Application Notes

How to design with video SFP

Early SFP

The SFP (small form-factor pluggable) was created to be used in telecommunication and datacommunication applications. The form-factor and the electrical interface (host board interface) are specified by a Multi-source agreement refereed as SFP-MSA. The early SFP were created to be transceiver modules, meaning one receiver port (optical receiver also known as ROSA) and one transmitter port (optical laser also known as TOSA).
These SFP were not design to support the SDI video pathological signal (for more information on the pathological signal, please read this article) and their performance with pathological signal were bad and the resulting bit error rate was high.

Video SFP

Generally speaking, the video emSFP is fully compliant with video SFP design and SFP cages and SFP+ cages; we will address this in the next topic. The basic difference is on the power rating of the emSFP, the advanced processing built inside the emSFP and the different bit rate supported by the emSFP, from DC up to 12G SDI.
NOTE: Because the emSFP have more processing power, unfortunately the overall power of emSFP (embrionix video SFP) is higher than standard SFPs (1 watt) and in the same range of SFP+ (1.5 watts).

FOR MORE INFORMATION : Please contact Embrionix sales team to get more information about the emSFP. sales@embrionix.com

SFP / SFP+ cage and host connector compatibility with video SFP and video emSFP

The host board interface of an SFP port is composed of 2 main parts, the cage which ensure the SFP, video SFP, SFP+ and the emSFP is hold in place and the connections are made correctly.
NOTE: The SFP, SFP+ and video SFP / video emSFP are design in a way that the ground connection will be made first, followed by the VCC and the other signals. When engineer starts new design a special care should be made on the selection of the SFP, video SFP, SFP+ or video emSFP.

FOR MORE INFORMATION : Please visit www.embrionix.com/tool

SFP and SFP+ CAGE

The SFP and SFP+ cage are composed of the metal body and the host connector. More specifically, the metal body have the EMI pins used to connect it to the final enclosure, the pins to be soldered or pressfit in the PCB and finally for the SFP, the retainer (small latch at the bottom of the metal enclosure).
NOTE: The retainer (latch) should also be carefully studied when choosing the SFP cage or SFP+ cages. This retainer is important to ensure the SFP, video SFP or video emSFP stays in place when insertion occurs.

SFP cage and retainer Embrionix
NOTE: Embrionix recommended using soldered cages to support the weight for coaxial cables & video SFP and other types of cables.

Retaining mechanism of video SFP… be careful

Importance should be taken when choosing a video SFP because the retaining mechanism (the triangle shown in the previous image) is important to avoid movement inside the cage, poor design result in a poor signals connection and a high Bit error rate.

The triangle specified in the SFP-MSA specification (link to the specification available on Embrionix website) should be respected to ensure the good retention.

The SFP design can greatly vary on how the SFP, video SFP or emSFP retainer is designed. Good Mechanical design consisted of the triangle height, width as describe in the MSA-SFP specification. Poor design can result of damaged parts and insertion/extraction problems.

SFP+ cage with heatsink

SFP+ cage can be ordered with an heatsink on top of the cage to ensure the support of SFP+ extra power. Those SFP+ cages can be used when a minimal airflow is present in system. Basically, when the SFP+ or video SFP from Embrionix or video emSFP are inserted inside a latch at over the SFP+ host connector is activated and the heatsink is pressed on the top of the cage ensure a good thermal conductivity.

SFP cage and heatsink for Embrionix video SFP
Embrionix team can help your engineer with the correct selection of the SFP or SFP+ cages.). please contact info@embrionix.com for more information.

Care should be taken when selecting video SFP suppliers. The SFP housing should have a angle at the back to correctly mate with SFP+ cages. This bevel ensures the heatsink latch mechanism isn’t blocking when inserring the video SFP or video emSFP. Embrionix video SFP and emSFP are design to ensure a good compatibility with the SFP cages and SFP+ cages from various manufacturers.

