AD847
A H igh Speed, Thr ee O p-Am p In-Am p
T he input amplifier (A1 and A2) is an AD827, which is a dual
version of the AD847. T his circuit has the optional flexibility of
both dc and ac trims for common-mode rejection, plus the abil-
ity to adjust for minimum settling time.
T he circuit of Figure 26 lends itself well to CCD imaging and
other video speed applications. It uses two high speed CB pro-
cess op-amps: Amplifier A3, the output amplifier, is an AD847.
EACH
AMPLIFIER
PIN 7 AD847,
+15V
COMM
–15V
+V
S
PIN 8 AD827
10µF
10µF
0.1µF
0.1µF
1µF
1µF
0.1µF
0.1µF
PIN 4
AD847 & AD827
–V
S
1/2
2–8pF
SETTLING TIME
AC CMR ADJUST
AD827
3
2
–V
IN
INPUT
1
A1
CMRR
FREQUENCY
2kΩ
100Hz
1kHz
10kHz
100kHz
1MHz
88.3dB
87.4dB
86.2dB
67.4dB
47.1dB
1kΩ
1kΩ
2kΩ
2
V
OUT
6
A3
R
G
2kΩ
3
R
L
2kΩ
AD847
1.87kΩ
5pF
6
5
7
A2
DC CMR
ADJUST
200Ω
+V
IN
1/2
AD827
2000Ω
CIRCUIT GAIN =
+ 1
R
G
BANDWIDTH, SETTLING TIME AND TOTAL HARMONIC DISTORTION VS. GAIN
THD + NOISE
SMALL
SIGNAL
SETTLING
TIME
BELOW INPUT
LEVEL
C
ADJ
GAIN
R
G
(pF) BANDWIDTH TO 0.1%
@ 10kHz
1
2
10
100
OPEN 2–8
16.1MHz
14.7MHz
4.5MHz
660kHz
200ns
200ns
370ns
2.5µs
82dB
82dB
81dB
71dB
2kΩ
226Ω
20Ω
2–8
2–8
2–8
Figure 26. A High Speed In-Am p Circuit for Data Acquisition
REV. F
–11–
ADI [ ADI ]
