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Help me find the VCO for a CPLD

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blitzwing

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Hi i have designed a PCB with a CPLD on it and i am
really having trouble finding VCO(voltage controlled oscillators) for the CPLD.

I want to feed the CPLD (Max II) with a clock 10Mhz.
Isn't any other way to avoid using a VCO.
I have seen different schematics for CLPD and FGPA and they all
use VCOs.

Thanks in advance guys:)
 

kishore2k4

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Re: Clock input CPLD

You can use normal TTL oscillators that are very widely available and relatively cheaper than VCOs. You can also use normal quartz crystals with a little feedback circuit consisting of resistors,capacitors and a not gate.

Normally you won't be needing a VCO unless you want to change your clock frequency. In which case you will have to use one.

https://futurlec.com/Crystals/OSC80000pr.shtml, they can ship to anywhere in the world for very little shipping costs. Check with your local electronic parts retailer, he may be having some selections.
 

echo47

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Clock input CPLD

As kishor24k suggested, most CPLD and FPGA projects use an ordinary fixed-frequency crystal oscillator (XO), not a Voltage Controlled Oscillator (VCO).

Be sure to buy an oscillator that has a compatible output voltage for your CPLD input.

If you can't find a suitable part near you, DigiKey in USA also stocks many types, and ships to many countries:
https://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=11195&Cat=34079628
 

blitzwing

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Re: Clock input CPLD

echo47 I live in Europe and i cant find anyone to give me a fixed-frequency crystal oscillator (XO). I thought VCO and XO where the same sorry. I'm trying to avoid digikey for now beacuse the cheapest shipping fee for Greece is about 40$.Farnell which is in UK doesnt have them.They sent me to Newark.

kishore2k4 u wrote that i could use normal quartz crystals with a little feedback circuit consisting of resistors,capacitors and a not gate. Can u show me some schematics?
I dont wont to change the frequency. As i said above i just want it to be 10Mhz. Nothing more.

Thank you
 

kishore2k4

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Re: Clock input CPLD

**broken link removed**, The circuit can be scaled to 10Mhz with CMOS/HCMOS Inverter.

https://futurlec.com/Crystals/OSC10000pr.shtml The oscillator costs $1.9 and standard shipping charges to anywhere in the world is only $5, so if you want something stable and reliable then definetly go for the latter.
 

    blitzwing

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