FireFox Synthesizer User Manual
52
© 2006 Jackson-Labs
10.0MHz = (4294967296 * 1GHz)/ 2^32
The advantage of integer mode is thus that this particular tuning word generates a cycle-accurate,
phase-drift-free 10MHz signal without any cycle slipping, or residual. The phase angle to the internal
10MHz OCXO is fixed, and remains drift free. The disadvantage of this mode is its granularity,
which is limited by the 32bit tuning word.
The frequency granularity with fractional mode turned off, and an output frequency ranging from
2MHz to 390MHz is thus exactly 0.23283064365386962890625Hz. Keep in mind that the absolute
accuracy of the output signal is limited by the accuracy of the 10MHz reference signal from the
OCXO.
To improve the frequency granularity of the output signal, a fractional-N mode can be enabled that
increases the frequency resolution by an additional 16bits. The disadvantage of this mode is that it is
not mathematically deterministic; there is a frequency uncertainty of about 1/2LSB that prevents this
mode from being cycle accurate.
By increasing the DDS resolution, the DDS residual is made very small (about 1GHz / 2^48 at a
10MHz output frequency). The frequency resolution with fractional-N mode turned on is thus
3.55µHz for an output ranging from 2MHz to 390MHz.
This DDS resolution is typically less than the systems' minimum resolution of 10µHz. The system
attempts to match the user selected 10µHz step setting to the closest frequency that the DDS can
generate. The frequency difference between the desired setting (selectable in 10µHz steps), and the
actual frequency being generated causes a very small error.
Summary of Contents for FireFox
Page 1: ...FireFox Synthesizer User Manual Document 0012008 Version 004 Date 10 April 2008...
Page 2: ...FireFox Synthesizer User Manual Copyright 2008 Jackson Labs...
Page 34: ...FireFox Synthesizer User Manual 28 2006 Jackson Labs...
Page 46: ...FireFox Synthesizer User Manual 40 2008 Jackson Labs SOURce POWer...