AD9696/AD9698
+V
S
LAYOUT CONSIDERATIONS
2kΩ
0.1µF
1– 40MHz
(VALUE
DEPENDS
ON FREQ.)
FOR USE WITH
OVERTONE
CRYSTAL
AD9696
+V
S
+IN
2
2kΩ
3
–IN
+
–
7
8
1
5
LATCH
ENABLE
Q
OUT
OSCILLATOR
OUTPUT
When working with high speed circuits, proper layout is critical.
Analog signal paths should be kept as short as possible and be
properly terminated to avoid reflections. In addition, digital sig-
nal paths should be kept short, and run lengths should be mat-
ched to avoid propagation delay mismatch. All analog signals
should be kept as far away from digital signal paths as possible;
this reduces the amount of digital switching noise that might be
capacitively coupled into the analog section of the circuit.
In high speed circuits, layout of the ground circuit is the most
important factor. A single, low impedance ground plane, on the
component side of the board, will reduce noise in the circuit
ground. It is especially important to maintain continuity of the
ground plane under and around the AD9696 or AD9698.
Sockets limit the dynamic performance of the device and should
be used only for prototypes or evaluation.
– V
S
+V
S
Q
OUT
–V
S
2kΩ
0.1µF
(220pF for Freq. > 10MHz)
4
6
GROUND
Figure 2. AD9696 Oscillator Circuit (Based on DIP Pinouts)
0.1µF
0.1µF
4
AD1
AD2
2
3
5
1
7
When generating frequencies using a nonfundamental mode
crystal, a choke and dc blocking capacitor are added. As an ex-
ample, a 36 MHz oscillator can be achieved by using a 12 MHz
crystal operating on its third overtone. To suppress oscillation at
the 12 MHz fundamental, the value of the choke is chosen to
provide a low reactive impedance at the fundamental frequency
while maintaining a high reactive impedance at the desired out-
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
36 MHz frequency.
AD9696
(8-PIN DIP)
8
6
GND
RESISTORS ARE 1kΩ ±5%
–0.9V
AD1
–1.7V
–0.9 V
AD2
–1.7V
5µs
Burn-In Circuit
REV. B
–7–
AD [ ANALOG DEVICES ]
