[SI-LIST] Re: TFT display modules with _min_ dot clock frequency spec
- From: Dimiter Popoff <dp@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 2 May 2007 12:43:21 +0300
> ... 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.
Well that's what I would have thought if someone else had posted this.
But the data sheets are quite clear, e.g. the best fit specifies
dot clock min. 35, typ. 40, max 42 MHz. Cannot imagine it any clearer
than that...
If they really need this frequency, it might be because the
transistors (those which drive the pixels) are dynamic, actually
I know they are - I remember how my first display faded away
within a few seconds after losing clock and all while powered,
it was going rainbow colours. So they might need the 60 Hz frame
rate nowadays. Or, more likely, they would work at 30 Hz but at
somewhat degraded optical characteristics, which may or may not
be acceptable, one has to see that.
Thanks,
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
> To: dp@xxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Date: Tue, 1 May 2007 18:57:31 -0700
> Subject: Re: [SI-LIST] TFT display modules with _min_ dot clock frequency spec
> From: 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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