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In a typical clocking circuit configuration, where a crystal is tied at the input to an amplifier such as is shown below:

Clock Circuit Configuration

The capacitance required for \$C_1\$ and \$C_2\$ would be based on the load capacitance equation (sorry, not sure how to format equations on SE):

$$C_L = \frac{C_{1}\times C_{2}}{C_{1}+C_{2}}+C_S$$

However, what happens when you use an oscillator... such as the ACH-25.000MHZ-EK?

There is nothing in the application notes about needing a capacitor, so do I actually need one? (and for oscillators in general?) I am thinking that because this is still an oscillating circuit, similar to the crystal (clock configuration circuit)... That I will still need some sort of capacitor to keep the oscillator stable. Or am I wrong, and do I not need to attach any capacitor(s) to either the output or GND pins?

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    \$\begingroup\$ You don't need a capacitor. This oscillator circuit is providing a clock signal out of the box (well, just power it...) \$\endgroup\$
    – Eugene Sh.
    Commented Feb 1, 2018 at 15:28
  • \$\begingroup\$ Additionally, having trouble viewing pictures I've pasted into my question... Not sure if others are having difficulties. \$\endgroup\$
    – Snoop
    Commented Feb 1, 2018 at 15:28
  • \$\begingroup\$ Ok @EugeneSh. but won't the rest of the circuit's capacitance, somehow have to factor into how the oscillator output should be stabilized? \$\endgroup\$
    – Snoop
    Commented Feb 1, 2018 at 15:30
  • \$\begingroup\$ @Snoopy: which CPU? datasheet! \$\endgroup\$
    – Curd
    Commented Feb 1, 2018 at 15:33
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    \$\begingroup\$ @Snoopy: but the AD9833 has only ONE clock input (no oscillator on chip, just a clock input); see also Evaluation Board Schematic in datasheet. So you question doesn't make sense. \$\endgroup\$
    – Curd
    Commented Feb 1, 2018 at 15:48

1 Answer 1

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No, you need no capacitor.
Just connect the external (crystal or whatever) oscillator output to the oscillator input of the CPU (OSC1 or OSC2; or maybe called XTAL1 or XTAL2) and leave the other terminal unconnected. Only one of them is input and you need to find out which one of them by looking into the datasheet. I'm sure the datasheet tells you how to connect the external clock.

Here is an example from the ATmega32 datasheet:

enter image description here

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  • \$\begingroup\$ The question specifically states that I am not talking about a crystal. \$\endgroup\$
    – Snoop
    Commented Feb 1, 2018 at 15:36
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    \$\begingroup\$ I'm also NOT talking about a crystal! Where do you read that I'm talking about a crystal?!? \$\endgroup\$
    – Curd
    Commented Feb 1, 2018 at 15:39
  • \$\begingroup\$ Yes, I re-read your answer. You are right. \$\endgroup\$
    – Snoop
    Commented Feb 1, 2018 at 15:39
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    \$\begingroup\$ Easy, more curt than curd here :-) \$\endgroup\$
    – TonyM
    Commented Feb 1, 2018 at 15:42

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