AD705AQ AD [Analog Devices], AD705AQ Datasheet - Page 7

• Manufacturer Part Number: AD705AQ
• Description: Picoampere Input Current Bipolar Op Amp
• Manufacturer: AD [Analog Devices]

REV. B
SQUARE WAVE
Figure 22d. Unity Gain Inverter Small Signal
Pulse Response C, = 1000 pF
Figure 24. Offset Null and Overcompensation
Connections
INPUT
V
100
0%
90
10
IN
100
0%
90
10
5k
Figure 23a. Follower Connected
in Feed-Forward Mode
5V
Figure 23b. Follower Feed-Forward
Pulse Response
5V
0.1µF
20mV
3
2
V
OS
2
3
AD705
4.1nF
1
10k
AD705
–V
ADJUST
–V
4
4
S
S
8
10pF
+V
20k
7
S
5
5
0.1µF
7
*
OVERCOMPENSATION
CAPACITOR
+V
S
6
5µs
6
0.1µF
*
5µs
RESPONSE IS
NEARLY IDENTICAL
FOR CAPACITANCE
VALUES OF 0 TO 100pF
0.1µF
V
INPUT
OUTPUT
OUT
–7–
A High Performance Differential Amplifier Circuit
Figure 25 shows a high input impedance, differential amplifier
circuit that features a high common-mode voltage, and which
operates at low power. Table I details its performance with
changes in gain. To optimize the common-mode rejection of
this circuit at low frequencies and dc, apply a 1 volt, 1 Hz sine
wave to both inputs. Measuring the output with an oscilloscope,
adjust trimming potentiometer R6 for minimum output. For the
best CMR at higher frequencies, capacitor C2 should be replaced
with a 1.5 pF to 20 pF trimmer capacitor.
Both the IC socket and any standoffs at the op amp’s input ter-
minals should be made of Teflon* to maintain low input current
drift over temperature.
*Teflon is a registered trademark of E.I. DuPont, Co.
Circuit R4
Gain
1
10
100
WARNING: POTENTIAL DANGER FROM HIGH SOURCE VOLTAGE.
THIS DIFFERENTIAL AMPLIFIER DOES NOT PROVIDE GALVANIC
ISOLATION. INPUT SOURCE MUST BE REFERRED TO THE SAME
GROUND CONNECTION AS THIS AMPLIFIER.
SOURCE
Table I. Typical Performance of Differential Amplifier
Circuit Operating at Various Gains
GND
Figure 25. A High Performance Differentials
Amplifier Circuit
V
V
( )
1.13 k
100
10.2
100M
100M
IN+
IN–
R1'
R1
5pF
C1
2
3
10M
R5
( )
10 k
9.76 k
10 k
R2
AD705
10M
5pF
R2'
C2
–V
+V
4
7
S
S
Trimmed
DC CMR
(dB)
500k
0.1µF
85
85
85
200k
R6
6
DC CMR
ADJUST
R3
0.1µF
R4
R5
Drift TC
( V/ C)
30
30
30
*
RTI Average Circuit
*
CIRCUIT GAIN, G = –
V
COMMON MODE INPUT RANGE =
RESISTORS R1 AND R1', R2 AND
*
SEE TABLE I
OUT
10 (V
R2' ARE VICTOREEN MOX-200
1/4 WATT, 1% METAL OXIDE.
V
CM
= G (V
V
S
RANGE = 135V
OUT
– 1.5V) FOR V
IN–
AD705
– V
Bandwidth
–3 dB
4.4 kHz
2.8 kHz
930 Hz
IN+)
R2+R3
R1
S
= 15V,
(1+
R5
R4
)