14
The PSG Vector Signal Generator
Two-tone and Multitone Personalities
Fundamentally, both the two-tone and multitone personalities operate in a similar manner.
First the user configures the signal parameters (tone spacing, initial phase, etc.) and
activates the application, then the baseband generator calculates the I/Q sample points
that represent the baseband multitone signal and loads them into baseband memory for
playback. The complex baseband signal is subsequently fed to the I/Q modulator for up-
conversion to the desired carrier frequency. The tones are placed symmetrically around the
carrier frequency of the PSG and the total power is divided among the tones based on the
relative tone power settings, Table 1.
Common multitone configurations
Number
Peak-to-average Maximum average Maximum average Maximum
of tones
ratio of composite power of composite power per tone relative tone
multitone signal
1
multitone signal
2
multitone signal
3
spacing
4
2 3 dB 15 dBm 12 dBm 80 MHz
8 9 dB 9 dBm 0 dBm 10 MHz
16 12 dB 6 dBm -6 dBm 5 MHz
32 15 dB 3 dBm -12 dBm 2.5 MHz
64 18 dB 0 dBm -18 dBm 1.25 MHz
Table 1. PSG multitone signal generation capability for common multitone configurations.
A key benefit derived from these PSG personalities is reduced test time. Of course,
calculation time increases with the number of enabled tones, however waveform build
speed is generally negligible. The PSG high-speed microprocessor is capable of calculating
waveforms with 64 enabled tones in just a few seconds. Waveform build time can also be
reduced to a one-time operation by taking advantage of the PSG waveform storage/recall
capability.
The I/Q waveforms created by the application can be stored in the instrument non-volatile
memory and quickly recalled for playback. Simply build a library of pre-configured test
signals and recall them at will or, to achieve the fastest waveform switching speed, use
the baseband generator waveform sequencing capability. This feature allows you to load
multiple test waveforms into baseband memory and arbitrarily define when and how long
each test waveform plays. Since all the waveforms are pre-loaded into baseband memory,
the waveform switching speed is only a few clock cycles during playback.
The signal quality can also be optimized from the instrument user interface or remotely by
using the PSG I/Q adjustment capability and fine-tuning the modulator attenuator setting.
Refer to the PSG manual set for additional information on optimizing signal quality. All
functionality of the two-tone and multitone application(s) is directly accessible from the
instrument front panel and can be automated remotely using the LAN or GPIB interface.
1. Assumes initial phase of tones are equal.
2. Assumes PSG maximum power (+18 dBm)
is decreased to account for the composite
signal peak-to-average signal.
3. Assumes PSG maximum power (+18 dBm)
is decreased to account for the composite
signal peak-to-average signal and relative
tone powers are set to 0 dB.
4. Tones are placed symmetrically around the
PSG carrier frequency.
(28 paginas)
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