# LVDS-based LCD Display, Minimum Clock Rates

Started by November 2, 2010
```I have a question regarding the minimum clock rates allowed on LVDS-
based LCD display panels.  Perhaps someone in the group has some
expertise here.

I have HD data coming in at 30 frames per second.  I have no place to
store a full frame.  The HD display panel requires a minimum clock
rate of at least 50 MHz (which, according to the display data sheet,
equates to about 50 frames per second).  I'd like to drive it at about
36 MHz.  Even if I had a frame buffer, the I/Os are not fast enough to
drive the display at more than about 300 megabits per second (the LVDS
is emulated with external resistors).

Do you know if the minimum specified clock rate is the absolute
minimum guaranteed clock frequency to guarantee that the display
operates, or is it the minimum clock frequency to guarantee the
display's specified response time?  Will the display actually operate
with a lower clock frequency.  I know that I should ask this of the
vendor, but unfortunately, there is little support for this display.

I have tested another vendor's LCD display at well below the data
sheet specified frequency and it operated just fine.

```
```On Nov 2, 10:57=A0pm, Prevailing over Technology <steve.kn...@prevailing-
technology.com> wrote:
> I have a question regarding the minimum clock rates allowed on LVDS-
> based LCD display panels. =A0Perhaps someone in the group has some
> expertise here.
>
> I have HD data coming in at 30 frames per second. =A0I have no place to
> store a full frame. =A0The HD display panel requires a minimum clock
> rate of at least 50 MHz (which, according to the display data sheet,
> equates to about 50 frames per second). =A0I'd like to drive it at about
> 36 MHz. =A0Even if I had a frame buffer, the I/Os are not fast enough to
> drive the display at more than about 300 megabits per second (the LVDS
> is emulated with external resistors).
>
> Do you know if the minimum specified clock rate is the absolute
> minimum guaranteed clock frequency to guarantee that the display
> operates, or is it the minimum clock frequency to guarantee the
> display's specified response time? =A0Will the display actually operate
> with a lower clock frequency. =A0I know that I should ask this of the
> vendor, but unfortunately, there is little support for this display.
>
> I have tested another vendor's LCD display at well below the data
> sheet specified frequency and it operated just fine.
>

Good question, one I have asked some years back myself. I wish I had
The minimum clock frequency spec began to appear perhaps 5 years ago
or less. I don't remember why now but I think TFT panels which won't
work below that frequency (my level of certainty is pretty low on
that,
however).
I have had displays which will operate at much much lower frequencies,
however below a certain one their contrast etc. parameters won't meet
their spec (the gates of the TFT can only hold charge for a limited
amount of time, if you have seen how a display fades into rainbow
colours a second or so after losing its clock etc. signals you'll
know what I mean).
I suppose the bottom line is "check that display you will use"...

Dimiter

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```