of the diode (the other end is called cathode and is usually marked with a black ring on the case), otherwise, the diode has a very high resistance. If the applied voltage is below the avalanche / blocking voltage (which is always negative), the diode breaks down and constitutes a shortcut.
The rarely used germanium diodes have a forward voltage of 0.3V, while the standard silicon diode has a forward voltage of 0.6V. (Graphic symbol)
Schottky diode
Diode with a P-N junction consisting of metal and silicon [?]. It is used for applications requiring fast switching, for instance ECL circuits.
Zener diode [Z-Diode]
As opposed to all other diodes, the Z diode is used in reverse direction. It has a defined avalanche voltage and is often used for voltage stabilizing.
Z diodes often have a blue, yellow or red base color. Common series are BZXxx, ZPDxx, and BZYxx, where xx is the avalanche voltage, e.g. ZPD4.7 or BZY9.1.
Tunnel diode
Only for very high frequency applications. Its function is not based on the avalanche effect, but on the tunnel effect.
DRAM Dynamic RAM. DRAM needs a continuous refresh (through the use of CAS and RAS signals), as the information in it is stored by very small capacitors.
Driver Sometimes called a Buffer. A driver's output level follows the input level if it is a non-inverting type, and it implements a NOT function, if it is an inverting type. Drivers are employed for
  • increasing the maximum output current of logical signals.
  • signal shaping - turn a noisy signal into a clean signal
  • protecting expensive chips
Examples:
  7404: hex inverter (6 inverters) 
	7414: hex inverter with Schmitt trigger inputs
  7405: hex inverter with O.C. outputs 
	7406: inverting driver with O.C. outputs (30V)
  7416: inverting driver with O.C. outputs (15V)
  7407: non-inverting driver with O.C. outputs (30V)
  4069: inverting CMOS driver
  4049: inverting CMOS driver, buffered
  4050: CMOS driver
ECL Emitter-Coupled-Logic. Very fast logic family and used in some processor designs such as the AMD2900 range.
EEPROM Electrically Erasable PROM. In contrast to EPROMs, EEPROMs don't need exposure to UV light to be erased, but can be erased electrically. A big advantage is that is accessed like an SRAM. Write accesses perform an automatic clear before write and thus make writing EEPROMs as easy as writing to SRAMs. Series designator: 28xx, where xx is the number of K bits stored.
Serial EEPROMs are labeled 24Cxx (8bit) or 93Cxx (16bit).
Low voltage eproms (PLCC): 3.3V are labeled 27Vxx.
Electron To be supplied.
EPROM Erasable PROM. EPROMs allow the contents to be erased by exposing its builtin window to UV light. After this process, all memory cells contain $ff and the EPROM can be written again.
Series designator: 27xx, where xx is the number of K bits stored.
Electrical
Equations
Ohm's Law. Additional equations.
EXOR (XOR) Exclusive OR. Logical function which is TRUE, if and only if, exactly one input is TRUE. Frequently called XOR.
 A B | A XOR B
-----+-------
 0 0 | 0
 0 1 | 1
 1 0 | 1
 1 1 | 0
Examples:
  7486 : 4 XOR gates with 2 inputs each
  74136: 4 XOR gates with 2 inputs each, open collector
  4070 : 4 CMOS XOR gates with 2 inputs each
FET Field Effect Transistor. As opposed to normal bipolar transistors, these uni-polar transistors have a negligible flow of current through their gate (bipolar: base), they consume virtually no power. NMOS-FETs and PMOS-FETs can be coupled to form CMOS circuits.
FLASH An EEPROM which can be written (and erased) in whole banks or sectors. Typically comes un Uniform Sectored or Bootstrap Sectored designs.
Series designator: 28Fxxx (12 V prg. voltage), 29Fxxx (5 V prg. voltage), and 29LVxxx/29SLxxx (3 V and below), where xxx is the memory capacity: 010 - 1 Mbit, 020 - 2 Mbit, etc. If the FLASH supports 16 bit organization, xxx is: 100 - 1 Mbit, 200 - 2 Mbit, etc. Early FLASH (before 1998) had a limit on the number of erase cycles (typically 100,000) but most modern FLASH has essentially no erase limits.
