AD830

Data Sheet

Rev. D | Page 14 of 20

Driving Cap Loads

The AD830 is capable of driving modest sized capacitive loads

while maintaining its rated performance. Several curves of

bandwidth versus capacitive load are given in Figure 34 and

Figure 37. The AD830 was designed primarily as a low

distortion video speed amplifier but with a trade-off, for

example, giving up very large capacitive load driving capability.

If very large capacitive loads must be driven, the network shown

in Figure 32 should be used to ensure stable operation. If the

objectionable, the optional feedback network shown may be

added to restore the lost gain.

*OPTIONAL

FEEDBACK

NETWORK

AD830

1

2

3

4

8

7

6

5

A = 1

C

0.1µF

100pF

1kΩ

INPUT

SIGNAL

Figure 32. Circuit for Driving Large Capacitive Loads

FREQUENCY (Hz)

3

10k

–27

100k

1M

10M

100M

±15V

±5V

–24

–21

–18

–15

–12

–9

–6

–3

0

Figure 33. Closed-Loop Response vs. Frequency with 100 pF Load and Series

Resistor Compensation

SUPPLIES, BYPASSING, AND GROUNDING

(FIGURE 34)

The AD830 is capable of operating over a wide range of supply

voltages, both single and dual supplies. The coupling may be dc

or ac, provided the input and output voltages stay within the

specified common-mode voltage limits. For dual supplies, the

device works from ±4 V to ±16.5 V. Single-supply operation is

possible over 8 V to 33 V. It is also possible to operate the part

with split-supply voltages, for example, +24 V or −5 V for

special applications such as level shifting. The primary

constraint is that the total potential between the two supplies

does not exceed 33 V.

Inclusion of power supply bypassing capacitors is necessary to

achieve stable behavior and the specified performance. It is

especially important when driving low resistance loads. At

minimum, connect a 0.1 μF ceramic capacitor at the supply lead

of the AD830 package. In addition, for the best bypassing, it is

best to connect a 0.01 μF ceramic capacitor and 4.7 μF tantalum

capacitor to the supply lead going to the AD830.

0.01µF

AND

AND

4.7µF

LOAD

GND

LEAD

LOAD

GND

LEAD

Figure 34. Supply Decoupling Options

The AD830 is designed to be capable of rejecting noise and

dissimilar potentials in the ground lines. Therefore, proper

care is necessary to realize the benefits of the differential

amplification of the part. Separation of the input and output

grounds is crucial in rejection of the common-mode noise at

the inputs and eliminating any ground drops on the input signal

line. For example, connecting the ground of a coaxial cable to

the AD830 output common (board ground) could degrade the

CMR and also introduce power-down loading on cable grounds.

However, it is also necessary as in any electronic system to

provide a return path for bias currents back to their original

power supply. This is accomplished by providing a connection

between the differing grounds through a modest impedance

Single-Supply Operation

The AD830 is capable of operating in single power supply

applications down to a voltage of 8 V, with the generalized

connection shown in Figure 35. There is a constraint on the

common-mode voltage at the input and output that establishes

the range for these voltages. Direct coupling may be used for

input and output voltages that lie in these ranges. Any gain

network applied needs to be referred to the output common

connection or have an appropriate offset voltage. In situations

where the signal lies at a common voltage outside the common-

mode range of the AD830, direct coupling does not work, so ac

coupling should be used. Figure 47 shows how to easily

accomplish coupling to the AD830. For single-supply operation

where direct coupling is desired, the input and output common-

mode curves (Figure 36 and Figure 37) should be used.