Agilent Technologies E8257D, Руководство пользователя

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Chapter 10 231
10
Two–Tone Waveform Generator
In the following sections, this chapter describes the two–tone mode, which is available only in
E8267D PSG vector signal generators with Option 601 or 602:
• “Overview” on page 231
• “Creating, Viewing, and Modifying Two–Tone Waveforms” on page 231
See also: “Arbitrary (ARB) Waveform File Headers” on page 80
Overview
The two–tone mode builds a waveform that has two equal–powered CW signals, or tones. The default
waveform has two tones that are symmetrically spaced from the center carrier frequency, and have
user–defined amplitude, carrier frequency, and frequency separation settings. The user can also align
the tones left or right, relative to the carrier frequency.
The two–tone waveform generator is designed for testing the intermodulation distortion
characteristics of non–linear devices, such as mixers or amplifiers. Intermodulation distortion (IMD)
occurs when non–linear devices with multiple input frequencies interfere with adjacent channels or
cause unwanted outputs at other frequencies. The two–tone waveform generator supplies a signal
whose IMD products can be measured using a spectrum analyzer and used as a reference when
measuring the IMD generated by a device–under–test.
Two–tone waveforms are created using the internal I/Q baseband generator and stored in ARB
memory for playback. Although the two–tone mode generates a high–quality waveform, a small
amount of IMD occurs. In addition to IMD, a small amount of carrier feedthrough and
feedthrough–related IMD may be present when the spacing between the tones is centered on the
carrier frequency. To minimize carrier feedthrough for a two–tone signal, you must manually adjust
the I and Q offsets while observing the center carrier frequency with a spectrum analyzer. For
measurements that require the absence of IMD and carrier feedthrough, you can create
distortion–free multitone signals using Agilent Technologies’ Signal Studio software Option 408.
NOTE For more information about two–tone waveform characteristics and the E8257D/67D PSG
Vector Signal Generator two–tone format, download
Application Note 1410 from our website
by going to http://www.agilent.com and searching for “AN 1410” in Test & Measurement.
Creating, Viewing, and Modifying Two–Tone Waveforms
This section describes how to set up, generate, and modify a two–tone waveform while viewing it
with a spectrum analyzer. Although you can view a generated two–tone signal using any spectrum
analyzer that has sufficient frequency range, an Agilent Technologies PSA Series High–Performance
Spectrum Analyzer was used for this demonstration. Before generating your signal, connect the
spectrum analyzer to the signal generator as shown in
Figure 10- 1 .