SU1548673A1 - Photodetector - Google Patents

Abstract

The invention relates to photodetectors and can be used to pre-measure the difference between two streams. The purpose of the invention is to improve the accuracy of measuring the difference between the two light fluxes by increasing the accuracy of the zero setting. A two-channel photodiode device containing two anti-parallel photodiodes 1, 2 connected to the input of amplifier 3 of the photocurrent, has two channels, which contain operational amplifiers 4 and 5, which are covered by negative feedback through transistors 6 and 7 and which are output through anti-logarithm transistors 8 and 9 are connected to the input of the amplifier 3 photocurrent. Transistors 10, 11, 12, 13 are connected to the bases of transistors 6, 7, 8, 9, respectively. Offsets generated by current sources 14, 15, 16, 17 set the scaling coefficients for converting photocurrent photodiodes 1, 2 into output currents of the channels. By changing the resistor 20, the loads of the current sources 18, 19 vary, which leads to a change in the voltages at the inputs of the current sources 16, 17, changing their output currents. This leads to a change in voltage across the scaling transistors 12, 13, and consequently to changes in the transmission coefficients of the channels through the photocurrent photodiodes 1, 2, which leads to a zero-amplifier of the photocurrent independent of the magnitude of the recorded light fluxes. 1 il.

Description

The invention relates to photodetectors and can be used in multi-purpose equipment for precision measurement of the difference between two light fluxes. 2

The aim of the invention is to improve the measurement accuracy by increasing the accuracy of the zero setting.

The drawing shows a diagram of the device, s

The device contains photodiodes 1 and 2, an operational amplifier 3, covered by resistor feedback, to the inverting input of which the anode of the first 1 and the cathode of the second 2 photodiodes are connected. The anode of the photodiode 1 and the cathode of the photodiode 2 are connected to communication channels, which include operational amplifiers 4 and 5, eight transistors 6–13, four transistors in each channel, six sources 14–19 of current, three current sources in each channel, as well as a variable resistor 20, regulating the output of which is connected to the common bus of the device, and a feedback resistor 21 of the amplifier 3, while the outputs of the operational amplifiers 4 and 5 are connected to the inverting inputs of the amplifiers 4 and 5 J teli 4 and 5, the base of transistors 6 and

7connected to current sources 14 and 15 and through shunt transistors

8 and 9, connected according to the diode circuit, are connected to a common bus, emitters of transistors 10 and 11 are connected to the outputs of operational amplifiers 4 and 5, collectors of transistors 10 and 11 are connected to the inverting input of operational amplifier 3, bases of transistors 10 and 11 are connected to series-connected sources 16 and 17, 18 and 19 of the current and through the transistors 12 and 13, connected according to the diode circuit, are connected to the common bus of the device, and the connection points of the current sources 16, 18 and 17, 19 are connected to the terminals of the variable resistor 20, the communication channel transistors connected The photodiode 1 connected to the anode and the communication channel connected to the cathode of the photodiode 2 have direct and reverse conductivity, respectively. Transistors 6 and 7 perform the functions of logarithmic elements, and transistors 8, 9 function as anti-logging elements.

The device works as follows.

The light fluxes incident on the photodiodes 1 and 2 excite in them the corresponding photocurrent If and 1d. The current If, flowing through the logarithm of the feedback transistor 6, creates a voltage U at the output of the amplifier 4. Supposing that the transistors 6 and 10 are made on a common substrate and, according to the same technology,

voltage U. can be expressed U4 Ind., - ,, / ij),

where if is the temperature potential;

 current source 15 current;

1ych - reverse current pn-junction;

Of - the transfer coefficient of the transistor 6, included in the scheme with a common base.

5154

Considering the fact that transistors 8

and 12 are made on a common substrate with transistors 6 and 10, the value of the collector current and the anti-logging transistor 8 can be expressed;

ri. ,, (Ј, .ЈЈ

one

to 8

where oig - current transfer coefficient of the transistor 8, included in the scheme with a common base; Iu - output current source 16

current.

Since o (t and o (, change almost equally with temperature), the collector current of transistor 8 is practically independent of temperature.

By analogy, get for the second communication channel

t - G-0 t LKQ i T) J-2

k9

The photocurrents and collector currents of transistors 8 and 9, which flowed through the feedback resistor 21 of amplifier 3, create a voltage at its output equal to

v {KrЈ -li +

40

where R is the magnitude of the resistor 21 of the feedback of the amplifier 3. As the slider of the variable 35 of the resistor 20 moves, the voltage at the control input of one of the current sources 17 or 16 increases (modulo) and at the other decreases The currents I. also change accordingly. Since the collector currents of transistors 8 and 9 are opposite in direction, then at the output of amplifier 3 a zero is shifted (balancing of light fluxes). Since the collector currents of transistors 8 and 9 are proportional to the in-phase change in the light fluxes, there is no error in the device associated with the zero shift when they are in-phase (change.

-

but

ten

15

20

,

25

thirty

40

35 45 ™

The use of the invention, for example, in the means of measuring the parameters of optics will significantly improve the accuracy of recording these parameters.

Claims (1)

Invention Formula A photodetector device containing the first and second photodiodes and the first operational amplifier, covered by resistor feedback, to the inverting input of which the anode of the first and the cathode of the second photodiodes are connected, in order to improve the measurement accuracy by improving the accuracy of the zero setting, to the cathode the first and the anode of the second photodiode are connected to the communication channels, each of which includes an operational amplifier, four transistors and three current sources, as well as a variable resistor regulating the output of which It is connected to the common bus of the device, while the output of the operational amplifier of the communication channel is connected to its inverting input through the first feedback transistor, the base of the first transistor is connected to the first current source and through the second shunt transistor connected to the common bus , the emitter of the third transistor is connected to the output of the operational amplifier of the communication channel, the collector of the third transistor is connected to the inverting input of the first Operational amplifier, the base of the third transistor is Connected to series-connected second and third current sources and through a fourth transistor connected according to a diode circuit, connected to the common bus of the device, with the output points of the variable resistor connected to the junction points of the second and third current sources of each communication channel, and transistors of the channel connected to the anode the first photodiode, and the channel connected to the cathode of the second photodiode, respectively, direct and reverse conductivity.