JPH07113945B2 - Signal processor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a signal processing device for processing a signal obtained from a light receiving element whose impedance changes according to a change in the amount of received light.

(Prior Art) In recent years, an electric signal indicating a change in the amount of received light according to a change in brightness, such as a bar code reader, an optical rotary encoder, an image reading device such as a facsimile or an image scanner, and an optical coordinate input device. A photoelectric device that converts the light into a light source is widely used.

Then, a photoelectric element and a resistor are provided in series between the power supply and the ground, and the impedance change of the photoelectric element according to the change in the amount of received light is converted into an electrical signal as a change in the divided voltage due to the photoelectric element and the resistance. To be done.

By the way, in the photoelectric element, even if the amount of received light is zero, the impedance does not become infinite and a dark current flows. Further, the amount of light applied to the photoelectric element is composed of reflected light from a printed object such as a bar code and ambient ambient light. For this reason, the current flowing through the light receiving element is a component in which a direct current component due to dark current, ambient light, or the like is superimposed on an alternating current component as a signal of a change in reflected light. This DC component is significantly affected by differences in ambient brightness, differences in the amount of light emitted from the light source to the barcode surface, differences in the barcode surface reflectance, differences in the dark current specific to the device, etc. Fluctuates.

Therefore, in order to prevent the DC component and extract the AC component as a signal, for example, AC coupling type signal processing has been conventionally performed. FIG. 5 is a circuit diagram of a conventional AC coupling type signal processing device. In FIG. 5, the light emitted from the LED 1 to the bar code surface is reflected by the bar code surface and is received by the phototransistor 2 which is a light receiving element. The phototransistor 2 and the resistor 3 are connected in series and are interposed between the power supply terminal and the ground, and the connection point between the phototransistor 2 and the resistor 3 is connected to the amplifier circuit 5 and the like in the subsequent stage via the DC blocking capacitor 4. It

In such a configuration, the DC component that greatly varies depending on the ambient brightness is blocked by the capacitor 4, and only the AC component as a signal is given to the amplifier circuit 5 and the like.

(Problems to be Solved by the Invention) By the way, in the above-mentioned AC coupling type signal processing device, until the DC potential difference between both ends of the capacitor 4 due to the DC component is discharged, FIG. )
The average value of the AC components appearing in the subsequent stage of the capacitor 4 changes. Therefore, if this AC component is binarized by a certain reference value, there is a problem that a binarized signal different from the signal width of the AC component of FIG.

Note that a DC-coupled signal processing device requires a large dynamic range with respect to a large change in the DC component, and a device with a low voltage such as a battery as a power source can have a large dynamic lens. I couldn't do it and was unsuitable.

An object of the present invention is to solve the above-mentioned problems of the conventional signal processing device, and to provide a signal processing device in which only the AC component corresponding to the impedance change of the light receiving element is amplified and output as a signal. To do.

(Means for Solving Problems) In order to achieve such an object, the signal processing device of the present invention applies a voltage to a light receiving element whose impedance changes in accordance with a change in the amount of received light, and outputs a current from the light receiving element. The current
This voltage is applied to the input terminal of the voltage conversion circuit, and the output voltage output to the output terminal of this current / voltage conversion circuit is applied to the voltage holding circuit via the voltage fluctuation detection circuit that operates against voltage fluctuations in one direction. The holding voltage held by the holding circuit and the reference voltage are compared by the first differential amplifier circuit, and the output voltage is given to the input terminal of the current / voltage conversion circuit via a resistor,
A second differential amplifier circuit amplifies the difference voltage between the output voltage output to the output end of the current / voltage conversion path and the reference voltage, and outputs a processed signal from an output terminal. There is.

