Glossary

NI Digital Waveform Generator/Analyzer Help

Edition Date: June 2013

Part Number: 370520P-01

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Prefix Meaning Value
p pico 10-12
n nano 10-9
µ micro 10-6
m milli 10-3
k kilo 103
M mega 106
G giga 109

Numbers and Symbols

° degrees
- negative of, or minus
< less than
> greater than
less than or equal to
greater than or equal to
Ω ohms
/ per
% percent
± plus or minus

A

A amps
aberration Signal distortions that cause imperfections in the shape or sharpness of the signal.
active drive A drive type where the generation voltage high level is configured as the voltage produced at the channel electronics when the Pattern Generation Engine generates a binary one.
ADE application development environment
any-rate clock An internal clock that can be configured to sub-Hertz resolution.
aperture time The interval during which the ADC reads the input signal from one channel. Aperture time is specified in seconds (s).
API application programming interface—a standardized set of subroutines or functions, along with the parameters that a program can call.
asynchronous For hardware, it is a property of an event that occurs at an arbitrary time, without synchronization to a reference clock. In software, it is the property of a function that begins an operation and returns prior to the completion or termination of the operation.
ATE automated test equipment—A term typically applied to computer-based systems for testing semiconductor components or circuit card assemblies.

B

b bits
B bytes
bidirectional data channels Data channels that can be programmatically configured as acquisition or generation.
bit Single value for a single position in time, on a single line. A bit can have four possible values: 0, 1, X, and Z.
buffer
  1. Temporary storage for acquired or generated data (software).
  2. A collection of samples.
bus
  1. Group of conductors that interconnect individual circuitry in a computer. Typically, a bus is the expansion vehicle to which I/O or other devices are connected.
  2. A logical grouping of multiple channels.

C

cache High-speed processor memory that buffers commonly used instructions or data to increase processing throughput.
channel Single digital terminal, used for generating and/or acquiring data.
characteristic impedance Transmission line parameter that determines how propagating signals are transmitted or reflected in the line.
clock
  1. Hardware component that controls timing for reading from or writing to channels.
  2. Periodic digital edges that can be used to measure time.
CompactPCI Core specification defined by the PCI Industrial Computer Manufacturer's Group (PICMG).
compare data Expected response data from your device under test (DUT).
control signals Signals that regulate/control the data transfer.
counter/timer A circuit that counts external pulses or clock pulses (timing).
crosstalk Ratio, in dB, of the level of the interference on the affected channel to the actual level of the interfering signal.
current sinking The ability to dissipate current for analog or digital signals.
current sourcing The ability to supply current for analog or digital signals.

D

DAQ Data Acquisition—Collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing. Also refers to collecting and measuring the same kinds of electrical signals with analog-to-digital and/or digital devices plugged into a PC, and possibly generating control signals with digital-to-analog and/or digital devices in the same PC.
Data Active event The Data Active event indicates when the Pattern Generation Engine is generating data. If the Pattern Generation Engine is waiting for a trigger or is paused, the Data Active event is deasserted. When the Pattern Generation Engine is generating data, the Data Active event is asserted, synchronous with the data.
data interpretation Data interpretation determines whether the input signal is acquired as a 0 or a 1, based on how it relates to the Acquisition Voltage High and Low Levels and the configured data interpretation mode.

In High or Low mode, when the input signal is sampled below Acquisition Voltage Low Level, a 0 is received. A 1 is not recognized until the acquired signal passes above Acquisition Voltage Low Level and above Acquisition Voltage High Level. Conversely, if the acquired signal was last sampled above Acquisition Voltage High (as a 1), the signal is not be sampled as a 0 until the signal is sampled below Acquisition Voltage High Level and below Acquisition Voltage Low Level.

