User manual

AR2010 USB Stick Synthesizer User Manual
2. FREQuency:PLLMode [INT|FRAC|1|0]
This command sets the Phase Lock Loop (PLL) mode of the USB Stick Synthesizer. A PLL mode of INT
or 1 indicates that the PLL is operating in Integer mode, while a PLL mode of FRAC or 0 indicates that
the PLL is operating in Fractional Mode.
When the PLL is placed in Integer mode (also referred to as Integer-N mode), the output frequency is an
integer multiple of the reference oscillator frequency divided by the reference divider. For example, if the
reference frequency is 20 MHz, and the reference divider is 2, then when placed in Integer mode, the
synthesizer would be capable of outputting a frequency of 9.0 GHz and 9.010 GHz, but not a frequency
of 9.005 GHz (10 MHz tuning resolution). If there reference is 10 MHz and the reference divider is 1, the
same would situation would apply.
When the PLL is placed in Fractional mode, the output frequency can be any non-integer multiple of the
reference oscillator frequency. In the above example, the synthesizer would be capable of outputting a
frequency of 9.005 GHz when operated in Fractional mode.
Table 4.1 summarizes the advantages and disadvantages of the two synthesizer operational modes.
Table 4.1: Comparison between Integer and Fractional PLL modes
Mode Advantages Disadvantages
Integer Lower Phase Noise Frequency must be an integer
multiple of the reference fre-
quency
Phase Synchronization between
modules is guaranteed
Fractional Any frequency can be outputted Increased Phase Noise
Phase synchronization is difficult
to achieve at best
Syntax
FREQ :PLLM Space INT|FRAC|1|0
?
Example
FREQ:PLLM 1 This command sets the PLL mode of the device to Integer mode.
Applied Radar, Inc. Revision 2.0.1 18