Flip-flop This edge-triggered element has two stable states, which are toggled on different events, depending on the type:
D flip-flop Delay flip-flop. The input is copied to the output delayed by one clock cycle. D-type flip-flops are normally positive (rising) edge triggered but both edge types are available.
T flip-flop Toggle flip-flop. The output alternates with each input signal change. To simulate a T flip-flop, you can simply connect a D flip-flop's complementary output Q' with its input.
JK flip-flop This type combines characteristics of of RS flip-flop and T flip-flop. It has two inputs J and K and a clock input C. If different signals are applied to J and K, the JK flip-flop acts like an RS flip-flop. If J=K, it acts like a T flip-flop.
Viewed technically, a JK flip-flop comprises of two coupled flip-flops (called Master and Slave), where one outputs the input signals on the rising edge, the other one on the falling edge of the clock signal. Therefore, it is sometimes called master slave flip-flop. Main applications of the JK flip-flop are counters and shift registers. J-K flip-flops are normally negative (falling) edge triggered but both edge types are available.
RS flip-flop Reset-Set flip-flop. These have a reset input and a set input. If reset is high, the output goes low, if set is high, the output goes high. Setting both reset and set to high is forbidden, as the results are indetermined.
Examples:
  7470 : JK flip-flop with 3 inputs each, preset and reset
  74L71: RS master slave flip-flop with 3 inputs each, preset and reset
  74171: 4 D flip-flops with clear input
Float An electronic signal is said to 'float' when its value is not defined under all conditions. Floating is generally a 'bad thing' since random effects (e.g. induction) could easily change the value with unexpected or unpleasant results. Signals that would otherwise 'float' are typically 'pulled-up'(High) or 'pulled-down'(Low) with a weak resistor such that they can be easily changed when driven.
Fuse A device designed to break a circuit when too much voltage or current is applied. The idea being that its cheaper to replace a fuse than a device.
Electronic fuses:
Domestic fuses: Histrically little glass tubes with a wire of defined maximum voltage and current which melts when its capacity is exceeded. There are two common formats: 5 x 20mm (German) and 6 x 30mm (American). Modern wiring typically uses circuit-breakers which can be reset rather than replaced.
Gate A gate is a circuit on a chip, which implements a logical function. A 7406, for example, contains 6 gates (non-inverting drivers).
IC Generic Term. Integrated Circuit. A set of gates etched on a silicon wafer. As ICs are very sensitive, they are enclosed or packaged in a plastic or ceramic case/carrier, with their inputs and outputs connected to metal pins or balls. An IC in a package is commonly referred to as a CHIP. Chips are also called ICs!
Impedance Expresed in Ohms is the vector sum of all opposition to the flow of current in a (typically AC) circuit which includes resistance, capacitance and inductance.
Inductance Measures in Henries. The ability of a component to store energy in the form of a magnetic field.
Inductor A passive device that stores electrical energy in the form of a magnetic field. Normally consists of a wire loop or coil. Inductors are typically used to smooth out voltage fluctuations in power supply circuits.
Insulator A material which doesn't conduct electrical current. The opposite is a conductor.
Inverter Gate inverting a logical signal, thus implementing a NOT function. For examples, see drivers.
Latch A set of flip-flops with a common clock signal. In each cycle, they take the logical input signals over to their outputs. Usually used to form multiplex address busses. As opposed to flip-flops, latches are level-triggered.
LED An LED (Light Emitting Diode) is a diode emitting light when operated in a forward direction. Since it is a diode, it has a nearly negligible resistance and MUST be operated with a series resistor.

