Date Sheet

AD8510/AD8512/AD8513

Rev. K | Page 19 of 21

TIME (2ms/DIV)

Figure 54. Pulse-Width Modulation

Crosstalk

Crosstalk, also known as channel separation, is a measure of

signal feedthrough from one channel to another on the same

IC. The AD8512/AD8513 have a channel separation of better

than −90 dB for frequencies up to 10 kHz and of better than

−50 dB for frequencies up to 10 MHz. Figure 56 shows the

typical channel separation behavior between Amplifier A

(driving amplifier) and each of the following: Amplifier B,

Amplifier C, and Amplifier D.

VOUT

1

2

7

6

5

4

3

8

+VS

20kΩ

2.2kΩ

5kΩ

5kΩ

–VS

VIN

18V p-p

CROSSTALK = 20 log

VOUT

10VIN

Figure 55. Crosstalk Test Circuit

FREQUENCY (Hz)

100

–160

10k

–140

–120

–80

1k

–60

–20

–40

100k

1M

10M

–100

0

CH D

CH C

CH B

Figure 56. Channel Separation

The AD8510 single has two additional active terminals that are

not present on the AD8512 dual or AD8513 quad devices. These

pins are labeled null and are used for fine adjustment of the

input offset voltage. Although the guaranteed maximum offset

voltage at room temperature is 400 μV and over the −40°C to

+125°C range is 800 mV maximum, this offset voltage can be

reduced by adding a potentiometer to the null pins as shown in

Figure 57. With the 20 kΩ potentiometer shown, the adjustment

range is approximately ±3.5 mV. The potentiometer parallels

low value resistors in the drain circuit of the JFET differential

input pair and allows unbalancing of the drain currents to

change the offset voltage. If offset adjustment is not required,

these pins must be left unconnected.

Caution must be used when adding adjusting potentiometers to

any op amp with this capability for several reasons. First, there is

gain from these nodes to the output; therefore, capacitive coupling

from noisy traces to these nodes injects noise into the signal

path. Second, the temperature coefficient of the potentiometer

does not match the temperature coefficient of the internal resistors,

so the offset voltage drift with temperature is slightly affected.

Third, this provision is for adjusting the offset voltage of the

op amp, not for adjusting the offset of the overall system. Although

it is tempting to decrease the value of the potentiometer to attain

more range, this adversely affects the dc and ac parameters.

Instead, increase the potentiometer to 50 kΩ to decrease the

range if needed.

1

5

4

7

3

6

2

AD8510

INPUT

OUTPUT

V+

VOS TRIM RANGE IS

TYPICALLY ±3.5mV

20kΩ

V–

–

+

Figure 57. Optional Offset Nulling Circuit