el5100iw Intersil Corporation, el5100iw Datasheet - Page 11

• Manufacturer Part Number: el5100iw
• Description: 200mhz Slew Enhanced Vfa
• Manufacturer: Intersil Corporation

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.
f = 10Hz, R = Z = 75Ω,
By using the circuit below, C could be reduced to C2 = 22µF.
The test result is shown on Figure 30.
C
=
2
π
×
1.00E+00
1
-10
-15
-20
-25
-30
-35
-40
-45
R
10
-5
5
0
×
1.00E+01
f
1.00E+02
C1
C
=
FIGURE 30. VIDEO-
(1) C1 = 1µF Vs = +10V
(2) C1 = 0.47µF Vs = +10V
(3) C1 = 0.47µF Vs = +5V
Conditions/comments:
1.00E+03
R1
R2
FREQUENCY (Hz)
C = 132µF
1.00E+04
11
20K
20K
1.00E+05
1.00E+06
U1
3
2
1.00E+07
+
-
1.00E+08
C4
EL5100, EL5101, EL5300
EL5104
1.00E+09
1n
6
R3
R8
C6
FIGURE 29.
10k
C2
3R3
33nF
C3
C5
22µF
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.
1.5µF
R6
R5
22µF
Vs+
500
500
R4
75
Z = 75Ω
R7
75
May 3, 2007
FN7330.3