5100IS Просмотр технического описания (PDF) - Intersil

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производитель

5100IS

200MHz Slew Enhanced VFA

Intersil 

EL5100, EL5101, EL5300

Application Information

Video Amplifier with Reduced Size Output

Capacitance

If you have a video line driver Z = 75Ω, the DC decoupling

capacitor could be relatively large.

C= 1

=

2π × R × f

f = 10Hz, R = Z = 75Ω,

C = 132µF

By using the circuit below, C could be reduced to C2 = 22µF.

C4

R8

1n

Vs+

C5

3R3

22µF

R1

C1

C

R2

20K

U1

3+

2-

20K

C6

33nF

EL5104

6

R3

C2

22µF

10k

R5

C3

R4

75

500

1.5µF

R6

500

Z = 75Ω

R7

75

FIGURE 29.

10

5

0

-5

-10

-15

Conditions/comments:

-20

(1) C1 = 1µF Vs = +10V

(2) C1 = 0.47µF Vs = +10V

-25

(3) C1 = 0.47µF Vs = +5V

-30

-35

-40

-45

1.00E+00 1.00E+02 1.00E+04 1.00E+06 1.00E+08

1.00E+01 1.00E+03 1.00E+05 1.00E+07 1.00E+09

FREQUENCY (Hz)

FIGURE 30. VIDEO-

The test result is shown on Figure 30.

By selecting a different value for C1, we could reduce the

effect, created by C3 R3 and get flat response from 16Hz

with an 1/5 value, price and size output capacitor. There is

another, very important issue by using high bandwidth

amplifiers.

In the past when the bandwidth of the operational amplifier

ended at a few hundred kHz even at few MHz, the power-

supply bypass was not a very critical issue, since a 0.1µF

capacitor “did the job”, but today’s amplifiers could have

bandwidth, what used to be reserved for microwave circuits

not to long time ago.

Therefore that high bandwidth amplifiers require the same

respect what we reserve for microwave circuits. Particularly

the power supply bypass and the pcb-layout could very

heavily influence the performance of a modern high

bandwidth amplifiers. It could happen above a few MHz, but

it will happen above 100MHz, that the capacitor will behave

like an inductor.

11

FN7330.3

May 3, 2007

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