| |
| AGP (Accelerated Graphics Port)
- mature PC graphics IO standard |
| |
| Analog signals - use multiple
voltage levels to represent information (i.e. gas
gauge receives 0 to 12 volts from tank level sensor
to represent empty to full) |
| |
| ASI (Advanced Switching Interconnect)
- high-end server serial IO standard |
| |
| ATCA (Advance TeleCom Architecture)
- PICMG's latest embedded telephony/industrial
computer and backplane/chassis standard |
| |
| ATM (Asynchronous Transfer Mode)
- high-end telephony IO standard |
| |
| Attenuation - refers to any
reduction in the strength of a signal (loss). It is
usually measured in decibels (dB) which is a
logarithmic term that ratios the output voltage or
power as a function of input voltage or power. As an
example, 3dB loss is equivalent to 30% loss of
voltage and 6dB loss is equivalent to 50% loss of
voltage. In the case of power, 1.5dB loss is
equivalent to 30% loss of power and 3dB loss is
equivalent to 50% loss of power. Typically, cables
are rated in dB loss per 100 feet.
AP = 10log (POUT
/PIN ), where AP = power
attenuation
AV = 20log (VOUT
/VIN ), where AV = voltage
attenuation
 |
| |
| Aurora - new open protocol and
physical layer spec from Xilinx |
| |
| Backward Crosstalk - see
near-end crosstalk |
| |
| Bandwidth - The bandwidth of a
signal is a measure of the range of frequencies that
comprise a signal. Typically, a digital
signal is composed of its fundamental
frequency (the one we always talk about) and several
higher order frequencies that give it its shape. The
term is also used in reference to the
frequency-response characteristics of electronic
components such as drivers, receivers, connectors,
and backplanes. All transmitted signals, whether
analog or
digital , have a certain bandwidth.
Typically a connector requires a bandwidth greater
than the frequency of the signal transmitted to
minimize the distortion of
the signal. Bandwidth figures are meaningless unless
they are defined as to how they were arrived at. For
example, the bandwidth of a connector might be
defined as 2 GHz, where 2 GHz is the frequency at
which a sine wave is attenuated by 3 dB. |
| |
| BER - the bit error rate (BER)
is the percentage of bits
that have errors relative to the total number of
bits received in a transmission, usually expressed
as ten to a negative power. For example, a
transmission might have a BER of 1 x 10-6,
meaning that, out of 1,000,000 bits transmitted, one
bit was in error. The BER is an indication of how
often a packet or other
data unit has to be retransmitted because of an
error. A high BER may indicate that a slower data
rate would actually improve overall transmission
time for a given amount of transmitted data since
the BER might be reduced, lowering the number of
packets that had to be resent. A BERT (bit error
rate test or tester) is a procedure or device that
measures the BER for a given transmission. |
| |
| Bit rate - number of
bits that pass through a given
point in a given amount of time, usually expressed
as Kbps (thousands of bits per second), Mbps
(millions of bits per second) or Gbps (billions of
bits per second) |
| |
| Bits - digital data is
transmitted and stored as strings of 1's and 0's,
each one of these 1's and 0's is a bit. See
digital signals . |
| |
| Broadside-coupled - refers to
differential PCB traces that are physically above
and below each other |
| |
| Bytes - a group of
bits make up a byte (word) (typically
8,16 or 32 bits to a byte) |
| |
| Capacitance - refers to the
ability of a device to store energy in the form of
an electrostatic field. In its simplest form, a
capacitor is a pair of parallel plates spaced apart
with a dielectric material
between them. Coax cables have a certain
capacitance per foot. The dielectric materials in a
cable affect the capacitance of the cable. If two
cables are identical in geometry, the cable with the
higher dielectric constant
insulator will have the higher capacitance
per foot and, thus, the lower impedance. The
standard unit of capacitance is the farad,
abbreviated F. This is a large unit; more common
units are the microfarad, abbreviated µF (1 µF = 10-6
F) and the picofarad, abbreviated pF (1 pF = 10-12
F). The reactance of a capacitor decreases as
frequency increases.
