What's the difference between 4 pin and 2 pin clock crystals

[Kasterborus]

I have a circuit requiring a 25MHz clock signal, all the components I
can find are 4 pin 25Mhz crystals - how do these differ from the 2 pin
crystals in my spec?

Dave

 

[Rich Webb]

On Thu, 15 May 2008 05:57:32 -0700 (PDT), Kasterborus
<kasterborus@yahoo.com> wrote:

I have a circuit requiring a 25MHz clock signal, all the components I
can find are 4 pin 25Mhz crystals - how do these differ from the 2 pin
crystals in my spec?

Links to what you have found and what you're looking for would help.

*Probably* what you're calling "4 pin crystals" are canned
oscillators. These take in Vcc and ground and then output a clock
signal. Using one relieves you of the need to match the load
capacitors to the "bare" (2 pin) crystal. They also typically have
enough drive capacity for additional clocked logic, if needed, where
many microcontroller crystal oscillators may not.

4 pin oscillator
http://www.ctscorp.com/components/Datasheets/008-0258-0_E.pdf

2 pin crystal
http://www.ctscorp.com/components/Datasheets/008-0309-0_C.pdf

--
Rich Webb Norfolk, VA

 

[Rich Webb]

On Thu, 15 May 2008 06:51:29 -0700 (PDT), Kasterborus
<kasterborus@yahoo.com> wrote:

OK,

Here's the spec of what I'm looking at:

http://www.kako.com/neta/2007-001/circuit1.png

So are the two series caps performing the function you mentioned?

Yes. The whole assembly of [74AC04 + 1 Mohm + crystal + caps] is
conceptually what's packaged inside of a canned (4-pin) oscillator.

--
Rich Webb Norfolk, VA

 

[Kasterborus]

OK,

Here's the spec of what I'm looking at:

http://www.kako.com/neta/2007-001/circuit1.png

So are the two series caps performing the function you mentioned?

 

[ĺnřn˙mřu§]

On Thu, 15 May 2008 06:51:29 -0700 (PDT), Kasterborus
<kasterborus@yahoo.com> wrote:

OK,

Here's the spec of what I'm looking at:

http://www.kako.com/neta/2007-001/circuit1.png
If you go with the four pin part you can dump the 74ac04, the 1M

resistor, the Xtal and the two 15pf caps.

Just add power and ground and send the output to pin7 of the ir drive.
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