DS90UB953A-Q1: Clock Rate & Synchronous Mode Questions

Go Bravos

Team,

We are using the DS90UB953ATRHBTQ1 for our serializer. We are running it with a MIPI camera, 2-lane CSI-2 at 1080p, 30 fps. We’re mostly interested in the following for this part:

Additional guidance on how to set the clock rate to ensure the FPD-Link rate is minimized but still meets the > CSI-2 bandwidth requirement for the FPD link to operate.
How to configure it for synchronous mode with a 24 MHz clock generated from the de-serializer part. Our camera appears to require a 24 MHz clock to run at 1080p, 30fps. We think the MIPI bandwidth will be <800 mbps per lane, but the camera datasheet lacks any information on the MIPI data rates. Any advice or guidance you have regarding the clocking and MIPI rate would be extremely helpful.
Guidance on how to configure the outputs for differential, STP style transmission and any layout guidelines regarding differential signal use of the FPD link. The datasheet and evaluation modules talk mostly about the use of a coaxial cable. We would want to run differential signals across a series of rigid-flex-rigid PCBs to get our signals back to the de-serializer.

Thank you.

over 6 years ago

0 Mandeep S over 6 years ago

TI__Expert 3390 points

Hi Go,

1) So you want to reduce the forward channel rate between the serializer and deserializer? The forward channel rate can run in two settings 4G or 2Gbps FPD. What is the total CSI rate that you inputting into the serializer?

2) To configure the deserializer into sync mode, you should configure the mode pin strap for Synchronous mode and make sure the deserializer REFCLK is being provided.

a) You want to also provide a clock to the camera? This can be done by the serializer CLKOUT pin.

3) The deserailizer and serializer drivers a differential. Nothing is need in the registers, you just need to route the P and N differentially. For the ac-coupling cap values, you can refer to the datasheets of each part.

In general, the method for making this work is you set-up the camera for whatever setting you require. Calculate the CSI rate and make sure it's less than what you plan to set for the Forward channel rate. So for example, if the CSI rate is 800Mbps, then the forward channel rate of the SerDes has to be 4Gbps, it cannot be 2G. A 4Gbps FPD channel will result in 3.2Gbps of CSI bandwidth. A 2Gbps FPD channel will result in 1.6Gbps of CSI bandwidth.

Regards,
Mandeep Singh

0 6192337 over 6 years ago in reply to Mandeep S

Prodigy 95 points

Hi Mandeep,

Thank you for the response. However, we were hoping for further clarification.

1) The data sheet shows two separate sections for Synchronous operation, 23MHz-26MHz and 11.5MHz - 13MHz. Does this mean that if I give a 11.5MHz - 13MHz clock to the deserializer the FPD link will operate in "2G" mode?

2) Your response above indicates that if the CSI2 bandwidth is >800MHz, you HAVE to operate in 4G mode. Are you making the assumption that we are using 4 lanes of CSI2? Above it was stated that a 2 lane CSI2 at 1080p @ 30fps. Would 2G operation be possible if our CSI2 bandwidth on those 2 lanes is <800MHz?

3) The datasheet gives a range of capacitance values with the assumption that COAX or STP will be used. If we are using differential signaling would we still use these values?

Thank you,

Tim

0 Mandeep S over 6 years ago in reply to 6192337

TI__Expert 3390 points

Hi Tim,

1) Yes, that is correct. The FC rate is f x 160, so with 11.5-13MHz, this would result in about 2G.

2) I was assuming 4-lane operation as an example, meaning total CSI input would be 3.2G, so 4G would be the option. If your total BW is about ~1.6Gbps CSI, then 2G is okay to use and you can do that with 4-lane or 2-lane.

3) STP is differential, so you would follow the STP guidelines.

Regards,

Mandeep Singh

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DS90UB953A-Q1: Clock Rate & Synchronous Mode Questions