XC = 1/(2πfC), where XC
= capacitive reactance
f=frequency and
C=capacitance |
| |
| Clock Speed - in a computer,
clock speed refers to the number of pulses per
second generated by an oscillator that sets the
tempo for the processor. Clock speed is usually
measured in MHz (megahertz, or millions of pulses
per second). A typical computer clock runs at
several hundred megahertz. The clock speed is
determined by a quartz-crystal circuit, similar to
those used in radio communications equipment. |
| |
| CML (Compact Multi-Lane) -
SFF-8088, mini-SAS IO connector |
| |
| Controlled Impedance - a
specific impedance that is maintained along the
length of the transmission line. See
impedance . |
| |
| cPCI (Compact PCI) - embedded
computer backplane/chassis standard |
| |
| Crosstalk - the effect whereby
a signal on one conductor will be transposed to an
adjacent conductor due to mutual
capacitance and mutual
inductance . It is usually measured as
a percentage of the applied voltage; for example, if
a 1 volt peak to peak signal is transmitted on one
line, a nearby line may show a 0.1 volt peak to peak
signal; this corresponds to 10% crosstalk. The
frequency or risetime of the signal must be
specified. In general, crosstalk will increase with
higher frequencies or faster risetimes. Measurements
are usually made with one or more active
lines and one quiet or victim
line. The active lines are the conductors that are
driven by a signal; the quiet or victim line is the
conductor being affected by the driven lines.
|
| |
| CSI (Coherent Scalable Interface)
- like SCI?, new Intel IO standard |
| |
| CX4 - Coax or twinax version of
10GEthernet 4 lanes x 3.125G |
| |
| DDWG (Digital Display Working Group)
- Business Consortium |
| |
| Dielectric Constant - the
property of a dielectric (insulator) which
determines the electrostatic energy that can be
stored. The higher the constant the higher the
energy stored within the capacitor. The dielectric
constant affects the properties of transmission
lines. The dielectric constant can change with
frequency; however, Teflon-based dielectrics are
quite constant over a wide frequency range. Common
dielectric constants: air = 1; foamed FEP = 1.53;
solid PTFE = 2.03; solid polypropylene = 2.18; FR-4
= 4.5
|
| |
| Dielectric Materials - are
insulators that are used to provide separation
between conductors. Examples are air, Teflon and
FR-4. Their inherent dielectric constant affects how
the conductors behave electrically. |
| |
| Differential Impedance - refers
to the impedance of a pair of conductors when driven
in a differential mode, that is, when the conductors
are driven by signals that have opposite polarity
edges. |
| |
| Differential Mode Transmission
- uses two conductors to carry the signal, and one
shield to provide the return path. The signal
conductors are driven by opposite polarity signals.
Typical examples: twinax, shielded twisted pair,
ribbon cable
 |
| |
| Digital Signals - use two
states (on/off, high/low, 1/0) to represent data |
| |
| Dispersion - the phenomenon in
cables and PCB's whereby higher frequency signals
propagate faster along the length of the conductor
than do lower frequency signals. This causes signal
distortion because most
digital signals are made up of many frequencies.
This can be due to dielectric constant changes with
frequency or to changes in reactance
of the cable with frequency. |
| |
| DisplayPort - new IO standard -
VESA.org |
| |
| Distortion - refers to the
changing of any of the attributes of a signal
because of the medium through which the signal flows
(i.e., a connector or cable) These attributes may be
amplitude, risetime, pulse width, etc. |
| |
| DVI (Digital Visual Interface)
- ddwg.org, display video IO standard |
| |
| Edge-coupled - refers to
differential PCB traces that are side-by-side |
| |
| Electrical length - refers to
the total time it takes for a signal to traverse a
conductor and may be expressed in nanoseconds. See
also propagation delay . |
| |
| Equalizer - a
reactance connected in series with a
transmission line to alter the frequency response
characteristics of the line. Typically this is used
as a high-pass filter which attenuates low
frequencies to compensate for the cable's
attenuation at high frequencies.
