HMC700LP4 datasheet(14/26 Pages) AD

14 / 26 page

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HMC700LP4 / 700LP4E

v11.0411

8 GHz 16-Bit Fractional-N PLL

FSK Modulation

the HMc700LP4(E) is capable of a simple binary Frequency Shift Keying (FSK) modulation. the internal modulation

is unshaped FSK. the loop bandwidth of the synthesizer must be fixed by the user to achieve symbol shaping as

required.

When the FSK mode of operation is enabled, via fsk_enable (table 13), and SEn is held low, the synthesizer will

output binary FSK frequency hops in response to data input on the SDi pin. When SEn is set, the FSK modulation will

stop and return to f0. ScK must not be toggled when transmitting data in FSK mode.

FSK modulation is normally defined by a deviation, Δƒ, and a modulation rate, ƒm. the deviation is defined as the

difference between the frequency transmitted when input data is 0, ƒ0, and the frequency transmitted when the input

data is 1, ƒ1.

ƒo

is the frequency programmed in the frequency registers as was defined in (EQ 4),

that is:

ƒ1

is the fractional frequency achieved by adding the value in the seed register to the

value in the frac register, that is:

Where

Nint

is the integer division ratio, an integer number between 36 and 65,567 (see integer

Nfrac

is the fractional part, a number from 1 to 224

Nseed

is the seed part, a number from 1 to 224

is the reference path division ratio

ƒref

is the frequency of the external reference input

in this case the deviation Δf is given simply by

FSK data bits on SDi will be latched into the synthesizer on the falling edge of the divided reference rate, ƒPFD. if for

example r=1, and ƒref = 50 MHz, the input FSK data would be oversampled every 20nsec on the falling edge of the

input reference.

the ƒm rate of the FSK data is simply the inverse of twice the period of the data bits. For example, if the data bit period

is 1msec the fm rate is 500 Hz.

if an unshaped binary FSK is desired, the closed loop bandwidth of the synthesizer should be larger than the ƒm

rate by a sufficient margin. For practical FSK transmissions the ƒm rate is limited by the radio link budget, channel

spectral emission restrictions and practical closed loop bandwidths of the fractional synthesizer.

(EQ 7)

(EQ 8)

(EQ 9)

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.

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

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