(Function) The input terminal of the current / voltage conversion circuit to which the current output of the light receiving element is given is connected to the output terminal of the differential amplifier circuit via a resistor,
The output voltage of the first differential amplifier circuit is controlled according to the difference voltage between the holding voltage held by the voltage holding circuit and the reference voltage according to the output voltage of the current / voltage conversion circuit, so that the current / voltage The converter is operated so that the output voltage of the converter matches the reference voltage. Then, the voltage fluctuation detection circuit
The holding voltage of the voltage holding circuit is changed only when the output voltage of the voltage conversion circuit rises or falls, and either the increase or decrease of the impedance of the light receiving element is the current or voltage. The converter circuit is operated so that the output voltage of the converter circuit varies with respect to the reference voltage. Further, the difference voltage between the output voltage of the current / voltage conversion circuit and the reference voltage is amplified and output by the second differential amplifier circuit, and only the AC component corresponding to the change in the impedance of the light receiving element is amplified and output as a signal.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a circuit diagram of an embodiment of a signal processing device of the present invention, FIG. 2 is a diagram for explaining the operation of FIG. 1 when the amount of light received by a phototransistor is small, and FIG. Is the first when the amount of light received by the phototransistor is large.
It is a figure explaining operation of a figure.

First, the configuration will be described with reference to FIG. Light emitted from the LED 1 to the bar code surface is reflected by the bar code surface and is received by the phototransistor 2, which is a light receiving element. The collector of this phototransistor 2 is connected to the power supply terminal,
The emitter is connected to the inverting input terminal of the first operational amplifier 10, and is also connected to the output terminal of the first operational amplifier 10 via the resistor (for example, 100 KΩ) 11, and further connected to the resistor (for example, 1 KΩ).
Ω) 12 and is connected to the output terminal of the third operational amplifier 13. The output terminal of the first operational amplifier 10 is connected to the non-inverting input terminal of the fourth operational amplifier 14, and
It is connected to the non-inverting input terminal of the operational amplifier 15. Further, the non-inverting input terminal of the first operational amplifier 10 is connected to the reference voltage circuit 16 which outputs the reference voltage V _S. The output terminal of the second operational amplifier 15 is connected to the cathode of the diode 17, and the anode of the diode 17 is connected to the inverting input terminal of the second operational amplifier 15. The anode of the diode 17 is connected to the third operational amplifier via the resistor 18.
Connected to 13 non-inverting inputs. The non-inverting input terminal of the third operational amplifier 13 is connected to the reference voltage circuit 16 via a parallel connection body of the capacitor 19 and the resistor 20, and the inverting input terminal is connected to the reference voltage circuit 16 via the resistor 21. At the same time, it is connected to the output terminal via the resistor 22. further,
The inverting input terminal of the fourth operational amplifier 14 is connected to the reference voltage circuit 16 via the resistor 23, and is also connected to the output terminal via the resistor 24. Further, the output terminal of the fourth operational amplifier 14 is connected to the output terminal 25.

In such a configuration, a current / voltage conversion circuit is formed by the first operational amplifier 10 and the resistor 11 to which the reference voltage V _S is applied to the non-inverting input terminal, and the second operational amplifier 15 and the diode 17 are formed.
By this, a voltage fluctuation detection circuit that operates in response to a voltage fluctuation in the output voltage of the first operational amplifier 10 is formed, and a voltage holding circuit is formed by a parallel connection body of a capacitor 19 and a resistor 20 to which the reference voltage V _S is applied at one end. Is formed, the first differential amplifier circuit is formed by the third operational amplifier 13 and the resistors 21 and 22, and the second differential amplifier circuit is formed by the fourth operational amplifier 14 and the resistors 23 and 24. The discharge time constant of the capacitor 19 is set to be large by the resistor 20.

Here, assuming that the phototransistor 2 does not face the bar code surface when the power is first turned on, the phototransistor 2 receives ambient ambient light. And the reference voltage circuit
The reference voltage V _S output from 16 is applied to the non-inverting input terminal, the inverting input terminal, and the output terminal of the third operational amplifier 13 via the resistors 20, 21, and 22, and the output terminal serves as the reference voltage V _S. Therefore,
A current flows from the power supply terminal to the output terminal of the third operational amplifier 13, the potential of the inverting input terminal of the first operational amplifier 10 is higher than the reference voltage V _S , and the first operational amplifier 10 outputs the “L” level output voltage. Try to become. Therefore, the current I ₁ flows from the inverting input terminal to the output terminal through the resistor 11, and the potential of the output terminal is set according to this current value. This output voltage is lower than the reference voltage V _S , and the anode of the diode 17 has a reference voltage V _S
Is given, the output of the second operational amplifier 15 becomes “L” level, the diode 17 conducts, the output of the second operational amplifier 15 is integrated by the resistor 18 and the capacitor 19, and the capacitor 9 changes the diode 17 to Charged through the forward direction. Therefore, the non-inverting input terminal the potential difference across only a low voltage of the capacitor 19 than the reference voltage V _S is applied to the third operational amplifier 13, a voltage lower than the reference voltage V _S by the potential difference V _e is outputted to the output terminal, the resistor 12 Increase the current I ₂ flowing through. As a result, the potential at the inverting input terminal of the first operational amplifier 10 drops, the current I ₁ flowing through the resistor 11 decreases, and the output voltage at the output terminal rises to match the reference voltage V _S.