It will improve the "eye opening" for a cable. See
also eye-pattern . |
| |
| Even mode coupling - the
coupling between the signal paths and ground within
a differential pair |
| |
| Even mode impedance - the
impedance of a single line in a coupled-line pair
when a common-mode signal drives both conductors
within the pair. |
| |
| ExpressCard - PCMCIA.org,
latest PCI Express packaging standard |
| |
| Eye-pattern - the name given to
the "picture" or pattern produced when multiple
traces are recorded on an oscilloscope by sending
multiple 1's and 0's down a cable assembly and
"looking" at the far end of the cable. The 1's and
0's are randomly generated so that many different
sequences of highs and lows are examined by the eye
pattern.
This test is an excellent way to look at how the
cable assembly will perform in the "real world". It
encompasses attenuation
and risetime degradation
(reduction in amplitude and risetime as a function
of frequency components of the pulse and bit pattern
sequence), dispersion
(jitter due to differing speeds of signal
transmission as a function of frequency) and
within-pair skew (offset
of differential signal due to differing electrical
lengths of the wires within the differential pair).
The "eye" of the input signal is compared to the
"eye" of the signal at the far end
. The height and width of the "eye"
(referred to as the "eye opening") show how the
signal has been distorted and can be used to analyze
if the user's receiving circuit can reliably
distinguish the logic 1's and 0's emerging from the
cable assembly. Ideally, the eye pattern would be a
square that is the same height and width as the
input signal. The X-axis plots time and the Y-axis
plots amplitude. Referring to the illustration,
1,2,.,8 are "snapshots" of the signal at equal
lengths of time apart (X number of clock cycles) and
these "snapshots" are superimposed one on top of
another yielding the eye-pattern in the lower left
of the illustration. (illustration courtesy of
Agilent Technologies and Electronic Design
)
|
| |
| Far end - refers to the
non-driven end of a transmission line
(the receiver end)
|
| |
| Far-end (forward) crosstalk -
the crosstalk measured near the end opposite the
driven end of the active signal line(s). |
| |
| FC (Fibre Channel) - highest
end T11.org storage serial IO standard |
| |
| FCIA (Fibre Channel Industry
Association) - Business Consortium |
| |
| Forward Crosstalk - see
far-end crosstalk |
| |
| FPDP (Front Panel Data Port) -
VITA-system parallel IO standard |
| |
| Giga - prefix denoting billions
or 1,000,000,000 or 10 to the 9th power. |
| |
| Ground bounce - the "raising"
or "lowering" of the voltage on a ground plane or
ground pin due to the inductance of the ground path.
This can cause the receiving circuitry to
misinterpret a 1 or 0. |
| |
| HDMI (High Definition Multimedia
Interface) - TV display IO standard |
| |
| Hertz vs. bits/sec vs. Bytes/sec
- Hertz refers to frequency at which a signal
repeats itself; Mbps refers to how many bits per
second are transferred; MBps refers to how many
bytes per second are transferred. Generally a byte
is 8 or 16 bits long. In general, MHz equals
one-half of Mbps, (Therefore 400Mhz = 800 Mbps. If a
byte is 8 bits long, then 800 Mbps = 100 MBps.)
|
| |
| HSSDC2 - High Speed Serial
Digital Connection style 2, 1x IO standard |
| |
| HT (HyperTransport) - High end
server parallel IO standard, AMD led, 1x-32x, 2.6Ghz
per diff pair |
| |
| IB (InfiniBand) - High end
server IO standard |
| |
| IBTA (InfiniBand Trade Association)
- www.infinibandta.org |
| |
| Impedance - the opposition of
an electronic component to the flow of current,
measured in ohms. Most commonly thought of as a
resistor, however, all devices have impedance
associated with them. In transmission
lines , it is a measure of the
characteristic impedance of a cable, a PCB trace or
an interconnect. The impedance of a transmission
line (ZO ) is defined as: ZO =
√(L/C), where C = capacitance and L = inductance. As
capacitance decreases or
inductance increases per
unit length, the impedance of the cable or connector
will increase. Conversely, as capacitance increases
or inductance decreases per unit length, the
impedance of the cable or connector will decrease.
