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SN75LVCP600S: SATA Return loss details

Shifali N
Expert 2085 points
Part Number: SN75LVCP600S
Other Parts Discussed in Thread: DS64BR111

Hi,

I am using SN75LVCP600S SATA redriver . Now I will be doing SI analysis for my board using this driver. My requirement is SATA 3.0. So what should be the value of return loss for RX and TX when measured @3GHz.

The SATA spec says TX Differential return loss @0.3GHz is -14dB. And the Differential slope is mentioned as -13dB. And maximum TX differential loss frequency is mentioned as 3GHz. Now what should be the value of TX differential return loss @3GHz.

Thanks in advance.

  • 0
    TI__Guru* 91440 points

    Hi Shifali,

    It should be between 3 to 13dB. Please note return loss highly depends on the pcb layout. So in your SI analyses you should use your pcb layout as well.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Expert 2085 points

    Hi Nasser,

    1. The value of 3 to 13dB mentioned will be only only for your IC or is this the general value that can be considered as per SATA spec for both TX and RX line? Is it -3 to -13dB or +3 to +13dB.

    2. Is the return loss value same for RX and TX line @3GHz.

    3. As per the SATA spec, for TX line return loss @0.3GHz is -14dB.
    The Return loss limit line starts at 300 MHz at -14 dB increasing at 13 dB/decade to 3 GHz as per SATA spec.
    The spec says that return loss shall remain below the line from the starting frequency to the ending frequency.

    So for TX, return loss shall remain below -14dB @0.3GHz and below -1dB @3GHz.

    4. As per the SATA spec, for RX line return loss @0.3GHz is -18dB.
    The Return loss limit line starts at 300 MHz at -18 dB increasing at 13 dB/decade to 6 GHz.
    The spec says that return loss shall remain below the line from the starting frequency to the ending frequency.
    So for RX, return loss shall remain below -18dB @0.3GHz and below -5dB @3GHz.

    Is my understanding correct.

  • 0 in reply to Shifali N
    TI__Guru* 91440 points

    Hi Shifali,

    1). Yes your understanding is correct. 3 to 13dB is for the IC at 2.4G to 3G. Lower frequency would have more or better return loss.

    2). The return loss value is almost the same for RX and TX. Please note data sheet parametric table.

    3). Yes your understanding is correct. In this case, for SN75LVCP600S, it will remain below -3dB at 3GHz - more than 2dB margin.

     4). It is my understanding that it shall be below -3dB at 3GHz. 

    Regards ,, Nasser

  • 0 in reply to Nasser Mohammadi
    Expert 2085 points

    Hi Nasser,

    Thank you for your response.

    As per the SATA spec, the return loss limit for  RX line starts at 300 MHz at -18 dB increasing at 13 dB/decade to 6 GHz. So  at 3GHz the return loss should be below -5dB. But for the SATA redriver SN75LVCP600S, minimum value of RX differential mode return loss from frequency 2.4-3GHz is -3dB as mentioned in Table:6.5 . Shouldn't the value minimum RL value be -5dB @3GHz. So does the IC satisfy the return loss requirement as per SATA spec?

    2. Also may I know why Differential model RL slope for RX line is from 0.3GHz to 6GHz  while for TX line slope is from 0.3GHz to 3GHz.

  • 0 in reply to Shifali N
    TI__Guru* 91440 points

    Hi Shifali,

    1). As far as  i know, SATA spec calls for 3dB. Please refer to the specification page 196.

    http://www.usedsite.co.kr/pds/file/SerialATA_Revision_3_0_RC11.pdf

    2). This measurement was done some times back and cannot find the reason behind this. There is another part - DS64BR111 - where this part has return loss measured at higher frequency.

    Regards ,, Nasser

  • 0 in reply to Nasser Mohammadi
    Expert 2085 points

    Hi Nasser,

    I referred to page 196 of the document shared by you, the return loss value of 3dB is mentioned for Gen2 and not for Gen3. I don't see any return loss value given for Gen3. For RX return loss below values are mentioned in specification;

    Minimum return loss value @0.3GHz=-18dB

    Slope=13dB

    Maximum slope frequency= 6GHz.

    I arrived at the value of -5dB using these values.

    The SN75LVCP600S is SATA 3.0 re-driver so shouldn't the value be compliant with Gen3.

    Whether can I consider the SATA Gen2 return loss values for SATA Gen3.

  • 0 in reply to Shifali N
    TI__Guru* 91440 points

    Hi Shifali,

    My apologies. This is one of the older parts and this data is not available. 

    Regards ,, Nasser