Datasheet
AD827
REV. C
–7–
VIDEO LINE DRIVER
The AD827 functions very well as a low cost, high speed line
driver for either terminated or unterminated cables. Figure 23
shows the AD827 driving a doubly terminated cable in a
follower configuration.
0.1 µF
0.1 µF
50Ω
AD827
1/2
R
BT
C
C
+V
S
V
IN
V
OU
T
–V
S
R
T
500Ω
50Ω
50Ω
500Ω
Figure 23. A Video Line Driver
The termination resistor, R
T
, (when equal to the cable’s
characteristic impedance) minimizes reflections from the far end
of the cable. While operating from ±5 V supplies, the AD827
maintains a typical slew rate of 200 V/µs, which means it can
drive a ±1 V, 30 MHz signal into a terminated cable.
Table I. Video Line Driver Performance Summary
Over-
V
IN
* V
SUPPLY
C
C
–3 dB B
W
shoot
0 dB or ±500 mV Step ±15 20 pF 23 MHz 4%
0 dB or ±500 mV Step ±15 15 pF 21 MHz 0%
0 dB or ±500 mV Step ±15 0 pF 13 MHz 0%
0 dB or ±500 mV Step ±5 20 pF 18 MHz 2%
0 dB or ±500 mV Step ±5 15 pF 16 MHz 0%
0 dB or ±500 mV Step ±50 pF11 MHz 0%
*–3 dB bandwidth numbers are for the 0 dBm signal input. Overshoot numbers
are the percent overshoot of the 1 V step input.
A back-termination resistor (R
BT
, also equal to the characteristic
impedance of the cable) may be placed between the AD827
output and the cable input, in order to damp any reflected
signals caused by a mismatch between R
T
and the cable’s
characteristic impedance. This will result in a flatter frequency
response, although this requires that the op amp supply ±2 V to
the output in order to achieve a ±1 V swing at resistor R
T
.
A HIGH SPEED THREE OP AMP INSTRUMENTATION
AMPLIFIER CIRCUIT
The instrumentation amplifier circuit shown in Figure 24 can
provide a range of gains. Table II details performance.
–
+
+
–
+
–
1
3
2
2
3
6
7
6
5
AD847
AD827
AD827
0.1µF
1kΩ
2kΩ
2kΩ
1kΩ
2kΩ
0.1µF
0.1µF
2kΩ
R
L
2 – 8pF
0.1µF
R
G
4
7
2kΩ
8
4
TRIM FOR BEST
SETTLING TIME
1/2
1/2
3pF
CIRCUIT GAIN =
+ 1
G
R
2000
TRIM FOR
OPTIMUM
BANDWIDTH
7 – 15 pF
NOTE: PINOUT SHOWN IS FOR MINIDIP PACKAGE
–V
IN
+V
S
–V
S
+V
IN
+V
S
–V
S
V
OUT
Figure 24. A High Bandwidth Three Op Amp
Instrumentation Amplifier
Table II. Performance Specifications for the
Three Op Amp Instrumentation Amplifier
Small Signal
Bandwidth
Gain R
G
@ 1 V p-p Output
1 Open 16.1 MHz
22 k 14.7 MHz
10 226 Ω 4.9 MHz
100 20 Ω 660 kHz