Typical transmission lines may have impedance of 50
or 100 ohms. When the impedance of a connector is
stated, the risetime of the pulse used to determine
that impedance should also be stated. |
| |
| Inductance - refers to the
ability of a device to store energy in the form of a
magnetic field. Cables have a certain inductance per
foot. In its simplest form, an inductor consists of
a wire loop or coil. The standard unit of inductance
is the henry, abbreviated H. This is a large unit.
More common units are the microhenry, abbreviated µH
(1 µH =10 -6 H) and the millihenry, abbreviated mH
(1 mH =10-3 H). Occasionally, the
nanohenry (nH) is used (1 nH = 10-9 H).
The reactance of an inductor increases as frequency
increases.
XL = 2πfL, where XL
= inductive reactance
f = frequency
and L = inductance |
| |
| Insertion loss - refers to the
losses resulting from the insertion of a cable,
connector or other device into an electrical system.
Includes, but is not limited to, DC losses from the
resistance of the conductor and skin
effect losses. |
| |
| Interlaken - new protocol and
physical layer spec, from Cisco |
| |
| Jitter - the shifting or
displacement of some aspect of the pulses in a
high-frequency digital signal. As the name suggests,
jitter can be thought of as shaky pulses. The
deviation can be in terms of amplitude
, phase timing
, or the width of
the signal pulse. Another definition is that it is
"the period frequency displacement of the signal
from its ideal location." Among the causes of jitter
are electromagnetic interference (EMI) and crosstalk
with other signals. Jitter can cause a display
monitor to flicker; affect the ability of the
processor in a personal computer to perform as
intended; introduce clicks or other undesired
effects in audio signals, and loss of transmitted
data between network devices. The amount of
allowable jitter depends greatly on the application. |
| |
| Kilo - prefix denoting
thousands or 1,000 or 10 to the 3rd power. |
| |
| Mega - prefix denoting millions
or 1,000,000 or 10 to the 6 th power. |
| |
| Microstrip - a specific
transmission line on a PCB where the signal trace is
on an outside surface of the PCB and is spaced above
a ground plane by the dielectric material, such as
FR-4.
 |
| |
|
Modeling - refers to the
creation and simulation of electronic circuits on a
computer. SPICE is the most common circuit simulator
in use. IBIS is a newer version that semiconductor
manufacturers prefer to use because it protects
their proprietary designs. The models can be created
using various methods including actual measurements
and computer programs. A model of a connector may
contain the inductance, capacitance, impedance and
time delay of the connector. These numbers can be
used in SPICE (and other) circuit simulation models
to simulate how the connector will perform in the
user's circuit. A "lumped" model uses R, L, and C
components to model the behavior of the device. A
lumped model is usually accurate then the device
being modeled is much "shorter" than the rise time
of the signal. A "distributed" model is a higher
order approximation that can more accurately
simulate the real world device.
