Can you recommend some devices for me,thank you.

Hello,

The DS25MB100 is the device that best fits your minimum specifications, as it is an LVDS compatible 2:1/1:2 Mux/Buffer for up to 2.5 Gbps data rates. The DS25MB100 has a single mux, and we also have the DS25MB200 which is a dual mux/buffer.

Do you have any other specifications that you may need to meet?

For example, if you need to transmit at higher speeds than 2.5 Gbps, then we have devices that support data rates up to 12.5 Gbps including the DS125MB203.

Best Regards,

Michael Schultis

Analog Factory Applications

High Speed Datapath Solutions

Hi Michael,

Thank you for your reply.

These chips are all +3.3V for supply VDD,and TLK2711A is 2.5V for VDD.

Can I connect the LVDS from DS25MB100 to  TLK2711A directly,or should I AC coupled and DC(2.5V) bias,then connect to TLK2711A?

Best

Vincent

Hi Vincent:

AC-coupling would be needed.  The maximum common-mode input voltage of TLK2711A is 1.6 V, while the DS25MB100 has an output common-mode of 2.7 V (nominal).  The TLK2711A will provide its own internal bias point (see Figure 12 in the datasheet), so you won’t need an external network to set the common mode.

Regards!

Luis Omar Morán 

HSI - Swat

Hi Michael and Luis,

 

My 2 pairs LVDS is from TLK2711A,and at the same time,1 pair LVDS is working only,the other pair LVDS is standby,so I should select a MUX to choose the LVDS.I have 2 quetions:

1、Is there a MUX can compatible with TLK2711A to simplify my design? 

2、If I choose the DS25MB100,Between TLK2711A and DS25MB100,should I AC-coupling and DC-bias?

From the datasheet of TLK2711A,the maximum common-mode input voltage is 2250mV,while the maximum input voltage differential is 1600mV.(page16 in the datasheet),please help me check it.

Best

Vincent

 

Hello Vincent,

I have a few questions for clarification.

1. My understanding is that you have 2 LVDS pairs. You would like to select 1 of these pairs with a MUX, and then send this signal to the TLK2711A. Is this correct?

2. What is the data rate of the LVDS signal?

3. Are you using the TLK2711A to deserialize the LVDS signal that you are selecting with the MUX?

4.  Where are you sending this signal, and is this output compatible with the device that is receiving the signal from the TLK2711A?

Best Regards,

Michael Schultis

Analog Factory Applications

High Speed Datapath Solutions

Hello Michael,

My answers are as follows:

1、Yes

2、The data rate is up to 1.6Gbps;

3、After selecting one of 2paris of LVDS signals,I will use the TLK2711A to deserialize,the deserialized data is composed of 16-bit parallel signals and 1 CLK,all 17 signals are sended to FPGA(7-serias of Xinlinx ).From the datasheet(the first page),I think the 16-bit parallel signals are TTL.

The dataflow in my board is:

Two pairs of LVDS which are serialized by 2 TLK2711As in other board are recieved by DS25MB100(for example,just one MUX)  ,select one of two pairs LVDS(at the same time,there is only one LVDS acting,the ohter is standby),send to TLK2711A,deserialize LVDS to 16-bits parallel TTL signals+1 RXCLK,send to FPGA.

From Luis's answer,I know that after DS25MB100,I only need to AC-coupling,do not need to DC-bias,because there is DC-bias in TLK2711A .

But I want to know,before DS25MB100,the LVDS is from TLK2711A,what should I do about AC-coupling and DC-bias.

Thank you very much for your reply.

Best

Vincent

Hello Vincent,

You are correct that the parallel output signal (Rx) from the TLK is TTL.

Regarding the signal from the TLK2711A to the DS25MB100.

The signal from the TLK2711A needs to be ac-coupled into the DS25MB100, and the DS25MB100 will set its own internal dc bias. However, care must be taken to ensure that the DS25MB100 will receive the signal from the TLK part.

The Serializer on the TLK part will generate a VML differential output. The VML differential voltage that the TLK generates has a 1480 or 1600 mV-pp(nom) range depending on the pre-emphasis setting (according to page 16). The differential peak to peak voltage can also reach levels as high as 2200 mVp-p under some conditions.