The forward voltages depend on the type:

Red 1.6V - 2.1V. Series resistor for 5V: 330 ohm.
Green 2.2V - 2.7V. Series resistor for 5V: 270 ohm.
Yellow 2.7V - 3.2V. Series resistor for 5V: 140 ohm.
White 3.3V - 4.2V. Series resistor for 5V: 75 ohm.
Blue 3.3 V - 4.2 V. Series resistor for 5V: 75 ohm.

While normal LEDs consume about 20mA, high efficiency LEDs require only currents from 2-4mA (depending on type and color), which means that you can directly connect them to standard logical outputs (74LSxx or CMOS 4000 series) without the need for a driver. Nevertheless you still need an appropriate series resistor. Resistor calculation = voltage drop x current required in amps

Logic Tester/Probe Detects and indicates logic TTL (and/or) CMOS voltage levels. It usually contains a pulse memory (comprising a flip-flop) that memorizes pulses too short to be noticed otherwise.
Mains voltage The voltage at the wall outlet.
Australia: 240V @ 50Hz
UK       : 230V @ 50Hz
Germany  : 230V / 400V @ 50Hz (formerly 220V / 380V)
Japan    : 100V @ 75Hz
USA      : 120V / 125V @ 60Hz

Note that since 1989, the standard European voltage is 230V @ 50Hz
Monoflop Also known as one-shot multivibrator. Flip-flop with only one stable state. It remains in the unstable state for a certain time determined by capacitors.
Examples:

74121: Monoflop with Schmitt trigger input 74221: 2 monoflops with Schmitt trigger input and reset 74122: Retriggerable monoflop with reset 74123: 2 retriggerable monoflops with reset

MOS Metal Oxide Semiconductor.
Multi emitter
Multi-meter An all-in-one measuring device. It combines a volt-meter, an amp-meter and an ohm-meter which usually also can act as continuity tester. Often it contains a transistor tester and measures capacities and inductivities (in a small range). There are both analog and digital types, the latter is the preferred choice.
Multiplexing
NAND   Logical function which is TRUE if and only if not all of the inputs are TRUE.
 
 A B | A NAND B
-----+---------
 0 0 | 1
 0 1 | 1
 1 0 | 1
 1 1 | 0
Examples:
  7400: 4 NAND gates with 2 inputs each
  7401: 4 NAND gates with 2 inputs each, open collector
  4012: 2 CMOS NAND gates with 4 inputs each
  4093: 4 CMOS NAND gates with 2 inputs each and Schmitt trigger
	
Negative logic Negative logic means that the signals are active low.
NMOS N-doped MOS.
NOR Logical function which is TRUE if and only if all inputs are FALSE.
 A B | A NOR B
-----+---------
 0 0 | 1
 0 1 | 0
 1 0 | 0
 1 1 | 0
Examples:
  7402: 4 NOR gates with 2 inputs each
  7423: 2 NOR gates with 4 inputs each and strobe
  4001: 4 CMOS NOR gates with 2 inputs each
  4002: 2 CMOS NOR gates with 4 inputs each
	
NOT Logical function which is TRUE if the input is FALSE.
 A | NOT A
---+-------
 0 | 1
 1 | 0
 
Inverters implement this function.
NTSC National Television Standard Code. Video encoding standard in the United States and in Japan. NTSC has 60 pictures/sec and 526 lines vertical resolution.
Ohm's Law Defines the relationship between voltage (E) current (I) and Resistance (R) in a circuit. For DC circuits Ohms law is:
I = E / R (amps = volts / resistance in ohms)
OR
E = I x R (volts = amps x resistance in ohms)
Additional equations.
Ohmmeter Device for measuring resistance. Usually part of a multi-meter.
Open collector A possible output connection of a TTL circuit. The output is formed by a single transistor, which is not connected to the supply voltage, therefore an external connection to the supply voltage (via a pull-up resistor) is required. Multiple open collector outputs can be connected together, the outputs carrying a 0 signal will override all other outputs.
Oscilloscope A test device which displays voltage curves graphically.
OR Logical function which is TRUE if at least one input is TRUE.
 A B | A OR B
-----+-------
 0 0 | 0
 0 1 | 1
 1 0 | 1
 1 1 | 1
Examples:
  7432 : 4 OR gates with 2 inputs each
  74832: 6 OR drivers with 2 inputs each
  4071 : 4 CMOS OR gates with 2 inputs each
  4072 : 2 CMOS OR gates with 4 inputs each
	
