Figure 10:
Internal Dual Clocking Architecture
/M
Phase
Frequency
Detector
Charge
Pump
/N-Fractional
Loop
Filter
Lock
Indicator
/2
VCO
PLL
CLKIN
PLL
LOCKED
PLL
CLKOUT
LCPLLCLKOUT_RATE
X20901-052418
The LCPLL VCO operates within 9.8 GHz—14.5 GHz. The Xilinx software tool chooses the
appropriate LCPLL setting based on application requirements.
shows how to
determine the PLL output frequency (GHz).
f
PLLClkout
= f
PLLClkin
* N + FractionalDivider
M*LCPLLCLKOUT _RATE
shows how to determine the line rate (Gb/s).
f
LineRate
= f
PLLClkout
*Modulation
show how to determine the fractional divider presented in
.
FractionalDivider = N
SDM
+ 0. < FractionalPart >
FractionalPart = SDMDATA
2
SDMWIDTH
The table below lists the allowable values.
Table 8: LCPLL Divider Settings
Factor
Attribute or Port
Valid Settings
M
LCPLL_REFCLK_DIV
1, 2, 3, 4
N
PLLFBDIV[7:0]
16–160 (Integer only)
LCPLLCLKOUT_RATE
LCPLLCLKOUT_RATE
1'b1
: 1 (Full),
1'b0
: 2 (Half)
Modulation
2 (NRZ), 4 (PAM4)
N
SDM
SDMDATA[SD 1:SDMWIDTH]
Integer part of fractional divider. (Two’s
complement) –2, –1, 0, 1
SDMDATA
SDMDATA[SDMWIDTH – 1:0]
Fractional part of fractional divider.
0 – (2
24
– 1)
SDMWIDTH
SDM_WIDTHSEL
16, 20, 24
Chapter 2: Shared Features
UG581 (v1.0) January 4, 2019
Virtex Ult GTM Transceivers
20