Glossary

NI RF Signal Generators Help (NI-RFSG 18.1)


Edition Date: June 2018
Part Number: 371025V-01
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Prefixes

Symbol Prefix Value
p pico 10 -12
n nano 10 -9
µ micro 10 -6
m milli 10 -3
k kilo 10 3
M mega 10 6
G giga 10 9
T tera 10 12

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

ADE application development environment—A software environment incorporating the development, debug, and analysis tools for software development. LabVIEW, Measurement Studio, and Visual Studio are examples.
ADC analog-to-digital converter—A hardware component that converts analog voltages to digitized values. An ADC can convert an analog signal to a digital signal representing equivalent information.
AE amplitude extender—Refers to the PXIe-5696 amplitude extender module that you can use to extend the capabilities of the PXIe-5654 RF signal generator.
ALC automatic level control
AM amplitude modulation—A modulation technique where the carrier is multiplied by the modulation signal. It effectively generates two symmetrical side bands and suppresses the carrier.
analog A signal with an amplitude that can have a continuous range of values.
API application programming interface—Programming interface for controlling some software packages, such as the instrument design libraries.
AWG arbitrary waveform generator—A waveform generator capable of generating waveforms of arbitrary, user-defined shapes. The desired signal is designed by the user, loaded into the waveform generator memory, and output through a DAC.

B

bandwidth The measure of a circuit or transmission channel to pass a signal without significant attenuation over a range of frequencies. Bandwidth can also refer to the information rate (in bits per second) that can pass through a circuit or transmission channel.
baseband The range in the frequency spectrum occupied by a DC-centered signal. Both the information signal and the downconverted complex I/Q signal are referred to as baseband signals.
baseband signal See message signal.
broadband noise A sound or other type of analog signal where the time history does not repeat itself. In the frequency domain, broadband noise has a continuous spectrum, meaning that energy is present at all frequencies in a given range. Broadband noise is considered noise because it usually lacks a discernible pitch.

C

carrier The signal that carries the information encoded or modulated on it. Typically, the carrier is a fixed frequency sine wave, which may be amplitude-, phase-, or frequency- modulated.
carrier frequency The frequency of the carrier signal that is a sinusoidal signal upon which the desired signal to be transmitted is modulated. The sinusoidal signal "carries" the modulation.
center frequency The frequency of the middle of the bandwidth of a channel.
chirp A very rapid sweep of a sine wave as a function of frequency.
CW continuous wave—A continuous sine wave that is the carrier wave in a radio transmission.

D

DAC digital-to-analog converter—An electronic device, often an integrated circuit, that converts a digital number into a corresponding analog voltage or current.
dBFS Decibels relative to full scale—A measure of decibel amplitude level in a digital system that has a defined maximum available peak level.
demodulation Describes the recovery, from a modulated wave, of a signal having the same characteristics as the original message signal.
DDC digital downconverter—A hardware component that performs IF to I/Q conversion in the digital domain. The DDC frequency-translates RF signals to center around a specified IF frequency, while filtering certain frequency bands and reducing the signal sampling rate.
DDS direct digital synthesis—A signal generation technique that yields very high-frequency resolution.
DMA direct memory access—Method by which data can be transferred to/from computer memory from/to a device or memory on the bus while the processor performs another task.
digital modulation A technique for encoding digital data on a carrier frequency.
downconverter A signal conditioning device that converts a specific band of high-frequency (RF) signals to lower, more manageable IF frequencies that can be digitized.
DSP digital signal processing
DUC digital upconverter
DUT device under test
dynamic range The range between the minimum detectable signal, typically the noise floor, and the -1 dB compression point.

E

EVM error vector magnitude—A measurement of demodulator performance in the presence of impairments. The soft symbol decisions obtained after decimating the recovered waveform at the demodulator output are compared against the ideal symbol locations. The root mean square (RMS) error vector magnitude and phase error are used to determine the EVM measurement over a window of N demodulated symbols.

