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DS25BR440: what is the difference compared to DS25BR100 (apart from the 4x channel)

Valko Zapalko
Prodigy 125 points
Part Number: DS25BR440
Other Parts Discussed in Thread: DS25BR100, , DS25BR400, DS25BR110

Hello

we have designed an evaluation board which connects two devices using a 1.25Gbps link over 1m twisted pair cable (sgmii 8b10b).

The first device generates test packets which are looped back in the second device and then the first device examines the received information for any bit/byte errors. We use a CAT7 patch cable and both links run over separate pairs (unidirectional).

The connections look as follows (FPGA1 and FPGA2 are of the same chip type meaning there is no difference in the LVDS interface, "MP" designates Measurement Point descrption below):

Link1: FPGA1(LVDS) -> DS25BR100 (MP1) -> 1m twisted pair -> (MP2) DS25BR100 (MP3) -> FPGA2(LVDS)

Link2: FPGA2(LVDS) -> DS25BR440 (MP4) -> 1m twisted pair -> (MP5) DS25BR440 (MP6) -> FPGA1(LVDS)

We are interested in the DS25BR400 because the end product requires four independent 1.25 Gbps links and we would like to use a single chip solution instead of 4x DS25BR100.

Now the actual problem:

Our test results show that link 1 seems to work as expected (stable link, no bit/byte errors) but link 2 suffers extensive issues (link breaks up and/or bit/byte errors). We have measured the eye diagrams at certain points in the system and see that the DS25BR440 output to the FPGA1 is distorted (I have attached some plots, the image numbers correspond to the measurement points (short MP) in the connection description above). As "distortion" is meant the degraded signal quality between (MP3) and (MP6).

For this reason we would like to know what is the difference between the two chips and what could be the source of the signal distortion that we are seeing. Our target link length is 5 meter and I wonder if the DS25BR440 is capable of reaching this?

Figure 1 in the DS25BR100 datasheet (SNLS217F) plots the achievable data rate over a cable length and I wonder why such an image is missing in the DS25BR440 datasheet (SNLS258B)? Why is that so?

Can the DS25BR440 be seen as 4x DS25BR100 or do they have different internal structure/data processing/capabilities?

Regards

Valentin


Measurement point 1:

Measurement point 2:

Measurement point 3:

Measurement point 4:

Measurement point 5:

Measurement point 6:

  • 0
    Prodigy 125 points

    I've made a typo: "We are interested in the DS25BR400 because the end product requires four independent 1.25 Gbps links and we would like to use a single chip solution instead of 4x DS25BR100."

    It was supposed to be DS25BR440 and not DS25BR400, sorry!

  • 0 in reply to Valko Zapalko
    TI__Guru* 93670 points

    Greetings,

    DS25BR100 and DS25BR440 are different in two different ways:

    1) DS25BR100 is a single die while DS25BR440 is a single die with multiple instances of 3G EQs. Therefor i expect BR100 would more channel to channel isolation.

    2). DS25BR100 and DS25BR440 use two different IP or high speed signal path circuit block.

    Checking and comparing your scope shots, it seems MP1 and MP4 - where we launch signal into 1m twisted pair cable - are quite different. It seems perhaps BR100 has more pre-emphasis. I am wondering if it is possible to sweep pre-emphasis first and then EQ on BR440(MP4)  such that MP5 would become more or less the same as MP2.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 125 points

    Hello Nasser

    thank you for your response. We have played with the emphasis and equalizer options (by driving the device pins PE and EQ) but didn't get any better results.

    You say that the DS25BR100 uses a "different IP or high speed signal path circuit block" compared to the DS25BR440. It would be best for us if we use two chips with the same features so my question is if there is a TI part which has one channel (for example the DS25BR100) and another one which has four channels (but with the same IP/circuit as the single chip one-channel device)? Could you propose us such a pair (1x and 4x channel chip with the same architecture)?

    I see that TI offers parts like DS25BR400 as well as the DS25BR110, does the name suppose to mean that the DS25BR440 is a 4x DS25BR110 (and that the DS25BR400 is a 4x DS25BR100) or that would be wrong?

    Regards, Valentin

  • 0 in reply to Valko Zapalko
    TI__Guru* 93670 points

    Hi Valentin,

    1). DS25BR440 has one monolithic die. I think what you are looking for is a substrate and then four dies(i.e four DS25BR100) or four individual dies in one pkg. Due to the manufacturing constrains, this is not available. Having said this, i believe DS25BR440 should work in this application. Comparing your eye diagrams, i think the trick is to make sure we can get the same eye quality at MP4 as MP1. It seems to me MP1 has more pre-emphasis and thus could be better suited for your 1m media. As an experiment, you can take out 1m cable and you should be able to run error free.

    2). BR25BR440 does not mean that it has 4 DS25BR110 devices. If space allows, you can use 4 X DS25BR110 for your application.

    Regards,, Nasser