In Valid or Invalid mode, signals sampled between the Acquisition Voltage High and Acquisition Voltage Low Levels are returned as a 1, while signals sampled either above Acquisition Voltage High Level or below Acquisition Voltage Low Level are returned as a 0.
data rate multiplier an attribute that specifies whether the device to acquires or generates in single data rate (SDR) mode or in double data rate (DDR) mode.
DC direct current
DC Voltage The direct current (non-changing) component of a voltage. In practice, the DC voltage should not change over the period of observation, that is, the measurement time.
DCL Driver-Comparator-Load
default setting Default parameter value recorded in the driver. In many cases, the default input of a control is a certain value (often 0) that means use the current default setting.
device Plug-in data acquisition board, card, or pad that can contain multiple channels and conversion devices. Plug-in boards, PCMCIA cards, and devices that connects to your computer parallel port, are all examples of DAQ devices.
differential circuitry Circuitry that actively responds to the difference between two terminals, rather than the difference between one terminal and ground.
digital trigger Level signal having two discrete levels: a high and a low level. See trigger.
DIO digital input/output
Direct DMA Direct DMA can be used to transfer waveform data to the onboard memory at rates well beyond the typical 5 to 30 MB/sec range in a standard PC-based architecture by establishing a direct connection between the onboard memory and a specialized waveform data source.
drift Clock drift occurs when the transmitter's clock period is slightly different from that of the receiver. After many clock cycles, the difference between the two periods becomes noticeable and may cause loss of synchronization and other errors.
drive data Provided stimulus data to your device under test (DUT) from your NI digital waveform generator/analyzer.
drive type Describes the behavior of the generation channels, and what the generation channels do when set to high level.
DUT device under test

E

End of Record event An event that indicates when the device enters its Record Complete state, which indicates that the current record has been acquired.
event Events are emitted to signify a device state change, the arrival of a certain kind of sample, the production of a certain number of samples, or the passage of time.
eye diagram Diagram constructed by looking at the outputs of a digital transmitter over three periods of the main system clock.

F

fall time The time that it takes a signal to fall from 80% to 20% of the voltage between the voltage low level and the voltage high level.
fetch An operation that transfers acquired waveform data from device memory to PC memory.
FPGA field-programmable gate array—Fundamentally, an FPGA is a semi-conductor device which contains a large quantity of gates (logic devices), which are not interconnected, and whose function is determined by a wiring list, which is downloaded to the FPGA.
frequency The basic unit of rate, measured in events or oscillations per second. Frequency (f) is the reciprocal of the period of a signal.
function Set of software instructions executed by a single line of code that can have input and/or output parameters and returns a value when executed.

G

group Collection of lines.

H

high level For generation, the high level is the voltage produced when a binary one is generated. For acquisition, the high level is the voltage threshold above which the input will be sampled as a binary one.

I

I/O input/output—Transfer of data to/from a computer system involving communications channels, operator interface devices, and/or data acquisition and control interfaces.
idle state Specifies the values of the channels when the generation operation is paused or has completed.
IIH current input high—The maximum amount of current required on the input pin when the voltage on the input pin is higher than VIH.
IIL current input low—The maximum amount of current required on the input pin when the voltage on the input pin is lower than VIL.
Initial state Specifies the values of the channels when the generation operation has not yet started.
instructions Statements used to define a script.
interrupt Computer signal indicating that the CPU should suspend its current task to service a designated activity.
inter-symbol interference In a digital transmission system, distortion of the received signal, in which distortion in the form of temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between state changes.
IOH current output high—The minimum amount of available current on the output pin when the logic device is driving a logic high.
IOL current output low—The minimum amount of available current on the output pin when the logic device is driving a logic low.

J

jitter The deviation from ideal timing of an event. Jitter is typically measured from the zero-crossing of a reference signal. Jitter typically comes from crosstalk, simultaneous switching outputs, and other regularly occurring interference signals.

L

line Represents the value of one bit of a sample over all samples. A line is independent of any hardware I/O connector.
line group A collection of lines displayed as a single plot on a digital waveform graph.
line name Name of a line within a sample or buffer.
low level For generation, the low level is the voltage produced when a binary zero is generated. For acquisition, the low level is the voltage threshold below which the input will be sampled as a binary zero.
LSB least significant bit
LVDM LVDM is an LVDS-compatible standard that allows for a 100  parallel termination at the source.
LVDS low voltage differential signaling. A low-noise, low-power, low-amplitude method for high-speed digital data transfer.

