It's been said that is obsolete, it'll be hard to find.Another improved version is recommended
https://www.analog.com/en/products/...igital-synthesis/ad9856.html#product-overview
There are many AN, for isntance
https://www.analog.com/media/en/technical-documentation/application-notes/AN-924.pdf
Read carefully, you'll find SSB modulation technique.
A software can be requested from AD but I warn you this IC produces pretty dirty spectrum.It's not very convenient for classic SSB communication.
Note that AD ICs are too expensive..
Good, old one cheaper one..The obsolete ad7008 costs 5$ on ebay and if you order 10 or so it can go up to $3!
Using a DDS for a PLL is different than using for transmission.DDSs are pretty dirty signal sources in term of spurious and their application field is very limited in transmission medium.Is the noise, the reason why these are usually locked to a PLL in communications receivers?
Because PLL is naturally analog system and it synthesize clean signals.I was wondering about why is the PLL needed since a DDS is used.
Read carefully mathematical analysis in this AN, you will understand how I Q modulators create SSB signals.I has a look at the AN you posted and there is a similar modulator to what the AD7008 uses. But I am not sure if this can produce ssb and how.
I have tried to, but it is too complicated for meRead carefully mathematical analysis in this AN, you will understand how I Q modulators create SSB signals.
Look at this ...I have tried to, but it is too complicated for me
I do not see any baseband input (eg audio input) pin on the chip, so that this signal can be SSB modulated, so how can the quadrature modulator be controlled?
I guess I miss many things...
As you will know DDS outputs a series of values from a DAC.Is the noise, the reason why these are usually locked to a PLL in communications receivers?
I was wondering about why is the PLL needed since a DDS is used.
As you will know DDS outputs a series of values from a DAC.
The higher the frequency division ratio within the DDS, the more output points per cycle you get, and the closer to a sinewave output you get.
As you get up closer to the Nyquist limit of only two output points per cycle, the more crappy the output waveform from a DDS looks.
Its just full of spurs, harmonics and general wideband crap.
Look at the raw unfiltered output of a DDS on an oscilloscope and you will be truly horrified. Low pass filtering is mandatory, bandpass filtering much better, but not always possible.
The way to really clean it up is by phase locking a VCO to the output of a DDS.
You then get a nice sine wave with just some harmonic distortion, but all the spurs and wideband noise will be gone.
Basically the PLL far more accurately interpolates the individual output points of a DDS thus cleaning it up.
Raw DDS output is barely good enough for a receiver. For a transmitter, the multiple wideband spurious outputs are just completely unacceptable.
Early DDS had very limited internal clocking speeds and sometimes a DAC with not too many bits resolution.
So if your input clock were only a 100 Mhz crystal, and your output frequency say 25 Mhz, you only get four output points per cycle. If your DAC has eight bits (or less) the output may look pretty ragged.
It will work a lot better at 500Khz output, where there would be 200 data points per cycle.
DDS these days are now being clocked at several GHz with some having a sixteen bit DAC.
Say 2.5 Ghz clock and 25 Mhz output, you get one hundred data points per output cycle. It will look like a fairly decent sine wave with just barely discernible faint ripple on it.
On a spectrum analyser it will look very clean with most spurs below the noise floor. DDS has come a very long way over the last couple of decades.
Many early DDS designs were forced to use a VCO to clean up the output. Today with a top end DDS you could probably get away without that, But I suppose it depends on your specification goals (and budget).
Agreed, direct synthesis of RF has taken huge leaps in the last five years alone. And AD does seem to have to best offering by a wide margin. It's hard to beat a fully digital modulator in a single chip, especially if you like frequency and phase hopping.On a spectrum analyser it will look very clean with most spurs below the noise floor. DDS has come a very long way over the last couple of decades.
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