Next, the operation when the amount of light received by the phototransistor 2 is small will be described with reference to FIG.

With the phototransistor 2 facing the bar code surface, a bar code in which a white portion w and a black portion y are alternately arranged is scanned from a white background portion as shown in FIG. 2 (a). Then, when the phototransistor 2 faces the white portion w, the reflected light becomes stronger, and the phototransistor 2 is set to the level p in FIG. 2 (b).
Receive the amount of received light. Then, the impedance of the phototransistor 2 decreases and the flowing current I ₃ increases, and the current I ₁ flowing through the resistor 11 increases to increase the potential of the inverting input terminal of the first operational amplifier 10 and the output voltage of the output terminal increases. Is reduced. The output terminal of the second operational amplifier 15 is "L".
Level, this output is integrated by the capacitor 19, the potential difference across the capacitor 19 increases, and the third operational amplifier 13
A lower output voltage is output to the output terminal of the. As a result, the current I ₂ flowing through the resistor 12 increases, and the first operational amplifier is
While the potential of the inverting input terminal of 10 is maintained, the current I ₁ flowing through the resistor 11 is also maintained constant, and the output voltage of the output terminal does not change and remains at the reference voltage V _S.

Here, when the phototransistor 2 scans the barcode, the amount of received light in the black portion y decreases as shown in FIG. 2 (b),
The impedance of the phototransistor 2 increases. Then, the current I ₃ flowing through the phototransistor 2 decreases as shown in FIG. 2C, and the current I ₁ flowing through the resistor 11 decreases as the potential of the inverting input terminal of the first operational amplifier 10 lowers. Output voltage rises above the reference voltage V _S. Here, the second operational amplifier 15 outputs the "H" level, but the diode 17 prevents the current from flowing into the capacitor 19. Therefore, the holding voltage of the potential difference between both ends of the capacitor 19 is held as it is without changing, and the third operational amplifier 13 is held.
The potential difference V _e between the output voltage and the reference voltage V _S does not change as shown in FIG. 2 (e), and the current I ₂ flowing through the resistor 12 does not change. Therefore, the current I ₁ flowing through the resistor 11 is not maintained constant and decreases. Therefore, the output voltage of the output terminal of the first operational amplifier 10 becomes higher than the reference voltage V _{S as} shown in FIG. Further, when the scanning of the bar code progresses and the amount of light received increases in the white portion w, and the impedance of the phototransistor 2 decreases, the current I ₃ flowing through the phototransistor 2 increases,
The current I ₁ flowing through the resistor 11 increases and the output voltage at the output end drops to the reference voltage V _S. Therefore, a signal having a voltage higher than the reference voltage V _S in the black portion y of the bar code is output to the output terminal of the first operational amplifier 10. Then, the difference voltage between the output voltage of the first operational amplifier 10 and the reference voltage V _S is amplified and output by the fourth operational amplifier 14, and is output to the output terminal 25 as shown in FIG. Only the AC component as in f) is output as a signal.

Further, the operation when the amount of light received by the phototransistor 2 is large will be described with reference to FIG.