PAL This acronym has two meanings:
  1. Phase-Alternation Lines. Video encoding standard used in European countries. PAL has 50 pictures/sec interlaced and a resolution of 625 lines [?].
  2. Programmable Array Logic. A chip which implements a sum-of-products logic equation. A PAL can be programmed only once. Type designator: xxyzz, where xx is the number of inputs, y is either L for active low outputs or H for active high outputs, and zz is the number of outputs; example: 16L8. A derivate [?] is the PLA.
PCB Printed Circuit Board. The circuit tracks or traces are etched photographically onto a media. PCBs may be single-sided (tracks on one side only), double-sided (both top and bottom surfaces are used) or multi-layer where tracks are placed on a number of separate layers which are then bonded together. Tracks are connected on multi-layer boards using VIAs (small holes). Holes are drilled in the board for thru-hole technology or solder pads provided for SMT or BGA devices. Components may be placed on the top or increasing on both the top and bottom of a PCB.
Photo diode Diode which is controlled by light.
Photo transistor Transistor which is controlled by light.
PLA Programmable Logic Array. The same as a PAL, but with a programmable OR matrix
PMOS P-doped MOS.
P-n junction
Positive logic Positive logic means that the signals are active HIGH. Negative logic means that signals are active LOW (most commonly in RS232 circuits).
Potentiometer A variable resistor the value of which is determined by the position of a slider or a knob.
PROM Programmable ROM. This memory type can be written once, then it behaves like a ROM. Series designator: 25xx, where xx is the number of kbits stored.
Pull-up/
pull-down resistor
Pull-ups (or pull-downs) have two primary purposes both of which are variations on a fundamental theme which is to prevent a short-circuit by adding a resistor in the path between Vcc and GND for a particular signal.
Configuration: Many ICs have pins which must be set to a HIGH or LOW to configure the chip. Unless the IC is defined to have an internal pull-up or pull-down you typically use a pull-up (the resistor is between the signal pin and Vcc) to set a HIGH (1) or a pull-down (the resistor is between the signal pin and GND) to set a LOW (0).
Floating Signals: If a signal is not being actively driven all the time it will float (i.e. take an arbitrary and maybe changing value). To prevent this it may be pulled-up (HIGH) or pulled-down (LOW) into a default state.
Pull-ups or pull-downs are usually weak (i.e high value resistors of 4.7K, 10K (most common) or 47K) since in the case of floating signals this allows the 'driven' level to overcome the resistance with a modest current. For minimum power loss especially in configuration functions use the highest value (47K). Since higher resistance values take longer to overcome than lower values if the signal needs to be stable very quickly you may need to go as low as 1K for the pull-up (pull-down).
RAM Random Access Memory. Information can be read and written in any order, the number of read or write accesses is not limited. RAM comes in different flavors: DRAM, SRAM, SDRAM, EDO-RAM, VRAM and many more.
Rectifier Circuitry transforming AC into DC, usually consisting of 4 diodes (aka bridge rectifier).
Resistance The resistance of a conductor (or an insulator) is how easily current can flow through it. Unit: ohm (capital omega) Symbol = R.
Resistor Electrical element with a defined resistance. It is used as voltage divider, current limiter or for ensuring that signals do not float. For small through-hole resistors, their value is not printed on the case, but encoded with color rings.
Radio Frequency (RF) Generic term defines equipment which works in the radio frequency range typically ? to ?.
RGB Red-Green-Blue. These three colors are additively mixed in color TVs and monitors and so give a picture which ranges from black over all rainbow colors to white. The number of colors displayed depends on the technology: TTL or ECL supply digital signals and thus a limited color resolution, usually 4 bits, which results in 16 colors; analog signals, however, make the color resolution practically infinite, the number of colors only depends on the graphics card's memory and on its RAMDAC or VRAM.
RMS Root Mean Square. The real peak value of an AC voltage, which is U * square root of 2, abbreviation Vrms.
ROM Read Only Memory. Unlike RAM, this type of electronic memory can only be read. The ROM's content is determined during the manufacturing process (mask programming). Derivatives are PROM, EPROM, EEPROM, and Flash-EPROM.
SDRAM Synchonous DRAM. Differs from conventional DRAM in that it internally gates (synchronises) all access using a single clock rather than separate column and row clocks (driven by CAS & RAS).
Schmitt trigger A logical device that outputs 0 if the input voltage is below a given threshold voltage and 1 otherwise. Used to cleanup the edges of digital signals. Often comes with a built-in inverter.
Semiconductor Pure semiconductor materials like silicon are insulators. But doping these materials with a very small amount of e.g. Bor makes them less insulating and, under certain circumstances, conduct electrical current. Common semiconductors are diodes and transistors, which are also etched into the silicon wafers of ICs.
SMD or SMT Surface mounted device (Surface mounted technology). A chip packaging technique. SMD technique means soldering elements (which have specially designed, very short pins) directly onto pads on the PCB surface without drilling holes. Other packaging techiques are 'Thu-hole' and Ball Grid Array (BGA).
Solder Solder is made of tin (Sn) and lead (Pb) and contains a rosin core, which makes the solder flow more easily.
Soldering iron A tool for soldering electrical conducting connections.
SRAM Static RAM. As opposed to DRAM, this type of memory doesn't need a continuous refresh, as the information in it is stored by flip-flops.
Three-state See tristate.
Thru-hole (THT) A chip packaging technology and requires holes in the PCB through which component pins were inserted and soldered on the reverse side. Through-hole is still widely use for connectors and other components that also have a physical use since the through hole provides a mechanical achoring function (e.g. DB25, RJ45 etc). Surface mount versions of these components exist but almost always use one or more mechanical locating holes or pins. Aternate packaing technologies are Surface Mount (SMT/SMD) and Ball Grid Array (BGA).
Thyristor Sometimes called a semiconductor controlled rectifier. It has 3 pins (anode, cathode and gate). When powered and Gate is ON (high) forward current only will flow from the anode to cathode (irrespective of state of the Gate) until it drops below a certain level (called the Holding Current). It can be used to rectify current.
Totem pole A possible output connection of a TTL circuit. A totem pole consists of two transistors, which are driven complementary. Depending on the desired output, only one of the two transistors is conducting. If two totem pole outputs are connected, a shortcut occurs if they carry different digital signals (0/1 or 1/0).
Transformer

