CS2000-CP

DS761PP1

21

5.3.7

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-Mods can be applied to both modes whereas Auto R-Mod is only

available in dynamic mode. The user defined ratio, ratio modifier, and automatic ratio modifier make up

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 14 summarizes the features involved in the calcu-

lation of the ratio values used to generate the fractional-N value which controls the Frequency Synthesiz-

er.

Figure 14. Ratio Feature Summary

Referenced Control

Register Location

Ratio0-3.................................“Ratio 0 - 3 (Address 06h - 15h)” on page 30

RSel[1:0] ...............................“Ratio Selection (RSel[1:0])” on page 28

LockClk[1:0] .......................... “Lock Clock Ratio (LockClk[1:0])” section on page 29

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

RModSel[2:0] ........................ “R-Mod Selection (RModSel[2:0])” section on page 28

AutoRMod .............................“Auto R-Modifier Enable (AutoRMod)” on page 29

FsDet[1:0]..............................“PLL Input Sample Rate Indicator (FsDet[1:0]) - Read Only” section on page 27

RefClkDiv[1:0] ....................... “Reference Clock Input Divider (RefClkDiv[1:0])” on page 31

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

Auto

R-Mod

AutoRMod

FsDet[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

≠

=

CLK_IN present

or FracNSrc=1

CLK_IN not present

or FracNSrc=0