User manual

3152B User Manual Publication No. 980935 Rev. M
1-22 Introduction Astronics Test Systems
PLL
Synchronization
PLL synchronization is another technique for synchronizing multiple
waveform generators. In this case, synchronization is not between
pairs of 3152B modules, but between the 3152B and any external
device that generates signals stable enough
to satisfy the PLL input
requirements. When placed in this mode, the 3152B measures the
profile of the input signal and determine whether or not it is valid.
Then, the built-in counter/timer circuit measures the frequency of
the signal and centers its lock-
in range on this frequency. The
3152B thus locks automatically onto
the frequency of the external
signal. Note that t
here is no need for manual initiation or operator
intervention for the PLL function to find and lock on
to an external
reference. The PLL range is 500 Hz to 10 MHz.
After phase locking has been established, the start
phase of the
3152B waveform can be shifted with respect to
the start phase of
the external reference within the range of -180° to +180°
, with
phase increments as low as 0.01° (fine phase control). The
reference signal is applied to the front-
panel TRIG/PLL connector.
In this way, the same reference can be applied to multiple modules
to generate multi-phase signal patterns. The TRIG/PLL input has
a
programmable trigger level and programmable slope.
Phase
Modulation
When the 3152B is placed in PLL mode, there are two ways to
control the phase offset. The first way is to modify the phase
offset
setting using SCPI commands. This method is quite accurate
, and
allows phase offset adjustments in increments of 0.01°.
The second way is to apply a voltage to the EXT 10MHz input
(or
the PM IN port if it is a 3152B with legacy-compatible pinout). This
changes the start phase of the synthesizer, proportional to the
voltage level at the phase modulation input. An input voltage of 1
V
modifies the phase by 20°. The phase changes between -180°
and
180° as the applied voltage goes from -9 V to 9 V. The instrument
responds to AC changes or the EXT 10MHz port (or PM IN port)
throughout the frequency range of DC to 10 kHz, but the
time to
lock depends on the lock frequency and the
number of waveform
samples.
Filters
The 3152B has two elliptic filters (60 MHz and 120 MHz) and two
Bessel filters (25 MHz and 50 MHz). You may switch these filters in
to reduce harmonics or high frequency spurs.
Access to the elliptic filters is disabled while the 3152B is
generating standard sine waveforms because these filt
ers are used
automatically to construct optimal sine waveforms.
Output State
For safety reasons, the 3152B powers up with its output turned off.
In fact, the output circuit is disconnected from the output connector
using a mechanical relay, which elimina
tes erroneous and
uncontrolled transitions that may occur during power-up. This