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AD811

Data Sheet

OPERATION AS A VIDEO LINE DRIVER

The AD811 has been designed to offer outstanding performance

at closed-loop gains of +1 or greater, while driving multiple

reverse-terminated video loads. The lowest differential gain and

phase errors are obtained when using ±15 V power supplies.

With ±12 V supplies, there is an insignificant increase in these

errors and a slight improvement in gain flatness. Due to power

dissipation considerations, ±12 V supplies are recommended

for optimum video performance. Excellent performance can be

achieved at much lower supplies as well.

The closed-loop gain versus the frequency at different supply

voltages is shown in Figure 42. Figure 43 is an oscilloscope

photograph of an AD811 line driver’s pulse response with

±15 V supplies. The differential gain and phase error versus the

supply are plotted in Figure 44 and Figure 45, respectively.

Another important consideration when driving multiple cables

is the high frequency isolation between the outputs of the

cables. Due to its low output impedance, the AD811 achieves

better than 40 dB of output-to-output isolation at 5 MHz

driving back-terminated 75 Ω cables.

Figure 41. A Video Line Driver Operating at a Gain of +2

Figure 42. Closed-Loop Gain vs. Frequency, Gain = +2

Figure 43. Small Signal Pulse Response, Gain = +2, VS = ±15 V

Figure 44. Differential Gain Error vs. Supply Voltage for

the Video Line Driver of Figure 41

Figure 45. Differential Phase Error vs. Supply Voltage for

the Video Line Driver of Figure 41

VIN

–VS

+VS

0.1

µF

0.1

µF

AD811

VOUT No. 2

VOUT No. 1

Ω CABLE

Ω

649

Ω

649

Ω

–

–6

–3

FREQUENCY (MHz)

100

VS = ±15V

RFB = 649Ω

VS = ±5V

RFB = 562Ω

G = +2

RL = 150Ω

RG = RFB

100

10ns

VIN

VOUT

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

SUPPLY VOLTAGE (V)

RF = 649Ω

FC = 3.58MHz

100 IRE

MODULATED RAMP

a. DRIVING A SINGLE, BACK-

TERMINATED, 75

Ω COAX CABLE

b. DRIVING TWO PARALLEL, BACK-

TERMINATED, COAX CABLES

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

SUPPLY VOLTAGE (V)

RF = 649Ω

FC = 3.58MHz

100 IRE

MODULATED RAMP

a. DRIVING A SINGLE, BACK-

TERMINATED, 75

Ω COAX CABLE

b. DRIVING TWO PARALLEL, BACK-

TERMINATED, COAX CABLES

Rev. G | Page 14 of 20

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