|
| |
| Mutual Capacitance and Mutual Inductance
- the capacitances and inductances related
to two or more conductors in close proximity to each
other. These can cause interaction among the
conductors in the form of crosstalk
. |
| |
| MicroTCA (Micro TeleCom Architecture)
- new picoCell blade/backplane/chassis standard
using edge connectors |
| |
| MIL-1533 - 1Mbs military device
IO standard - new 10Mbs revision |
| |
| Myrinet - High end server
serial IO standard; 10G w/4 lanes x 3.125G |
| |
| Near end - refers to the driven
end of a transmission line
 |
| |
| Near-end (backward) crosstalk -
the crosstalk measured on
the victim line near the driven end of the active
signal line(s). |
| |
| Noise - refers to unwanted
signals or energy present on a data line. Noise can
be due to many outside influences such as
electromagnetic interference from transformers or
lightning. It can also be due to nearby circuits,
such as crosstalk. |
| |
| NPF (Network Processing Forum)
- business consortium - www.npf.org |
| |
| NUMA-Link (Non-Uniform Memory
Architecture) - wide-parallel semi-custom
IO interface for highest end servers |
| |
| Odd mode coupling - the
coupling between two signal paths within a pair that
is driven differentially |
| |
| Odd mode impedance - the
impedance of a single line in a coupled-line pair
when a differential signal drives both conductors
within the pair. |
| |
| OIF (Optical Internetworking Forum)
- www.oiforum.org |
| |
| OIF CEI (OIF Common Electrical
Interface) - cu backplane standard |
| |
| Packet - the unit of data that
is routed between an origin and a destination on the
Internet or any other packet-switched network. When
any file (e-mail message, HTML file, GIF file, URL
request, and so forth) is sent from one place to
another on the Internet, the Transmission Control
Protocol (TCP) layer of TCP/IP divides the file into
"chunks" of an efficient size for routing. Each of
these packets is separately numbered and includes
the Internet address of the destination. The
individual packets for a given file may travel
different routes through the Internet. When they
have all arrived, they are reassembled into the
original file (by the TCP layer at the receiving
end).
A packet-switching scheme is an efficient way to
handle transmissions on a connectionless network
such as the Internet. An alternative scheme,
circuit-switching, is used for networks allocated
for voice connections. In circuit-switching, lines
in the network are shared among many users as with
packet-switching, but each connection requires the
dedication of a particular path for the duration of
the connection. |
| |
| Packet-switched - describes the
type of network in which relatively small units of
data called packets are routed through a network
based on the destination address contained within
each packet. Breaking communication down into
packets allows the same data path to be shared among
many users in the network. This type of
communication between sender and receiver is known
as connectionless (rather than dedicated). Most
traffic over the Internet uses packet switching and
the Internet is basically a connectionless network.
Contrasted with packet-switched is
circuit-switched, a type of network such as the
regular voice telephone network in which the
communication circuit (path) for the call is set up
and dedicated to the participants in that call. For
the duration of the connection, all resources on
that circuit are unavailable for other users. Voice
calls using the Internet's packet-switched system
are possible. Each end of the conversation is broken
down into packets that are reassembled at the other
end.
Another common type of digital network that uses
packet-switching is the X.25 network, a widely
installed commercial wide area network protocol.
Internet protocol packets can be carried on an X.25
network. The X.25 network can also support virtual
circuits in which a logical connection is
established for two parties on a dedicated basis for
some duration. |
| |
| PCI (Peripheral Component Interface)
- parallel bus standard |
| |
| PCI-SIG (PCI Special Interest Group)
- www.pcisig.org |
| |
| PCIe (PCI Express) - serial
link standard 2.5, 5Gbs per diff pair, 8x, 16x, 32x
links |
| |
| PDH (Plesiochronous Digital Hierarchy)
- legacy telephony IO standard |
| |
| Phase timing - the timing
relationship between the clock signal edges and the
data signals edges |
| |
| PICMG (PCI Industrial Manufacturer
Group) - embedded computer business
consortium |
| |
| pRIO - Mature parallel Rapid IO |
| |
| Propagation delay - the speed
or rate with which a signal travels between the
input and output of a transmission line, usually
expressed in nanoseconds per foot. The materials
surrounding the conductor affect this speed. Space
or vacuum is the fastest medium (1 nsec/ft), whereas
air is 1.0167 nsec/ft. Teflon is slower than air
(1.45 nsec/ft), and FR-4 is slower than Teflon (2.12
nsec/ft). See also electrical length
.
