REV. A

OP471

–8–

RS – SOURCE RESISTANCE –

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)

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

voltage noise of the OP471 is the major contributor to peak-to-peak

The crossover point between the OP471 and the OP400 for

W.

The OP470 is a lower noise version of the OP471, with a typical

noise voltage density of 3.2 nV/

÷Hz @ 1 kHz. The OP470 offers

lower offset voltage and higher gain than the OP471, but is a slower

speed device, with a slew rate of 2 V/

ms compared to a slew rate

of 8 V/

ms for the OP471.

R1

5

R3

1.24k

OP471

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)

For reference, typical source resistances of some signal sources

are listed in Table I.

TABLE I.

Source

Device

Impedance

Comments

Strain gauge

< 500

W

Typically used in

low-frequency applications.

Magnetic

< 1,500

W

tapehead

self-magnetization problems

when direct coupling is used.

Magnetic

< 1,500

W

phonograph

coupled applications. OP471

cartridges

will not introduce any

self -magnetization problem.

Linear variable

< 1,500

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.