| Padcap |
A special flavor of circuit board used for
high-reliability military applications. Distinguished by the fact that the outer surfaces
of the board have pads but no tracks. Signal layers are only created on the inner planes,
and tracks are connected to the surface pads by vias.
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| Pad |
An area of metalization on a substrate used
for probing or to connect to a via, plated through-hole, or an external interconnect.
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| Pad Grid Array (PGA) |
A packaging technology in which a device's
external connections are arranged as an array of conducting pads on the base of the
package.
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| Pad Stack |
Refers to any pads, anti-pads, and thermal
relief pads associated with a via or a plated through-hole as it passes through the layers
forming the substrate.
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| Parallel-In Serial-Out (PISO) |
Refers to a shift register in which the data
is loaded in parallel and read out serially.
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| Parasitic Effects |
The effects caused by undesired resistance,
capacitance, or inductance inherent in the material or topology of a track or component.
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| Passivation Layer (see Overglassing) |
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| Passive Trimming |
A process in which a laser beam is used to trim components such
as thick-film and thin-film resistors on an otherwise unpopulated and unpowered hybrid or
multichip module substrate. Probes are placed at each end of a component to monitor its
value while the laser evaporates some of the material forming the component.
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| Pass-Transistor Logic |
A technique for connecting MOS transistors
such that data signals pass between their source and drain terminals. Pass-transistor
logic minimizes the number of transistors required to implement a function, and is
typically employed by designers of cell libraries or full-custom integrated circuits.
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| PCB (Printed Circuit Board) |
A
type of circuit board which has conducting tracks superimposed, or "printed", on
one or both sides, and may also contain internal signal layers and power and ground
planes. An alternative name, Printed Wire Board (PWB), is commonly used in America.
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| Peta |
Unit qualifier (symbol = T) representing one
thousand million million, or 1015. For example, 3PHz stands for 3 x 1015
Hertz.
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| PGA (Pad Grid Array or Pin Grid
Array) |
PGA
may refer to a pad grid array or a pin grid array. A pad grid array
refers to a packaging technology in which a device's external connections are arranged as
an array of conducting pads on the base of the package. A pin grid array refers
to a packaging technology in which a device's external connections are arranged as an
array of conducting leads, or pins, on the base of the package.
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| PHB (Photochemical Hole Burning) |
An
optical memory technique, in which a laser in the visible waveband is directed at a
microscopic point on the surface of a slice of glass which has been doped with organic
dyes or rare-earth elements. The laser excites electrons in the glass such that they
change the absorption characteristics of that area of the glass and leave a band, or hole,
in the absorption spectrum.
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| Photochemical Hole Burning (PHB) |
An optical memory technique, in which a laser
in the visible waveband is directed at a microscopic point on the surface of a slice of
glass which has been doped with organic dyes or rare-earth elements. The laser excites
electrons in the glass such that they change the absorption characteristics of that area
of the glass and leave a band, or hole, in the absorption spectrum.
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| Photo-Transistor |
A special transistor which converts an optical
input in the form of light into an equivalent electronic signal in the form of a voltage
or current.
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| Pico |
Unit qualifier (symbol = p) representing one
millionth of one millionth, or 10-12. For example, 3pS stands for 3 x 10-12
Seconds.
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| Pin (see Lead) |
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| Pin Grid Array (PGA) |
A packaging technology in which a device's
external connections are arranged as an array of conducting leads, or pins, on the base of
the package.
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| PISO (Parallel-In
Serial-Out) |
Refers
to a shift register in which the data is loaded in parallel and read out serially.
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| Place-Value |
Refers to a numbering system in which the
value of a particular digit depends both on the digit itself and its position in the
number.
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| Plasma |
A gaseous state in which the atoms or
molecules are dissociated to form ions.
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| Plated Through-Hole (PTH) |
(1)A hole in a double-sided or multilayer
board that is used to accommodate a through-hole component lead and is plated with copper.
(2)An alternative name for the lead through-hole technique for populating circuit boards
in which component leads are inserted into plated through-holes.
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| PMOS (P-channel MOS) |
Refers to the order in which the semiconductor
is doped in a MOS device. That is, which structures are constructed as P-type versus
N-type material.
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| PNP (P-type - N-type -
P-type) |
Refers to the order in which the semiconductor
is doped in a bipolar junction transistor.
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| Polysilicon Layer |
An internal layer in an integrated circuit
used to create the gate electrodes of MOS transistors. In addition to forming gate
electrodes, the polysilicon layer can also be used to interconnect components. There may
be several polysilicon layers separated by dielectric (insulating) layers.
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| Populating |
The act of attaching components to a
substrate.
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| Positive-Edge |
A transition from
a logic 0 to a logic 1. Also known as a rising edge.
