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HMC704LP4E

v04.0215

For price, delivery and to place orders: Analog Devices, Inc., One Technology Way, Norwood, MA 02062

978-250-3343 tel • 978-250-3373 fax • Order online at www.analog.com/hittitemw

Application support: Phone: 978-250-3343 or RFMG-apps@analog.com

It should be noted that actual phase noise near the corner frequency of the loop bandwidth is affected by loop parame-

ters and one should use a more complete design tool such as Hittite PLL Design for better estimates of the phase noise

performance. Noise models for each of the components in Hittite PLL Design can be derived from the FOM equations

or can be provided by Hittite applications engineering.

Spurious Performance

Integer Operation

The VCO always operates at an integer multiple of the PD frequency in an integer PLL. In general spurious signals

originating from an integer PLL can only occur at multiples of the PD frequency. These unwanted outputs are often sim-

ply referred to as reference sidebands.

spurs unrelated to the reference frequency must originate from outside sources. External spurious sources can modu-

late the VCO indirectly through power supplies, ground, or output ports, or bypass the loop filter due to poor isolation of

the filter. It can also simply add to the output of the PLL.

The HMC704LP4E has been designed and tested for ultra-low spurious performance. Reference spurious levels are

typically below -100 dBc with a well designed board layout. A regulator with low noise and high power supply rejection,

such as the HMC860LP3E, is recommended to minimize external spurious sources.

Reference spurious levels of below -100 dBc require superb board isolation of power supplies, isolation of the VCO

from the digital switching of the PLL and isolation of the VCO load from the PLL. Typical board layout, regulator design,

demo boards and application information are available for very low spurious operation. Operation with lower levels of

isolation in the application circuit board, from those recommended by Hittite, can result in higher spurious levels.

Of course, if the application environment contains other interfering frequencies unrelated to the PD frequency, and if

the application isolation from the board layout and regulation are insufficient, then the unwanted interfering frequencies

will mix with the desired PLL output and cause additional spurs. The level of these spurs is dependant upon isolation

and supply regulation or rejection (PsRR).

Fractional Operation

Unlike an integer PLL, spurious signals in a fractional PLL can occur due to the fact that the VCO operates at frequen-

cies unrelated to the PD frequency. Hence intermodulation of the VCO and the PD harmonics can cause spurious side-

bands. spurious emissions are largest when the VCO operates very close to an integer multiple of the PD. When the

VCO operates exactly at a harmonic of the PD then, no in-close mixing products are present.

of operation is used, the difference, Δ, between the VCO frequency and the nearest harmonic of the reference, will cre-

ate what are referred to as integer boundary spurs. Depending upon the mode of operation of the PLL, higher order,

lower power spurs may also occur at multiples of integer fractions (sub-harmonics) of the PD frequency. That is, frac-

ous product. Higher values of m produce smaller amplitude spurious at offsets of mΔ and usually when m>4 spurs are

very small or unmeasurable.

width. This is the “in-band fractional boundary” case.

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

For price, delivery, and to place orders: Analog Devices, Inc.,

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106

Phone: 781-329-4700 • Order online at www.analog.com

Application Support: Phone: 1-800-ANALOG-D