5.3.3 Output Driver Settings for LVPECL, LVDS, HCSL, and CML
Each differential output has four settings for control:
1. Normal or Low Power Format
2. Amplitude (sometimes called Swing)
3. Common Mode Voltage
4. Stop High or Stop Low
The normal Format setting has a 100 Ω internal resistor between the plus and minus output pins. The Low Power Format setting
removes this 100 Ω internal resistor and then the differential output resistance will be
> 500 Ω. However, as long as the termination impedance matches the differential impedance of the PCB traces, the signal integrity
across the termination impedance will be good. For the same output amplitude, the Low Power Format will use less power than the
Normal Format. The Low Power Format also has a lower rise/fall time than the Normal Format. See the Si5341/40 data sheet for the
rise/fall time specifications. For LVPECL and LVDS standards, ClockBuilder Pro does not support the Low Power Differential Format.
Stop High means that when the output driver is disabled, the plus output will be high, and the minus output will be low. Stop Low means
that when the output driver is disabled, the plus output will be low, and the minus output will be high.
Differential Normal Swing Mode—This is the usual selection for differential outputs and should be used, unless there is a specific
reason to do otherwise. When an output driver is configured in normal swing mode, its output swing is selectable as one of 7 settings
ranging from 200 mVpp_se to 800 mVpp_se in increments of 100 mV. The output impedance in the Normal Swing Mode is 100 Ω
differential.
Differential High Swing Mode—When an output driver is configured in high swing mode, its output swing is configurable as one of 7
settings ranging from 400 mVpp_se to 1600 mVpp_se in increments of 200 mV. The output driver is in high impedance mode and
supports standard 50 Ω PCB traces The use of High Swing mode will result in larger pk-pk output swings that draw less power. The
trade off will be slower rise and fall times.
Vpp_diff is 2 x Vpp_se as shown below:
OUTx
OUTx
Vpp_se
Vpp_se
Vpp_diff = 2*Vpp_se
Vcm
Vcm
Vcm
Figure 5.2. Vpp_se and Vpp_diff
The Format, Amplitude, and Common Mode settings for the various supported standards are shown in the following table.
Table 5.4. Settings for LVDS, LVPECL, and HCSL
OUTx_FORMAT
Standard
VDDO Volts
OUTx_CM (Deci-
mal)
OUTx_AMPL
(Decimal)
001 = Normal Differential
LVPECL
3.3
11
6
001 = Normal Differential
LVPECL
2.5
11
6
002 = Low Power Differential
LVPECL
3.3
11
3
002 = Low Power Differential
LVPECL
2.5
11
3
001 = Normal Differential
LVDS
3.3
3
3
001 = Normal Differential
LVDS
2.5
11
3
001 = Normal Differential
Sub-LVDS
1.8
13
3
002 = Low Power Differential
LVDS
3.3
3
1
002 = Low Power Differential
LVDS
2.5
11
1
002 = Low Power Differential
Sub-LVDS
1.8
13
1
002 = Low Power Differential
3.3
11
3
002 = Low Power Differential
HCSL
2.5
11
3
Si5341, Si5340 Rev D Family Reference Manual • Output Clocks
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.3 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • July 26, 2021
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