PD (nsec/ft) = (√K)/Co
, where PD = propagation delay
K = dielectric
constant and Co = speed of light » 1 ft/nsec
 |
| |
| Reactance - the resistive
properties of capacitors and inductors at various
frequencies. See capacitance
and inductance . |
| |
| Remote IO - IBM high end
parallel/serial server IO standard; sometimes known
as RIO |
| |
| Return loss - refers to
distortion measured at the near end of the
transmission line due to reflections at
discontinuities (changes in characteristic
impedance) within the transmission line. These
losses are the result of part of the signal being
sent back to the source. |
| |
| RIO (Rapid IO) - high end
serial switch fabric IO standard; www.rapidio.org |
| |
| Risetime degradation - refers
to the increase in the risetime and falltime of a
pulse as it travels through a transmission line.
This means that a pulse with a 100 psec risetime
entering a cable or connector will exit that cable
or connector with a risetime longer than 100 psec.
 |
| |
| RPR (Resilent Packet Ring) -
IEEE-802.17 MAN IO standard |
| |
| SAS (Serial Attached SCSI) -
mid level T10.org storage IO standard |
| |
| SATA (Serial ATA) - the lower
end T13.org storage IO standard |
| |
| SCI (Scalable Coherent Interface)
- IEEE-1596 server parallel IO standard |
| |
| SCSI (Small Computer System Interface)
- storage parallel IO legacy standards |
| |
| SDH (Synchronous Digital Hierarchy)
- European standard equivalent to SONET |
| |
| SDI (Serial Digital Interface)
- the SMPTE-292 video IO standard |
| |
| SFPDP - serial FPDP IO
standard, www.vita.org |
| |
| SID (Society of Information Displays)
- International business consortium - promotes new
display technologies but not interfaces |
| |
| Signal - typically composed of
voltage and current travelling on a conductor (wire)
to convey information, data, or commands; has two
main characteristics: namely, amplitude
and time base |
| |
Signal attributes: -
Amplitude - indicates
voltage (or current) levels ("height" of signal)
Pulse Width - length of time
that digital signal is high (or low) measured at
50% of amplitude
Risetime - length of time
for digital signal to go from low to high;
usually defined as the Period of time that it
takes to go 10-90% or 20-80% of the high level
Rule of thumb :
10-90% risetime » 1.33 times the 20-80% risetime
Frequency - number of times
per second that a repeating signal (i.e., sine
wave, clock) repeats itself; usually expressed
as kHz (thousands of cycles per second), MHz
(millions of cycles per second) or GHz (billions
of cycles per second)
Period - length of time
before a repeating signal (i.e., sine wave,
clock) repeats itself. Period=1/frequency
Data Transfer Rate - see bit
rate
Wavelength - the physical
length of a period of
a signal. In air, the formula is l = c/f, where
l = wavelength, f = frequency and c = the speed
of light in air. In another dielectric, the
wavelength scales as 1/ Ö K, where K =
dielectric constant. Therefore, in any
dielectric, l = c/(f x Ö K). Wavelength in
air at 100 MHz = 120 inches; at 1 GHz = 12
inches; at 5 GHz = 2.4 inches
 |
| |
| Signal integrity (SI) - a term
used to refer to the quality of an electrical signal
after it has been sent down a conductor. It
encompasses many parameters such as
distortion , delay
, attenuation ,
ringing, crosstalk ,
dispersion ,
impedance , etc. |
| |
| Single-ended transmission -
also called single mode, uses two conductors, one
carries the signal, and one provides the return
path. Typical examples: coax, twin lead, twisted
pair, ribbon cable
 |
| |
| Skew - the difference in the
time that a pair of identical signals takes to get
from point A to point B going down two different
paths. Skew is the result of different electrical
lengths which in turn are the result of different
physical lengths (i.e. 12 inches vs. 12.5 inches)
and different velocities of propagation
. This property is important in
relation to the synchronization of data signals to
clock signals. See phase timing
. |
| |
| Skin effect - refers to the
phenomena whereby the signal traveling through a
conductor will be conducted only on the outer
surface (skin) of the wire as the frequency
increases. At lower frequencies the current travels
through the entire cross section of the conductor.
