HMC1197LP7FE datasheet(30/57 Pages) AD

30 / 57 page

For price, delivery, and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824

Phone: 978-250-3343

Fax: 978-250-3373

Order On-line at www.hittite.com

Application Support: Phone: 978-250-3343 or apps@hittite.com

HMC1197LP7FE

v03.0314

Wideband direct Quadrature Modulator

w/ Fractional-n Pll & Vco, 100 - 4000 MHz

Figure 40. Exact Frequency Tuning

Some fractional PLLs are able to achieve this by adjusting (shortening) the length of the Phase Accumulator

(the denominator or the modulus of the Delta-Sigma modulator) so that the Delta-Sigma modulator phase

accumulator repeats at an exact period related to the interval frequency (fVCOk - fVCO(k-1)) in Figure 40.

Consequently, the shortened accumulator results in more frequent repeating patterns and as a result often

leads to spurious emissions at multiples of the repeating pattern period, or at harmonic frequencies of

fVCOk - fVCO(k-1). For example, in some applications, these intervals might represent the spacing between

radio channels, and the spurious would occur at multiples of the channel spacing.

The Hittite method on the other hand is able to generate exact frequencies between adjacent integer-N

boundaries while still using the full 24 bit phase accumulator modulus, thus achieving exact frequency

steps with a high phase detector comparison rate, which allows Hittite PLLs to maintain excellent phase

noise and spurious performance in the Exact Frequency Mode.

1.3.7.6 using Hittite exact Frequency Mode

If the constraint in (EQ 16) is satisfied, HMC1197LP7FE is able to generate signals with zero frequency error

at the desired VCO frequency. Exact Frequency Mode may be re-configured for each target frequency, or

be set-up for a fixed fgcd which applies to all channels.

1.3.7.6.1.1

configuring exact Frequency Mode For a Particular Frequency

Calculate and program the integer register setting Reg 03h = NINT = floor(fVCO/fPD), where the

floor function is the rounding down to the nearest integer. Then the integer boundary frequency

fN = NINT ∙ fPD

Calculate and program the exact frequency register value Reg 0Ch = fPD/fgcd, where

fgcd = gcd(fVCO,fPD)

Calculate and program the fractional register setting Reg 04h

(

)

ceil

VCOk

FRAC







−

, where ceil

is the ceiling function meaning “round up to the nearest integer.”

Example: To configure the HMC1197LP7FE for exact frequency mode at fVCO = 2800.2 MHz where Phase

Detector (PD) rate fPD = 61.44 MHz Proceed as follows:

Check (EQ 16) to confirm that the exact frequency mode for this fVCO is possible.

(

)

















≥

gcd

gcd(

)

61.44 10

gcd 2800.2 10 ,61.44 10

120 10

3750

VCO

and f

Since (EQ 16) is satisfied, the HMC1197LP7FE can be configured for exact frequency mode at

fVCO = 2800.2 MHz as follows:

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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.

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

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

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