Rohde & Schwarz SMM100A, User Manual

Page: 276 / 1088

Adding noise and predistortions, and impairing the signal
R&S
®
SMM100A
276 User Manual 1179.1341.02 ─ 05
5.2 Impairing the signal
In the R&S SMM100A, analog and digital linear impairments such as I/Q imbalance
and quadrature error can be added to the generated signal.
The instrument can also simulate the effect of non-linear memoryless effects like
AM/AM and AM/PM conversion.
See user manual R&S SMM-K540, R&S SMM-K541 Envelope Tracking and AM/AM,
AM/PM Predistortion.
5.2.1 Required options
The base unit is sufficient. Additional options are not required.
5.2.2 About the linear I/Q impairments
Signal impairments ( I/Q Impairments ) are well-defined arithmetic modifications of the
data. Every data sample is modified in the same way.
Adding linear impairments to the data stream is provided for the following purpose:
●
To simulate frequent sources of distortions in a real signal-processing chain as, it is
required for tests with dirty transmitter conditions (receiver tests)
●
To compensate the faults of the I/Q demodulator in the receiver
See Chapter 5.2.4, "How to optimize the carrier leakage and sidebands suppression" ,
on page 282.
The R&S SMM100A offers functions to impair the internally generated signal or the
externally fed analog I/Q signal linearly:
●
Each generated I/Q stream can be impaired digitally
●
Analog impairments can be added to the externally applied analog I/Q signal,
before it is passed to in the I/Q modulator (see
"Defining the input signal of the I/Q
modulator" on page 284)
●
The internal signal can be impaired twice, analog and digital. If both types of
impairments are enabled, they superimpose each other in the signal.
Impairments caused by the I/Q modulator are automatically corrected by the Adjust I/Q
Modulator Current Frequency function.
See also Chapter 16.3.3.2, "How to use the internal adjustments" , on page 1024.
5.2.2.1 Gain and gain imbalance
An I/Q gain is a multiplication of all I/Q amplitudes by a common factor. The effect is
equivalent to two identical I and Q gain factors. The effect of an increased gain factor
in the I/Q constellation diagram is shown on
Figure 5-4 .
Impairing the signal