DS34RT5110 Output image flashing with horizontal rows

Stefano2

Other Parts Discussed in Thread: DS34RT5110

We developed a prototype using DS34RT5110, when we tried it, we saw the output image flashing on and off and with horizontal rows on it.
To exclude the possibility that this behaviour was due to mistakes in our design, we bought the DS34RT5110-EVKH, when we tried it, we found the same behaviour we had with our circuit.

The configuration we used for tests is the following:
-Kramer 840 signal generator (resolution 800x600@60Hz)
-1m DVI-HDMI cable to connect the generator to the DS34RT5110-EVKH
-1m HDMI-DVI cable to connect the DS34RT5110-EVKH to the display
-Display BARCO MDSC-2226 (or others the behaviour is the same)

The DS34RT5110-EVKH settings are:
-DE(U11)=0
-EQ(U6)=0
-MODE(JP52)= open (LOW as default)
-BYPASS(JP24)=GND
-VOD_CRL=12K

Making some other tests we found that:
-changing equalization,de-emphasis,vod or mode settings the problem persist
-BYPASSING THE CDR (BYPASS<=VDD) THE PROBLEM DISAPPEAR, the output image is ok
-changing the Kramer 840 resolution in some cases the chip work fine and in some others no
-using other signal generators (i.e. Kramer 840XL) the chip work fine

Watching the eye diagram of the TMDS signals it looks good,
I attached the eye diagram of one of the differential signals referred to ground (800x600@60Hz).

Did anyone noticed the same problem?
Do you know what could be the cause of this problem?

Many Thanks in advance.

over 11 years ago

0 Nasser Mohammadi over 11 years ago

TI__Guru* 93670 points

Greetings,

I believe you already mentioned if you pull Bypass to Vcc the image goes through fine. Could you please run one more test. What happens if you leave Bypass normal(Bypass = GND) but you pull Mode = Vcc. Do you still have image quality issue?

Regards,,nasser

0 Stefano2 over 11 years ago in reply to Nasser Mohammadi

Prodigy 40 points

Greetings,

Yes, if I pull Bypass to Vcc the image goes through fine.

Leaving Bypass to GND and pulling Mode to Vcc I have the same behaviour, the image flash and have horizontal rows.

0 Nasser Mohammadi over 11 years ago in reply to Stefano2

TI__Guru* 93670 points

Hi Stefano,

I believe what is happening is that the HDMI source TMDS signals are too jittery such that it is beyond DS34RT5110 jitter tolerance. This could explain why in Bypass mode it works or when you use another HDMI source this could work as well.

Regards,,nasser

0 Stefano2 over 11 years ago in reply to Nasser Mohammadi

Prodigy 40 points

Hi Nasser,

Ok, I agree with your hypothesis, but the source we use is HDMI compliant and there is only 1m cable between it and the DS34RT5110-EVKH (watching the eye diagram of the input signal it seems good, I'm pretty sure it satisfy mask requirements, especially at 800x600 resolution), so, i wonder why the DS34RT5110 isn't able to lock the signal?
Are there specifications about the input jitter tolerance?
Do you think changing the loop filter RC can I obtain improvements?

Thank you for your help.

Stefano

0 Nasser Mohammadi over 11 years ago in reply to Stefano2

TI__Guru* 93670 points

Hi Stefano,

I believe what is happening is that the HDMI source jitter is beyond the jitter tolerance of DS34RT5110. By increasing the RC you are increasing the device loop bandwidth and this may help. However, we have not tried tested or characterized this.

Regards,,nasser

0 Stefano2 over 11 years ago in reply to Nasser Mohammadi

Prodigy 40 points

Hi Nasser,

Ok, I'll do some trials,
thank you for the help.

Regards, Stefano

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DS34RT5110 Output image flashing with horizontal rows