RU1777231C - Photodetector - Google Patents

Abstract

The invention relates to radio electronics and can be used in optical communications to exchange information. The purpose of the invention is to increase sensitivity and reduce distortion. The photodetector contains a comparator 1, a capacitor 2, resistors 3-6, photodiodes 7, transistors 8 and 9 of the current reflector. With the background illumination of photodiode 7, the capacitor 2 has time to reach the voltage drop across the first resistor 3, without violating the equal potentials at the inputs of the comparator 1. When pulsed illumination of the photodiode 7 sharply increases the potential at the first and second resistors 3 and 4. The capacitor 2 does not manages to replenish to this level and at the first input of the comparator 1, the potential will be lower than at the second. At the output of comparator 1, a logic unit is displayed. Light pulse information is received. 1 ill.

Description

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The invention relates to the electronics industry and can be used in optical communications to exchange information.

A known photodetector comprising a comparator, a capacitor, four resistors and a photodiode, one output of which is connected through the first resistor to the first power bus and directly to the first input of the comparator, and the second output directly to the second power bus and through the second resistor to the second input of the comparator which, through a third resistor connected in parallel with the capacitor, is connected to the first power line, wherein the input of the comparator is shunted by the fourth resistor.

A disadvantage of the known photodetector is the low sensitivity and distortion of the light pulse at lower parts of their repetition, due to the presence of an HC chain in series with the photodiode at the input of the comparator.

An object of the present invention is to increase sensitivity and reduce distortion of light pulses.

This goal is achieved by the fact that in the photodetector containing a comparator, a capacitor, four resistors and a photodiode, one output of which is connected through the first resistor to the first power bus and, directly, to the first input of the comparator, the second input of which is connected to this bus through the second resistor , a current reflector is introduced, the input of which is connected to the second output of the photodiode, and the output to the second input of the comparator, while the third resistor is connected in parallel with the photodiode, and the capacitor is connected in parallel with the first resistor and Inonii fourth resistor to the second power bus.

The drawing shows a circuit diagram of the proposed photodetector.

The photodetector consists of a comparator 1, a capacitor 2. a first resistor 3, a second resistor 4, a third resistor 5, a fourth resistor 6, a photodiode 7, a first current reflector transistor 8, a second current reflector transistor 9 and a first bus 10 and a second photodetector power bus 11.

The proposed photodetector works as follows,

In the initial state, the photodiode 7 is darkened. The capacitor 2 is charged to the level of the voltage drop across the resistor 3. The collector currents of the transistors 8 and 9 are equal to each other, because the latter are included in the current reflector circuit.

If the resistors 3 and 4 are equal, the potentials at the inputs + and - of the comparator 1 are equal to each other. At the output of the latter, the potential is zero. When the background illumination of the photodiode 7, its resistance decreases, by shunting the resistor 5, limiting the current in the control circuit of the current reflector. The current in the base circuit of transistors 8 and 9 increases. This will cause an identical increase in currents in the collectors of transistors 8 and 9. At the same time, the voltage drop across resistors 3 and 4 connected to the inputs of comparator 1 will increase by equal values without causing changes to it

5 output

With pulsed illumination of photodiode 7, the current in the collectors of transistors 8 and 9 will change sharply, which will cause a pulse increase in voltage drops across the resistors

0 3 and 4. The capacitor 2 will for some time shunt the increase in this voltage across the resistor 3. The potential at the inverted input of the comparator 1 will be slightly lower than the potential at the non-inverted

5 entrance. At the output of comparator 1, a logic unit is displayed. A light information pulse is received.

Selecting the capacitance of capacitor 2 or the values of resistors 3 and 4, are 0 from the influence of the background illumination of photodiode 7 and increase the sensitivity when receiving low frequencies of light pulses. The characteristics of the electrical pulses at the output of the comparator 1 is not

5 depends on the value of the capacitance of the capacitor 2 and the value of the constant component of the light flux (background) supplied to the photodiode 7. This allows receiving light information in different frequency

In formats with a sufficiently high speed (18 thousand pulses per second and higher) and without interference, the upper frequency limit of the received pulses is practically limited by the capabilities of transistors 8 and 9 and comparator 1 and is regulated by resistor 5. Using the resistor 6, the characteristic bias is adjusted a photodetector above the background illumination of the photodiode 7,

Claims (1)

0 Thus, thanks to the use of a current reflector, the input of which is connected to the second output of the photodiode 7, connected in parallel with the resistor 5, and the output is connected to the second input of the comparator 1, it became possible to increase the sensitivity of the photodetector and reduce the distortion of received light pulses. SUMMARY OF THE INVENTION A photodetector comprising a photodiode, one output of which is through a first resistor connected to the first power bus and the non-input of which is connected to the second terminal only to the first input of the comparator, photodiode, and the output to the second input of the com- second input of which, through the second resistor, is parallel to the first power supply and connected to the first power bus, as well as to the resistor a capacitor is connected in parallel with the third and fourth resistors, a capacitor, 5 a third resistor is connected to the photodiode, and the fourth is characterized in that. for the purpose, a fourth resistor is connected between the second increase in sensitivity and the decrease-input of the comparator and the second distortion supply bus, a current reflector is inserted, neither.