HMC704LP4E【PDF 6/44 页】IC FRACT-N PLL 16BIT 24QFN

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Sheet目录1996

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5 - 14

HMC704LP4E

v03.1211

8 GHz fractionaL-n PLL

For price, delivery, and to place orders: Hittite Microwave Corporation,20 Alpha Road, 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

where:

Phase Noise Contribution of the PLL (rads2/Hz)

Frequency of the VCO (Hz)

fpd

Frequency of the Phase Detector (Hz)

Frequency offset from the carrier (Hz)

Fpo

Figure of Merit (FOM) for the phase noise floor

Fp1

Figure of Merit (FOM) for the flicker noise region

PLL Noise Floor

PLL 1/f Flicker Noise

VCO 1/f2 Noise

VCO 1/f3 Noise

Typical Closed Loop Phase Noise

LOG OFFSET FREQUENCY (fm)

PHA

NOISE

(dBc/Hz)

Closed Loop

Bandwidth

Figure 24. Figures of Merit Noise Models for the PLL

If the free running phase noise of the VCO is known, it may also be represented by a figure of merit for both 1/f2 , Fv2,

and the 1/f3, Fv3, regions.

The Figures of Merit are essentially normalized noise parameters for both the PLL and VCO that can allow quick esti-

mates of the performance levels of the PLL at the required VCO, offset and phase detector frequency. Normally, the

PLL IC noise dominates inside the closed loop bandwidth of the PLL, and the VCO dominates outside the loop band-

width at offsets far from the carrier. Hence a quick estimate of the closed loop performance of the PLL can be made by

setting the loop bandwidth equal to the frequency where the PLL and free running phase noise are equal.

The Figure of Merit is also useful in estimating the noise parameters to be entered into a closed loop design tool such as

Hittite PLL Design, which can give a much more accurate estimate of the closed loop phase noise and PLL loop filter

component values.

Given an optimum loop design, the approximate closed loop performance is simply given by the minimum of the PLL

and VCO noise contributions.

(

)

0 ,,

f f f

Φ=

PLL Phase Noise

Contribution

(EQ 1)

(EQ 2)

(

)

f f

Φ=

VCO Phase Noise

Contribution

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