R1

R2

R3

R4

10 k:

VIN

VOUT

-

V

+

V

-

-

V

+

V

-

= 1 +

R2

R1

R4

R3

+

VOUT

+

-

-

RA

CF

VIN = KI

+

-

IR RADIATION

INTENSITY, I

THERMOPILE

RB

VOUT RA

K(RA + RB)

I =

LMP7711

SNOSAP4F – SEPTEMBER 2005 – REVISED MAY 2013

www.ti.com

Figure 61. Thermopile Sensor Interface

PRECISION RECTIFIER

Rectifiers are electrical circuits used for converting AC signals to DC signals. Figure 62 shows a full-wave

precision rectifier. Each operational amplifier used in this circuit has a diode on its output. This means for the

diodes to conduct, the output of the amplifier needs to be positive with respect to ground. If VIN is in its positive

half cycle then only the output of the bottom amplifier will be positive. As a result, the diode on the output of the

bottom amplifier will conduct and the signal will show at the output of the circuit. If VIN is in its negative half cycle

then the output of the top amplifier will be positive, resulting in the diode on the output of the top amplifier

conducting and, delivering the signal on the amplifier's output to the circuits output.

For R2/ R1 ≥ 2, the resistor values can be found by using the equation shown in Figure 62. If R2/ R1 = 1, then R3

should be left open, no resistor needed, and R4 should simply be shorted.

Figure 62. Precision Rectifier

20

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