Author Topic: Newbie question about Oscillators (not crystals!) and Load Capacitance  (Read 2408 times)

0 Members and 1 Guest are viewing this topic.

Offline PsychedelicBreakfastTopic starter

  • Contributor
  • Posts: 29
I'm looking to purchase a 8MHz oscillator for a project, and I've settled on this http://www.txccrystal.com/images/pdf/7c-tight.pdf. Most of this is straightforward, but I'm confused about the term "Load Capacitance" - doesn't apply to crystals? When using a crystal with a uC, one has to use capacitors of 22pf or so to make it work. Do I need such capacitors to use with oscillators too?

I intend to use this with Altera CPLDs. The development also has a 10Mhz oscillator onboard and when I look at the schematic, I did not see "load capacitors" so I'm kinda confused on how to proceed. Would appreciate some help.
 

Online jahonen

  • Super Contributor
  • ***
  • Posts: 1055
  • Country: fi
Re: Newbie question about Oscillators (not crystals!) and Load Capacitance
« Reply #1 on: December 02, 2011, 10:00:32 am »
You don't need any extra load capacitance. Load capacitance is critical only with crystals to tune the oscillator at right frequency. Put one series resistor (something like 22-47 ohms or so) right at the oscillator output to provide some series termination.

Regards,
Janne
 

Offline wkb

  • Super Contributor
  • ***
  • Posts: 1004
  • Country: nl
Re: Newbie question about Oscillators (not crystals!) and Load Capacitance
« Reply #2 on: December 02, 2011, 10:00:39 am »
This is most likely the maximum capacitive load the oscillator can drive at a given supply voltage. 

Why they mention multiple capacitances per supply voltage ??

Wilko
 

alm

  • Guest
Re: Newbie question about Oscillators (not crystals!) and Load Capacitance
« Reply #3 on: December 02, 2011, 09:36:10 pm »
The same question came up earlier:
Oscillator load capacitance.

Still no answer what the multiple capacitance numbers per voltage mean.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf