AD8628/AD8629/AD8630
The results shown in Figure 56 to Figure 6± 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
Model
AD8628
6
9
Competitor A
Competitor B
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
If interstage ac coupling is used, as in Figure 62, low offset and
drift prevent the output of the input amplifier from drifting close to
saturation. The low input bias currents generate minimal errors
from the output impedance of the sensor. As with pressure sensors,
the very low amplifier drift with time and temperature eliminate
additional errors once the temperature measurement is calibrated.
The low ±/f noise improves SNR for dc measurements taken
over periods often exceeding one-fifth of a second.
A
= –50
V
V
IN
OUT
V
0V
Figure 62 shows a circuit that can amplify ac signals from ±00 μV to
300 μV up to the ± V to 3 V levels, with a gain of ±0,000 for
accurate analog-to-digital conversion.
10kΩ
100kΩ
TIME (500µs/DIV)
100Ω
100kΩ
Figure 60. Negative Input Overload Recovery for Competitor A
5V
5V
100µV TO 300µV
10µF
1/2 AD8629
IR
0V
1/2 AD8629
DETECTOR
10kΩ
CH1 = 50mV/DIV
CH2 = 1V/DIV
f
≈ 1.6Hz
C
A
= –50
V
TO BIAS
VOLTAGE
V
IN
Figure 62. AD8629 Used as Preamplifier for Thermopile
V
OUT
0V
TIME (500µs/DIV)
Figure 61. Negative Input Overload Recovery for Competitor B
Rev. I | Page 17 of 24
ROCHESTER [ Rochester Electronics ]