As the frequency increases, the current only travels
nearer the outer surface of the conductor. The
thickness of this "skin" scales as 1/√f, where f =
frequency. At 1 GHz the signal travels only on the
outer 2 microns (0.00008 inches) of a copper wire. |
| |
| SMPTE (Society of Motion Picture and
Television Engineering) - Society of Motion
Picture and Television Engineering - international
technical consortium for broadcast IO standards |
| |
| SONET (Synchronous Optical Network)
- WAN comm IO standard |
| |
| Speed - can refer to frequency,
bit rate, or velocity of propagation. High speed is
ambiguous; high speed to a PC designer may be 400
MHz but to a telecomm designer it may be 2.5 GHz. As
velocity of propagation, it refers to the speed at
which the signal travels from one point to another
along a conductor. The materials surrounding the
conductor affect this speed. For example, in air,
the velocity of propagation is 300 million meters
per second and in FR-4 printed circuit boards it is
about half that speed. See dielectric
constant .
Speedsignal = Co
/(√K), where Co = the speed of light and
K = dielectric constant
Speedsignal » 1 foot/nsec
in air and 6 inches/nsec in FR-4
Therefore, a 1nsec risetime is 6 inches long in a
PCB and 12 inches long in air |
| |
| sRIO (Serial RIO) - Sometimes
known as SRIO |
| |
| SSPI (Scalable SPI) - new high
end comm IO standard with NPF and OIF |
| |
| STA (SCSI Trade Association) -
business consortium - www.sta.org |
| |
| Stripline - a specific
transmission line on a PCB where the signal trace is
buried within the PCB and is spaced above and below
a ground plane by the dielectric material, such as
FR-4.
|
| |
| TDR (Time Domain Reflectometer) - TDR, is
a combination of a sampling oscilloscope and a fast
risetime signal source that can be used to measure
impedance, velocity of propagation, electrical
length, propagation delay, risetime degradation and
skew of cables and connectors. |
| |
| TDM (Time Division Multiplexing)
- a mature telephony interface |
| |
| Transmission line - commonly
used to denote a controlled impedance
conductor path that has a defined
velocity of propagation .
Geometry and dielectric materials determine many of
the properties of a transmission line. Examples are
coaxial cable, twinax or parallel paired cable,
twisted pairs, parallel traces on a PCB. |
| |
| UDI (Universal Display Interface)
- new display IO standard with DDWG |
| |
| Utopia - mature
intra/inter-rack telephony wide parallel IO standard |
| |
| VAUI (Vitesse Attachment Unit Interface)
- similar to XAUI |
| |
| Velocity of propagation - the
actual speed at which the signal travels from one
point to another along a conductor. The materials
surrounding the conductor affect this speed. For
example, in air, the velocity of propagation is 300
million meters per second and in FR-4 printed
circuit boards it is about half that speed. It is
usually expressed as a percentage of the speed of
light. Air is the fastest medium (100%), Teflon is
slower than air (70%), and FR-4 is slower than
Teflon (47%). Typically connectors are faster than
printed circuit boards; those connectors with the
most air being fastest. Velocity of propagation
affects skew . See
dielectric constant .
VP (%) = 1/(√K) x 100
where VP
= velocity of propagation and K = dielectric
constant |
| |
| VESA (Video Electronic Standards
Association) - display IO standards |
| |
| VITA (VME International Trade
Association) - www.vita.org |
| |
| VME (VERSA Modular Eurocard) -
European military IO standard |
| |
| VXS (VME Switched Serial) - a
4x 2.5 10Gbs VITA-41 IO standard |
| |
| XAUI - 10Gbs attachment unit
interface - 10G Ethernet interface |
| |
| XAUI-2 - 6Gbs per pair XAUI
interface from Intel 4x - SFF-8470 four lane, 8 diff
pair, IO connector used with IB and SAS |
