Video Cable Driver Using

±5 Volt Supplies

The AD844 can be used to drive low impedance cables. Using

±5 V supplies, a 100 Ω load can be driven to ±2.5 V with low

distortion. Figure 35a shows an illustrative application which

provides a noninverting gain of 2, allowing the cable to be

reverse-terminated while delivering an overall gain of +1 to the

Figure 35a. The AD844 as a Cable Driver

Figure 35c. Differential Phase for the Circuit of Figure 35a

load. The –3 dB bandwidth of this circuit is typically 30 MHz.

Figure 35b shows a differential gain and phase test setup. In

video applications, differential-phase and differential-gain

characteristics are often important. Figure 35c shows the varia-

tion in phase as the load voltage varies. Figure 35d shows the

gain variation.

Figure 35b. Differential Gain/Phase Test Setup

Figure 35d. Differential Gain for the Circuit of Figure 35a

Applications–AD844

REV. C

–11–

High Speed DAC Buffer

The AD844 performs very well in applications requiring

current-to-voltage conversion. Figure 36 shows connections for

use with the AD568 current output DAC. In this application

the bipolar offset is used so that the full-scale current is

± 5.12 mA, which generates an output of ±5.12 V using the

1 k

Ω application resistor on the AD568. Figure 37 shows the

full-scale transient response. Care is needed in power supply

Figure 36. High Speed DAC Amplifier

decoupling and grounding techniques to achieve the full 12-bit

accuracy and realize the fast settling capabilities of the system.

The unmarked capacitors in this figure are 0.1

µF ceramic (for

example, AVX Type SR305C104KAA), and the ferrite induc-

tors should be about 2.5

µH (for example, Fair-Rite Type

2743002122). The AD568 data sheet should be consulted for

more complete details about its use.

Figure 37. DAC Amplifier Full-Scale Transient Response