Review: Analog Devices ADF4351

The ADF4351 from Analog Devices (ADI) is a modern wideband PLL synthesizer with integrated low phase noise VCO. It is capable of generating signals between 35 MHz to 4400 MHz with a very low jitter of typical 0.3 ps. ADI agreed to send me the EVAL-ADF4351EB1Z, an evaluation board for the ADF4351, for review purposes. Let’s check it out!

The ADF4351 has an integrated voltage-controlled oscillator (VCO) with a fundamental output frequency ranging from 2200 MHz to 4400 MHz. In addition, divide-by-1/-2/-4/-8/-16/-32/-64 circuits allow the user to generate RF output frequencies as low as 35 MHz. For applications that require isolation, the RF output stage can be muted. The mute function is both pin- and software-controllable. An auxiliary RF output is also available, which can be powered down when not in use. Control of all on-chip registers is through a simple wire interface. The device operates with a power supply ranging from 3.0 to 3.6 V and can be powered down when not in use.

ADF4351 evaluation board

ADI ships the EVAL-ADF4351EB1Z with a USB cable and a CD. The CD contains all software necessary to get started right away. The board itself makes a very clean impression. Despite the surface mount technology, all case styles of the components used can comfortably be handled with appropriate hand soldering tools. This allows for easy application specific modifications.

There are two 4 mm jacks for power (3.75 V to 5.5 V), a small USB connector, and 3 SMA connectors on the board. The first SMA connector serves as reference input for an external reference signal. Alternatively, it can be used as an output for the on-board reference (25 MHz). The other two SMAs are the primary RF output of the ADF4351. It is a differential pair. For best performance, make sure to terminate both outputs correctly (50 Ohms) even if just one output is being used.

Power can either be supplied through the 4 mm banana jacks or the USB port. Switches S1 and S2 are used to select the power source. Switch S1 is used to power the ADF4351 from the external DC connector and switch S2 to power from the USB port. The USB clock can cause spurs in the RF signal if power is derived from the USB port.

Plenty of test points on the board allow easy troubleshooting. An additional 100 mil / 2.54 mm header can be populated to gain easier access to the most important logic signals.

The external loop filter on the eval board has a bandwidth of 35 kHz. This value can easily be changed by changing the value of the corresponding components. The software package ‘ADIsimPLL’ from Analog Devices is a great tool for designing an application specific loop filter.

Make sure to install the software from the CD before connecting the evaluation board to the PC for the first time. Once the software is installed properly, connect the board to the PC and start the ADF4351 software package. If the two power LEDs on the board (D5 and D6) do not light up upon connection, verify S1 and S2 for proper selection of the desired power source.

ADF4351 Application Software

The software is self-explanatory. It allows accessing and manipulating of all functions and registers of the ADF4351. Additionally, the software allows you to use the evaluation board as a sweep generator and it can do frequency hopping between two frequencies.

After trying this board out for a while, I highly recommend this chip. It is small, inexpensive ($8.25, 100 QTY) and extremely simple to integrate.

I can think of many applications for the ADF4351 in the amateur radio community. The ADF4351 a perfect 21st century alternative for older SP5055 based designs. The SP5055 was a very popular synthesizer chip used in many older amateur radio projects.

The chip is predestined to be used as a flexible Local Oscillator (LO) in amateur radio transverters. A flexible LO frequency allows to cover more bandwidth in the target frequency range than the IF transceiver itself offers. Paired with a baseband processor and a power amplifier, this chip easily transform into an inexpensive amateur television (ATV) transmitter. I will show some practical designs and applications in future articles. Stay tuned!

Links and Sources:

[1] ADF4351, ADI: http://www.analog.com/

[2] ADF4351 Datasheet, ADI: http://www.analog.com/

[3] Evaluation Board User Guide, ADI: ftp://ftp.analog.com/