On page 6 of the DS25MB100 datasheet, it says the receiver accepts differential signals up to 1560 mVp-p (Max) above 1.25 Gbps.

This means that the DS25MB100 can accept the signal from the TLK, but only under certain conditions, and the device would have to have a LOW pre-emphasis setting. We would suggest having some attenuation in the signal between the TLK2711A and the DS25MB100 in order to ensure the voltage output swing of the TLK falls within the maximum acceptable voltage swing on the DS25MB100, which is 1560 mVp-p.

You also mentioned that the signalling data rate is up to 1.6 Gbps. Would the data rate be less than 1.6 Gbps at any point? In that case, the TLK2711A may not perform as expected.

Regards,

Michael Schultis

Analog Factory Applications

High Speed Datapath Solutions

Hi Michael,

1、Is not the TXP/TXN of TLK2711A LVDS? It is VML?

2、The signal from TLK2711A is VML,but the DS25MB100 do not support VML from datasheet,it only supports CML, can I use DS25MB100 to realize the MUX directly(select one of  two pairs of LVDS(OR VML) )?

3、If I do not want to use some attenuation,is there other MUX that can compatible with TLK2711A completely,so that

I can simplify my design.

4、My data rate is up to 1.6Gbps indeed,becasue it is from TLK2711A.

Best

vincent

Hi Michael,

1、Is there reference schematic design?If you have this reference,can you send to my email:wancheng.jiang@ejitec.com.

In TI's official web,I only find reference design about TLK1221.The user guide of  TLK2711A's EVM,there is not schematic.

Best!

Vincent

Hello Vincent,

1. The TXP/TXN is not LVDS. As stated on the top of page 9 in the TLK2711A datasheet, the output driver is voltage mode logic (VML). This VML signal is compatible with LVPECL when AC-coupled, as they have the same voltage swing.
Refer to
http://www.ti.com/lit/an/slla120/slla120.pdf
for more information about the signaling levels.

2. The datasheet does not explicitly say that the DS25MB100 supports VML, but it supports CML and LVPECL, which have the same voltage differentials as VML (refer to app note above). So, with AC-coupling, they should be compatible since the devices set their own DC-bias values. With low pre-emphasis and under nominal conditions, the signaling is 1480mVpp, which falls under the maximum for the DS25BR100 (1560 mVp-p above 1.25 Gbps). The same warning holds, however, in that the DS25MB100 accepts 1560 mVp-p signals, while the TLK could generate signals (in worst case conditions) up to 2200 mVp-p.

3. I was not able to find any parts that are directly compatible with the TLK2711A for your application. However, the attenuation can be achieved in a couple of ways, which do not require anything more than passive components.
The first method is simpler and would only require you to put a resistor in series with the ac coupling capacitor. The drawback to this method would be increased line reflections.
The second method is slightly more complex, but still only uses passives. You can create a balanced T-pad attenuator so that the signal is attenuated, but the line impedance is the same, thereby reducing any potential line reflections.
Here is a reference to an online T-pad calculator.
http://www.daycounter.com/Calculators/PI-T-Pad-Attenuator-Calculator.phtml

4. When you say that your data rate is up to 1.6 Gbps, does this mean that your parallel input TTL signal into the first pair of TLK devices and your reference clock are 80 MHz? The input signal and clock must be 80 MHz at a minimum for this device to work properly.

5. I was not able to find any reference schematic design for the TLK2711A, but I can look more into it and let you know if I find anything that would be helpful.

Regards,
Michael Schultis
Analog Factory Applications
High Speed Datapath Solutions

Hi Michael,
Thank you for your reply promptly!
My understanding is as follows:
The DS25MB100(MUX) can be used in my design normally,and I must do AC-coupling,and do not need DC-bias becasuse these chips all have DC-bias internal.In the worst case,I should design one couple of attenuations that you recomended.
The customer's board realize changing 16-bits data@100MHz to VML via TLK2711A.
If you find anything helpful,please let me know.
Best!
Vincent

Hello Vincent,

Yes, your understanding is correct.
I am looking further into seeing if we have any additional information or reference designs available, and I will let you know if I am able to acquire anything.

Best Regards,
Michael