SFP and SFP+ host connector

The SFP and SFP+ host connector can look the same, but in reality they are different, the SFP+ host connector have been optimized for signals over 10Gbps and the SFP has been specified for 5Gbps or lower. Embrionix recommends using SFP+ host connector with video SFP and video emSFP for 6G SDI and 12G SDI.

cross section of the SFP connector Embrionix
NOTE: The SFP host connectors are specified for 100 insertion /extraction. The insertions affected the pins and the plating on the pins. To correct this manufacturer supplied SFP cages with higher amount of gold platted on the pins, some SFP host connector are specified for 1000 insertion / extraction, this is good enough for normal usage of video SFP and video emSFP, but care should be taken when designing the system.

SFP+ host connector

The SFP+ host connector is optimized for high speed differential signals. The specification SFF-8431 includes measurements to ensure the compatibility between the host board (product) and the SFP+ modules.

NOTE: For more information about the measurements methods and resulting values, please visit the SFF-8431 specification from page 50 to 72.

Design rules for video SFP and video emSFP (up to 3Gbps 3G-SDI)


MSA SFP definition


Because video SFP are inspired by MSA SFP (datacommunication and telecommunication ones), it make sense to start the explanation from the original MSA SFP. In the design rules, we will explore the ports on SFP, data input pair, data output pair, communication link I2C and power. The following table (reference INF-8071, page 21) shows the pin definition and their mating order (the SFP fingers should design to allow this power mating sequence).

table MSA

Low speed pin definition of MSA SFP

TX Fault is an open collector/drain output, which should be pulled up with a 4.7K – 10KΩ resistor on the host board. Pull up voltage between 2.0V and VccT, R+0.3V. When high, output indicates a laser fault of some kind. Low indicates normal operation. In the low state, the output will be pulled to < 0.8V.

NOTE: No special care should be done when routing the TX Fault.

TX disable

TX disable is an input that is used to shut down the transmitter optical output. It is pulled up within the module with a 4.7 – 10 KΩ resistor. Its states are: Low (0 – 0.8V): Transmitter on (>0.8, < 2.0V): Undefined High (2.0 – 3.465V): Transmitter Disabled Open: Transmitter Disabled

NOTE: No special care should be done when routing the TX disable.

MOD_DEF2, MOD_DEF1

Mod-Def 0,1,2. These are the module definition pins. They should be pulled up with a 4.7K – 10KΩ resistor on the host board. The pull-up voltage shall be VccT or VccR Mod-Def 0 is grounded by the module to indicate that the module is present. Mod-Def 1 is the clock line of two wire serial interface for serial ID. Mod-Def 2 is the data line of two wire serial interface for serial ID.

NOTE: Care should be taken when routing the I2C bus, capacitor should be minimized and limited to 400pF of load (reference I2C specification) and only 1 SFP could be connected to the I2C bus otherwise contention will append when communicating with the SFP. The I2C addresses of the SFP could not be changed. A0(hex) contain the EEPROM and A2 contains the warnings and alarms.

Rate Select

This is an optional input used to control the receiver bandwidth for compatibility with multiple data rates (most likely Fibre Channel 1x and 2x Rates). If implemented, the input will be internally pulled down with > 30kΩ resistor. The input states are: Low (0 – 0.8V): Reduced Bandwidth (>0.8 , < 2.0V): Undefined High (2.0 – 3.465V): Full Bandwidth Open: Reduced Bandwidth

NOTE: No special care should be taken when connecting Rate Select, not implemented in Video SFP.

LOS

LOS (Loss of Signal) is an open collector/drain output, which should be pulled up with a 4.7K – 10KΩ resistor. Pull up voltage between 2.0V and VccT, R+0.3V. When high, this output indicates the received optical power is below the worst-case receiver sensitivity (as defined by the standard in use). Low indicates normal operation. In the low state, the output will be pulled to < 0.8V.

NOTE: No special care should be taken when connecting LOS.

