VCO+PLL to synthesise 20-100Mhz for laser range finder project

Yannick wrote: : I am trying to find a VCO with sinusoidal output to generate between : 20 and 100Mhz (or more). The VCO's i saw from analog devices are for : +300Mhz. Anyone know some IC's wich are capable of doing this. A : complete Pll+VCO integrated would be even better ofcourse.

: I am now using the AD9850 DDS as a frequency synthesiser but there is : much spur on the signal even after a 3th order elleptical filter.

A short search (at least at minicircuits) shows that there are no wide range VCO available...

Bye

: > I am trying to find a VCO with sinusoidal output to generate between : > 20 and 100Mhz (or more). The VCO's i saw from analog devices are for : > +300Mhz. Anyone know some IC's wich are capable of doing this. A : > complete Pll+VCO integrated would be even better ofcourse. : > : > I am now using the AD9850 DDS as a frequency synthesiser but there is : > much spur on the signal even after a 3th order elleptical filter. : > : > Thanks in advance!

: There is a resistor controller oscillator, the LTC6905, from : linear technology, which uses 3 ranges (dividers) between 17 : and 170 MHz. : There also are a few others.

If Yannick complains about spurs with a DDS, how do you think he will like a square wave oscillator?

There is a resistor controller oscillator, the LTC6905, from linear technology, which uses 3 ranges (dividers) between 17 and 170 MHz. There also are a few others.

Rene

Unless I'm missing something, you are mis-applying the 9850. It is rated for a maximum clock rate of 125 MHz. What frequency are you clocking it at?

You can't generate a 100 MHz signal from a 125 MHz DAC. In general I would try to stay below 30 or 40 % of the DAC frequency on a DDS. So for the

Also, the 9850 uses a 10-bit DAC. Why don't you try one of Analog Devices'

Anyway, I don't think anybody does DDS's better than Analog Devices, and I don't think you are going to find an easier or more accurate way of generating frequencies than using a DDS. I do suggest that you call or email an applications engineer at AD to see if they can help you with your application. Also, their datasheets usually tell you how much spur you will get.

--Mac

You're right. However, the spurs of the DDS are fixed at the clocking frequency, whereas a squarewave oscillator has the odd harmonics only. For going onto a mixer, a rectangular signal is usually ok. It makes it switch faster.

Rene

What, exactly, is the point of posting that?

It doesn't seem to have anything to do with the topic at hand.

--Mac

Use an AD9852ASQ clocked at 300 MHz, or (preferably) one of the newer AD9950 parts.

-- jm

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