FreeLists / si-list / [SI-LIST] Re: TFT display modules with _min_ dot clock frequency spec

[olaney@xxxxxxxx]

This might be obvious, but it's worth a mention anyway.  Absent a PLL,
the LCDs I've worked with generally have static clocking down to DC.  It
is conceivable that the design might use dynamic logic speed up on-panel
circuits built with amorphous silicon, but it is hard to believe that the
resulting minimum clock would be so high.  So, take a close look at the
spec sheet and check if the 25 MHz number is actually a minimum for the
maximum clock rate, i.e. the thing will crap out at some faster rate, but
never at a slower one.
Regards,
             Orin

On Wed, 2 May 2007 4:21:53 +0300 Dimiter Popoff <dp@xxxxxxxxxxx> writes:
> Posted this to two newsgroups, then I thought actually I might have
> better chances to find someone in the TFT module industry via the
> Si-list, so here it goes.
> 
> I have been looking around for a TFT module for a design (5" to 8"
> sized, 800x480 min.,thin) and found some really good looking.
>  The problem I have is that some of them specify a minimum dot 
> clock
> frequency, typically well above 25 MHz.
>  Now apart from a PLL they may have inside the module I can think
> of little reasons why they need that; and I have not heard of such 
> a
> thing, but I am far from the insides of these (hence my posting 
> :-).
>  I could pretty well live at a 30 Hz or even 20 Hz frame rate,
> which would mean 16 MHz clock or below, thus lower power,
> less memory bandwidth etc.
>  TFTs don't flicker, I have played with the first one I had 5-6 
> years
> back and there was absolutely no visible benefit of increased clock
> frequency.
> 
> Anyone know why this minimum clock spec? Any knowledge on that?
> Some of the best fits I find do specify it and it is in conflict 
> with
> a really major simplification I can make to the design....
> So my hope is that this spec is put in order to keep some high 
> enough
> frame rate to satisfy some common controller thing, not really a 
> must.
> I'll try to ask the manufacturers directly, but perhaps I have a
> better chance to find out something via usenet.
> 
> Thanks,
> 
> Dimiter
> 
> ------------------------------------------------------
> Dimiter Popoff               Transgalactic Instruments
> 
> http://www.tgi-sci.com
> ------------------------------------------------------
> 
> 
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