F

FFT fast Fourier transform—An efficient mathematical algorithm used for spectrum analysis. Refer to Fourier transform.
FIR finite-impulse response—Used to describe a filter with no feedback elements.
FM frequency modulation—A process that varies the frequency of a sinusoidal carrier wave from a center frequency by an amount proportional to the instantaneous value of the message signal. In FM, the center frequency is the carrier frequency.
frequency deviationRefers to the maximum absolute difference, during a specified period, between the instantaneous frequency of the modulated wave and the carrier frequency.
Fourier transform A mathematical technique that resolves a given signal into the sum of sines and cosines. Widely used as the FFT (fast Fourier transform), which is the basis for spectrum analysis.
frequency The number of cycles per unit time. The International System of Units has set hertz (Hz) as the standard unit of measurement for frequency, where 1 Hz equals one cycle per second.
FSK frequency-shift keying—A type of frequency modulation which assigns bit values to discrete frequency levels.

G

gain Amplification of a signal. A gain of two corresponds to a doubling of the signal level.

H

harmonic In a complex signal, a component with a frequency that is a multiple of the fundamental frequency.

I

IF intermediate frequency—Refers to the signal passed from the AWG module front panel CH 0 SMA connector to the upconverter module front panel INPUT SMA connector. This signal is upconverted to the requested RF output signal.
I/Q data The translation of the magnitude and phase data of a signal from a polar coordinate system to a complex Cartesian (X,Y) coordinate system.
I/Q signal A control signal for changing an RF carrier signal.

L

linearity For signal measurement systems, linearity refers to mechanical response of hardware to signals. A linear system will respond in a determinable way to signals. A nonlinear system contains components that do not respond to signals in a determinable way for a variety of reasons that include, but are not limited to: temperature susceptibility, improperly terminated connections, and inherent device design. This nonlinear response to signals contributes noise to a system. If a system is nonlinear, the system response to signals produces noisy results.
LO local oscillator—Refers to an internal oscillator in a radio, receiver, or instrument that tunes the frequency of the device. The local oscillator is mixed with a fixed frequency oscillator, which generates a sum and difference component. Also refers to the PXI/PXIe-5650/5651/5652 RF signal generators that are used with the PXIe-5450/5451 AWG module and the PXIe-5611 I/Q modulator module to comprise the PXIe-5673/5673E.
lowpass filter A circuit that attenuates the high-frequency components in an analog signal and only passes low frequencies. For imaging, a lowpass filter removes detail and blurs the image.

M

message signal Contains the data for transmission. The message signal is used to modulate the carrier wave to create the modulated wave for transmission. The message signal data is recovered from the modulated wave by a process of demodulation. The message signal is often referred to as the baseband signal or the information signal.
MER modulation error ratio—A measure of the signal-to-noise ratio (SNR) in a digitally modulated signal. Like SNR, MER is usually expressed in dB.
mixer A nonlinear analog circuit that multiplies two signals. Mixers are typically used to shift signal frequencies. A mixer receives two sinusoidal input signals at different frequencies and returns a signal with components at frequencies equal to the sum and difference of the two original input frequencies. Nonlinear mixers are used when performing amplitude modulation of RF carrier signals.
mixer level Represents the attenuation to apply to the input RF signal as it reaches the first mixer in the signal chain.
modulated wave The signal for transmission, which consists of the carrier wave modulated by the message signal. The message signal is recovered by the receiver through a process of demodulation.
modulation A process, or the result of a process, by which characteristics of a carrier wave are altered according to information in the information signal to give rise to a modulated wave, which is transmitted.
module Refers to the PXI/PXIe-5650/5651/5652, PXIe-5654/PXIe-5654 with PXIe-5696 hardware, or to one of the hardware components of the PXI-5670/5671, PXIe-5672/5673/5673E vector signal generator: the AWG module or the upconverter module.
MSK minimum shift keying—A subtype of FSK modulation. MSK uses a half-cycle sinusoidal pulse, making the phase change linear and keeping side lobes low to control adjacent-channel interference.
MXI Multisystem Xtension Interface—A high-speed serial interface bus designed to connect computers to PXI, or to connect multiple PXI chassis. In this document, MXI refers to NI MXI-3 or MXI-4 systems.

