Issue
130 May 2001
DDS-GEN—Part
2: The Generator
by
Robert Lacoste
Lucky
for us it was a cloudy night in France when Robert was
scheduled to write the second part of the article on
his DDS-GEN project! Don’t miss out as he covers
everything from hardware selection to software design
to prototype contruction this month.
Start •Direct Digital Synthesis?
• The AD9852 monster chip •Hardware
• Prototype Construction •On The Software Side •Design Methodology •What’s Next? •Sources & PDF
What’s
Next?
It wasn’t
easy, but the DDS-GEN prototype works (see Photo 4). The
hardware worked 99% flawlessly during the first run, even
if I still have HF unwanted cross-talk and occasionally
a microcontroller randomly resets at HF output. A new
four-layer PCB probably will be required to solve them.
The software still needs work, mainly on the AM/FM/PM
code, which is crude because of lacking space. And, I
still have a list of leftover bugs taped on the prototype.
a) b)
 c)
|
| Photo 4—The DDS-GEN
generated these examples. (a) is a ramped 300- to
1200-Hz FSK signal with a 3.6-ms ramp time. (b)
is a 200-kHz signal with 90° PSK modulation. Finally,
(c) is a 5-kHz signal in Shaped Keying mode with
a 0.6-ms ramp up/down delay. |
Soon, I want
to build an arbitrary signal generator plug-in that will
dramatically extend the possibilities of the DDS-GEN.
Basically, this board will include another 87LPC764, I2C
EEPROM to store waveforms, cache RAM chip, some kind of
EPLD, and a DAC. I also have firmware extensions in mind,
like an integrated, 1-kHz pseudo-sinus modulation generator.
Well, I have some interesting nights ahead, unless Circuit
Cellar readers want to take over part of the job…
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