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convert sine wave to other wave forms

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,
 
M

mike

Jan 1, 1970
0
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,

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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J

John Larkin

Jan 1, 1970
0
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,


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
 
F

Fred Bloggs

Jan 1, 1970
0
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.

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.
 
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_AD9858,00.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,
 
J

John Larkin

Jan 1, 1970
0
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_AD9858,00.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,

[email protected] wrote:


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
 
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?

I am looking for a DDS that can output upto a 1GHZ Sine Wave. Does
anyone know of a chip that can do this?

Thanks,
 
M

Mac

Jan 1, 1970
0
On Fri, 25 Feb 2005 20:23:52 -0800, george_barr wrote:

[top-post re-arranged]
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?

No. The input clock can be up to 2 GHz, but when it is, it is mandatory to
use the divide by 2 feature, which slows the internal clock back down to 1
GHz. I have used that chip, but I am not re-reading the datasheet right
now. So if you think I am wrong, please quote me chapter and verse from
the datasheet.

And the 9858 is the fastest DDS that I know of. I don't think it is much
good beyond 400 MHz output.
I am looking for a DDS that can output upto a 1GHZ Sine Wave. Does
anyone know of a chip that can do this?

You should explore the possibility of using frequency multipliers
and/or mixers to attain your goals. For example, if you clock the DDS at 1
GHz, you can mix the 1 GHz with the DDS output to obtain either 1 GHz -
Fdds, or 1 GHz + Fdds, depending on how you filter the output. Fdds is the
DDS output frequency.

The DDS chip actually has a mixer built into it, but I think it is set up
for down-conversion only. So you probably want to find a mixer elsewhere.
Realistically, if you want to operate somewhere near 930 MHz, you should
probably operate the DDS at, say, 700 MHZ, then output 230 MHz, and
upconvert by mixing the 700 MHz with the DDS output to obtain 930 MHz
and 470 MHz. A high-pass filter should get rid of the 470 MHz. Note,
however, that I am not really an RF guy, so...

Also, please don't top-post. It forces others to read the thread
out-of-order.

--Mac
 
J

John Larkin

Jan 1, 1970
0
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?

Read the data sheet, for Pete's sake.

John
 
G

Glenn Gundlach

Jan 1, 1970
0
'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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