[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 23:25:05 +0300
> Dimiter unless there is some really crummy dynamic logic, ...
Well the entire TFT matrix is dynamic, after all. And 60 Hz refresh
frequency is not that high, 16.7 mS... so may be twice that will be
visible, or perhaps just measurable (some do specify 400 times contrast
ratio, which is a lot). But if I knew I'd get half the contrast,
that is, 200, I'd be fine, my main problem is not to design a board
that will not be able to work with its display at all...
> I suspect that is actually a maximum clock rate / minimum clock
> interval and is a victim of Japanese to English translation.
That's what I thought when I encountered such a spec first.
But then I saw it over and over again, at different manufacturers,
and it definitely does not look like a translation error.
My latest guess/hope is that they specify that in order to guarantee
the optical contrast spec, which might degrade at lower frequencies
and may be over temp. (OK, over the narrow temp range TFTs work
I doubt the gate capacitors of the matrix will change behaviour
a lot but then I may be surprised on that as well).
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
>
> Date: Tue, 01 May 2007 22:35:49 -0700
> To: dp@xxxxxxxxxxx
> From: steve weir <weirsi@xxxxxxxxxx>
> Subject: Re: [SI-LIST] TFT display modules with _min_ dot clock frequency spec
>
> Dimiter unless there is some really crummy dynamic logic, or as you
> mention a PLL involved it doesn't seem to make sense to me either. I
> suspect that is actually a maximum clock rate / minimum clock
> interval and is a victim of Japanese to English translation.
>
> Steve.
> At 06:21 PM 5/1/2007, you wrote:
> >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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