Keysight x-series Measurement Guide

221
Concepts
Baseband I/Q Inputs (Option BBA) Measurement Concepts
Baseband I/Q Inputs (Option BBA) Measurement Concepts
The N9020A Option BBA Baseband I/Q Inputs provides the ability to analyze
baseband I/Q signal characteristics of mobile and base station transmitters. This
option may be used only in conjunction with the following modes:
• IQ Analyzer (Basic)
• 802.16 OFDMA (WiMAX/WiBro)
• cdma2000
•GSM/EDGE
• TD-SCDMA
What are Baseband I/Q inputs?
Option BBA consists of a Baseband Input module, four input connectors, and a
calibration output connector. The connectors are at the left side of the front panel.
The two ports labeled “I” and “Q” are the “unbalanced” inputs.
An unbalanced or “single-ended” baseband measurement of an I or Q signal is made
using a probe connected to the I or Q connector. A simultaneous I/Q unbalanced
single-ended measurement may be made using two probes connected to the I and Q
input connectors.
If “balanced” signals are available, they may be used to make a more accurate
measurement. Balanced signals are signals present in two separate conductors, are
symmetrical about ground, and are opposite in polarity, or out of phase by 180
degrees.
Measurements using balanced signals can have a higher signal to noise ratio
resulting in improved accuracy. Noise coupled into each conductor equally in a
“common mode” to both signals may be separated from the signal. The measure of
this separation is “common-mode rejection”.
To make a balanced measurement, the two connectors labeled “I” and “Q” are used
in conjunction with the I and Q inputs. The terms “I-bar” and “Q-bar” may be
applied to the signals, as well as the inputs themselves. Probes (customer provided)
must be used to input balanced baseband I/Q signals. This may be referred to as a
balanced measurement.
Balanced baseband measurements are made using the I and connectors for I only
signal measurements, while the Q and connectors are used for a Q only signal
measurement. Balanced measurements of I/Q require differential probe connections
to all four input connectors. For details of probe selection and use, refer to
“Selecting input probes for baseband measurements” on page 223.
What are Baseband I/Q signals?
In transmitters, the term baseband I/Q refers to signals that are the fundamental
products of individual I/Q modulators, before the I and Q component signals are
combined, and before upconversion to IF or RF frequencies.

Keysight x-series Specifications

General

Analysis Bandwidth	Up to 1 GHz (depending on model)
Real-Time Bandwidth	Up to 1 GHz (depending on model)
Form Factor	Benchtop
Connectivity	LAN, USB, GPIB
Resolution Bandwidth	1 Hz to 10 MHz (depending on model)