LMH1251: Input to output delay when YPbPr to RGBHV conversion mode is selected & using luminance input without sync information

Akhil Abraham

Part Number: LMH1251

Hi,

What is the input to output delay when YPbPr to RGBHV mode is selected?

I wish to use this chip only for conversion of YPbPr to RGB. The sync information (H, V) is not required. Will the conversion work if I provide Y without any sync information? (i.e. shorting Y and sync on Y inputs, and the input contains only picture information)

Regards,

Akhil

over 2 years ago

0 Alec Saebeler over 2 years ago

TI__Mastermind 22654 points

Hello Akhil,

First, please see this prior thread on floating pins on the LMH1251: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/910740/lmh1251-can-the-unused-inputs-be-left-floating

Second, I have a couple items to consider & clarify:

1. Will you be needing the non-sync portion of the Y (luma/luminescence) signal? Y does not only carry sync, and you will probably need that signal for color conversion. I would not short Y and Y sync to GND or another value. If you have a Y signal to apply, I would recommend applying it to the Y pin (10) and also the Y' pin (11).

2. Please set pin 24 (the input select pin) to '1', to select the YPbPr input channels. Also refer to the auto vs. manual setting of picture quality detection to see if you need to implement a certain set of controls for your use case: page 2 of LMH1251 datasheet.

3. You may find after testing you do not need to supply a signal to Y' (pin 11); but I believe you will need the Y (luma) signal on pin 10 from your source. While the chroma parts of the signal are strictly the color portions (Pb, Pr), you might want the luminescence values too, depending on your application.

Best,

Alec

0 Akhil Abraham over 2 years ago in reply to Alec Saebeler

Prodigy 20 points

Hello Alec,

Thank you for the reply. I hope the points below will give you the clarity regarding my question.

1) I have an input luminance signal which has only picture information but no embedded sync in it. Will the color conversion work (YPbPr -> RGB) without any embedded sync? I do not need the H and V outputs from the chip.

2) What is the input to output delay in YPbPr to RGBHV mode?

0 Sima Jalaleddine over 2 years ago in reply to Akhil Abraham

TI__Mastermind 28645 points

Hello Akhil,

I am redirecting this thread to the correct group to answer your questions above. The signal conditioning team will be able to assist you shortly.

Thank you,
Sima

0 Alec Saebeler over 2 years ago in reply to Sima Jalaleddine

TI__Mastermind 22654 points

Hello Akhil,

Please see the following existing discussions and resources on the LMH1251 part. The device is quite old and I do not think I can find the additional information you seek at this time. You can attempt to approximate the input to output delay by examining the signal timings present in datasheet tables. As for the color conversion viability, I do not see why the chip would have a shutdown preventing the part from being used solely as a color converter. There may be other TI video amplifiers which can perform color conversion without a sync signal; you would have to look through the available devices and find a more suitable device if the LMH1251 is not viable. I still recommend testing the device to see how it performs.

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/910740/lmh1251-can-the-unused-inputs-be-left-floating

https://www.ti.com/lit/ug/snoa526a/snoa526a.pdf

SV012649-001-LMH1251EVAL-NOPB_Test (1).docx

Best,

Alec