Cirrus Logic AN300 REV1 - Manual (Page 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
R1
100
R2
64.9k
C1
0.015 µF
Dexter Research
Thermopile 1M
+5 V
1 mV/V
- +
350 Ω
200 Ω
200 Ω
0.047 µF
0.1 µF
VREF
AIN+
AIN1 V-
V+
CS
SDO
SCLK
CS5510/12
µC
+5 V
Counter/Timer
-
+
71.5 k Ω
0.47 µF
0.1 µF
CS3001
88.7 k Ω
100 Ω
0.1 µF