REV. B

OP470

–10–

Figure 6 shows peak-to-peak noise versus source resistance over

voltage noise of the OP470 is the major contributor to peak-to-peak

The crossover point between the OP470 and the OP400 for

W.

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

10

100

100k

100

10k

1k

OP11

OP400

OP471

OP470

RESISTOR

NOISE ONLY

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.

R1

5

R3

1.24k

OP470

DUT

R2

5

R5

909

OP27E

R4

200

C1

2 F

R6

600k

R9

306k

OP15E

R8

10k

D1

1N4148

D2

1N4148

C2

0.032 F

R10

65.4k

R11

65.4k

C3

0.22 F

OP15E

C4

0.22 F

R13

5.9k

R12

10k

R14

4.99k

C5

1 F

GAIN = 50,000

Figure 7. Peak-To-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)

Table I.

Device

Source

Impedance

Comments

Strain gage

<500

W

Typically used in

low frequency applications.

Magnetic

<1500

W

tapehead

self-magnetization problems

when direct coupling is used.

Magnetic

<1500

W

phonograph

coupled applications. OP470

cartridges

will not introduce any self-

magnetization problem.

Linear variable <1500

W

Used in rugged servo-feedback

differential

applications. Bandwidth of

transformer

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.

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.

3. Sudden motion in the vicinity of the device can also “feedthrough”

to increase the observed noise.