SU1430763A1 - Photometer - Google Patents

Abstract

The invention relates to photometry and is intended to measure stationary light fluxes in various areas of optoelectronics. The aim of the invention is to increase the resolution of a photometer. The photometer contains a photodiode I, whose cathode is connected to the inverting input of amplifier 2, and the anode to its output, a comparator 3, a quadratic form voltage generator 4 (and, Up.At), a switching element 6 that supports the cathode of the photodiode 1 or to the exemplary voltage source 7 and to charge the eMKOctb of the photodiode 1, or to the generator, to compensate the ground current to compensate for the dark current during photometric detection. Under the action of the luminous flux, the capacitance of the photodiode 1 is discharged and the linearly increasing voltage at the output of amplifier 2 comparing with the comparator 3 with the voltage of the generator 4. At the moment of equal voltage the single vibrator 5 is started and a pulse of fixed duration is generated at its output, which switches the switching voltage element 6, gating the comparator 3 and starting the generator 4. The pulse period at the output of the one-shot 5 is directly proportional to the power of the optical radiation. 2 Il. and AftSSSU IL tnn .4 with OO

Description

SriE.1

The invention relates to photometry and is intended to measure stationary light fluxes in various areas of optoelectronics.

The aim of the invention is to increase the resolution of the photometer by linearizing its output characteristic.

Fig. 1 shows a functional diagram of the photometer: Fig. 2 shows time diagrams of operation under various illumination conditions.

The photometer contains a photodiode 1, the cathode of which is connected to the inverting input of the amplifier 2g, and the anode to its output and to the inverting input of the comparator 3, the noninverting input of which is connected to the output of the generator 4 of a quadratic voltage output - to the input of a single vibrator 5. The output of the one-vibrator 5 is connected to the input of a voltage generator 4 of a quadratic form and the control input commutes; its element 6, the first switched input of which is connected to the positive terminal of the exemplary voltage source 7, and the second to the output r nerator 8 compensating current. The output of the switching device 6 of the element 6 is connected to the inverting input of the amplifier 2 and to the cathode of the photodiode 1, and non-inverting the input of the amplifier 2 is connected to the luminous zero potential. In addition, the input of the delay element 9 is combined with the input of the generator 4 on the quadratic-shaped spacing, and its output is connected to the gate input of the comparator 3,

The voltage generator of a quadratic form realizes the following functional dependence:

but

and „and. + At

(one)

where and is the voltage at the output of the generator 4;

Up is the displacement voltage; . And - coefficient;

t - time

Generators of this type can be implemented either using digital computing devices (i.e., calculating a function in a digital code and then converting it to analog form)} or using analog methods used in analog computing devices.

d

5 G 5 Q Q

five

0

The device works as follows

At the moment of turning on the photometer, the single-oscillator 5 generates a pulse of fixed duration that arrives at the control input of the commuta- tion E. 6, the latter connects the inverting input of amplifier 2 to the positive side of the exemplary voltage source 7, and a negative voltage is set at the output of the amplifier 2, which causes a charge charge of the photodiode a 1 generating a voltage of the form UU + At, and the switching element 6 is connected-. Em to the inverting input of amplifier 2 is a generator of 8 compensating current. The pulse duration of the one-shot 5 is chosen such that the barrier capacitance of the photodiode 1 is fully charged. with the photodiode 1 being discharged, it is charged by the generator current equal in magnitude to the dark current, i.e. dark current compensation is performed,

As the capacitance of the photodiode 1 is discharged, the voltage at the output of amplifier 2 linearly increases, and the voltage at the quadratic law at the output of generator 4 increases simultaneously. Both of these voltages are compared with comparator 3, which triggers a one-shot vibrator at the moment of equality of these voltages. In this case, the duration of the time interval between the end of the pulse at the output of the single-vibrator 5 and the switching moment of the switch 3 linearly depends on the power of the optical radiation.

The voltage at the output of the amplifier is determined by the expression

TT - TT J. I4f t, „,

and - + Q U;

where K is the gain factor. letter;

 max max negative pressure at the output

an amplifier at the moment of termination of a one-shot pulse;

-the capacity of the photodiode;

- time of photodiode capacitance photocurrent;

1f - photodiode current (photocurrent). Since the capacitance of the photodiode is linearly depleted,

WITH

t

1f s (P,

(3)

where P is the optical power;

o (- proportionality coefficient.

The output voltage of the amplifier can be described by the following expression

and,

 and.

ppt

W

 Out

where uo k.

 c (K TG

If the voltage at the output of the amplifier l 2 is determined by formula (A), and the voltage at the output of the generator A is defined by formula (1), then the condition for the equality of these voltages is determined by the expression

.2

Uo + / i Pt UQ + At

(five)

from where

P A / p. t,

where A / is the proportionality coefficient.

Since at the initial moment of time the voltages at the outputs of amplifier 2 and generator 4 are very close in value, to eliminate the false positives of the comparator, which can be caused by pulsations of the device power, temperature drift of the parameters of the elements of the devices and other non-stationary disturbances, it is gated. In this case, the start of the comparator is carried out with a delay relative to the start of the start of the generator 4, determined by the parameters of the delay element 9.

After restarting the one-shot 5, the cycle of operation of the photometric device is repeated.

The choice of the coefficient A at the quadratic term of expression (5) is determined by the optimal power of optical radiation P

(see Fig. 2). The minimum time T for which

Mikes

0

five

0

five

0

five

0

five

0

five

the voltage at the output of amplifier 2 reaches the value of I on, which is determined by the value of the l1-neck area of the output characteristic of photodiode 1, is determined from (4)

 T, (won - and „) // 3. .

In order to satisfy the equality and b op -at t T, KOZFFITSI-. ent A with a quadratic term U dol-. wives be equal to A p / ().

Thus, with the device parameters determined by the indicated algorithm, the duration of the photometric time interval is directly proportional to the optical radiation power. The value of T cannot be less than the value of t, determined by element 9. As an illustration of the operation of the device in FIG. Figure 2 shows the values of the time intervals To and Tj, corresponding to the powers of the optical radiation Pj and RE.

For consistency and ease of perception, the levels of all stresses are given in the same coordinate axes.

FIG. 2, the following notation is used: Uj, 5p is the output level of the exemplary source 3 of voltage 1; Upp is the level of a constant reference voltage limiting the linear gpask of the output signal of s silitel 2; 11 ((ax max negative voltage at the output of amplifier 2 with fully charged photodiode capacitance; Ug ,, i, - yyhe output voltage at the output of amplifier 2 npai different optical radiation powers T - time intervals corresponding to different m of optical radiation, - Р; voltage at the output of the generator 4; RP G quality photometer; maximum radiation power is measured at a predetermined ratio EMA A generator 4.

Claims (1)

Invention Formula A photometer containing a photodiode, the cathode of which is connected to the inverting input of the amplifier, and the current to the output of the amplifier, the non-inverting input of which is connected to the zero-potential bus, and the output to the inverting input of the comparator, the output of which is connected to the control the input of the switching element, the first and second switching inputs of which are connected respectively to the exemplary voltage source and the generator of the compensating current, and the output of the commutator switching element Inen with a photodiode cathode, characterized in that, by increasing the resolution of the photometer by linearizing its output characteristic, a delay element and a quadratic voltage generator are additionally introduced, U realizing the function one Ur and, + Af where up a t displacement voltage; constant coefficient; time and the comparator is gated, with the generator output of the quadratic form connected to the non-inverting input of the comparator, the output of the delay element is connected to the gate input of the comparator, ° and the inputs of the generator and the delay element are combined and connected to the output of the single-oscillator.