AD8628/AD8629
The results shown in Figure 56 to Figure 61 are summarized in
Table 5.
0V
CH1 = 50mV/DIV
CH2 = 1V/DIV
Table 5. Overload Recovery Time
A
= –50
V
Positive Overload
Recovery (µs)
Negative Overload
Recovery (µs)
V
IN
Product
AD8628
LTC2050
LMC2001
6
9
650
40,000
25,000
35,000
V
OUT
0V
INFRARED SENSORS
Infrared (IR) sensors, particularly thermopiles, are increasingly
being used in temperature measurement for applications as
wide-ranging as automotive climate control, human ear
thermometers, home insulation analysis, and automotive repair
diagnostics. The relatively small output signal of the sensor
demands high gain with very low offset voltage and drift to
avoid dc errors.
TIME (500µs/DIV)
Figure 59. Negative Input Overload Recovery for the AD8628
0V
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
= –50
V
V
IN
OUT
V
If interstage ac coupling is used (Figure 62), low offset and drift
prevents the input amplifier’s output from drifting close to
saturation. The low input bias currents generate minimal errors
from the sensor’s output impedance. As with pressure sensors,
the very low amplifier drift with time and temperature elimi-
nates additional errors once the temperature measurement has
been calibrated. The low 1/f noise improves SNR for dc
measurements taken over periods often exceeding 1/5 s.
0V
Figure 64 (shows a circuit that can amplify ac signals from
100 µV to 300 µV up to the 1 V to 3 V level, with gain of
10,000 for accurate A/D conversion.
TIME (500µs/DIV)
Figure 60. Negative Input Overload Recovery for LTC2050
10kΩ
100kΩ
100Ω
100kΩ
5V
5V
0V
CH1 = 50mV/DIV
CH2 = 1V/DIV
100µV – 300µV
10µF
A
= –50
V
1/2 AD8629
IR
1/2 AD8629
V
DETECTOR
IN
10kΩ
f
≈ 1.6Hz
C
V
OUT
TO BIAS
VOLTAGE
Figure 62. AD8629 Used as Preamplifier for Thermopile
0V
TIME (500µs/DIV)
Figure 61. Negative Input Overload Recovery for LMC2001
Rev. C | Page 17 of 20
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