AD830

REV. A

–14–

Loop Through or Line Bridging Amplifier (Figure 37)

The AD830 is ideally suited for use as a video line bridging am-

plifier. The video signal is tapped from the conductor of the

cable relative to its shield. The high input impedance of the

AD830 provides negligible loading on the cable. More signifi-

cantly, the benign loading is maintained while the AD830 is

powered-down. Coupled with its good video load driving per-

formance, the AD830 is well suited to video cable monitoring

applications.

45

36

AD830

1

2

8

7

A=1

0.1µF

0.1µF

75

Ω

75

Ω

499

Ω

499

Ω

249

Ω

C

Figure 37. Cable Tap Amplifier

Resistorless Summing

Direct, two input, resistorless summing is easily realized from

below in Figure 38. The AD830 summing circuit possesses sev-

eral virtues not present in the classic op amp based summing

circuits. It has high impedance inputs, no resistors, very precise

summing, high reverse isolation and noninverting gain. Achiev-

ing this function and performance with op amps requires signifi-

cantly more components.

45

36

AD830

1

2

8

7

A=1

OUT

C

Figure 38. Resistorless Summing Amplifier

2

Gain Bandwidth Line Driver

A gain of two, without the use of resistors, is possible with the

wired connection. The output is exactly twice the applied volt-

tions for this highly useful application. The most notable

characteristic of this alternative gain of two is that there is no

loss of bandwidth as in a voltage feedback op amp based gain of

+2 where the bandwidth is halved, therefore, the gain band-

width is doubled. Also, this circuit is accurate without the need

for any precise valued resistors, as in the op amp equivalents,

and it possess excellent differential gain and phase performance

as shown in Figures 40 and 41.

45

36

AD830

1

2

8

7

A=1

0.1µF

0.1µF

75

Ω

75

Ω

C

Figure 39. Full Bandwidth Line Driver (G = +2)

SUPPLY VOLTAGE –

±Volts

.10

15

.03

.01

6

.02

5

.06

.04

.05

.07

.08

.09

14

13

12

11

10

9

8

7

.20

.06

.02

.04

.12

.08

.10

.14

.16

.18

PHASE

GAIN

GAIN = +2

R

FREQ = 3.58MHz

0 TO 0.7V

Figure 40. Differential Gain and Phase for the Circuit of

Figure 39

0.2

–0.3

–0.8

100k

100M

10M

1M

10k

–0.2

–0.1

0

0.1

–0.7

–0.6

–0.5

–0.4

FREQUENCY – Hz

V

V

V

R

GAIN = +2

Figure 41. 0.1 dB Gain Flatness for the Circuit of Figure 39