AD8510ARM-R2 datasheet(18/20 Pages) AD

18 / 20 page

AD8510/AD8512/AD8513

Rev. E | Page 18 of 20

TIME (2ms/DIV)

Signal Transmission Applications

One popular signal transmission method uses pulse-width

modulation. High data rates may require a fast comparator

rather than an op amp. However, the need for sharp and

undistorted signals may favor using a linear amplifier.

The AD8510/AD8512/AD8513 make excellent voltage

comparators. In addition to a high slew rate, the AD8510/

AD8512/AD8513 have a very fast saturation recovery time. In

the absence of feedback, the amplifiers are in open-loop mode

(very high gain). In this mode of operation, they spend much of

their time in saturation.

The circuit in Figure 54 compares two signals of different

frequencies, namely a 100 Hz sine wave and a 1 kHz triangular

wave. Figure 56 shows a scope photograph of the output wave-

form. A pull-up resistor (typically 5 kΩ) may be connected from

the output to VCC if the output voltage needs to reach the posi-

tive rail. The trade-off is that power consumption will be higher.

Figure 56. Pulse-Width Modulation

Crosstalk

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

signal feedthrough from one channel to the other on the same

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

−90 dB for frequencies up to 10 kHz, and better than −50 dB for

frequencies up to 10 MHz. Figure 57 shows the typical channel

separation behavior between amplifier A (driving amplifier),

with respect to amplifiers B, C, and D.

VOUT

–15V

+15V

FREQUENCY (Hz)

100

–160

10k

–140

–120

–80

–60

–20

–40

100k

10M

–100

CH-D

CH-C

CH-B

Figure 54. Pulse-Width Modulator

VOUT

+VS

20k

Ω

2.2k

Ω

–VS

VIN

18V p-p

CROSSTALK = 20 LOG

VOUT

10VIN

Figure 57. Channel Separation

Figure 55. Crosstalk Test Circuit

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