AD829
+15V
–17
–20
–23
0.1F
50⍀
COAX
CABLE
50⍀
COAX
V
؎5V
IN
CABLE
–26
–29
–32
–35
–38
–41
–44
–47
50⍀
2k⍀
AD829
V
OUT
؎15V
50⍀
50⍀
3pF
C
–15V
0.1F
COMP
V
R
R
= –20dBM
= 1k⍀
= 1k⍀
IN
L
2k⍀
F
GAIN = –1
= 4pF
C
COMP
Figure 17. Noninverting Amplifier Connection Using
Current Feedback Compensation
1
10
100
FREQUENCY (MHz)
+15V
Figure 16. Closed-Loop Frequency Response vs. Supply
for the Inverting Amplifier Using Current Feedback
Compensation
0.1F
75⍀
COAX
V
IN
CABLE
A Low Error Video Line Driver
75⍀
V
AD829
OUT
The buffer circuit shown in Figure 18 will drive a back-terminated
75 Ω video line to standard video levels (1 V p-p) with 0.1 dB
gain flatness to 30 MHz with only 0.04° and 0.02% differential
phase and gain at the 4.43 MHz PAL color subcarrier frequency.
This level of performance, which meets the requirements for high
definition video displays and test equipment, is achieved using
only 5 mA quiescent current.
75⍀
75⍀
0.1F
300⍀
OPTIONAL
2pF to 7pF
FLATNESS
TRIM
–15V
30pF
C
COMP
300⍀
A High Gain, Video Bandwidth, Three Op Amp In Amp
Figure 19 shows a three op amp instrumentation amplifier circuit
that provides a gain of 100 at video bandwidths. At a circuit gain
of 100, the small signal bandwidth equals 18 MHz into a FET
probe. Small signal bandwidth equals 6.6 MHz with a 50 Ω load.
The 0.1% settling time is 300 ns.
Figure 18. A Video Line Driver with a Flatness over
Frequency Adjustment
The input amplifiers operate at a gain of 20, while the output
op amp runs at a gain of 5. In this circuit, the main bandwidth
limitation is the gain/bandwidth product of the output amplifier.
Extra care should be taken while breadboarding this circuit, since
even a couple of extra picofarads of stray capacitance at the com-
pensation pins of A1 and A2 will degrade circuit bandwidth.
3pF
(G = 20)
2pF to 8pF
SETTLING TIME
AC CMR ADJUST
+V
IN
A1
AD829
1k⍀
2k⍀
1pF
200⍀
200⍀
AD848
R
G
A3
1pF
210⍀
INPUT
2k⍀
FREQUENCY CMRR
(G = 5)
2k⍀
100 Hz
1 MHz
10 MHz
64.6dB
44.7dB
23.9dB
3pF
970⍀
AD829
DC CMR
ADJUST
50⍀
+V
+15V
COMM
–15V
PIN 7
S
A2
10F
10F
1F
1F
0.1F
0.1F
0.1F
+V
IN
EACH
AMPLIFIER
(G = 20)
0.1F
3pF
4000⍀
G
CIRCUIT GAIN =
+ 1 5
(
(
R
–V
PIN 4
S
Figure 19. A High Gain, Video Bandwidth, Three Op Amp In Amp Circuit
REV. G
–13–
ADI [ ADI ]
