Valon Technology 5009a Operations Manual – Version 1.38
Page 31
4.10
Configuration Commands
Configuration commands are used to control settings that are secondary to the operation of the
synthesizers or affect operation of both synthesizers together.
4.10.1
REFerence; <F> <U>
REF
sets the reference frequency used by both sources. The reference frequency is the used by
the PLL circuitry in both synthesizers and is the fundamental clock that determines the accuracy,
stability, phase noise, and overall quality of the output signals. The default reference frequency
is 20MHz. If an external reference is being used, that is not 20MHz (10MHz for example) then
the reference,
REF
must be set to correspond to that frequency. Setting
REF
to something other
than the actual internal or external frequency will result in indeterminate or unstable
performance.
The optimum range for the reference frequency is 20MHz to 100MHz. The minimum frequency
is 5MHz and the maximum frequency is 200MHz.
The query form is
REF?
[U]
4.10.2
REFTrim; <0|1|2|...255>
REFerence Trim command can be used to trim or "spot" the synthesizers' frequency when using
the internal reference. Reference trim changes the voltage sent to the VCTCXO by setting the
reference DAC output voltage. Reference trimming can be used to minimize the internal
reference frequency error. Reference trim can also be used when a small frequency offset is
desired. The trimming range is >±10ppm.
Note: The EFC circuit is connected to the external reference input through a lowpass filter
networks. The EFC voltage is summed with the REFTrim DAC. Any dc path such as a termination
or dc coupled source on the external reference input will shunt part of the REFTrim voltage to
ground. A dc coupled external reference should be disconnected when using the internal
reference.
4.10.3
REFerenceSource;
REFS
sets the reference source to either internal or external.
REFS 0
set the reference to
internal
REFS 1
set the reference source to external.
REFS?
returns the state of the reference source.
4.10.4
Source <1|2>; PFD <F> <U>
By default, Phase/Frequency Detector (PFD) is 40MHz when the 5009 is supplied with either a
40MHz or 20MHz TCXO. The synthesizer loop filters are optimized for the lowest phase noise
with a PFD frequency in the range of 20MHz ~50MHz. A block diagram of the synthesizer
reference divider circuit is shown below. The permitted PFD range is 1MHz to 140MHz.
