OP27A, OP27C

LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL-AMPLIFIER

SLOS100E − FEBRUARY 1989 − REVISED FEBRUARY 2010

18

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

unity gain buffer applications (continued)

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 32. Low-Noise, Multiplexed Thermocouple Amplifier and

0.1-Hz to 10-Hz Peak-to-Peak Noise Voltage