OP270 Datasheet, PDF (9/16 Pages) Analog Devices – Dual Very Low Noise Precision Operational Amplifier

100
10 OP200
OP270
RESISTOR
NOISE ONLY
1
100
1k
10k
R_S – SOURCE RESISTANCE (⍀)
100k
Figure 4. Total Noise vs. Source Resistance
(Including Resistor Noise) at 10 Hz
1000
OP200
100
OP270
RESISTOR
NOISE ONLY
10
100
1k
10k
R_S – SOURCE RESISTANCE (⍀)
100k
Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) vs.
Source Resistance (Includes Resistor Noise)
OP270
Figure 5 shows peak-to-peak noise versus source resistance over the
0.1 Hz to 10 Hz range. Once again, at low values of R_S, the voltage
noise of the OP270 is the major contributor to peak-to-peak
noise, with current noise the major contributor as R_S increases.
The crossover point between the OP270 and the OP200 for
peak-to-peak noise is at R_S = 17 kW.
The OP271 is a higher speed version of the OP270, with a slew
rate of 8 V/ms. Noise of the OP271 is slightly higher than that of
the OP270. Like the OP270, the OP271 is unity-gain stable.
For reference, typical source resistances of some signal sources
are listed in Table I.
Table I.
Device
Strain gage
Source
Impedance
<500 W
Magnetic
tapehead,
microphone
<1500 W
Magnetic
phonograph
cartridge
<1500 W
Linear variable <1500 W
differential
transformer
Comments
Typically used in low
frequency applications.
Low I_B very important to reduce
self-magnetization problems
when direct coupling is used.
OP270 I_B can be neglected.
Similar need for low I_B in
direct coupled applications.
OP270 will not introduce any
self-magnetization problem.
Used in rugged servo-feedback
applications. Bandwidth of
interest is 400 Hz to 5 kHz.
R3
1.24k⍀
R1
5⍀
–
R2
5⍀
OP270
DUT
+
+
OP27E
–
R5
909⍀
R4
200⍀
C1
2␮F
R6
600⍀
D1, D2
1N4148
R8
10k⍀
+
OP27E
– R9
306k⍀
C2
0.032␮F
C4
0.22␮F
R10
65.4k⍀
R11
65.4k⍀
C3
0.22␮F
+
OP42E
–
R13
5.9k⍀
R12
10k⍀
Figure 6. Peak-to-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
R14
4.99k⍀
e_OUT
C5
1␮F
GAIN = 50,000
V_S = ؎15V
REV. C
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