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.
Table I.
Device
Impedance
Source
Comments
Strain gage
<500 W
Typically used in
low frequency applications.
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.
Magnetic
tapehead
<1500 W
Low IB very important to reduce
self-magnetization problems
when direct coupling is used.
OP470 IB can be neglected.
1000
OP11
Magnetic
phonograph
cartridges
<1500 W
Similar need for low IB in direct
coupled applications. OP470
will not introduce any self-
magnetization problem.
OP400
OP471
Linear variable <1500 W
differential
transformer
Used in rugged servo-feedback
applications. Bandwidth of
interest is 400 Hz to 5 kHz.
100
OP470
For further information regarding noise calculations, see “Minimization of Noise
in Op Amp Applications,” Application Note AN-15.
RESISTOR
NOISE ONLY
NOISE MEASUREMENTS—
PEAK-TO-PEAK VOLTAGE NOISE
10
100
1k
10k
100k
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:
R
– SOURCE RESISTANCE –ꢅ
S
Figure 6. Peak-To-Peak Noise (0.1 Hz to 10 Hz) vs. Source
Resistance (Includes Resistor Noise)
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.
For reference, typical source resistances of some signal sources
are listed in Table I.
2. For similar reasons, the device must be well-shielded from
air currents. Shielding also minimizes thermocouple effects.
3. Sudden motion in the vicinity of the device can also “feedthrough”
to increase the observed noise.
R3
1.24kꢅ
R1
5ꢅ
C1
OP470
DUT
R2
2ꢀF
5ꢅ
OP27E
C4
R6
0.22ꢀF
R5
909ꢅ
600kꢅ
R10
R11
65.4kꢅ
65.4kꢅ
R4
D1
D2
R14
OP15E
R9
200ꢅ
1N4148
1N4148
4.99kꢅ
C3
e
OUT
OP15E
0.22ꢀF
C5
306kꢅ
1ꢀF
R13
5.9kꢅ
R8
10kꢅ
C2
R12
0.032ꢀF
10kꢅ
GAIN = 50,000
= ꢂ5V
V
S
Figure 7. Peak-To-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)
–10–
REV. B
ADI [ ADI ]