N

NCO numerically controlled oscillator—An oscillator that has a frequency that is controlled by a digital pattern.
noise figure An expression of the noise generated within a device, specified in dB, above the theoretical noise floor of a given bandwidth. Thus, a device with a noise figure of 0 dB has achieved the theoretically lowest noise. The noise figure of a unit under test (UUT) is the ratio of its noise power to the noise power that a matched resistive load would deliver at room temperature.
NPD noise power density—The spectral density of random noise normalized to 1 Hz bandwidth. See PSD.

O

OCXO oven-controlled crystal oscillator
OOK on-off keying—A modulation scheme which consists of keying a sinusoidal carrier signal on and off with a unipolar binary signal.
OSP onboard signal processing

P

passband The range of frequencies which a device can properly propagate or measure.
passband flatness A measure of the amplitude accuracy of the frequency response with respect to frequency. Passband flatness is typically specified in ±dB and referenced to the amplitude of the frequency response at a designated frequency.
PCI Express peripheral component interconnect express—A version of PCI that maintains the PCI software usage model and replaces the physical bus with a high-speed serial bus serving multiple lanes.
peer-to-peer stream The flow of data in a peer-to-peer system. The peer-to-peer stream acts like a single, unidirectional pipe from which data can flow directly from one device to another.
peer-to-peer streaming A data streaming architecture used to transfer data between hardware devices. Use of this architecture allows two or more devices to transfer data directly to each other without first going through the host processor.
PFI Programmable Function Interface—I/O channels to the digital waveform generator/analyzer. Functionality and specifications vary by device and operation.
phase noise The noise of a carrier signal due to unwanted phase and frequency modulation the signal. Phase noise is normally very close to the carrier, and is measured in dBc, that is, decibels relative to the carrier frequency.
phase offset The ability to delay the phase of a signal with respect to a reference signal or an external signal.
PLL phase-locked loop—An electronic circuit which forces an output frequency to be locked to the same phase as a reference frequency.
PM
  1. The modulation of pulsed signals, where the duration of the pulse is proportional to some characteristic of the modulating signal, for example, its amplitude. Several common forms of pulse modulation are pulse amplitude modulation (PAM) and pulse-width modulation (PWM).
  2. Modulation of the phase of the carrier.
PRBS pseudorandom bit sequence
PSD power spectral density—The power of a signal measured in the frequency domain and normalized to a 1 Hz bandwidth.
PSK phase-shift keying—Refers to, in digital transmission, a type of angle modulation in which the phase of the carrier is discretely varied to represent data being transmitted—either in relation to a reference phase or to the phase of the immediately preceding signal element.
PXI A rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features. The PXIbus standard was originally developed by National Instruments in 1997, and is now managed by the PXIbus Systems Alliance.
PXI Express PCI Express eXtensions for Instrumentation—The PXI implementation of PCI Express, a scalable full-simplex serial bus standard that operates at 2.5 Gb/s and offers both asynchronous and isochronous data transfers.
PXI Express compatible module A PXI module compatible with existing PXI slots and PXI hybrid slots. PXI Express compatible modules maintain hardware and software compatibility, with the exception of local bus.
PXI trigger bus PXI equivalent of the RTSI bus, with additional timing and synchronization capabilities.

Q

quadrature modulation Any modulation scheme that uses two carrier waves out of phase by 90° that are modulated by separate information signals.

