AD9696/AD9698

–7–

REV. B

2

AD9696

–IN

+IN

1– 40MHz

LATCH

ENABLE

+

–

OSCILLATOR

OUTPUT

GROUND

2k

Ω

0.1µF

(220pF for Freq. > 10MHz)

0.1µF

FOR USE WITH

OVERTONE

CRYSTAL

(VALUE

DEPENDS

ON FREQ.)

3

1

5

7

8

4

6

2k

Ω

2k

Ω

Figure 2. AD9696 Oscillator Circuit (Based on DIP Pinouts)

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.

LAYOUT CONSIDERATIONS

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.

8

7

6

5

4

3

2

1

AD9696

(8-PIN DIP)

0.1µF

0.1µF

AD1

AD2

GND

RESISTORS ARE 1k

Ω ±5%

5µs

–0.9V

AD1

AD2

–0.9 V

–1.7V

–1.7V

Burn-In Circuit