AD9630

–4–

REV. B

12

Ω, capacitive loads of up to 50 pF can be driven with mini-

mal settling time degradation.

The output stage has short circuit protection to ground. The

output driver will shut down if more than approximately

130 mA of instantaneous sink or source current is reached. This

level of current ensures that output clipping will not result when

driving heavy capacitive loads during high slew conditions,

although average load currents above 70 mA may reduce device

reliability.

LAYOUT CONSIDERATIONS

Due to the high frequency operation of the AD9630 attention to

board layout is necessary to achieve optimum dynamic perfor-

mance. A two ounce copper ground plane on the top side of the

board is recommended; it should cover as much of the board as

possible with appropriate openings for supply decoupling ca-

pacitors as well as for load and source termination resistors, (see

Figure 3).

Optimum settling time and ac performance results will be

achieved with surface mount 0.1

µF supply decoupling ceramic

chip capacitors mounted within 50 mils of the corresponding

device pins with the other side soldered directly to the ground

plane. For best high resolution (<0.02%) settling times, the op-

tional power supply pins should be decoupled as shown above.

If the optional power supply pins are not used, they should be

left open.

If surface mount capacitors cannot be used, radial lead ceramic

capacitors with leads less than 30 mils long are recommended.

Low frequency power supply decoupling is necessary and can be

accomplished with 4.7

µF tantalum capacitors mounted within

0.5 inches of the supply pins. Due to the series inductance of

these capacitors interacting with the 0.1

µF capacitors and

power supply leads, high frequency oscillations might appear on

2

<0.1MHz

1

0

–1

–2

–3

–4

–5

–6

–7

–8

100MHz

200MHz

300MHz

10pF

25pF

50pF

the device output. To avoid this occurrence, the power supply

leads should be tightly twisted (if appropriate). Ferrite beads

mounted between the tantalum and ceramic capacitors will

serve the same purpose.

All unused pins (except the optional power supply pins) should

be connected to ground to reduce pin-to-pin capacitive coupling

and prevent external RF interference. If the source and drive

electronics require “remote” operation (> 1 inch from the

AD9630), the PC board line impedances should be matched

with the buffer input and output resistances. Basic microstrip

as close to the AD9630 as possible.

With only minimal pulse overshoot and ringing, the AD9630

can drive terminated cables directly without the use of an output

can be either standard carbon composition or microwave type.

For matching characteristic impedances, precision microwave

resistors of 1% or better tolerance are preferred.

The AD9630 should be soldered directly to the PC board with

as little vertical clearance as possible. The use of zero insertion

sockets is strongly discouraged because of the high effective pin

inductances. Use of this type socket will result in peaking and

possibly induce oscillation.

8

1

6

AD9630

0.1 F

5

2

*

*

4.7 F

0.1 F

0.1 F

0.1 F

4.7 F

*SEE PINOUTS

**SEE FIGURE 1

Figure 3. AD9630 Application Circuit