SU1679210A1 - Illumination-to-frequency converter - Google Patents

Abstract

The invention relates to a technique and means for measuring continuous light flux and. can be used in devices for measuring luminous flux. The purpose of the invention is to improve the measurement accuracy. The converter contains a photodiode 1. a timing capacitor 2, a source repeater 3 on a matched pair of field-effect transistors and an integral timer; 6 with a discharge resistance 10. When the photodiode 1 is illuminated, the capacitor 2 begins to charge linearly and thermally compensated the source follower 3. When the signal at the output of the repeater reaches a threshold value specified by the integrated divider of the integral timer 6, the trigger of the latter triggers and discharges with the key capacitor 2 through a resistor 10. The trigger frequency depends linearly on the photodiode illumination. 1 il.

Description

The invention relates to techniques and means for measuring the intensity of a continuous light flux and can be used both as a stand-alone device and as a part of various devices using light flux measurement.

The purpose of the invention is improving the accuracy of measurements.

The drawing shows a diagram of the Converter.

The converter contains a photodiode 1, a timing capacitor 2. a source follower 3 on a pair of field effect transistors 4 and 5, an integral timer 6 with elements. 7 and 8 comparison and trigger 9 and discharge resistance 10.

The converter operates as follows.

Under the influence of radiation incident on the photodiode 1, a photocurrent is generated. This current linearly charges the timing capacitor 2. The voltage level of the capacitor is fed to the input of the source follower 3, which transmits a linear increase in voltage to the inputs of the comparison elements (comparators) of the integral timer 6.

The construction of the source follower on a matched pair of field effect transistors 4 and 5 allows you to maintain a constant level of zero or a given offset at the output when the temperature changes over a wide range.

When the voltage increases at the inputs of the timer 6 to its value at the upper point of the internal three-link resistive divider, the comparison element 7 is activated, setting the trigger 9 in the unit state (output Q of the trigger). This opens the key transistor, discharging through the resistance 10 of the capacitor 2. With the voltage drop below the level set at the specified point of the voltage divider, the element 7 returns to its original state. In this case, the trigger 9 remains in the state of unity at the output (the trigger is controlled by a positive signal difference).

When the voltage across the capacitor as a result of the discharge decreases to the voltage level at the lower point of the voltage divider, the comparison element 8 is triggered, returning trigger 9 to its previous state. At the same time, the key transistor closes and the capacitor charges the current of the photodiode. Another increase in voltage causes the element 8 to return to its original state. The trigger 9 remains in a static state until the next operation of the element 7.

The alternation of charge / discharge cycles / causes the appearance of negative rectangular signals at the output of timer 6 I 5, the duration of which is determined by the values of capacitor 2 and discharge resistance 10.

The charge time of the capacitor 2 to the threshold voltage Un has an inverse dependence on the magnitude of the charging current, reaching a maximum value under the influence of only a dark current of 1 _{ton of the} photodiode. The magnitude of the charging current 1zar 15 is leap -

Un C гдеι where T1 is the charge time under the influence of a dark current;

C is the capacitance of the capacitor.

With an increase in the charging current, i.e. under the influence of a dark and 25 photocurrent If, the duration of the charge decreases, and the current value is determined by the expression

1zar = I _F +1 _and _p with ^t t ₂ where T ₂ is the charge time under the action of the sum of the dark and photocurrent.

In this case, the photocurrent value corresponds to 35

If = and _n С

T ₂

Un C Τι

The duration of the oscillation period T _p due to the influence of the light flux on the detector is

Un C _ 1___

J___1_ f ₂ - f! ''

T ₂ Τι where fi and f ₂ are frequencies corresponding to periods; Τι and Т ₂ , and the frequency of oscillations generated by the action of the photocurrent corresponds to the difference in frequencies fi and f ₂ , since

The invention improves the conversion linearity due to the operation of the photodiode 1 in the photodiode mode, as well as5 increase the accuracy by compensating for the temperature drift of the repeater and the sensitivity of the device by reducing the influence of the dark current of the detector.

Claims (1)

FORMULA AND SECTION 5 Illumination converter is a frequency that contains a photodiode connected by an output to the first output of the capacitor, connected by the second output to a common bus, as well as a threshold circuit and a key at its output, connected to a common point of the photodiode and capacitor, which differs in that, in order to increase accuracy of measurement, a source follower on an agreed pair of field-effect transistors is additionally introduced into it, and the threshold circuit and key are made in the form of an integral timer, the output of which is the output of the device, while the input of the photodiode connected to the device power bus, and the source follower on an agreed pair of field-effect transistors is connected between the common point of the photodiode and the capacitor and the integral timer input.