LVDS signals drive strength

cancel
Showing results for 
Search instead for 
Did you mean: 

LVDS signals drive strength

205 Views
Mihir2
Contributor I

Hi NXP team,

We are using i.MX8M Plus for our custom design.

 

While validating eye-diagram testing, we observed that signal has higher over-shoot and pre-shoot. Due to that signal gets distorted.

 

Is there any option to modify drive strength of LVDS clock and data lines?

 

Thank you in advance !

Regards,

Mihir

0 Kudos
7 Replies

148 Views
AndreasMaquet
Contributor I

Hello Igor, or NXP team!

I have the same question regarding this, using i.MX8QM. It's of most urgent need for us to get an answer since we are quickly coming up to a deadline and the LVDS is giving us EMC emission troubles. 

And, no we have no problems with layout, in fact it's the cable between our PCB and the TFT which is hard to shield good. Less driver strength within LVDS spec. would be very, very helpful.

Thanks in advance!

0 Kudos

137 Views
Mihir2
Contributor I

Hello @AndreasMaquet ,

We are experimenting drive strength for LVDS signals, using details shared by NXP over email.

During our experiment, we also observed that we had a parallel termination of 100 Ohms between P and N lines (mounted on display side and not on our board). We removed those termination resistors and our signal distortion gets reduced and eye-diagram quality is improved.

Hope this helps!

Thanks,

Mihir 

0 Kudos

43 Views
Mihir2
Contributor I

Hello NXP team,

 

We have 100 ohms parallel termination resistors mounted on destination side on all 5 differential pairs. We removed those resistors and re-measured eye-diagram pattern. Overall signal quality gets improved and eye-diagram opening is better compared to previous one. Our signal quality distortion issue looks like resolved.

We have not changed any LVDS drive strength on our board.

I hope this helps other NXP member as well!!

 

Thanks and Regards,

Mihir 

0 Kudos

26 Views
AndreasMaquet
Contributor I

Hello Mihir!

As a designer I would say that you then have 100 ohm termination already inside the receiver chip and that those extra redundant 100 ohm resistors made your termination to 50 ohms, which is bad for signal integrity and current rush. 

I've received the information from NXP now and I can get a reduction of around 5 dB emitted when pulling down driver strength. Every little helps...

0 Kudos

123 Views
AndreasMaquet
Contributor I

Thanks for your reply!

I'm still looking forward for NXPs answer though. 

BR/
Andreas

 

0 Kudos

195 Views
igorpadykov
NXP TechSupport
NXP TechSupport

Hi Mihir

 

additional details were sent via mail.

 

Best regards
igor

0 Kudos

122 Views
AndreasMaquet
Contributor I

(I think I replied to the wrong post up here...)

Hello Igor, or NXP team!

I have the same question regarding this, using i.MX8QM. It's of most urgent need for us to get an answer since we are quickly coming up to a deadline and the LVDS is giving us EMC emission troubles. 

And, no we have no problems with layout, in fact it's the cable between our PCB and the TFT which is hard to shield good. Less driver strength within LVDS spec. would be very, very helpful.

Thanks in advance!

0 Kudos