IC for Wide Range VCO

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maziar

Joined: 06 Jun 2001
Posts: 257
Helped: 4
Location: Islamic republic of Iran

14 Feb 2002 5:51 vco for 50 mhz with mc1648

i very need wide range vco 1Mhz to 50Mhz sine wave vco
if av. chip to do it ?

Pim

Joined: 26 Jan 2002
Posts: 78

14 Feb 2002 21:31

There exists many solutions to this problem, I am sure. How high distortion can be acceptable for your application? Are there any requirements of having a linear tuning range (meaning that for example a steering voltage of 0.1V equals 1MHz and 5.0V equals 50MHz)?

I think that many PLL-chips are able of producing this great frequency span (if only using the oscillator part of them). There are often application notes to those chips included as well in the manufacturers datasheets.

/Pim

maziar

Joined: 06 Jun 2001
Posts: 257
Helped: 4
Location: Islamic republic of Iran

15 Feb 2002 7:15

i need sine with max .7% for 1mhz to 50mhz sine distrotion

what vco can do it ?

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hwswboy

Joined: 02 Jul 2001
Posts: 109

15 Feb 2002 10:02

hxxp://www.euroquartz.co.uk/vcxo-sine.htm

hxxp://www.mtron.com/osclindx.htm

hxxp=http

unkarc

Joined: 28 Apr 2001
Posts: 287
Helped: 36

15 Feb 2002 10:02

Hi,

It would be a complex task to build that kind of "VCO" you need. Though it can be built as a system; for instance you may design a PLL-type VCO for some hundred MHz where the 50MHz span can easily be achieved and the output of this VCO can be downconverted with a crystal/double balanced mixer to your needed band coverage (1-50MHz).

There would be a more modern solution: that is the use of DDS chips. See for instance Analog Devices DDS family at h**p://www.analog.com/library/analogDialogue/archives/30-3/single_chip.html (* -> t) and some newer members of that line.
That would be a good solution for you. Data sheets/application notes are also downloadable from analog.com site.

Regards, unkarc

Chinaski

Joined: 17 May 2001
Posts: 217
Helped: 5
Location: Spain

15 Feb 2002 11:55

I agree with Unkarc. We have just finished a classic PLL synth for an HF Tx/Rx (3-30 MHz, 1st IF OL 48-75 MHz, 1KHz step) and we need 3 IC (1 PLL, 1 VCO and 1 OPA) A lot of space, too many power supplies, expensive varicaps, coils...etc. Analog Devices AD9851 DDS can do it better; better SDFR, mHz step, one PWR supp etc...
But if you only need a VCO I should try motorola MC1648 ("the good oldie") or it's smd "new" version MC12148. Maxim's wideband VCOs are another alternative but keep in your mind you have to face with two "words": coils (Coilcraft is a good choice) and varicaps (another world)
Good luck
PS: I forgot Minicircuits' VCOs (no external comp. needed)

[ This Message was edited by: Chinasky on 2002-02-15 12:04 ]

maziar

Joined: 06 Jun 2001
Posts: 257
Helped: 4
Location: Islamic republic of Iran

15 Feb 2002 15:27

thanks all
i last i see analog device dds.

but one qustion :
how can generate other wave (for example triangle by analog device DDS)

syzzler

Joined: 05 Jan 2002
Posts: 27
Location: Europe

17 Feb 2002 22:59

Hi Maziar,

many DDS have internal (fixed) "sine" lookup table but other can be programmed externally making so an Arbitrary waveform generator. Setting up tables for canonical waveforms is almost an easy task.
Take a look to Harris and Qualcomm prods too.
Hope this will be helpful.

Syzzler.