convert sine wave to other wave forms

Guest
Hello,

I have a DDS that can generate sine waves upto 1Ghz. I want to be able
to convert this sine wave to other wave forms like square wave,
saw-tooth, triangle, and etc. Can someone tell me how to do each of of
these (or just 1 of them)? I can't use a DAC since it cannot generate
signals at upto 1Ghz.

Thanks,
 
george_barr@yahoo.com wrote:
Hello,

I have a DDS that can generate sine waves upto 1Ghz. I want to be able
to convert this sine wave to other wave forms like square wave,
saw-tooth, triangle, and etc. Can someone tell me how to do each of of
these (or just 1 of them)? I can't use a DAC since it cannot generate
signals at upto 1Ghz.

Thanks,
Click to expand...
It's usually easier to start with the triangle and go from there.
A PLL can fix up the frequency.

Assuming you have a clean sine wave, you can easily generate the square
wave with a "suitable" comparator. You can get the triangle with an
integrator and amplitude leveling loop(s).

Be aware that you need 3X the output bandwidth to get ANY difference at
all. 5X is better. And that's without significant phase shift so the
harmonics sum properly. I expect you're doing all this with chips and
wire bonds. Calculate how many nanohenries of series inductance you
can have in your integrating cap and how much C you can have in your
current switch.

I've assumed that you really want triangles and squares at 1GHz.
If you don't care that they all look like sinewaves, your problem is
much simpler.
mike

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On 23 Feb 2005 17:29:52 -0800, george_barr@yahoo.com wrote:

Hello,

I have a DDS that can generate sine waves upto 1Ghz. I want to be able
to convert this sine wave to other wave forms like square wave,
saw-tooth, triangle, and etc. Can someone tell me how to do each of of
these (or just 1 of them)? I can't use a DAC since it cannot generate
signals at upto 1Ghz.

Thanks,
Click to expand...

Do you mean that your DDS generates sine-weighted digital data,
without a DAC? If so, what's the data clock rate... 2 GHz?

What DDS is it? What are the logic levels?

Why do you want sine/square/sawtooth/triangle waveforms at 1 GHz?

John
 
I have a DDS that can generate sine waves upto 1Ghz. I want to be
able to convert this sine wave to other wave forms like square wave,
saw-tooth, triangle, and etc. Can someone tell me how to do each of
of these (or just 1 of them)? I can't use a DAC since it cannot
generate signals at upto 1Ghz.
Click to expand...
How many bits of resolution and linearity do you want on those other
waveforms? Will 16 do? And will it be sufficient to have amplitude
limited to 100V into 50 ohms?
 
You do realize, don't you, that you will have to have at least 3 to 5
of the first odd harmonics for reasonable fidelity (low THD)? This
translates to 7-11 GHz for a 1 GHz fundamental. And this holds
regardless of how you choose to create the non-sinusoidal waveform.
Your easiest solution is probably to wave shape starting with a
triangle waveform. "The Art of Electronics" has a circuit for doing
this using a diode shaping network. The disadvantage of this circuit is
that it works properly with only 1 signal amplitude.
 
On 24 Feb 2005 15:14:06 -0800, george_barr@yahoo.com wrote:

Thanks for the replies. I am absolute a beginner in circuits. I am
trying to build a frequency generator since it is cheaper than buying
one. This freq. generator will be used to generage RF freq. in the
930Mhz bandwidth. Here is the info for the analog.ocm AN9858 DDS chip
I plan to use.

http://www.analog.com/en/prod/0,,770_843_AD9858%2C00.html

http://www.analog.com/UploadedFiles/Data_Sheets/37263106237625AD9858_a.pdf

Can this DDS chip produce sine waves at upto 1Ghz? Can someone point
me to the right direction?

Thanks,

george_barr@yahoo.com wrote:
Click to expand...

Hi, George,

This chip includes a dac, but it can only synthesize frequencies up to
Fclk/2 in theory, somewhat less in practice. Figure maybe 400 MHz
sinewave with a good output filter.

Frankly, designing a good 1 GHz sinewave oscillator is not for
beginners, sort of like tackling Everest alone on your first climb.
You might consider some used gear on ebay or something. Non-sine waves
at this speed are *seriously* difficult.

John
 
On 25 Feb 2005 20:23:52 -0800, george_barr@yahoo.com wrote:

The Analog AD9858 DDS chip has a max of 2,000MSPS speed when using a
divide by 2 thing. So, does this mean that the maximum sine wave
frequency is 2,000M / 2 = 1GHZ Sine Wave?
Click to expand...
Read the data sheet, for Pete's sake.

John
 
'I am an absolute beginner...'. There is a reason a 1 GHz generator is
expensive. I suspect you will find that even at minimum wage rates,
this is going to eat some serious time for a beginner (lots less for a
Larkin but still significant). A good lesson I learned a long time ago
is-- Don't re-invent the wheel unless you can REALLY improve it. Great
buys sometimes on eBay.

GG
 
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