6.4 Output Signal Format
The differential output swing and common mode voltage are both fully programmable covering a wide variety of signal formats including
LVDS, LVPECL, and HCSL. For CML applications, see Section
6.4.9 Setting the Differential Output Driver to Non-Standard Amplitudes
.
The differential formats can be either normal or low power. Low power format uses less power for the same amplitude but has the draw-
back of slower rise/fall times. The source impedance in low power format is much higher than 100 Ω. See Section
Differential Output Driver to Non-Standard Amplitudes
for register settings to implement variable amplitude differential outputs. In addi-
tion to supporting differential signals, any of the outputs can be configured as LVCMOS (3.3, 2.5, or 1.8 V) drivers providing up to 8 (for
the Si5396) single-ended outputs, or any combination of differential and single-ended outputs. Note also that CMOS output can create
much more crosstalk than differential outputs so extra care must be taken in their pin replacement so that other clocks that need the
lowest jitter are not on nearby pins. See
AN862: Optimizing Jitter Performance in Next Generation Internet Infrastructure Systems
for
additional information.
Table 6.3. Output Signal Format Control Registers
Setting Name
Hex Address [Bit Field]
Function
Si5397A/B
Si5397C/D
Si5396
OUT0_FORMAT
OUT1_FORMAT
OUT2_FORMAT
OUT3_FORMAT
OUT4_FORMAT
OUT5_FORMAT
OUT6_FORMAT
OUT7_FORMAT
0109[2:0]
0113[2:0]
0118[2:0]
011D[2:0]
0127[2:0]
012C[2:0]
0131[2:0]
013B[2:0]
0109[2:0]
011D[2:0]
0127[2:0]
012C[2:0]
—
—
—
—
0113[2:0]
0118[2:0]
0127[2:0]
012C[2:0]
—
—
—
—
Selects the output signal format as differential or
LVCMOS.
Si5397/96 Reference Manual
Outputs
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