Fig.3: complete circuit diagram
for the ADF4351 frequency
synthesiser module.Fig.4: when connecting the ADF4351 synthesiser module to an Arduino-based device, a few extra resistors are needed.
These resistors form a voltage divider, as the module can only handle 3.3V signals, while the Arduino’s outputs have a
swing of 5V. Note the changes needed if using a V2 module at the end of this article.The ‘LOCK DETECT’ block monitors
the phase comparator and provides a
high logic output on the LD pin when
the PLL is locked. Multiplexer C allows
either of the two phase comparator in-
puts or this lock status to be fed to the
MUXOUT pin.
The fast lock switch provides a sig-
nal which can be fed into the externallow-pass filter (between the CPOUT
and VTUNE pins) when in ‘fast lock’
mode. So that covers the operation
of the IC itself.The synthesiser module
The full circuit of the module is shown
in Fig.3, and most of the real work is
done by IC1.All of the programming and sta-
tus monitoring signals to and from
the module are available at CON1.
This includes the DATA, CLK and LE
lines (ie, the serial bus) and also the
CE (chip enable), LD (lock detect),
MUXOUT and PDBRF (power down
RF buffer) lines.
The reference signal is provided by a
25MHz crystal oscillator (XO), shown
at upper left, with its output fed to the
REFIN pin of IC1 via a loading/coupling
circuit comprising two 1nF capacitors
and a 51Ω resistor.Reproduced by arrangement with
SILICON CHIP magazine 2019.
http://www.siliconchip.com.au