Cirrus-logic AN300 REV1 Manual do Utilizador descarregar pdf (Página 14)

14 AN300REV1

AN300

Figure 18 illustrates a thermopile amplifier set for a gain of 640 V/V. The Dexter Research 1M thermopile is a thin

film device that exhibits a typical thermal noise of 7 nV/√Hz

. In a typical infrared sensing application, the device may

output only a few millivolts of signal. The CS3001 operational amplifier provides very high open loop gain and a low

spot noise of 6 nV/√Hz

. The circuit can readily amplify a 5 mV signal to several volts.

Figure 18. Thermopile Amplifier with Gain of 650 V / V

The thermopile, like the thermocouple, must be “cold junction” compensated. This would require a second sensor

on the thermopile for this function. Manufacturers of thermopile sensors generally offer devices that include a sensor

for cold junction sensing. This second sensor necessary for cold junction correction is not shown in Figure 18.

4.2 Load Cell Amplifiers

Load cells output small signals, typically less than 10 mV. To maintain high signal to noise, this small signal must

be amplified with a low noise, low drift, high gain amplifier.

Cirrus Logic's chopper-stabilized amplifiers are very suitable for this type of application.

The combination of the CS3001 amplifier and the CS5512 A/D converter can provide a high resolution digitizer for

a load cell as shown in Figure 19.

Figure 19. High-resolution Digitizer for a Load Cell

The CS3001 amplifier exhibits low noise, low drift, and incredibly high open loop gain.

CS3001

100

64.9k

0.015µF

Dexter Research

Thermopile 1M

+5 V

1 mV/V

350 Ω

200 Ω

0.047 µF

0.1 µF

VREF

AIN+

AIN1

V-

V+

SDO

SCLK

CS5510/12

µC

+5 V

Counter/Timer

71.5 kΩ

0.47 µF

0.1 µF

CS3001

88.7 kΩ

100 Ω

0.1 µF

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