AD8628/AD8629/AD8630

Rev. F | Page 17 of 20

TIME (500µs/DIV)

0V

0V

CH1 = 50mV/DIV

CH2 = 1V/DIV

Figure 59. Negative Input Overload Recovery for the AD8628

TIME (500µs/DIV)

0V

0V

CH1 = 50mV/DIV

CH2 = 1V/DIV

Figure 60. Negative Input Overload Recovery for LTC2050

TIME (500µs/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, 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 1/f noise improves SNR for dc measure-

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

Figure 62 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 analog-to-digital conversion.

5V

100kΩ

10kΩ

5V

100µV – 300µV

100Ω

TO BIAS

VOLTAGE

10kΩ

IR

DETECTOR

100kΩ

10µF

1/2 AD8629

1/2 AD8629

Figure 62. AD8629 Used as Preamplifier for Thermopile