CS2000-CP

22

DS761F1

5.3.6

Ratio Configuration Summary

ister space. The RSel[1:0] or LockClk[1:0] bits then select the user defined ratio to be used (depending

ratio mode, by setting LFRatioCfg. R-Mod is applied if selected. The user defined ratio, and ratio modifier

effective ratio is then corrected for the internal dividers. The frequency synthesizer’s fractional-N source

selection is made between the static ratio (in frequency synthesizer mode) or the dynamic ratio generated

from the digital PLL (in Hybrid PLL mode) by either the FracNSrc bit for manual mode or the presence of

CLK_IN in automatic mode. The conceptual diagram in Figure 18 summarizes the features involved in the

calculation of the ratio values used to generate the fractional-N value which controls the Frequency Syn-

thesizer.

Figure 18. Ratio Feature Summary

Referenced Control

Register Location

Ratio0-3.................................“Ratio 0 - 3 (Address 06h - 15h)” on page 31

RSel[1:0] ...............................“Ratio Selection (RSel[1:0])” on page 29

LockClk[1:0] .......................... “Lock Clock Ratio (LockClk[1:0])” section on page 30

LFRatioCfg ............................ “Low-Frequency Ratio Configuration (LFRatioCfg)” on page 32

RModSel[2:0] ........................ “R-Mod Selection (RModSel[2:0])” section on page 29

RefClkDiv[1:0] ....................... “Reference Clock Input Divider (RefClkDiv[1:0])” on page 32

FracNSrc ............................... “Fractional-N Source for Frequency Synthesizer (FracNSrc)” section on page 30

Ratio Format

Frequency Reference Clock

(CLK_IN)

SysClk

PLL Output

Frequency

Synthesizer

Digital PLL &

Fractional N Logic

R Correction

N

Ratio 0

Ratio 1

Ratio 2

Ratio 3

12.20

20.12

12.20

only

RSel[1:0]

LockClk[1:0]

LFRatioCfg

Ratio

Modifier

RModSel[2:0]

Ratio

Modifier

RSel[1:0]

LockClk[1:0]

≠

CLK_IN sense

(auto selection)

RSel[1:0] = LockClk[1:0]

FracNSrc

(manual selection)

R Correction

RefClkDiv[1:0]

Timing Reference Clock

(XTI/REF_CLK)

Divide

RefClkDiv[1:0]

Static Ratio

Dynamic Ratio