High speed pin definition of MSA SFP

RD pair

RD-/+: These are the differential receiver outputs. They are AC coupled 100 Ω differential lines which should be terminated with 100 Ω (differential) at the user SERDES. The AC coupling is done inside the module and is thus not required on the host board. The voltage swing on these lines will be between 370 and 2000 mV differential (185 – 1000 mV single ended) when properly terminated.

TD pair

TD-/+: These are the differential transmitter inputs. They are AC-coupled, differential lines with 100Ω differential termination inside the module. The AC coupling is done inside the module and is thus not required on the host board. The inputs will accept differential swings of 500 – 2400 mV (250 – 1200 mV single-ended), though it is recommended that values between 500 and 1200 mV differential (250 – 600 mV single-ended) be used for best EMI performance.

Video SFP definition


Video is different that data communication, one fundamental difference is that the video is transported in a uni-directional way. Data communication and telecommunication SFP have to transport the data in both ways to establish a link. A video link could be simply a signal fiber or coax signal transported. This reason has been the main driver to create different pinouts for the video SFP.

The following table shows the difference of the direction of the signals( /presentation/Embrionix_Pinout_Table.pdf

Video SFP pinout table

video SFP low speed pin definition

TX disable

TX disable is present on transceiver video SFP, single transmitter video SFP and two separate TX disable are present on dual transmitter video SFP

TX disable is an input that is used to shut down the transmitter optical output. It is pulled up within the module with a 4.7 – 10 KΩ resistor. Its states are: Low (0 – 0.8V): Transmitter on (>0.8, < 2.0V): Undefined High (2.0 – 3.465V): Transmitter Disabled Open: Transmitter Disabled

NOTE: No special care should be done when routing the TX disable.

SDA and SCL

These are the module definition pins. They should be pulled up with a 4.7K – 10KΩ resistor on the host board. The pull-up voltage shall be VccT or VccR SCL is the clock line of two wire serial interface for serial ID. SDA is the data line of two wire serial interface for serial ID.

NOTE: Care should be taken when routing the I2C bus, capacitor should be minimized and limited to 400pF of load (reference I2C specification) and only 1 SFP could be connected to the I2C bus otherwise contention will append when communicating with the SFP. The I2C addresses of the SFP could not be changed. A0(hex) contain the EEPROM and A2 contains the warnings and alarms.

LOS

LOS is present on transceiver video SFP, single receiver video SFP

LOS (Loss of Signal) is an open collector/drain output, which should be pulled up with a 4.7K – 10KΩ resistor. Pull up voltage between 2.0V and VccT, R+0.3V. When high, this output indicates the received optical power is below the worst-case receiver sensitivity (as defined by the standard in use). Low indicates normal operation. In the low state, the output will be pulled to < 0.8V.

NOTE: No special care should be taken when connecting LOS.

High speed pin definition of Video SFP

RX pair(s)

1 RX pair is present on transceiver video SFP and single receiver video SFP, 2 RX pairs are present on dual receivers

RX-/+: These are the differential receiver outputs. They are AC coupled 100 Ω differential lines which should be terminated with 100 Ω (differential) at the user SERDES. The AC coupling is done inside the module and is thus not required on the host board. The voltage swing on these lines will be between 370 and 2000 mV differential (185 – 1000 mV single ended) when properly terminated.

TX pair(s)

1 TX pair is present on transceiver video SFP and single transmitter video SFP, 2 TX pairs are present on dual transmitters

TX-/+: These are the differential transmitter inputs. They are AC-coupled, differential lines with 100Ω differential termination inside the module. The AC coupling is done inside the module and is thus not required on the host board. The inputs will accept differential swings of 500 – 2400 mV (250 – 1200 mV single-ended), though it is recommended that values between 500 and 1200 mV differential (250 – 600 mV single-ended) be used for best EMI performance.

Design rules for video SFP and video emSFP (up to 12Gbps 12G-SDI)


FOR MORE ADVANCED INFORMATION : Please contact Embrionix sales team to get more information about the 12G-SDI emSFP. sales@embrionix.com