R

record A group of samples. Acquired data is stored into device onboard memory as a record. When configuring an acquisition session, you can determine how many samples are stored in a record.
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 level The reference level represents the maximum expected power of an input RF signal.
resolution The smallest signal increment that can be detected by a measurement system. Resolution can be expressed in bits, in proportions, or in percent of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244 percent of full scale.
RMS root–mean–square—The square root of the average value of the square of the instantaneous signal amplitude; a measure of signal amplitude. The RMS voltage of a signal is computed by squaring the instantaneous voltage, integrating over the desired time, and taking the square root.

S

Sample Clock Signals that are used to clock samples in or out of ADCs and DACs. Samples are generated or acquired based on Sample Clock cycles.
sample rate The rate at which a device acquires an analog signal, expressed in samples per second (S/s). The sample rate is typically the clock speed of the analog-to-digital converter (ADC).
SFDR spurious free dynamic range—The separation or distance, expressed in dB, from the amplitude of the fundamental frequency and the next highest spur.
signal bandwidth Twice the maximum baseband signal deviation from 0 Hz. Usually, the baseband signal center frequency is 0 Hz. In such cases, the signal bandwidth is simply the baseband signal's minimum frequency subtracted from its maximum frequency, or fmax – fmin.
SINAD signal-to-noise distortion
sinusoid A mathematical function that describes a repetitive oscillation. Sinusoid is synonymous with sine wave.
SMA A small type of threaded coaxial signal connector typically used in higher frequency applications.
SMB sub-miniature type B—A small coaxial signal connector typically used in high-frequency applications. SMC uses a threaded connector, while the SMB "snaps" to the mating connector.
SMC sub-miniature type C—A small coaxial signal connector typically used in high-frequency applications. SMC uses a threaded connector, while the SMB "snaps" to the mating connector.
SNRsignal-to-noise ratio—The ratio of the desired signal amplitude to the noise signal amplitude at a given point in time. SNR is expressed as 20 times the logarithm of the amplitude ratio, or 10 times the logarithm of the power ratio. SNR is usually expressed in dB and in terms of peak values for impulse noise and root-mean-square values for random noise. In defining or specifying the SNR, specify the signal and noise characterizations, for example, peak-signal-to-peak-noise ratio to avoid ambiguity.
spectral densityA measure of total signal power in a specified spectral bandwidth divided by the bandwidth, expressed in watts per hertz (W/Hz).
spurs spurious effects—Undesired signals. Spurious signals can be considered in two classes: 1) Stationary, that is, their frequency and amplitude do not change significantly, 2) Non-stationary, where the frequency and/or amplitude change significantly over short time periods.

T

THD total harmonic distortion—The ratio of the sum of the powers of the first five harmonics above the measured fundamental frequency to the power of the fundamental frequency. THD is usually expressed in dB or dBc. Measurements for calculating the THD are made at the output of a device under specified conditions.
TOI third order intercept—The theoretical level at which the third order harmonic distortion component has the same level as the fundamental tone.
transient A brief oscillation resulting from a sudden change of voltage, current, or load.
trigger Any event that causes, starts, or stops some form of data capture. An external stimulus that initiates one or more instrument functions. Trigger stimuli include a front panel button, an external input voltage pulse, or a bus trigger command. The trigger may also be derived from attributes of the actual signal to be acquired, such as the level and slope of the signal.
TTL Transistor-Transistor Logic
tuning speedThe time required by a signal to lose lock on one frequency and jump to another frequency within a given frequency tolerance.

U

upconverter A signal conditioning device that converts a baseband signal to a real signal with the same frequency content centered at a higher frequency.

V

VCO voltage-controlled oscillator
VCXO voltage-controlled crystal oscillator
VSA vector signal analyzer
VSG vector signal generator
VST vector signal transceiver
VSWR voltage standing wave ratio—The loss due to the mismatch introduced into the signal by the load or source signal path characteristics. The ratio of the highest voltage to the lowest voltage found in the signal.

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