AD811 查看數據表（PDF） - Analog Devices

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AD811

High Performance Video Op Amp

Analog Devices 

AD811

OPERATION AS A VIDEO LINE DRIVER

The AD811 has been designed to offer outstanding perform-

ance 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 43. Figure 44 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 45 and Figure 46, 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.

649Ω

649Ω

+VS

75Ω CABLE

75Ω

VOUT No. 1

75Ω

7

2–

75Ω CABLE

VIN

AD811

3+

4

75Ω

0.1µF

0.1µF

75Ω CABLE

6

75Ω

VOUT No. 2

75Ω

–VS

Figure 42. A Video Line Driver Operating at a Gain of +2

12

G = +2

9

RL = 150Ω

RG = RFB

6

VS = ±15V

RFB = 649Ω

3

VS = ±5V

RFB = 562Ω

0

–3

–6

1

10

100

FREQUENCY (MHz)

Figure 43. Closed-Loop Gain vs. Frequency, Gain = +2

1V

100

VIN 90

10ns

VOUT 10

0%

1V

Figure 44. Small Signal Pulse Response, Gain = +2, VS = ±15 V

0.10

0.09

0.08

RF = 649Ω

FC = 3.58MHz

100 IRE

MODULATED RAMP

0.07

0.06

0.05

0.04

0.03

0.02

b

0.01 a

a. DRIVING A SINGLE, BACK-

TERMINATED, 75Ω COAX CABLE

b. DRIVING TWO PARALLEL, BACK-

TERMINATED, COAX CABLES

0

5 6 7 8 9 10 11 12 13 14 15

SUPPLY VOLTAGE (V)

Figure 45. Differential Gain Error vs. Supply Voltage for

the Video Line Driver of Figure 42

0.20

0.18

0.16

RF = 649Ω

FC = 3.58MHz

100 IRE

MODULATED RAMP

0.14

b

0.12

0.10

0.08

a

0.06

a. DRIVING A SINGLE, BACK-

TERMINATED, 75Ω COAX CABLE

b. DRIVING TWO PARALLEL, BACK-

TERMINATED, COAX CABLES

0.04

0.02

0

5 6 7 8 9 10 11 12 13 14 15

SUPPLY VOLTAGE (V)

Figure 46. Differential Phase Error vs. Supply Voltage for

the Video Line Driver of Figure 42

Rev. E | Page 14 of 20

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