DS90UB936-Q1: AC couple capacitor selection recommendation

Hi Hamzeh,

Thanks a lot for your reply.

For below reply still has some questions need to double check:

Hamzeh Jaradat said:

If using 25MHz REFCLK and synch clocking Mode then yes, the forward channel datarate is fixed 4Gbps. If you want to use 2Gbps then you should change register 0x58[2:0] from 110 to 101.

Reply [JW]: Do you mean change the back channel frequency also would change the FPD LINKIII data rate? if customer change the back channel rate to 10Mbps, then would FPD-LINKIII data rate also would change to 800Mbps? Is that correct?

Hamzeh Jaradat said:

Please refer to the UB936 datasheet "Table 8-4 Design Parameters"

From table 8-4, it is not show the condition of 2Gbps FPD-LINKIII datarate with 25Mbps back channel situation, we can only see the synchronous mode would use 33nf/15nf for coax, and 47nf/100nf for non-synchronous. It is not very clear both for customer and our side, this is the reason why we need to double check with your team for more detail information. Also from section 8.2.2, we noticed that for 2Gbps or back channel rate <10Mbps, we recommend to use 47nf/100nf. So could you please kindly help to check again for the condition of 2Gbps FPD-LINKIII datarate with 25Mbps back channel, what kind of AC capacitor we would recommend?  Would 47nf/100nf be OK here?

Hamzeh Jaradat said:

This depends on your PoC design. If it was designed to support minimum of 25MHz or 12.5MHz!

Could you please kindly help to clarify for POC design? Do you mean if customer use 25Mbps backchannel, then their POC should support 25MHZ or 12.5MHZ bandwidth?  If customer use 10Mbps backchannel, then, how much POC bandwidth should support for POC? 

Thanks again for your support to clarify for above questions. Since this question comes from customer project which near to SOP and they met some RE problem at 1.6Gbps, so for above question we should make it very clear for customer to give a correct guidance for them,  it would be appreciated if we could get some clear response from your side by tomorrow. 

Best regards

Jie

Hello Jie,

Jessica Wu74 said:

Reply [JW]: Do you mean change the back channel frequency also would change the FPD LINKIII data rate? if customer change the back channel rate to 10Mbps, then would FPD-LINKIII data rate also would change to 800Mbps? Is that correct?

No this is not correct. Changing back-channel speed will result in changing FC rate only in Synch Mode, where 25 and 50Mbps are valid.

If you change to 10Mbps that means you want to put the device into the non-synch mode, where the SER uses an external Clock source for generating the FC at 4Gbps rate.

Jessica Wu74 said:

From table 8-4, it is not show the condition of 2Gbps FPD-LINKIII datarate with 25Mbps back channel situation, we can only see the synchronous mode would use 33nf/15nf for coax, and 47nf/100nf for non-synchronous. It is not very clear both for customer and our side, this is the reason why we need to double check with your team for more detail information. Also from section 8.2.2, we noticed that for 2Gbps or back channel rate <10Mbps, we recommend to use 47nf/100nf. So could you please kindly help to check again for the condition of 2Gbps FPD-LINKIII datarate with 25Mbps back channel, what kind of AC capacitor we would recommend?  Would 47nf/100nf be OK here?

Yes, in this case, please use the 47nF and 100nF capacitors.

Jessica Wu74 said:

Could you please kindly help to clarify for POC design? Do you mean if customer use 25Mbps backchannel, then their POC should support 25MHZ or 12.5MHZ bandwidth?  If customer use 10Mbps backchannel, then, how much POC bandwidth should support for POC? 

If your back channel is 25Mbps and 2Gbps FC, then your PoC must have the bandwidth from 12.5MHz to 1GHz.

If you are using non-Synch mode, then your BC is 10Mbps. That means your PoC must have the bandwidth 5MHz to the max supported FC frequency (based on the used External CLK frequency on the SER side)

For calculating the FC datarate in non-Synch mode, please refer to the 935 SER datasheet, Table 7-7

Hi Hamzeh,

Thanks a lot for your support for above questions clarify. It helps a lot.

Customer has one more question want to check, because they want to use same BOM for their other camera module platform(DS90UB935-Q1) , so they want to double check if they could use 15nf/33nf  for both 2Gbps FC datarate and 4Gbps FC datarate. 

Thanks again for your help.

Best regards

Jie