AD847 Analog Devices, AD847 Datasheet - Page 10

• Manufacturer Part Number: AD847
• Description: High Speed, Low Power Monolithic Op Amp
• Manufacturer: Analog Devices

Specifications of AD847

• -3db Bandwidth: 50MHz
• Slew Rate: 300V/µs
• Vos: 500µV
• Ib: 3.3µA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 15nV/rtHz
• Vcc-vee: 9V to 36V
• Isy Per Amplifier: 4.8mA
• Packages: DIP,SOIC

AD847
VIDEO LINE DRIVER
The AD847 functions very well as a low cost, high speed line
driver for either terminated or unterminated cables. Figure 23
shows the AD847 driving a doubly terminated cable in a fol-
lower configuration.
The termination resistor, R
teristic impedance) minimizes reflections from the far end of the
cable. While operating from 5 V supplies, the AD847 main-
tains a typical slew rate of 200 V/ s, which means it can drive a
V
0 dB or 500 mV Step
0 dB or 500 mV Step
0 dB or 500 mV Step
0 dB or 500 mV Step
0 dB or 500 mV Step
0 dB or 500 mV Step
*–3 dB bandwidth numbers are for the 0 dBm signal input. Overshoot numbers
A back-termination resistor (R
impedance of the cable) may be placed between the AD847 out-
put and the cable input, in order to damp any reflected signals
caused by a mismatch between R
impedance. This will result in a flatter frequency response, al-
though this requires that the op amp supply 2 V to the output
in order to achieve a 1 V swing at resistor R
are the percent overshoot of the 1 volt step input.
V
1 V, 30 MHz signal into a terminated cable.
IN
IN
*
COAX
75
Table I. Video Line Driver Performance Chart
75
Figure 23. Video Line Driver
100
R
IN
AD847
SEE TABLE I
–V
V
+V
T
S
15
15
15
5
5
5
SUPPLY
S
, (when equal to the cable’s charac-
BT
C
C
0.1 F
, also equal to the characteristic
T
0.1 F
and the cable’s characteristic
C
20 pF 23 MHz
15 pF 21 MHz
0 pF
20 pF 18 MHz
15 pF 16 MHz
0 pF
C
500
500
75
R
BT
T
–3 dB B
13 MHz
11 MHz
.
COAX
75
W
75
R
T
Over-
shoot
4%
0%
0%
2%
0%
0%
V
OUT
–10–
Figure 24 shows the AD847 driving 100 pF and 1000 pF loads.
FLASH ADC INPUT BUFFER
The 35 MHz unity gain bandwidth of the AD847 makes it an
excellent choice for buffering the input of high speed flash A/D
converters, such as the AD9048.
Figure 25 shows the AD847 as a unity inverter for the input to
the AD9048.
(0V TO +2V)
CONVERT
ANALOG
SIGNAL
INPUT
TTL
Figure 24. AD847 Driving Capacitive Loads
Figure 25. Flash ADC Input Buffer
1.5k
50
1.5k
AD847
0.1
1k
AD589
10k
0.1
AD741
0.1 F
43
100
2k
1k
V
CONVERT
–5.2V +5.0V
–5.2V
IN
V
AD9048
2N3906
R
EE
B
5
27
0.1 F
V
CC
R
T
D1
(MSB)
D8
(LSB)
REV. F
0.1 F