LMH0318_15 Datasheet, PDF (44/57 Pages) Texas Instruments – LMH0318 3 Gbps HD/SD SDI Reclocker with Integrated Cable Driver

LMH0318
SNLS508 – SEPTEMBER 2015
www.ti.com
Typical Application (continued)
SMPTE specifies the requirements for the Serial Digital Interface to transport digital video at SD, HD, 3Gb/s and
higher data rates over coaxial cables. One of the requirements is meeting the required return loss. This
requirement specifies how closely the port resembles 75 Ω impedance across a specified frequency band.
Output return loss is dependent on board design. The LMH0318 meets this requirement. To gain additional
return loss margin, a return loss network, as shown in Figure 18, can be used on the output .
VDD
VDD
VDD
FPGA
FPGA
ENABLE
.:
MODE_SEL
.:
0.01 PF
0.01 PF
3.3 nH
OUT
6
11
IN0+
100: Differential T-Line 4.7 PF
OUT
12
IN0-
OUT
8 _IN1+
100: Differential T-Line 4.7 PF
OUT
9 _IN1-
SS_N
2
1
7
LMH0318
21
:
4.7 PF
OUT0+ ₂₀
:T-Line
:
4.7 PF
OUT0- ₁₉
DAP
VSS ₂₄
VSS ₁₀
3.3 nH
:
4.7 PF
OUT1+
23
100: Differential T-Line
IN+
FPGA
OUT1-
IN-
22
3 4 13 15 16
SCK
MOSI
LOS_INT_N
MISO
LOCK
Figure 18. LMH0318 SPI Mode Configuration with Return Loss Network
9.2.1 Design Requirements
For the LMH0318 design example, the requirements noted in Table 9 apply.
Table 9. LMH0318 Design Parameters
DESIGN PARAMETER
Input AC coupling capacitors
Output AC coupling capacitors
DC Power Supply Coupling Capacitors
Distance from Device to BNC
High Speed IN0, IN1, OUT0, and OUT1 trace impedance
REQUIREMENT
Required. 4.7 µF AC coupling capacitors are recommended.
Capacitors may be implemented on the PCB or in the connector.
Required. Both OUT0 and OUT1 require AC coupling capacitors.
OUT0 AC Coupling capacitors is expected to be 4.7 µF to comply
with SMPTE wander requirement.
To minimize power supply noise, use 0.01 µF capacitors as close to
the device VDD pins as possible.
Keep this distance as short as possible.
Design differential trace impedance of IN0, IN1, and OUT1 with 100
Ω ± 5%, single-ended trace impedance for OUT0 with 75 Ω ± 5%
44
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