A transformer changes one AC voltage into another AC voltage. It consists of two coils (actually not separate coils, but windings) with a different number of turns, where one coil (transformer primary winding) encloses the other (transformer secondary winding). The current flowing through the transformer primary (the one where the input voltage is applied) invokes a magnetic field which in turn induces a voltage in the transformer secondary, the amount of which is determined by the ratio of the number of turns of the windings.

A transformer can have more than one secondary, resulting in more than one output voltage.

Transistor "Transfer Resistor". Invented in 1948 by John Bardeen and Walter Houser Brattain. In principle, this element is an electrically controllable semiconductor resistor. It has three terminals C(ollector), E(mitter), and B(ase). Basically, when there is no voltage applied to the base, the transistor acts as an insulator and blocks current flow between C and E.

It is used both as an amplifier and an electronic switch.

Triac Provides similar functionality to a thyristor but supports bi-directional current flow.
Tristate
(or three-state)
The output lines of tristate circuits can have three states: HIGH, LOW, and HIGH IMPEDANCE (HI-Z), where the latter is equivalent to not being connected.
TTL Transistor-Transistor-Logic. The TTL family needs a supply voltage of 4.75V-5.25V, the switching threshold is less than 0.8V for LOW and greater than 2.4V for HIGH.
Type    Meaning                         typ. t [ns]   Power[mW/G]
----------------------------------------------------------------
74xx    Standard                                10            10
74ALSxx Advanced Low Power Schottky              4             1
74ASxx  Advanced Schottky                      1.5            20
74Fxx   Fast Schottky                            2             4
74Hxx   High Power                               6            20
74Lxx   Low Power                               30             1
74LSxx  Low Power Schottky                       9            20
74Sxx   Schottky                                 5            20

* tpd = propagation delay time. Time for an output level change after the input level changed.

Voltage Electrical entity which is the cause for current flow. When talking about AC voltages, peak-to-peak voltage means - as the name suggests - the absolute amount of voltage between the upper and the lower bound; Abbreviation: Vcc. Unit: Volt (V).
Voltmeter Device for measuring electrical voltage. Usually part of a multimeter.
VRAM Video RAM. VRAM is dual-ported, so that you can read and write simultaneously, resulting in a much smaller access time. As the name suggests, VRAMs are employed as memory on graphic cards.
XOR See EXOR


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