ADF4382ABCCZ datasheet(20/82 Pages) AD

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Data Sheet

ADF4382A

THEORY OF OPERATION

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Rev. A | 20 of 82

OUTPUT FREQUENCY

When the loop is locked, the fVCO (in Hz) produced at the output of

the VCO is determined by fREF and the O, R, and N values given by

the following equation.

fVCO=fREF×D×N×OR

(1)

where:

fREF is the reference frequency.

D is the reference doubler.

R is the reference divider.

O is the output divider.

fPFD is given by the following:

fPFD=fREF × DR

(2)

and fVCO can be alternatively expressed as follows:

fVCO=fPFD×N×O

(3)

The output frequency, fRFOUT, produced at the output of the output

divider is given by the following:

fRFOUT=fVCOO

(4)

N is the feedback divider and is given by the following:

N=NINT+FRAC1WORD+FRAC2WORD

MOD

2WORD

MOD

1WORD

(5)

Output Frequency Calculation Procedure

The following is a worked example for a fractional mode fRFOUT

using the formulas in the Output Frequency section.

For fRFOUT = 20.132 GHz and a channel spacing (fCHSP) of 1 Hz.

Where fREF = fPFD = 250 MHz.

Since fREF = fPFD, the reference divider is set to divide by 1 (R_DIV

= 1) and the reference doubler is bypassed (EN_RDBLR = 0).

The output frequency is within the fundamental VCO frequency

range (fVCO). This means that the output divider (O) is set to divide

by 1 (RFOUT_DIV = 0).

The steps to calculate all N-divider component values are outlined

as follows:

1. Calculate the overall N-value required based on the fRFOUT and

fPFD provided

N = fRFOUTfPFD

(6)

N= 20.132 GHz

250 MHz

=80.528

(7)

2. Separate the NINT and NFRAC components

NINT = INTN = 80

(8)

NFRAC= N − NINT = 0.528 (9)

3. Calculate the FRAC1WORD

NFRAC1WORD = NFRAC×MOD

1WORD (10)

Where MOD1WORD is a fixed value of 225 = 33554432

NFRAC1WORD = 0.528 ×33554432

= 17716740.096

(11)

FRAC

1WORD= INTNFRAC1WORD

= 17716740

(12)

FRAC2WORD and MOD2WORD are only required if

NFRAC1WORD is not an integer number. If NFRAC1WORD is an

integer, then no further calculation is required. In this case,

VAR_MOD_EN is set to 0 to disable FRAC2WORD and

MOD2WORD.

4. Calculate the MOD2WORD

a. Determine the remainder of the fractional word

NREMAINDER= NFRAC1WORD

−FRAC

1WORD = 0.096 (13)

NREMAINDER= 17716740.096

−17716740 = 0.096

(14)

b. Find the greatest common divisor (GCD) between fFPD and

MOD1WORD × fCHSP.

GCDMOD

1WORD×fCHSP, fPFD

(15)

GCD225×1, 250 MHz =128 (16)

c. Calculate initial MOD2WORD Calculation

MOD

2WORDINITIAL

= fPFD

GCDMOD

1WORD×fCHSP, fPFD

(17)

MOD

2WORDINITIAL = 250 MHz128

= 1953125

(18)

d. Compare with MOD2WORDMAX

In this example, phase resynchronization is not required.

Therefore, MOD2WORDMAX = 224 − 1 = 16777215 and

the MOD2WORD = 1953125 previously calculated can be

used.

If phase resynchronization were required, then

MOD2WORDMAX = 217 − 1 = 131071. Then fCHSP is need-

ed to be increased in order to reduce MOD2WORD ≤

MOD2WORDMAX.

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