OP270
100
10
1
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 RS, the voltage
noise of the OP270 is the major contributor to peak-to-peak
noise, with current noise the major contributor as RS increases.
The crossover point between the OP270 and the OP200 for
peak-to-peak noise is at RS = 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.
OP200
OP270
For reference, typical source resistances of some signal sources
are listed in Table I.
RESISTOR
NOISE ONLY
Table I.
Source
100
1k
10k
100k
R
– SOURCE RESISTANCE (⍀)
S
Device
Impedance Comments
Figure 4. Total Noise vs. Source Resistance
(Including Resistor Noise) at 10 Hz
Strain gage
<500 W
Typically used in low
frequency applications.
Magnetic
tapehead,
microphone
<1500 W
Low IB very important to reduce
self-magnetization problems
when direct coupling is used.
OP270 IB can be neglected.
1000
100
10
OP200
Magnetic
phonograph
cartridge
<1500 W
Similar need for low IB in
direct coupled applications.
OP270 will not introduce any
self-magnetization problem.
OP270
Linear variable <1500 W
differential
transformer
Used in rugged servo-feedback
applications. Bandwidth of
interest is 400 Hz to 5 kHz.
RESISTOR
NOISE ONLY
100
1k
10k
100k
R
– SOURCE RESISTANCE (⍀)
S
Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) vs.
Source Resistance (Includes Resistor Noise)
R3
1.24k⍀
R1
5⍀
–
C1
2F
OP270
DUT
+
+
R2
5⍀
C4
OP27E
0.22F
D1, D2
1N4148
R6
600⍀
–
R5
909⍀
R10
65.4k⍀
R11
65.4k⍀
+
R14
4.99k⍀
+
OP27E
R4
200⍀
C3
0.22F
e
OP42E
OUT
–
R9
C5
306k⍀
R13
5.9k⍀
–
1F
R8
10k⍀
R12
10k⍀
C2
0.032F
GAIN = 50,000
= ؎15V
V
S
Figure 6. Peak-to-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
REV. C
–9–
ADI [ ADI ]
