JPS62100622A - Light intensity detector - Google Patents

Abstract

PURPOSE:To make a detector economical and adapted for an integration by connecting the input terminal of a series circuit to the junction between a photodiode and a switching element and connecting the output terminal of the series circuit to the control terminal of the switching element. CONSTITUTION:When a light with a predetermined intensity is directed to a photodiode 1, for example, at a time t1, since an N-MOS transistor 2 is in an off condition, a charging current is supplied to an inverter 4-1 to raise an input voltage. When the output of an inverter 4-n becomes '1' at a time t3, the transistor 2 is turned on, the change of the inverter 4-1 is discharged, the input voltage is reduced to '0' at a time t4 and the output of the inverter 4-n becomes '0' at a time t5. Thus, the transistor 2 is turned off and the current is again supplied. By repeating such operations, pulse signals with a frequency (f) corresponding to the light intensity are outputted from the inverter 4-n. This can make a detector economical and adapted for an integration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light intensity detection device having an economical structure suitable for integration.

[Conventional technology]

In recent years, it has become common in various fields to combine sensors such as photodiodes that detect the intensity of irradiated light with control devices such as microprocessors to control controlled devices according to the light intensity. ing. By the way, since a sensor such as a photodiode outputs an analog signal corresponding to the light intensity, conventionally, the analog signal output from the sensor is generally converted into a digital signal using an AD converter, and then the microprocessor However, there was a problem in that an expensive AD converter had to be used. In this case, it is also possible to integrate a photoelectric conversion element such as a photodiode and an AD converter into a single chip, but since the AD converter includes a capacitor and a resistor in addition to the L-transistor, There are problems in that it is difficult to make the knob small and the yield is low.

(Problems to be Solved by the Invention) The present invention has solved the above-mentioned problems, and its purpose is to provide a light intensity detection device with an economical structure that is suitable for integration.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a switch element connected in series with a photodiode, and a series circuit in which a plurality of inverters each consisting of a MOS transistor are connected in series, and an input terminal of the series circuit is provided. is connected between the photodiode and the switch element, and the output terminal of the series circuit is connected to the control terminal of the switch element.

〔Example〕

FIG. 1 is a block diagram of an embodiment of the present invention, where 1 is a photodiode and 2 is an N-MOS transistor 4-1 to 4.
-n is an inverter composed of a C-MO3I-transistor, etc., 5 is a buffer, and 6 is an output terminal. Incidentally, an even number of inverters 4-1 to 4-n are connected in series, and the output terminal of inverter 4-n is N-MO.
It is connected to the gate terminal of the S transistor 2.

In addition, in Fig. 2, the photodiode 1 has an intensity of L1 to L5.
Irradiate the light of (L5>L4>L3>L2>Ll) and
-Voltage Vi applied to the gate of MOS transistor 2
FIG. 2 is a diagram showing the voltage Vout appearing across the N-MO3I-transistor 2 when n is changed.

Now, suppose that, for example, at time t1, the photodiode 1 is irradiated with light having a predetermined intensity. At this time, N-MO
Since the S transistor 2 is in the off state as shown in FIG. @stream is supplied,
The input voltage of the inverter 4-1 gradually increases as shown in FIG. If it is greater than or equal to VS, the input is logic''
1”, therefore, inverter 4-
If the input of 1 is represented by logic "l" and "O", it becomes what is shown in the same figure (bl).Here, the said Tpl is the inverter 4-1
The larger the charging current to the gate capacitance of , that is, the greater the intensity of the light irradiated to the photodiode 1, and the smaller the resistance value of the photodiode 1, the smaller it becomes.

Then, at time t2, the input of the inverter 4-1 becomes "1", so that the output of the inverter 4-n is changed to the time t3 after Tpa from the time t2, as shown in FIG.
It becomes "1" at . Here, Tp3 is T, where Tp is the delay time of each of the inverters 4-1 to 4-n.
It is expressed as p3=n-Tp. and time t3
When the output of the inverter 4-n becomes "1", the N-MOS transistor 2 is turned off as shown in fdl in the same figure, and as a result, the voltage stored in the gate capacitance of the inverter 4-1 is The charge is discharged, and the input voltage of the inverter 4-1 gradually decreases as shown in FIG. 2(a), and becomes equal to or lower than the level Vs at time t4, which is after Tp2 from time t3. That is, at time t4, inverter 4
An input of -1 becomes "O" as shown in fb) in the same figure.

Then, the input of the inverter 4-1 is “
As a result, the output signal of the inverter 4-n becomes 0'' at time t5 after Tp3 from time t4, as shown in tc) in the figure. Then, at time t5,
Since the output signal of Impark 4-n becomes “0”,
N-MO3I-ranjisk 2 is turned off as shown in the figure (dl), and as a result, a charging current is supplied to the gate capacitance of inverter 4-1 through photodiode 1, and the input voltage of inverter 4-1 becomes the same. As shown in Figure (al), it gradually rises and exceeds the level Vs at time t6, which is Tpl after time t5.In other words, at time t6, the input to inverter 4-1 increases as shown in Figure (bl). Then, at time L6, the human power of the inverter 4-1 becomes "1", so that the inverter 4
The output signal of -n becomes 1" at time t7 after time Tp3 from time L6 as shown in FIG.
A pulse signal having a frequency f shown in is output.

f = 1/ (Tpl+Tp2+2 n-Tp3)
--(1) Here, as mentioned above, Tpl becomes shorter as the intensity of the light irradiated to the photodiode 1 increases, so the pulse signal output from the inverter 4-n corresponds to the light intensity. frequency. The pulse signal output from the inverter 4-1 is applied to a control device Q such as a microprocessor via a buffer 5 and an output terminal 6, and the control device performs processing corresponding to the frequency of the applied pulse signal, that is, Photodiode 1
Processing is performed in accordance with the intensity of light irradiated to the area.

On the other hand, although not explained in the above embodiment, the auxiliary current sources 3, 3' have a current source load consisting of a photodiode 1 and an N-MOS I-transistor 2, depending on the light intensity to be operated. This is to adjust the DC operating point of the inverter circuit. That is, when the operation target is light with low light intensity, the auxiliary current source 3 is used to supply current to the inverter circuit 7, and when the operation target is light with high light intensity, the auxiliary current source 3 is used. The current flowing through the photodiode 1 is shunted.

(Song of the Invention) As explained above, the present invention provides an inverter comprising switch elements such as N-MQSl transistors and MQSl transistors connected in series with the first and fourth nodes. The input terminal of the series circuit is connected between the photodiode and the switch element, and the output terminal of the series circuit is connected to the control terminal (gate terminal) of the switch element. connected,
Since it does not use an AD converter unlike the conventional example, there is an advantage that the device can be constructed economically. Further, even when integrating the device, there is no need to create elements such as resistors and capacitors, so there is an advantage that chip size can be reduced and yields can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an input/output characteristic diagram, and FIG. 3 is an explanatory diagram of the operation of FIG. 1. Reference numeral 1 designates transistors 1 to diodes 1-12, 3.3' is an auxiliary current source, 4-1 to 4-n are inverters, 5 is a buffer, and 6 is an output terminal.

Claims (1)

[Claims] It consists of a switching element connected in series with a photodiode, and a series circuit in which a plurality of inverters each composed of MOS transistors are connected in series, and an input terminal of the series circuit is connected to the photodiode and the switching element. 1. A light intensity detection device, characterized in that the output terminal of the series circuit is connected to the control terminal of the switch element.