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Oscillator...

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hykwei

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Hi Guys..

I am try building a circuit which involves with a AD9854 DDS(Direct Digital Synthesis) chip to generate a frequency controlable sine wave for me...

The problem for me is that the Master clock supply for the chip need to be around 200MHz...I don't know whether there is any crystal oscillator that can perform this function...or maybe there are some CMOS programmable oscillator chips that can do the trick for me...?

Here is the link of the chip:
**broken link removed**

Thank you guys for ur help!!
 
Look at the datasheet. The part has an internal PLL clock multiplier. You can input a REFCLK as low as 15MHz for the internal 300MHz clock generator. 200MHz should be no problem.
 
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Why not a 555 timer oscillator? You can use it in astable mode, but if you dont know how to use them, you can click on my kpsec.freeuk link and click on 555 at the top. Teaches you everything you need to know(then just scroll down until you see astable operation)!
 
Ron is spot on there. It has an internal PLL, so you just need a reference clock.

A 555 would have issues running at 15Mhz+ (if at all?!), and even if it did it, it would hardly be accurate enough, especially for DDS. Many links on the web for DDS circuits, as far as I remember, most seem to use those canned oscillator modules. A bit more expensive than the crystal alone (we're talking, what? 2USD max?), but they a CMOS/TLL output, and are very stable and accurate (all the driving stuff is in there). 25 and 50Mhz ones are freely available and are ideal for this task.

Just my two cents,

Blueteeth
 
Souper man said:
Why not a 555 timer oscillator? You can use it in astable mode, but if you dont know how to use them, you can click on my kpsec.freeuk link and click on 555 at the top. Teaches you everything you need to know(then just scroll down until you see astable operation)!
Damn few 555's can oscillate at 200 MHz., or even 15 MHz. Careful reading is helpful in constucting meaningful answers.
 
Did you see the max operating current of the DDS chip? 1.2A! It will fry itself.
They say it is a challenge to keep it cool enough.
 
Papabravo said:
Damn few 555's can oscillate at 200 MHz., or even 15 MHz. Careful reading is helpful in constucting meaningful answers.

Tee-hee.. :D 555 at 200MHz... besides, I dont think the OP wants to construct HF sinewaves with an imprecise, drifty, jittery source frequency.
High quality 15MHz crystals are available.
 
Thank you guys all for your help....

For some reasons my DDS chip need to generate a fairly accurate sineusoidal signal...I have read through the data sheet and its application notes...they point out that if one using the internal PLL function of the chip, it will degrade the quality of the signal...as the output sine wave is strongly depends on the quality of the master clock signal.

Thank again for ur help!
 
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