When the phototransistor 2 is directed toward the bar code surface in FIG. 3 (a) and receives a large amount of received light of level p'in FIG. 3 (b) at the white portion w, the impedance of the phototransistor 2 is greatly reduced. For this, the current I flowing through the phototransistor 2 _'3 becomes larger as the FIG. 3 (c), the current I potential of the inverting input terminal also flows through the resistor 11 trying rise of the first operational amplifier 10' is also ₁ The output voltage drops greatly as it tries to increase. Therefore, the output terminal of the second operational amplifier 15 becomes "L" level, and the capacitor 19
Of the third operational amplifier 13 increases, the potential difference V _e ′ between the output voltage of the third operational amplifier 13 and the reference voltage V _S increases as shown in FIG. 3 (e), and the output voltage of the third operational amplifier 13 decreases. increasing the current I _'2 that flows through the 12. Then, until the output voltage of the output terminal of the first operational amplifier 10 becomes the reference voltage V _S ,
The potential difference V _e ′ between the output voltage of the operational amplifier 13 and the reference voltage V _S increases, the output voltage of the third operational amplifier 13 decreases, and the current I ′ ₂ increases as shown in FIG. 3 (c). Then, when the phototransistor 2 scans the barcode, the amount of light received in the black portion y decreases, the impedance of the phototransistor 2 increases, and the current I ′ ₃ decreases. Therefore, current I _'1 to the potential of the inverting input terminal of the first operational amplifier 10 through the resistor 11 trying drop decreases, the voltage at the output terminal increases. Here, the potential difference V _e ′ between the output voltage of the third operational amplifier 13 and the reference voltage V _S is blocked by the diode 17 and does not change, and the current I ₁ flowing through the resistor 11 decreases without being maintained constant. As a result, at the output terminal of the first operational amplifier 10, the black portion y of the bar code is output as a high voltage signal with respect to the reference voltage V _{S as} shown in FIG. 3 (d). The differential voltage from the voltage V _S is amplified by the fourth operational amplifier 14 and only the AC component corresponding to the change in the impedance of the phototransistor 2 is output as a signal to the output terminal 25 as shown in FIG. 3 (f). . The voltage of the signal of only the AC component output to the output terminal 25 in the black portion y increases as the amount of light received by the phototransistor 2 increases.

In the above embodiment, the black portion y is based on the impedance of the phototransistor 2 in the white portion w.
Is detected as a signal, but by reversing the direction of the diode 17, the white part w is referenced with the impedance of the phototransistor 2 in the black part y as a reference.
Can be detected as a signal.

FIG. 4 is a circuit diagram of another embodiment of the signal processing device of the present invention. In FIG. 4, the same circuits as those in FIG. 1 are designated by the same reference numerals to omit redundant description.

4 is different from that in FIG. 1 in that the collector of the phototransistor 2 is connected to the inverting input terminal of the first operational amplifier 10, the emitter is grounded, and the output terminal of the second operational amplifier 15 is a diode 17. The cathode of this diode 17 is connected to the anode of
It is connected to the non-inverting input terminal of the operational amplifier 13.

In such a configuration, a current flows from the output end of the third operational amplifier 13 through the resistor 12 to a certain impedance of the phototransistor 2 when the power is turned on, and the potential of the inverting input end of the first operational amplifier 10 is increased. Becomes lower than the reference voltage V _S, an output voltage of “H” level is about to be output to the output terminal of the first operational amplifier 10, and the current I ₁ ″ flowing through the resistor 11
Sets the output voltage. Then, the second operational amplifier 15 outputs "H" level, this output charges the capacitor 19 through the diode 17 in the forward direction, and the third operational amplifier 13 outputs a voltage higher than the reference voltage V _S. . Then, the potential at the inverting input terminal of the first operational amplifier 10 rises,
The current I ₁ ″ flowing through the resistor 11 decreases and the first operational amplifier 10
The output voltage of the output terminal is equal to the reference voltage V _S decreases.

Here, when the phototransistor 2 scans the barcode, the phototransistor 2 receives the strongly reflected light facing the white portion w, the impedance of the phototransistor 2 decreases, and the flowing current I ₃ ″ increases. 1 operational amplifier
The current I ₁ ″ flowing through the resistor 11 increases and the output voltage at the output end rises as the potential at the inverting input end of 10 decreases, and the output end of the second operational amplifier 15 becomes “H” level. The output is integrated by the capacitor 19, the potential difference between both ends of the capacitor 19 increases, and a higher output voltage is output to the output end of the third operational amplifier 13. As a result, the resistance
The current I ₂ ″ flowing through 12 increases, the potential at the inverting input terminal of the first operational amplifier 10 is maintained, and the current I ₁ ″ flowing through the resistor 11 is also maintained constant, and the output voltage at the output terminal changes. Without, it remains at the reference voltage V _S.

