VCO at 10MHZ (sinewave)

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7rots51

Joined: 17 May 2002
Posts: 1427
Helped: 14

20 Sep 2007 17:48 vco 10mhz

Hello

Please help on design of VCO about 10~20MHZ (sinewave).Do you know any circuit or IC?

Abhishekabs

Joined: 12 Jan 2007
Posts: 727
Helped: 84
Location: India

22 Sep 2007 7:05 10 mhz vco

You can use IC 8038

7rots51

Joined: 17 May 2002
Posts: 1427
Helped: 14

22 Sep 2007 16:51 sine wave vco

its max freq is 300KHZ

tzoupkas

Joined: 31 Dec 2005
Posts: 17
Helped: 1

22 Sep 2007 19:21 10 mhz vco

hello my friend you can use max038 its the only ic which will give you 10 and 20Mhz. i am constructing a function generator with that. i bought it from http://www.futurlec.com/cgi-bin/search/search.cgi. or you can use dds technology. i hoped i helped you. (dds offers better sine wave purity).

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

23 Sep 2007 4:02 ic for vco 10 mhz

Another approach, you could build some sort of simple voltage controllable pulse generator that goes from 20-40 MHz, divide it by two with a flip-flop to get a 10-20 MHz square wave, and then feed it through a low-pass filter that passes everything up to 20 MHz and blocks everything above 30 MHz.

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23 Sep 2007 4:02 Ads

petarpav

Joined: 25 Mar 2002
Posts: 557
Helped: 8

23 Sep 2007 5:04 10mhz sine vco

Hi. Look here:
\http://www.analog.com/en/subCat/0,2879,770%255F843%255F0%255F%255F0%255F,00.html

Best Regards.

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

23 Sep 2007 8:54 sine wave vco 10 mhz

I haven't seen any DDS chips with voltage-controllable frequency (VCO). Do they exist?

7rots51

Joined: 17 May 2002
Posts: 1427
Helped: 14

24 Sep 2007 18:54 generate vco with 566

DDS generate sinewave digitally,no need to analog VCO!

I tested AD9834 DDS(50MHZ DDS from ADI) (for up to 12.5MHZ sine wave)

But it have many noise in output ,there is also clcok sine wave in out put!

I placed a passive LC filter at out put but the clock harmonic will remained!

MAX038 is not recommended for new designs and is absolote!

hasmir

Joined: 01 Jan 2005
Posts: 20
Helped: 2

25 Sep 2007 1:13 how to generate 10mhz sinewave

In my opinion, for a low cost sine wave oscillator use low cost TCXOs. Some of them produce 10 MHz pulse trains. If it's the case just put a bandpass or lowpass filter after that.
Anyway discrete configurations are also very easy to implement in this freq.

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

25 Sep 2007 6:32 ic 8038 vco

If you can use an NCO instead of a VCO, that's great! A DDS can make a pretty good sinewave.

If your AD9834 circuit is outputting lots of weird harmonics and clock feedthrough, then your LC filter probably needs improvement. It needs to strongly attenuate the clock frequency and above. Be sure to use good RF construction techniques.

7rots51

Joined: 17 May 2002
Posts: 1427
Helped: 14

25 Sep 2007 17:55 dds vco

I used 5th order butterworth LC network but it does not remove clcok harmonic(50MHZ clcok for DDS AD9834)

My LPF 3db corner freq is 12MHZ.

My RF PCB is also good and I designed it carefully.

(I want ADJUSTABLE source and stable in freq )

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

26 Sep 2007 7:55 vco 10-20mhz

A 5th order butterworth should attenuate the clock by over 60dB. If it doesn't, then something is wrong with the filter.
Or maybe the filter is working fine, and it's just a measurement problem such as a long ground lead on the oscilloscope probe.