ADI ADF5610, suitable for communication and measurement systems
VCO integration eliminates the need for additional circuitry and lookup tables
Achieving rms jitter values below 38 fs with PLL


With the demand for higher bandwidth and faster data rates, the demand for system frequencies and modulation rates continues to increase. Low power characteristics are also becoming important as applications once used only in military or defense applications are being used in commercial markets.

Developers must now meet the above demands without sacrificing electrical performance or functionality. To achieve this, things like the signal-to-noise ratio (SNR), bit error rate (BER), and quality of service (QoS) must be improved, and the phase noise of the local oscillator (LO) must also be reduced.

The ADF5610 from Analog Devices (ADI) is a microwave wideband synthesizer with an integrated phase-locked loop (PLL) and voltage controlled oscillator (VCO), designed for solutions that address the above requirements.


Wide frequency coverage
The ADF5610 supports a total of 8 octaves, and the VCO fundamental frequency is 3.65 GHz to 7.3 GHz, which is transferred to the PLL to minimize phase noise.

The single-ended output (RFOUT) doubles the fundamental frequency range to provide 7.3 GHz to 14.6 GHz, while the differential output supports the full operating range of 57 MHz to 14.6 GHz using divide by 1/2/4/8/16/32/64/128 settings.

The ADF5610's VCO architecture not only provides wideband synthesizer performance, Maintains a nominal open-loop phase noise performance of -114 dBc/Hz at 10 GHz and 100 kHz offset.

The internal state machine achieves a frequency settling time of less than 40ms using only a passive loop filter. No additional circuitry or lookup table (LUT) is required unless a faster settling time is required.


PLL performance suitable for converter clocks
The ADF5610's PLL has a modest figure of merit (FOM) of -229 dBc/Hz (-232 dBc/Hz in high current mode), but when combined with the 1/f noise (-129 dBc/Hz) and VCO phase noise characteristics, it can achieve rms jitter figures of less than 38 fs (1 kHz to 100 MHz integration limit).

This makes the ADF5610 ideal for demanding converter clock applications.

To reduce thermal noise and high frequency (100MHz), the loop filter resistance value should be kept to a minimum. Achieving this level of performance requires a reference source with extremely low noise.


LO for communications and instrumentation applications
The ADF5610 also has features that make it ideal for use as an LO for wireless communications and instrumentation applications. The fractional resolution is modest at 24 bits, but when combined with the ADF5610’s frequency mode capability, it can generate frequencies with 0 Hz error.

Using the ADF5610 as LO allows driving active mixers directly from the RFOUT port, as the output power is nominally 5 dBm. Therefore, no additional amplification is required, saving board space.

The output power of the differential divider (PDIVOUT/NDIVOUT) is nominally 2 dBm when used single-ended, but can be increased by a few dB or even doubled when coupled through a low-loss balun or hybrid coupler for narrowband applications.

Another advantage is that it consumes less than 700mW (in low current mode with the output divider disabled) all the way down to just over 1W under worst-case conditions (in high-performance mode with the output divider set to divide by 128).

Even in low current mode, the phase noise performance increases by only 2 dBc/Hz. Additionally, PFD spurious is as low as -105 dBc and in-band unfiltered integer edge spurs are nominally -45 dBc.


Small footprint solution with minimal additional decoupling
The ADF5610 PLL/VCO is available in a 7 mm × 7 mm 48-pin LGA package. It requires minimal additional decoupling and provides maximum performance in a small footprint solution.

If you need to achieve the best performance, we recommend using high-quality LDO regulators such as the ADM7150, LT3045/LT3042, and HMC1060.

The VCO requires a 5V supply, and the rest of the circuitry is powered from a 3.3V rail. Simulating the ADF5610 with ADIsimPLL™ enables design of the appropriate external circuitry required to implement a complete PLL synthesizer.

As a result, ADI's ADF5610 is ideal for use in demanding modern communications and instrumentation systems.



This article is a summary of the article titled, “Microwave Synthesizer Offers Multioctave Frequency Coverage and Excellent Phase Noise Performance” by Marty Richardson, Senior Applications Engineer, Analog Devices.