When the impedance of the phototransistor 2 increases in the black portion y and the current I ₃ ″ decreases, the current I ₁ ″ flowing through the resistor 11 decreases, and the output voltage at the output end decreases. Then, the second operational amplifier 15 outputs the "L" level, but it is blocked by the diode 17, the potential difference across the capacitor 19 does not change, and the output voltage of the third operational amplifier 13 does not change. As a result, the black portion y of the bar code to the output terminal of the first operational amplifier 10 is output as a low voltage signal to the reference voltage V _S, the voltage difference between the output voltage and the reference voltage V _S is the fourth Only the AC component that is amplified by the operational amplifier 14 and that corresponds to the change in the impedance of the phototransistor 2 is output to the output terminal 25 as a signal.

In the above embodiment shown in FIG. 4, the diode is also used.
By reversing the direction of 17, the white part w can be detected as a signal with the black part y as a reference.

(Effects of the Invention) As described above, according to the signal processing device of the present invention,
A device that uses a low voltage such as a battery as a power source without requiring a large dynamic range because only the AC component corresponding to the change in impedance of the light receiving element is output as a signal regardless of the difference in the amount of light received by the light receiving element. It has an excellent effect that it is suitable for

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a signal processing device of the present invention, FIG. 2 is a diagram for explaining the operation of FIG. 1 when the amount of light received by a phototransistor is small, and FIG. FIG. 4 is a diagram for explaining the operation of FIG. 1 when the amount of light received by the phototransistor is large, FIG. 4 is a circuit diagram of another embodiment of the signal processing device of the present invention, and FIG. FIG. 6 is a circuit diagram of a conventional AC coupling type signal processing device, and FIG. 6 is a diagram for explaining the operation of FIG. 2: Phototransistor, 10: First operational amplifier, 11,12,18,20,21,22,23,24: Resistor, 13: Third operational amplifier, 14: Fourth operational amplifier, 15: Second operational amplifier , 16: reference voltage circuit, 17: diode, 19: capacitor, 25: output terminal, V _S : reference voltage.

Claims (2)

[Claims] 1. A voltage is applied to a light receiving element whose impedance changes according to a change in the amount of received light, a current output of this light receiving element is applied to an input end of a current / voltage conversion circuit, and an output end of this current / voltage conversion circuit. The output voltage output to the voltage holding circuit is applied to the voltage holding circuit via the voltage fluctuation detection circuit that operates in response to voltage fluctuations in one direction, and the holding voltage and the reference voltage held by the voltage holding circuit are fed to the first differential amplifier. A circuit compares the output voltage to the input terminal of the current-voltage conversion circuit via a resistor, and outputs the difference voltage between the output voltage and the reference voltage output to the output terminal of the current-voltage conversion circuit. A signal processing device which outputs a signal processed by an output terminal after being amplified by a second differential amplifier circuit. 2. The current / voltage conversion circuit supplies the current output of the light receiving element to an inverting input terminal of a first operational amplifier, and connects the inverting input terminal to an output terminal via a resistor, and further, non-inverting. The voltage fluctuation detection circuit is formed by applying the reference voltage to the input terminal, and the output voltage of the current-voltage conversion circuit is applied to the non-inverting input terminal of the second operational amplifier, and the output terminal is connected to one end of the diode. Connected, the inverting input terminal is connected to the other end of the diode, and the other end of the diode is formed to output a signal voltage according to the voltage fluctuation.The voltage holding circuit is formed by connecting a capacitor and a resistor in parallel. The parallel connection body is formed by applying a signal voltage output from the voltage fluctuation detection circuit to one end of the parallel connection body and applying the reference voltage to the other end of the parallel connection body to form the first differential amplifier circuit with a third op amp. The non-inverting input of the fourth operational amplifier is formed by applying the holding voltage of the voltage holding circuit to the non-inverting input terminal of the amplifier and the reference voltage to the inverting input terminal. The signal processing device according to claim 1, wherein the signal processing device is formed by applying an output voltage of the current / voltage conversion circuit to an end and applying the reference voltage to an inverting input end.