M

Marker event The Marker event is a general-purpose event that is configured within a generation script. The Marker event can be asserted synchronous to any even numbered sample within a waveform within a script.
MB/s Unit for data transfer that means one million or 106 bytes per second.
Measurement & Automation Explorer (MAX) Controlled, centralized configuration environment that allows you to configure all of your National Instruments DAQ, GPIB, HSDIO, IMAQ, IVI, Motion, and VISA devices.
MSB most significant bit

N

NIM noise immunity margin—Extra margin between the voltage level being driven by the source and the voltage level required at the destination.

O

On Board Clock For NI Digital Waveform Generator/Analyzers, this term refers to the onboard voltage-controlled crystal oscillator (VCXO) clock source.
Onboard Reference clock On PCI devices, the Onboard Reference Clock is the 10 MHz signal you can export to RTSI 7 on the RTSI trigger bus.
open collector A drive type where the generation voltage high level is configured as the high-impedance state.
overshoot Overshoot is a peak distortion following an edge.

P

parallel termination Termination that matches the characteristic impedance of the medium at the end of the transmission line.
Pause trigger Trigger used to indicate to the device that it should stop generating and/or acquiring. The device resumes when the pause trigger becomes inactive.
PFI Programmable Function Interface. I/O channels to the digital waveform generator/analyzer. Functionality and specifications will vary by device and operation.
pin number See terminal.
posttrigger Acquiring data that occurs after a trigger.
PPMU per pin parametric measurement unit—A device capable of sourcing and measuring DC voltage and current with moderate accuracy.
preshoot Preshoot is a peak distortion preceding an edge.
pretrigger Acquiring data that occurs before a trigger.
programmable function interface See PFI.
propagation delay The amount of time required for a signal to pass through a circuit.
protocol The exact sequence of bits, characters and control codes used to transfer data between computers and peripherals through a communications channel, such as the GPIB.
PXI PCI eXtensions for Instrumentation—Rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features.
PXI trigger bus PXI equivalent of the RTSI bus, with additional timing and synchronization capabilities.

R

Ready for Advance event An event that indicates when the device enters its Wait for Advance Trigger state, which indicates that the acquisition of the previous record is complete.
Ready for Start event For both acquisition and generation, the Ready For Start event indicates that the NI digital waveform/generator analyzer is configured and ready to receive a Start trigger.
real time Property of an event or system in which data is processed as it is acquired instead of being accumulated and processed at a later time.
Reference clock Clock to which a device phase locks another, usually faster, clock. A common source for the reference clock is the 10 MHz oscillator present on the PXI backplane.
Reference trigger This trigger establishes the reference point that separates pretrigger and posttrigger samples.
remote sensing A method of monitoring the output voltage directly at the load rather than at the source's output terminals. Remote sensing improves regulation when in voltage mode.
ringing The oscillating characteristic of a square wave that may occur immediately after the transition from one level to another. The ringing occurs due to resonances in the circuit that the signal passes through.
rise time The time that it takes a signal to rise from 20% to 80% of the voltage between the voltage low level and the voltage high level.
round trip delay Time required for the data to move from the digital tester, through the cable and DUT, and back to the tester.
Rsource source impedance
RTD See round trip delay.
Rterm termination impedance
RTSI bus Real-Time System Integration Bus—The National Instruments timing bus that connects DAQ devices directly, by means of connectors on top of the devices, for precise synchronization of functions.

