DS90UB964-Q1: input port have 84kHz noise

Hello Betty,

Have you disabled the unused RX lanes in register 0x0C?

Best Regards,

Casey 

Hi Casey,

I will check with customer. 

one more question. for unused RX lanes, why it have 84kHz noise? Where does the noise come from?

thanks.

Hello Betty,

I believe this may be from the back channel driver which is active for the ports which are not disabled and floating 

Best Regards,

Casey 

Hi Casey,

Thanks.

customer disable back channel can help improve this problem. we would like to know why the back channel have this noise?

one more question. If customer disable the back channel of 964, whether 933 need change the configuration or it can be the same as before for normal operation?

if need change the 933, which register need to be update?

thanks

Hi Casey,

there have new problem.now, customer connect two camera and SERs, they write 0x00 to reigister 0x58, disable back channel, found no MIPI clock.

my understanding, disable back channel shoud not affect camera signal, right? if they enable BC channel, still have noise.

Therefor, we have below qeustions need your help:

1. why no MIPI clock output after disbale the BC of 964. does 933 need change the configuration?

2. customer have connect the SER, if enable the BC, still have noise. we didn't find the root cause.

thanks.

Betty,

You should only disable back channel for unused (floating) ports. For example, if you are using RX0 and RX1, but not RX2 and RX3, then you should disable RX2 and RX3 in RX_PORT_CTL. You can also disable back channel for RX2/RX3 in 0x58 with the following setting:

0x4C = 0x0C

0x58 = 0x00

Which RX ports are you using? All of them?

Best Regards,

Casey 

yes, they connect four ser, all RX ports are used

Hello Betty,

Ok, what type of cable and connector is being used here? Can you share any pictures of the test setup?

Best Regards,

Casey 

Hi Casey,

please check it .964.pptx

Hi Casey,

more information:

1. since customer disable BC can help decrease noise, we think the cable should be ok.

2.We wonder if it's snyc? 

Hello Betty,

I was asking about pictures of the EMC test setup where this noise violation is being measured. 

Best Regards,

Casey 

Hi Casey,

sorry make confusion. this nosie is not found on EMC test, That is the nosie affact customer Tuner. The Tuner is placed on the same board with 964.

we have took below test:

1. 964 work in Pattern Generation mode, no Ser connected, enable BC, found 84kHz noise at input port of 964.

2. 964 work in Pattern Generation mode, no Ser connected,diable BC, found no 84kHz noise at input port of 964.

3. connect Ser and camera, 964 work in normal, enbale BC, found 84kHz noise

4. connect Ser and cmaera, 964 work in noram, disable BC, no 84kHz noise, but the MIPI clock also no output.

Hello Betty,

It is typically best practice to route sensitive signals away from high speed communications lines like the 964 interface. If you can provide the layout, then we could give some suggestions on how to better route the signal to avoid coupling. In this case, the noise is probably coming from the back channel communications from the 964 to the remote SER device

Best Regards,

Casey