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OP470 View Datasheet(PDF) - Analog Devices

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OP470 Datasheet PDF : 17 Pages
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OP470
Figure 6 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 OP470 is the major contributor to peak-to-peak
noise with current noise the major contributor as RS increases.
The crossover point between the OP470 and the OP400 for
peak-to-peak noise is at RS = 17 kW.
The OP471 is a higher speed version of the OP470, with a slew
rate of 8 V/ms. Noise of the OP471 is only slightly higher than
the OP470. Like the OP470, the OP471 is unity-gain stable.
1000
OP11
OP400
OP471
100
OP470
RESISTOR
NOISE ONLY
Table I.
Source
Device
Impedance
Comments
Strain gage <500 W
Typically used in
low frequency applications.
Magnetic
tapehead
<1500 W
Magnetic
phonograph
cartridges
<1500 W
Low IB very important to reduce
self-magnetization problems
when direct coupling is used.
OP470 IB can be neglected.
Similar need for low IB in direct
coupled applications. OP470
will not introduce any self-
magnetization problem.
Linear variable <1500 W
differential
transformer
Used in rugged servo-feedback
applications. Bandwidth of
interest is 400 Hz to 5 kHz.
For further information regarding noise calculations, see “Minimization of Noise
in Op Amp Applications,” Application Note AN-15.
10
100
1k
10k
RS – SOURCE RESISTANCE –
100k
Figure 6. Peak-To-Peak Noise (0.1 Hz to 10 Hz) vs. Source
Resistance (Includes Resistor Noise)
For reference, typical source resistances of some signal sources
are listed in Table I.
NOISE MEASUREMENTS—
PEAK-TO-PEAK VOLTAGE NOISE
The circuit of Figure 7 is a test setup for measuring peak-to-peak
voltage noise. To measure the 200 nV peak-to-peak noise speci-
fication of the OP470 in the 0.1 Hz to 10 Hz range, the following
precautions must be observed:
1. The device must be warmed up for at least five minutes. As
shown in the warm-up drift curve, the offset voltage typi-
cally changes 5 mV due to increasing chip temperature after
power-up. In the 10-second measurement interval, these
temperature-induced effects can exceed tens of nanovolts.
2. For similar reasons, the device must be well-shielded from
air currents. Shielding also minimizes thermocouple effects.
R3
1.24k
R1
5
3. Sudden motion in the vicinity of the device can also “feedthrough”
to increase the observed noise.
R2
5
OP470
DUT
C1
2F
OP27E
C4
R5
909
R6
600k
0.22F
R10
R11
R4
200
D1
1N4148
D2
1N4148
OP15E
R9
65.4k
65.4k
C3
0.22F
OP15E
R14
4.99k
eOUT
306k
C5
R13
1F
5.9k
R8
10k
C2
0.032F
R12
10k
GAIN = 50,000
VS = ؎5V
Figure 7. Peak-To-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
–10–
REV. B
 

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