OP27A, OP27C, OP27E, OP27G

OP37A, OP37C, OP37E, OP37G

LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL AMPLIFIERS

SLOS100B – FEBRUARY 1989 – REVISED AUGUST 1994

2–20

POST OFFICE BOX 655303

POST OFFICE BOX 1443

APPLICATION INFORMATION

To Gate

Drive

#1

+

–

Typical

Multiplexing

FET Switches

#2

+

–

#24

+

–

Cold-Junction

Circuitry

+

–

–

+

Output

0.05

µF

100 k

Ω

High-Quality

Single-Point Ground

10

Ω

AVD = 10,000

Type S Thermocouples

5.4

µV/°C at 0°C

60

40

20

0

0

246

80

100

t – Time – seconds

120

810

OP27

NOTE A: If 24 channels are multiplexed per second and the output is required to settle to 0.1 % accuracy, the amplifier’s bandwidth cannot be

limited to less than 30 Hz. The peak-to-peak noise contribution of the OP27 will still be only 0.11

µV, which is equivalent to an error

of only 0.02

°C.

Figure 40. Low-Noise, Multiplexed Thermocouple Amplifier and 0.1-Hz To 10-Hz

Peak-to-Peak Noise Voltage