Phase advance for ambient light suppression in phototransistors

Details Phase advance for ambient light suppression in phototransistors Phase advance for ambient light suppression in phototransistors

1991-06-24

1992-02-25

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

330308, H01J 4014

Patent

active

050916408

ABSTRACT:
The invention provides an oscillatory suppression circuit (54) for use in a photosensor loop circuit (10) employing a phototransistor (14). The oscillation suppression circuit (54) prevents oscillation in the photosensor loop circuit (10) caused by detected unmodulated high frequency light. The oscillatory suppression circuit (54) includes a resistor (58) and a capacitor (62) connected in series, and also connected in parallel with a base resistor (38) of a feedback transistor (26). The oscillatory suppression circuit (54) adds a small amount of phase advance to a feedback circuit (50). This small phase advance counteracts any additional negative phase shift produced when intense light pluses are detected by the phototransistor (14) and amplified by the high gain of the feedback circuit (50).

REFERENCES:
patent: 4247765 (1981-01-01), Bergstrom
patent: 5008524 (1991-04-01), Reutter et al.

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