AM336 datasheet(6/12 Pages) AD

6 / 12 page

IC FOR OPTO DETECTOR

AM 336

analog microelectronics

February 2005

6/12

frequency it to high the signal detection is not triggered. In case of a too low frequency a pulsed

signal could occur at the output stages.

Connection pins: FO, IRD, P/B

AMPLIFIER:

The input stage for the photo current is a transimpedance–amplifier. His impedance depends on the

input frequency to reject ambient light.

The input current, coming from pin INA, appears multiplied by the impedance between INA and

OUTA at pin OUTA. For low frequencies this impedance is approximately RB (internal resistor)

and for high frequencies RA (external resistor).

Connection pins: INA, OUTA, ALR.

SIGNAL DETECTION STAGE:

The signal of the input stage is connected via a high–pass filter (CIN between OUTA and IND, RIN

internal) to the inputs of comparator A and B (window comparator). The threshold voltages VTA

and VTB and the hysteresis voltages VHA and VHB are generated by a constant current across the

resistors RTA and RTB (RTA = 2 × RTB). The hysteresis is switched by the output signals of the D–

flip–flops. Threshold and hysteresis levels are determined by external resistors (RD RH) and

temperature compensated by an internal voltage reference (VR). The resistors have to be located as

IND

VTB

VTB-VHA

VTA+VHA

VTA

IRD

LED

VTB=1.5 *VTA

VHB=1.5*VHA

Figure 2: Functional diagram

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