Installation guide

Troubleshooting
Block Descriptions for Option UNJ and Option 506
1-136
The 1 GHz STW is split with one leg being divided down to 10 MHz. This signal is then phase compared to the
10 MHz OCXO with the difference driving an integrator. The integrator tunes the 1 GHz STW ensuring both
reference signals are phase locked together. The other leg of the 1 GHz signal is routed to the A15 Sampler
and A13 Output.
A16 Frac-N (Option UNJ or Option 506)
The A16 Frac-N is used to fine tune the YO on the A21 YTO Driver. Two proprietary application specific
integrated circuits (ASIC), named Paren and Tesera, are used to tune a VCO on the A16 Frac-N. The VCO is
capable of being tuned from 500 MHz to 1000 MHz. The VCO is routed to the A15 Sampler where it is down
converted and compared to a sampled frequency of the YO.
The tuning of the VCO begins with a 10 MHz signal from the A18 Reference. The 10 MHz reference is divided
down to 5 MHz to reduce fractional spurs in the phase detector. The 5 MHz reference is then phase compared
to a divided down VCO output. The primary division of the VCO is performed within the Tesera pre scaler
ASIC. The pre scaler divisor is provided by the Paren ASIC. The output of the phase detector is integrated
and then used to tune the VCO.
The baseband FM and PM from the A18 Reference are added to the VCO on the A16 Frac-N. There are two
different paths for the modulation to be added to the VCO which are dependent on the modulation rate. If the
modulation rate is outside the VCO PLL bandwidth, the baseband signal is scaled and applied to the VCO. A
portion of the baseband signal is also split off and routed to the A21 YTO Driver’s FM coil. If the baseband
rate is within the PLL bandwidth, the signal is scaled and sent to the Sigma-Delta Modulator for digitizing.
The digitized signal is used by Paren and Tesera to change the VCO tuning and implements the FM.
A15 Sampler (Option UNJ or Option 506)
A portion of the A21 YTO Driver’s YO signal is split off and routed to the A15 Sampler. This signal is sampled
and phase compared to a down converted VCO from the A16 Frac-N. The difference signal is integrated and
sent back to the A21 YTO Driver’s main coil to tune the YO.
The process begins with a 1 GHz signal from the A18 Reference. The signal is split with one leg being divided
down to 250 MHz. This signal is used as an LO for a mixer. The RF to the mixer is the 1 GHz reference. The
750 MHz IF is split twice, which means that there are three 750 MHz reference signals being used on the
A15 Sampler. For clarity, let us label these references as 750 MHz (A), 750 MHz (B), and 750 MHz (C). The
750 MHz (C) reference is multiplied by a variable fraction, which is less than one, to reduce the frequency.
This signal is phase compared to a Mixer IF (14 to 150 MHz). The difference is integrated and used to tune a
VCO (618 to 905 MHz) on the A15 Sampler.
The output of the VCO on the A15 Sampler is split with one leg being mixed with the 750 MHz (B) reference
signal to produce the Mixer IF. The other leg of the VCO on the A15 Sampler is used as the LO for the
sampler. The RF for the sampler is provided by the A21 YTO Driver’s YO signal. The Sampler IF
(30 to 70 MHz) is one input to a phase comparator. The other input to the phase comparator is the down
converted VCO on the A16 Frac-N. Depending on the instrument mode of operation, the VCO on the
A16 Frac-N has two independent paths for down conversion. Mode 1 optimizes phase noise for
offsets < 10 kHz by dividing down the VCO on the A16 Frac-N. Mode 2 optimizes phase noise for
offsets > 10 kHz, by mixing the VCO on the A16 Frac-N with the 750 MHz (A) reference. In either mode, the
down converted signal is the other input to the phase converter. The output of the phase comparator is
integrated and routed back to the A21 YTO Driver’s main coil to tune the YO.
A21 YTO Driver
The operating frequency of the YO on the A21 YTO Driver is from 4 to 8 GHz. YO tuning is accomplished by
varying the current through the main coil. This causes the coil's magnetic field to change, which tunes the YO
resonant frequency. When the signal generator's frequency is changed, a coarse tune DAC voltage is
converted to a current to bias the main coil. The YO output is split with a portion of the YO signal being fed