REV. C

OP270

–9–

100

100

1k

10k

100k

1

10

RESISTOR

NOISE ONLY

OP200

OP270

Figure 4. Total Noise vs. Source Resistance

(Including Resistor Noise) at 10 Hz

1000

100

1k

10k

100k

10

100

RESISTOR

NOISE ONLY

OP200

OP270

Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) vs.

Source Resistance (Includes Resistor Noise)

Figure 5 shows peak-to-peak noise versus source resistance over the

noise of the OP270 is the major contributor to peak-to-peak

The crossover point between the OP270 and the OP200 for

W.

The OP271 is a higher speed version of the OP270, with a slew

rate of 8 V/

ms. Noise of the OP271 is slightly higher than that of

the OP270. Like the OP270, the OP271 is unity-gain stable.

For reference, typical source resistances of some signal sources

are listed in Table I.

Table I.

Source

Device

Impedance

Comments

Strain gage

<500

W

Typically used in low

frequency applications.

Magnetic

<1500

W

tapehead,

self-magnetization problems

microphone

when direct coupling is used.

Magnetic

<1500

W

phonograph

direct coupled applications.

cartridge

OP270 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.

R1

5

R2

5

OP270

DUT

–

+

R3

1.24k

OP27E

–

+

R4

200

R5

909

C1

2 F

R6

600

R8

10k

D1, D2

1N4148

OP27E

–

+

R9

306k

C2

0.032 F

R10

65.4k

R11

65.4k

C4

0.22 F

C3

0.22 F

OP42E

–

+

R12

10k

R13

5.9k

R14

4.99k

C5

1 F

GAIN = 50,000

Figure 6. Peak-to-Peak Voltage Noise Test Circuit (0.1 Hz to 10 Hz)