Datasheet AD9696, AD9698 (Analog Devices) - 7

AD9696/AD9698 +VS LAYOUT CONSIDERATIONS
When working with high speed circuits, proper layout is critical.
2k
Ω Analog signal paths should be kept as short as possible and be
0.1µF 1– 40MHz
properly terminated to avoid reflections. In addition, digital sig- nal paths should be kept short, and run lengths should be mat-
AD9696 LATCH (VALUE
ched to avoid propagation delay mismatch. All analog signals
ENABLE DEPENDS +VS
should be kept as far away from digital signal paths as possible;
ON FREQ.) 1 5
this reduces the amount of digital switching noise that might be
+IN QOUT FOR USE WITH
capacitively coupled into the analog section of the circuit.
2 + 7 OVERTONE 3 – 8 OSCILLATOR CRYSTAL
In high speed circuits, layout of the ground circuit is the most
2k
Ω
–IN Q OUTPUT OUT
important factor. A single, low impedance ground plane, on the component side of the board, will reduce noise in the circuit
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ground. It is especially important to maintain continuity of the
–VS GROUND
ground plane under and around the AD9696 or AD9698.
2k
Ω Sockets limit the dynamic performance of the device and should be used only for prototypes or evaluation.
0.1µF (220pF for Freq. > 10MHz) – VS +VS
Figure 2. AD9696 Oscillator Circuit (Based on DIP Pinouts)
0.1µF 0.1µF
When generating frequencies using a nonfundamental mode
4 1
crystal, a choke and dc blocking capacitor are added. As an ex-
AD1 2 7
ample, a 36 MHz oscillator can be achieved by using a 12 MHz
AD9696 AD2
crystal operating on its third overtone. To suppress oscillation at
3 8 (8-PIN DIP)
the 12 MHz fundamental, the value of the choke is chosen to
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provide a low reactive impedance at the fundamental frequency while maintaining a high reactive impedance at the desired out-
GND
put frequency (for 36 MHz operation, L = 1.8 µH). The shunt capacitor at the inverting input has a value of 220 pF for a stable
RESISTORS ARE 1k
Ω
±5%
36 MHz frequency.
–0.9V AD1 –1.7V 5µs –0.9 V AD2 –1.7V
Burn-In Circuit REV. B –7–