OP470AY Datasheet, PDF (10/16 Pages) Analog Devices – Very Low Noise Quad Operational Amplifier

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 R_S, the
voltage noise of the OP470 is the major contributor to peak-to-peak
noise with current noise the major contributor as R_S increases.
The crossover point between the OP470 and the OP400 for
peak-to-peak noise is at R_S = 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 I_B very important to reduce
self-magnetization problems
when direct coupling is used.
OP470 I_B can be neglected.
Similar need for low I_B 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
R_S – 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
2␮F
OP27E
C4
R5
909⍀
R6
600k⍀
0.22␮F
R10
R11
R4
200⍀
D1
1N4148
D2
1N4148
OP15E
R9
65.4k⍀
65.4k⍀
C3
0.22␮F
OP15E
R14
4.99k⍀
e_OUT
306k⍀
C5
R13
1␮F
5.9k⍀
R8
10k⍀
C2
0.032␮F
R12
10k⍀
GAIN = 50,000
V_S = ؎5V
Figure 7. Peak-To-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
–10–
REV. B