Quonset Microwave
www.quonsetmicrowave.com
QM2010-6000
USB RF Synthesizer Module
25 MHz – 6 GHz output
Integer and Fractional Modes of Operation
The QM2010 RF Synthesizer Module is capable of operating in integer or fractional mode. In integer mode,
the frequency resolution of the QM2010-6000 is dependent on the frequency range of operation. This is due to
the design topology of the QM2010-6000, which has a fundamental frequency range of 1500 MHz to 3000
MHz from which all other tuned frequencies are derived. When operating in this fundamental frequency range
in integer mode, the frequency resolution is equal to
𝑓𝑟𝑒𝑠
=
𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑟𝑒𝑓
𝑑𝑖𝑣𝑖𝑑𝑒𝑟
. For frequencies above 3000 MHz, a
doubler is applied to the fundamental, doubling the frequency resolution to
𝑓𝑟𝑒𝑠
=
𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑟𝑒𝑓
𝑑𝑖𝑣𝑖𝑑𝑒𝑟
∗
2
. For
frequencies below 1500 MHz, a divider is applied to the output frequency, lowering the frequency resolution to
𝑓𝑟𝑒𝑠
=
𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑟𝑒𝑓
𝑑𝑖𝑣𝑖𝑑𝑒𝑟
∗
1
𝑓𝑟𝑒𝑞
𝑑𝑖𝑣𝑖𝑑𝑒𝑟
. The frequency divider can be any even integer value between 2 and 62,
dependent on the output frequency. All frequency divider and doubler calculations take place in synthesizer
firmware automatically when a frequency is set.
For example, in integer mode, tuning to an output frequency of 25 MHz requires a fundamental frequency of
1550 MHz divided by 62. We can check the feasibility of this request by first checking if the fundamental
frequency divided by the reference frequency is an integer value
𝑁
𝑖𝑛𝑡
=
𝑓𝑟𝑒𝑞
𝑓𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙
𝑟𝑒𝑓
=
1550𝑒6
20𝑒6
= 77.5
.
Since the fundamental frequency is not a tunable integer value, we cannot tune to exactly 25 MHz in integer
mode. The previous integer step is not a tunable frequency
𝑁
𝑖𝑛𝑡
∗𝑟𝑒𝑓
62
=
77∗20𝑒6
62
= 24.838
𝑀𝐻𝑧
, so we must
use the next integer step
𝑁
𝑖𝑛𝑡
∗𝑟𝑒𝑓
62
=
78∗20𝑒6
62
= 25.161
𝑀𝐻𝑧
. If we multiply the tuning frequency by the
frequency divider
25.161
𝑀𝐻𝑧 ∗
62
≈
1560
𝑀𝐻𝑧
, which will get rounded down to 1550 MHz with a reference
of 50 MHz and a reference divider of 1.
If the synthesizer is unable to tune to the exact frequency in integer mode, it will tune to the closest tunable
frequency. For example, 1555 MHz is not a tunable frequency in integer mode with a 50 MHz reference. The
synthesizer will therefore tune to 1550 MHz.
Fractional mode will allow for a frequency step size of 1 kHz. When operating in fractional mode, it is
recommended that the reference divider value always be set to 1.
Table 1 –
Integer vs. Fractional Mode Comparison
Parameter
Integer Mode
Fractional Mode
Phase Noise
•
Comparable to fractional mode phase
noise at offset frequencies ≤ 100 kHz,
if
the reference divider value is ≤ 2
•
Degrades as reference divider increases
•
Comparable to integer mode at offset
frequencies
≤ 100 kHz,
if
the reference
divider value = 1 (should always be 1 for
best performance).
Spurious Content
•
Better spurious performance
•
Additional spurs present at frequency
offsets
≤ 5 MHz
Recommendation
•
Use whenever possible for best
performance
•
Use when fine frequency resolution is
required
-3-
Revised Dec 23, 2015
For price, delivery, and to place orders, please contact Quonset Microwave: a subsidiary of Applied Radar, Inc.
315 Commerce Park Road, North Kingstown, RI 02852 Phone: 401-295-0062