S

s seconds
S sample
sample The value being generated/acquired on all of the digital data channels during a single sample clock cycle.
Sample clock Samples are generated or acquired based on Sample clock cycles.
Sample Error event An event that indicates when the device detects a sample where the actual response and the expected response do not match.
script Collection of instructions that describe the order and timing of one or more waveforms.
Script trigger General-purpose trigger that has a role that is determined by the context of the script.
self-calibration A form of calibration that establishes the relationship of an instrument's measurement to the value provided by an internal standard. When that relationship is known, the instrument can then adjust itself for the best accuracy.
series termination Termination that places series impedance equal to the characteristic impedance at the source of the transmission line.
settling time Time required for an amplifier, relay, or other circuits to reach a stable mode of operation.
signal Means of conveying information. In this help file, signal refers to a digital transmission.
sink A device that can dissipate power.
sinking The ability to dissipate power from active circuitry.
software trigger Programmed event that triggers an operation such as data acquisition.
source The device that can supply power to an external device.
sourcing The ability to supply power for external circuitry.
SMU source-measure unit—A device capable of sourcing and measuring DC voltage and current with high precision.
Start trigger The Start trigger transitions a device into a state where the device can respond to Sample clocks. For an acquisition session, the device starts sampling and storing data. For a generation session, the device starts generating samples.
static acquisition Software-timed (nonclocked) that returns the current digital logic state of the configured data channels with each read.
static generation Software-timed (nonclocked) that sets the current state of the configured data channels to the requested digital logic state.
Stop Trigger The Stop Trigger stops active generation regardless of the the current state of the generation. The stop trigger is a request to stop, not an immediate synchronized trigger; therefore, it will take some clock cycles for the device to actually stop. The Stop Trigger is only valid for generation sessions and only available on the NI PXIe-6544/6545/6547/6548.
streaming A method of generating waveforms that are too large to fit in device onboard memory by filling an allocated portion of onboard memory with the first part of the waveform; and as the waveform is generated and space becomes free in onboard memory, refilling the space with new waveform data.
strobed I/O Any operation where every data transfer is timed by hardware signals. For software, it is a property of a function that begins an operation and returns only when the operation is complete.
synchronous For hardware, it is a property of an event that occurs at a particular time, synchronized to a clock.

T

terminal Named location where a signal is either produced (generated) or consumed (acquired).
tfall fall time
tpd propagation delay
transfer rate Rate, measured in bytes/s or samples/s, at which data is moved from source to destination after software initialization and set up operations; the maximum rate at which the hardware can operate.
trigger A signal sent to the device to control the device in some way. In the context of the NI digital waveform generator/analyzer, triggers are essentially the opposite of events.
trise rise time
ts settling time
TTL transistor-transistor logic

U

unstrobed I/O Basic digital I/O operations that do not involve the use of control signals in data transfers. Unstrobed data transfers are controlled by software commands. Also known as software-timed I/O.

V

V volts
VCXO voltage-controlled crystal oscillator
vector See sample.
VHDCI very high-density connector interface
VI Virtual Instrument
  1. A combination of hardware and/or software elements, typically used with a PC, that has the functionality of a classic stand-alone instrument.
  2. A LabVIEW software module (VI), which consists of a front panel user interface and a block diagram program.
VIH voltage input high—The input voltage level at or above which the logic device senses a binary one.
VIL Input voltage level at or below which the logic device senses a binary zero.
virtual channels Channel names that can be defined outside the application and used without having to perform scaling operations.
VOD differential output voltage—The difference in voltage between the positive and complementary conductors of a differential transmission. Can be thought of as the difference of the two conductors.
VOH voltage output high—The generated voltage level at the output pin when the logic device outputs a binary one.
VOL voltage output low—The generated voltage level at the output pin when the logic device outputs a binary zero.
VOS offset voltage—The common mode of the differential signal. Can be thought of as the average of the two conductors.
VRANGE input voltage range—The absolute voltage, referenced to common, allowed by the receiver.
VTH threshold voltage—the differential voltage threshold at which the receiver registers a valid logic state.

W

waveform A collection of digital samples generated or acquired at the DDC connector.

X

x Bit state meaning that the channel is ignored.

Z

z Bit state meaning that the channel is set to high-impedance.
Z0 The characteristic AC impedance of the transmission line.
Zs The impedance at the source of the transmission line.
Zt The impedance at the destination of the transmission line.

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