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| Positive Ion |
An atom or group of atoms lacking an electron.
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| Positive Logic |
A convention which dictates the relationship
between logical values and the physical voltages used to represent them. The more positive
potential is considered to represent TRUE and the more negative potential is considered to
represent FALSE. Also known as positive true logic.
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| Positive Resist |
A process where radiation passing through the
transparent areas of a mask causes previously cured resist to be degraded. The degraded
areas are then removed using an appropriate solvent.
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| Positive-True |
A
convention which dictates the relationship between logical values and the physical
voltages used to represent them. The more positive potential is considered to represent
TRUE and the more negative potential is considered to represent FALSE. Also known as positive
logic.
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| Power Plane |
A conducting layer in or on the substrate
providing power to the components. There may be several power planes separated by
insulating layers.
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| Precedence of
Operators |
Determines the order in which operations are
performed. For example, in standard arithmetic the multiplication operator has a higher
precedence than the addition operator. Thus, in the equation
6 + 2 x 3, the multiplication is performed before the addition and the result is 12.
Similarly, in Boolean Algebra, the AND operator has a higher precedence than the OR
operator.
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| Prepreg |
Non-conducting semi-cured layers of FR4 used
to separate conducting layers in a multilayer circuit board.
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| Primitives |
Simple logic functions such as BUF, NOT, AND,
NAND, OR, NOR, XOR, and XNOR may be referred to as primitive logic gates or primitives.
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| Printed Circuit Board (PCB) |
A type of circuit board which has conducting
tracks superimposed, or "printed", on one or both sides, and may also contain
internal signal layers and power and ground planes. An alternative name, Printed Wire
Board (PWB), is commonly used in America.
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| Printed Wire Board (PWB) |
A type of circuit board which has conducting
tracks superimposed, or "printed", on one or both sides, and may also contain
internal signal layers and power and ground planes. An alternative name, Printed Circuit
Board (PCB), is predominantly used in Europe and Asia.
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| Product-of-Sums |
A Boolean equation in which all the maxterms
corresponding to the lines in the truth table for which the output is a logic 0 are
combined using AND operators.
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| Product Term |
A set of literals linked by an AND operator.
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| Programmable Array Logic (PAL) |
A programmable logic device in which the AND
array is programmable but the OR array is pre-defined.
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| Programmable Logic Array (PLA) |
The most user-configurable of the traditional
programmable logic devices, because both the AND and OR arrays are programmable.
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| Programmable Logic Device (PLD) |
The generic name for a device constructed in
such a way that the designer can configure, or "program" it to perform a
specific function.
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| Programmable Read-Only Memory
(PROM) |
A programmable logic device in which the OR
array is programmable but the AND array is pre-defined. Usually considered to be a memory
device whose contents can be electrically programmed (once) by the designer.
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| PROM (Programmable Read-Only
Memory) |
A
programmable logic device in which the OR array is programmable but the AND array is
pre-defined. Usually considered to be a memory device whose contents can be electrically
programmed (once) by the designer.
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| Proposition |
A statement that is either true or false with
no ambiguity. For example, the proposition "I just
tipped a bucket of burning oil into your lap," is
either true or false, but there's no ambiguity about it.
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| Protein |
A complex organic molecule formed from chains
of amino acids, which are themselves formed from combinations of certain atoms, namely:
carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally phosphorous or iron.
Additionally, the chain of amino acids "folds in on itself" forming an extremely
complex three-dimensional shape. Organic molecules have a number of useful properties, not
the least that their structures are intrinsically "self healing" and reject
contamination. Also, in addition to being extremely small, many organic molecules have
excellent electronic properties. Unlike metallic conductors, they transfer energy by
moving electron excitations from place to place rather than relocating entire electrons.
This can result in switching speeds that are orders of magnitude faster than their
semiconductor equivalents.
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| Protein Memory |
A form of memory based on organic proteins
(see also Protein).
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| Protein Switch |
A form of switch based on organic proteins
(see also Protein).
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| Pseudo-Random |
An artificial sequence of values that give the
appearance of being random.
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| PTH (Plated Through-Hole) |
(1)A
hole in a double-sided or multilayer board that is used to accommodate a through-hole
component lead and is plated with copper. (2)An alternative name for the lead through-hole
technique for populating circuit boards in which component leads are inserted into plated
through-holes.
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| P-type |
A piece of semiconductor doped with impurities
that make it amenable to accepting electrons.
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| PWB (see Printed
Wire Board) |
A
type of circuit board which has conducting tracks superimposed, or "printed", on
one or both sides, and may also contain internal signal layers and power and ground
planes. An alternative name, Printed Circuit Board (PCB), is predominantly used in Europe
and Asia.
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