Issue
130 May 2001
DDS-GEN—Part
2: The Generator
Start •Direct Digital Synthesis?
• The AD9852 monster chip •Hardware
• Prototype Construction •On The Software Side •Design Methodology •What’s Next? •Sources & PDF
Prototype
Construction
All but the
user interface fits on a 7.4² × 6.7², double-sided PCB,
including the power supply and its transformer (see Photo
2). The user interface is mounted behind the front panel.
The high-frequency analog parts are EMC-protected by a
metallic can (see Photo 3).
|
(Click
here to enlarge)
|
Photo
2—The DDS-GEN prototype shows that the I2C-MMI
board is behind the front panel. The main transformer
and filtered power plug are in the back. The power
supply components are in the back right corner and
the plug-in slots are visible in the front right corner.
The high-frequency parts are to the left between the
front panel plugs and transformer. |
|
(Click
here to enlarge)
|
Photo
3—The AD9852 is under the big heatsink, a converted
TO3. The shield that holds the two high-frequency
filters (with their 20 CMS coils) and the AD8002 amplifier
are on the top side. On the bottom, you can see the
two 74LVT245 buffers and the 87LPC764. The two metallic
components left of the transformer are the high-frequency
relays. |
In order to
maximize performance, all high-frequency components are
surface-mounted. And, a large ground plane is integrated
on both sides of the PCB (an analog ground plane on the
topside for the HF areas and a digital ground plane on
the bottom for the digital parts). But, a full four-layer
PCB is a must. A metallic enclosure and a filtering power
socket are also mandatory to limit the spurious emissions
and meet UL/CE specifications.
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