Atec HP-Agilent-8904A - Manual (Page 3)

3
Stimulus for audio circuits
The 8904A has many characteristics
and features which make it well suited
as a stimulus for audio circuits. The
output of the 8904A is characterized
by low spurious and harmonic content.
Total harmonic distortion plus noise
(including all spurs) can be as low as
–78 dBc. With low distortion, the
8904A can be used to test many high
performance audio devices. Another
unique characteristic of the 8904A is
its exceptional level flatness. From
0.1 Hz to 100 kHz, the 8904A offers
±0.009 dB level flatness relative to
1 kHz. This state-of-the-art perform-
ance is a real plus for high perform-
ance audio test applications. Ground
loops can be one of the most difficult
problems to correct in audio tests.
The 8904A is equipped with an elec-
tronically floating, 50
Ω
output ampli-
fier which makes overcoming ground
loops easy.
Two outputs
Option 002 adds a second, identical
synthesizer and floating output section
to make the 8904A TWO synthesizers
in one half-rack width instrument.
Frequency, amplitude, waveform, and
phase can be independently set for
each of the two synthesizers. The
flexibility provided by two sources is
needed in a variety of applications.
When simultaneous external modula-
tion of a signal generator is required,
the 8904A Option 002 provides an
accurate, low-cost method of generat-
ing two independent modulating sig-
nals. Many two-input applications,
such as differential amplifier testing,
can benefit from the ability of the
8904A Option 002 to generate two
independent test signals at the same
time. Modern ATE systems designed
to test complex systems or products
require a number of sources to fully
stimulate the device being tested. In
these cases one or more 8904A Option
002 Multifunction Synthesizers can be
used to provide multiple test signals.
Two instruments provide four synthe-
sizers and occupy only one 5.25-inch
full rack space.
Phase offset
Although both synthesizers are inde-
pendent, the relative phase between
the two outputs can be precisely con-
trolled. Either synthesizer can be var-
ied in phase from 0 degrees to 359.9
degrees with a resolution of 0.1 degree.
Direct digital synthesis ensures accu-
rate, repeatable phase differentials.
Phase accuracy between outputs is
specified to be better than ±0.1 degree
or 30 ns (whichever is greater) up to
100 kHz. Testing phase detectors, servo
systems, shaft encoders, sonar, and
other phase-sensitive two-port devices
is easy and accurate with the 8904A
Option 002. One unique application of
the 8904A’s phase capabilities is in
driving balanced loads or lines. By
operating the two synthesizers 180
degrees out of phase, the 8904A can
function as a balanced source with
much higher voltage output capability.
In this configuration, the 8904A can
deliver +23.8 dBm (12 volts rms) into
a balanced 600
Ω
load with a 100
Ω
effective source impedance.
. . . And . . .
Then add another . . .