UG-435 Datasheet, PDF (4/20 Pages) Analog Devices – Evaluation Board for the ADF4351 Fractional-N PLL Frequency Synthesizer

UG-435
EVALUATION BOARD HARDWARE
The EVAL-ADF4351EB1Z schematics are shown in Figure 22
to Figure 24.
POWER SUPPLIES
The EVAL-ADF4351EB1Z can be powered either from the USB
port or via dc power connectors (4 mm banana connectors).
When feeding via banana connectors, 3.75 V to 5.5 V is a
suitable feeding voltage. The power supply circuitry allows
the user to use one or two separate LDOs to feed the ADF4351
(using fewer LDOs increases the risk of spur contaminated dc
feeds). Consult the board schematic in Figure 22, Figure 23,
and Figure 24 to determine a suitable setting.
An LED, D6, indicates when USB power is available, and
another LED, D5, indicates when the ADF4351 is powered.
Switch S1 is used to power the ADF4351 from the external
dc connectors USB port and Switch S2 to power from the
USB port.
In case the USB processor or clock causes spurs on the RF
output signal, the user may feed the evaluation board via the
dc connectors and unplug the USB cable, thereby removing
power from the USB interface circuitry. There is also a
grounded frame surrounding the USB interface circuitry
to allow mounting of a shielding box.
INPUT SIGNALS
The 25 MHz TCXO from Rakon provides the necessary reference
signal. An external REFIN may be used if desired. In this case,
disable the on-board TCXO by removing L10 and R59. R9 can
be populated with 50 Ω to adjust impedance matching of the
evaluation board to the external reference source.
LOOP FILTER
The loop filter schematic is included in the board schematic on
Figure 22. The loop filter component placements are clarified in
Figure 2.
Evaluation Board User Guide
Figure 3. Evaluation Board Silkscreen
OUTPUT SIGNALS
The EVAL-ADF4351EB1Z has two SMA output connectors
(differential outputs). The device is quite sensitive to impedance
unbalance. If only one port of a differential pair is used,
terminate the other with a 50 Ω load.
The board contains 7.5 nH shunt inductors on the RF output
stages, which is optimum for a frequency range of 1 GHz to
4.4 GHz. Lower frequencies than this require larger output
stage inductors, or a 50 Ω resistor to VDD, which provides lower
output power, but wider frequency bandwidth than the
inductors. Consult the ADF4351 data sheet for more
information.
The MUXOUT signal can be monitored at the test point labeled
MUXOUT.
Figure 2. Loop Filter Placement
Rev. 0 | Page 4 of 20