AD8628ART-R2 datasheet(18/24 Pages) AD

18 / 24 page

AD8628/AD8629/AD8630

Rev. E | Page 18 of 24

TIME (500

μs/DIV)

VOUT

VIN

CH1 = 50mV/DIV

CH2 = 1V/DIV

AV = –50

The results shown in Figure 58 to Figure 63 are summarized in

Table 5.

Table 5. Overload Recovery Time

Positive Overload

Recovery (μs)

Negative Overload

Recovery (μs)

Product

AD8628

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.

Figure 61. Negative Input Overload Recovery for the AD8628

TIME (500

μs/DIV)

VOUT

VIN

CH1 = 50mV/DIV

CH2 = 1V/DIV

AV = –50

If interstage ac coupling is used, as in Figure 64, low offset and

drift prevent 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-

nate additional errors once the temperature measurement is

calibrated. The low 1/f noise improves SNR for dc measure-

ments taken over periods often exceeding one-fifth of a second.

Figure 64 shows a circuit that can amplify ac signals from

100 μV to 300 μV up to the 1 V to 3 V levels, with gain of

10,000 for accurate A/D conversion.

Figure 62. Negative Input Overload Recovery for LTC2050

100k

10k

100

μV – 300μV

100

TO BIAS

VOLTAGE

10k

fC ≈ 1.6Hz

DETECTOR

100k

μF

1/2 AD8629

TIME (500

μs/DIV)

VOUT

VIN

CH1 = 50mV/DIV

CH2 = 1V/DIV

AV = –50

Figure 64. AD8629 Used as Preamplifier for Thermopile

Figure 63. Negative Input Overload Recovery for LMC2001

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