DS90UB954-Q1: Encoding format of FPD-LINK

Denis,

FPD-Link is a bidirectional protocol which uses both forward and back channel signaling on the same conductor. You can find more information about the basics of the protocol here: https://training.ti.com/ti-precision-labs-what-is-fpd-link?context=1139747-1138099-1139854-1139837 

The bidirectional signal will not transmit properly through an isolation transformer for this reason so unfortunately this is not a supported topology. PoC is not a hard requirement for FPD-Link though. You could power each side separately and then provide only the FPD-Link signal across the cable if DC power isolation is the concern. 

Best Regards,

Casey 

Hi Casey:

My original design was to add an isolation IC in MIPI-CS2 interface of 954 (ADN4654, maximum bandwidth 1.1Gbps)

The ADN4654 datasheet mentions that it can support MIPI-CS2 (page-20), In fact, there is a problem.

The LPTX signal cannot be transnitted. I asked this question and I have never received a response from the FAE.

That's why I want to do isolation in FPD-LINK.

Certification regulations require that I must isolate the power and signal of FPD-LINK at the same time.

I have seen the link you gave me (Training of FPD-LINK).

PoC will be injected between the transformer and the connector.

Do you think that high-frequency transformers cannot achieve bidirectional data transmission? Or do you have other concerns?

If I cannot use a high-frequency transformer to isolate the FPD-LINK,

Can I replace (DS90UB953-Q1 + DS90UB954-Q1) with (DS90UB953-Q1 + DS90UB934-Q1)?

The interface between the DS90UB953-Q1 and the image sensor is MIPI, but the output of the DS90UB934-Q1 is LVDS. I can isolate the LVDS interface.

Can you give me some suggestions?

Thanks & Regards

Denis

Hello Denis,

The problem is that transformer isolation is unidirectional. For example on the ADN4654 you can see each channel has a direction assigned but FPD-Link has electrical signals traveling both directions on the same conductor so it will not work with this type of isolation between.

934 is a viable alternative option but please note that it does not output LVDS. It outputs single ended CMOS signals so I'm not sure if you have an isolation solution in mind for those which can also meet the speed requirements/skew requirements to ensure that the video signal is not affected.

What exactly is the isolation requirement. If you disregard the power over cable requirement is it not sufficient that FPD-Link is an AC coupled interface? 

Best Regards,
Casey  

Hi Casey :

The certification is IEC60601-1.

This image sensor will enter the human body, for safety reasons, so the entire sensor and power must be isolated from the host.

I already know that the focus of this problem is the unidirectional transmission of the transformer.

I will discuss it with the designer of the transformer manufacturer. Maybe I can do a small experiment before making a decision

I would like to ask you another question. When using 2MP/60fps image sensor, the FPD-LINK data rate is 4.16Gbps.

If 2MP/30fps image sensor is used, will the FPD-LINK rate be reduced to 2.08Gbps?

Thanks & Regards

Denis