AD9545 datasheet(75/157 Pages) AD

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Data Sheet

AD9545

Rev. A | Page 75 of 157

The NCO, VCO, TDCs, and the APLL PFD inputs each have

specific frequency limits. The following formulas relate fNCO,

fVCO, fTDC and fPFD to Z, fREFx, fOUTx, and divider values. Note that

each formula has two solutions: one with respect to the input

frequency (fREFx) and the other with respect to the output

frequency (fOUTx). The user must ensure that fNCO, fVCO, fTDC, and

fPFD are within their specified frequency bounds.

fTDC = fREFx/Rx

= (Z/Ry) × fOUTx

(11)

fNCO = fPFD = ((2 × Q × Ry)/(Rx × M)) × fREFx

= (2 × Q/M) × fOUTx

(12)

fVCO = ((2 × Q × Ry)/(Rx × Z)) × fREFx

= 2 × Q × fOUTx

(13)

When the reference source is auxiliary NCO 0, auxiliary NCO 1

or the feedback from the other DPLL, then in Equation 11

through Equation 13, use Rx = 1.

Although the feedback divider (N-divider) does not appear in

Figure 65, it requires special treatment for external zero delay

operation. See the DPLL Feedback Divider (N-Divider section

for details.

REFx

REFy

TDC

OUTxyN/

OUTxyP

REFx

TDC

AD9545

REFy

TDC

AUX

NCO 0/NCO 1

TDC

OTHER DPLL

FEEDBACK

TDC

DIGITAL CROSS

POINT MUX

TIME STAMP PROCESSOR,

DIGITAL LOOP FILTER,

TUNING WORD PROCESSOR

AND NCO

PFD

AND

LOOP

FILTER

M-DIVIDER

OUTPUT

DISTRIBUTION

DPLL

SYSTEM

CLOCK

LFx

XOA XOB

APLL

VCO

÷2

Figure 65. External Zero Delay PLL Configuration

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