AD8628/AD8629

Rev. C | Page 17 of 20

TIME (500

µs/DIV)

0V

0V

CH1 = 50mV/DIV

CH2 = 1V/DIV

Figure 59. Negative Input Overload Recovery for the AD8628

TIME (500

µs/DIV)

0V

0V

CH1 = 50mV/DIV

CH2 = 1V/DIV

Figure 60. Negative Input Overload Recovery for LTC2050

TIME (500

µs/DIV)

0V

0V

CH1 = 50mV/DIV

CH2 = 1V/DIV

Figure 61. Negative Input Overload Recovery for LMC2001

The results shown in Figure 56 to Figure 61 are summarized in

Table 5.

Table 5. Overload Recovery Time

Product

Positive Overload

Recovery (µs)

Negative Overload

Recovery (µs)

AD8628

6

9

LTC2050

650

25,000

LMC2001

40,000

35,000

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.

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.

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.

5V

100k

Ω

10k

Ω

5V

100

µV – 300µV

100

Ω

TO BIAS

VOLTAGE

10k

Ω

IR

DETECTOR

100k

Ω

10

µF

1/2 AD8629

1/2 AD8629

Figure 62. AD8629 Used as Preamplifier for Thermopile