Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1984-11-07
1986-11-18
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
330 59, H01J 4014
Patent
active
046237860
ABSTRACT:
The front end of an optical receiver circuit (10) is of the type having a field-effect device transimpedance amplifier (16,21) which receives at its input (14) the photocurrent of a photodiode (12). A field-effect device shunt impedance (26) to protect against amplifier overloading is connected between the input and ground through a decoupling capacitor (28). The shunt (26) is controlled by a controller (30), which has its input connected to the output (24) of the amplifier (16) and its output connected to the gate of the shunt (26). The controller (30) compares the output (24) of the amplifier (16) to a threshold reference voltage for determining whether to activate the shunt (26) and regulates the gate voltage of the shunt (26) by means of an AGC amplifier. A direct current feedback resistor (32) is connected between the output (24) of the amplifier (16) and the source of the shunt (26). This prevents the d.c. component of large photocurrents from significantly changing the input bias voltage level of the amplifier (16).
REFERENCES:
patent: 4415803 (1983-11-01), Muoi
patent: 4459475 (1984-07-01), Flint et al.
patent: 4498001 (1985-02-01), Smoot
AT&T Bell Laboratories
Gatto James G.
Nelms David C.
Ulbrich Volker R.
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