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MIPI CSI-2 Voltage level

Luigi Maggi
Prodigy 110 points
Other Parts Discussed in Thread: AWR1243, AWR1243BOOST

Hi,

i'm trying to connect the MIPI receiver to MIPI CSI-2 bus of AWR1243 component.

The main issue is that the level of the output signals from AWR1243 is not comliant with the specifications of MIPI standard beacause the level of VOH is about 0.9V instead of 1.2V.

I attached the sceenshot of the signals measured with oscilloscope. The first figure shows the differential signals with 100ohms termination while in the second figure the same signals without any termination. Both of them have the high level VOH about 0.9V.

In the following the specifications declared in the AWR1243 datasheet:

HSPTX

VOD (HS transmit differential voltage): 200mV

VCM (HS transmit static common-mode voltage): 200mV

VOHHS (HS output high voltage): 360mV (max)

LPTX

VOL: 50mV

VOH: 1.2V

Why the voltage level is 0.9V instead of 1.2V? what am I doing wrong?

  

  • 0
    TI__Mastermind 26985 points
    Hello Luigi,

    Is this on one of our EVMs? Or is this your own custom board?

    Regards,

    Adrian
  • 0 in reply to aozer
    Prodigy 110 points
    Hi Adrian,

    the board is AWR1243BOOST and I've measured the signals on the J1 connector.

    Regards,

    Luigi
  • 0 in reply to Luigi Maggi
    TI__Mastermind 26985 points
    Hello Luigi,

    Let me try to test it on my end on an EVM and see if I get similar results. It will get back to you with my results next week as I need to find the bandwidth to test it.

    Regards,

    Adrian
  • 0 in reply to aozer
    Prodigy 110 points

    Hello Adrian,

    In addition to the issue of the initial level of 0.8V on the signals I encountered another problem.

    Below I'll show you the measurements of the MIPI CSI-2 of CSI2_TXP[0] and CSI2_TXM[0] on the J1 connector.

    The first figure shows the voltage level without any termination (all signal are floating) while the second one with 150 ohm termination placed between CSI2_TXP[0] and CSI2_TXM[0].

    As highlighted in the second figure the LP signals integrity are compromised and the status LP10 is disappeared.

    Could you tell me what am i doing wrong?

    Thanks

    Best Regards

    Luigi

  • 0 in reply to Luigi Maggi
    TI__Mastermind 26985 points
    Hello Luigi,

    How are you adding the 150 ohm termination to the board? And why are you terminating with 150 ohm?

    LP mode should be unterminated, where as the HS is usually terminated with 100 ohms.

    Regards,

    Adrian
  • 0 in reply to aozer
    Prodigy 110 points

    Hello Adrian,

    I've mounted the resistor between the pad of R49 and R48. With 100 ohm instead of 150 ohm the result doesn't change much.

    The hardware setup scheme is as the following:

    The measurement is carried out between the J1.56 and J1.58 pins of J1 connector

    Best regards

    Luigi

  • 0 in reply to Luigi Maggi
    TI__Mastermind 26985 points
    Hello Luigi,

    But in that case, you are still terminating the LP signals when they should not be terminated. The LP signals act as single ended signals.

    Regards,

    Adrian
  • 0 in reply to aozer
    Prodigy 110 points

    Hi Adrian,

    I think there is a misunderstanding. AWR1243 generates only D-PHY P and N differential signals. I've to convert this differential signal to LP and HS signals for receiver but the measurements is carried directly on CSI2_TXP[0] G15 and CSI2_TXM[0] G14 pins.

    The problem occurs when I connect 100ohm termination to the output of AWR1243 MIPI differential signals (G15 and G14 pins) because it is no longer compliant to MIPI standar for two reason:

    1. The start level voltage is 0.8V instead of 1.2V
    2. After connecting 100ohm termination to the differential signals at the output of CSI-2 there is a problem in the LP01 state.

    Could you give me a solution? What resistor network I have to use to resolve the issue and generate the right LP and HS signals for the receiver?

    Thanks for your time.

    Best regards

    Luigi

  • 0 in reply to Luigi Maggi
    Prodigy 110 points

    Hi Adrian,

    Have you any update? Please, I've based the project on the component AWR1243 and I need to understand how to fix the issue on the MIPI CSI-2 Communication.

    Thank for your time.

    Best regards

    Luigi Maggi

  • 0 in reply to Luigi Maggi
    TI__Mastermind 26985 points
    Hello Luigi,

    Sorry for the delayed response. I was able to take a look at the VOH on an EVM and I am seeing the expected 1.2V with no termination. Can you confirm that with your EVM returned to a completely unmodified state you are seeing 0.8V?

    I am looking into the termination requirements.

    Regards,

    Adrian
  • 0 in reply to aozer
    Prodigy 110 points

    Dear Adrian,

    I'm bought several TIBOOST EVM (5 pieces) and the VOH is about 0.8V in all boards without any modification on them. I confirm you that the measurement is carried out with no termination and with oscilloscope probe direct to R48 and R49 resistors (corrisponding to CSI2_TXP[0] and CSI2_TXM[0] signals on the J1 connector) as I 've shown you with the figures in previous reply.

    Today I've carried out a new measurements but i have the same results and I confirm you I see 0.8V.

    After I program the TI AWR1243 with SPI the component AWR1243 starts to send the data via MIPI CSI-2 bus. Such bus is floating (there is no connection to the J1 connector) therefore there are no resistor termination.  

    Apart from this Have you had the opportunity to evaluate the second point of my previous reply?:

    "After connecting 100ohm termination to the differential signals at the output of CSI-2 there is a problem in the LP01 state"

    Could you confirm if you get the same behavior with a resistor termination of 100ohm?

    Best regards

    Luigi

  • 0 in reply to Luigi Maggi
    Prodigy 110 points

    Hi Adrian,

    Have you any update?

    Best regards

    Luigi

  • 0 in reply to Luigi Maggi
    Prodigy 110 points

    In reply to Luigi Maggi:

    Hi Adrian,

    Have you any update?

    Best regards

    Luigi

  • 0 in reply to aozer
    Prodigy 110 points
    Hi Adrian,

    Have you any update?

    Best regards

    Luigi