OP270
100
TOTAL NOISE (nV/
Hz)
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.
RESISTOR
NOISE ONLY
10 OP200
OP270
1
100
Table I.
1k
10k
100k
R
S
– SOURCE RESISTANCE ( )
Figure 4. Total Noise vs. Source Resistance
(Including Resistor Noise) at 10 Hz
Device
Strain gage
Magnetic
tapehead,
microphone
Magnetic
phonograph
cartridge
Source
Impedance
<500
W
<1500
W
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.
1000
OP200
PEAK-TO-PEAK NOISE (nV)
<1500
W
100
OP270
RESISTOR
NOISE ONLY
Linear variable <1500
W
differential
transformer
10
100
1k
10k
100k
R
S
– SOURCE RESISTANCE ( )
Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) vs.
Source Resistance (Includes Resistor Noise)
R3
1.24k
R1
5
R2
5
–
OP270
DUT
+
+
OP27E
–
R5
909
C1
2 F
R6
600
D1, D2
1N4148
+
OP27E
C4
0.22 F
R10
65.4k
R9
306k
R11
65.4k
C3
0.22 F
+
OP42E
–
R12
10k
R13
5.9k
R4
200
R14
4.99k
C5
1 F
–
e
OUT
R8
10k
C2
0.032 F
GAIN = 50,000
V
S
= 15V
Figure 6. Peak-to-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
REV. C
–9–
AD [ ANALOG DEVICES ]
