AM336 Datasheet, PDF (6/12 Pages) Analog Microelectronics – IC FOR OPTO DETECTOR

IC FOR OPTO DETECTOR
AM 336
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 R_B (internal resistor)
and for high frequencies R_A (external resistor).
Connection pins: INA, OUTA, ALR.
SIGNAL DETECTION STAGE:
The signal of the input stage is connected via a high–pass filter (C_IN between OUTA and IND, R_IN
internal) to the inputs of comparator A and B (window comparator). The threshold voltages VT_A
and VT_B and the hysteresis voltages VH_A and VH_B are generated by a constant current across the
resistors R_TA and R_TB (R_TA = 2 × R_TB). The hysteresis is switched by the output signals of the D–
flip–flops. Threshold and hysteresis levels are determined by external resistors (R_D R_H) and
temperature compensated by an internal voltage reference (VR). The resistors have to be located as
I ND
VTB
VTB-VHA
VTA+VHA
VTA
I RD
VTB=1.5 *VTA
V H B = 1.5 * V H A
QO
LED
Figure 2: Functional diagram
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February 2005
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