simple oscillator circuit?

[[email protected]]

Hi,

I am trying to use a at9sam7256 microcontroller.. i am using a
programmable clock out line of this chip to drive a omnivision 9640
camera chip.
The problem is that the clock signal seems very unstable.. i.e. the
video comes out, but is very unstable and has a lot of noise. When i
use the clock line that is on the omnivision reference board the camera
data looks great.. so i know that the problem is the clock signal that
i am feeding it since that is the only thing i changed.

Is there any way to clean up that clock signal that is coming from my
microcontroller?
I also dont mind creating a separate oscillator circuit with a 48mhz
crystal.. but i am a newbie and i dont know how to create such a
circuit... could someone explain? Also, are there single chip
osclilators that simply have a clock out line that i could feed into
the camera chip?

thanks - bob

 

[Jasen Betts]

Hi,

I am trying to use a at9sam7256 microcontroller.. i am using a
programmable clock out line of this chip to drive a omnivision 9640
camera chip.
The problem is that the clock signal seems very unstable.. i.e. the
video comes out, but is very unstable and has a lot of noise. When i
use the clock line that is on the omnivision reference board the camera
data looks great.. so i know that the problem is the clock signal that
i am feeding it since that is the only thing i changed.

Is there any way to clean up that clock signal that is coming from my
microcontroller?

are you using a crystal to clock the micro?
how are you generating the clock using the micro?

I also dont mind creating a separate oscillator circuit with a 48mhz
crystal.. but i am a newbie and i dont know how to create such a
circuit... could someone explain? Also, are there single chip
osclilators that simply have a clock out line that i could feed into
the camera chip?

there are single part oscilators.

Bye.
Jasen

 

[Chris]

Hi,

I am trying to use a at9sam7256 microcontroller.. i am using a
programmable clock out line of this chip to drive a omnivision 9640
camera chip.
The problem is that the clock signal seems very unstable.. i.e. the
video comes out, but is very unstable and has a lot of noise. When i
use the clock line that is on the omnivision reference board the camera
data looks great.. so i know that the problem is the clock signal that
i am feeding it since that is the only thing i changed.

Is there any way to clean up that clock signal that is coming from my
microcontroller?
I also dont mind creating a separate oscillator circuit with a 48mhz
crystal.. but i am a newbie and i dont know how to create such a
circuit... could someone explain? Also, are there single chip
osclilators that simply have a clock out line that i could feed into
the camera chip?

thanks - bob

Hi, Bob. You're not entirely clear on the frequency of the output
signal you're feeding to your camera chip.

If you are feeding 48MHz, or you're dividing dowm to some other common
frequency, you might be able to purchase a separate clock oscillator
(which has the crystal, oscillator circuit and buffer built-in to
provide a good HC-type output). If 48MHz is the ticket, you can get
one from Jameco as their P/N 325738 for $1.35 USD, and it will plug
directly into an 8-pin IC socket. Just supply +5V, and you're done.

http://www.jameco.com/

These ICs have higher drive capability than your uC output pin, and
that might help.

Your problem also might be that you may be getting noise or reflections
on the line going from your uC to the camera, or the trace inductance
or capacitance between signal lines may be distorting your signal. If
you're not using a PC board, keep the line as short and straight as
possible. Look in the docs for the camera chip, and see if there's
anything there about loading the signal.

Hope this helps. If not, feel free to post again and describe more
about your problem.

Good luck
Chris

 

[John Fields]

On 28 May 2006 22:29:36 -0700, [email protected] wrote:

....

Also, are there single chip
osclilators that simply have a clock out line that i could feed into
the camera chip?

---
Yes. go to:

http://www:digikey.com

and enter "crystal oscillator" in the "Parts Search" box.

Then, when the next screen comes up, click on "Oscillators(3962
items)."

When the next screen comes up, scroll the "Frequency" column until
you get to "48.000MHz", click on it, and then click on "Apply
Filters".

On the next screen, click on "View Page" and then choose the
oscillator you want from the 59 available.

Digi-Key has a better search engine than Mouser does, plus they have
a "handling charge" if you don't order a $25 minimum, so once you
find the oscillator you want, you might want to go to:

http://mouser.com

and see if they have the same oscillator, since they don't have a
minimum or a handling charge.