JPH07113946B2 - 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. Therefore, the current flowing through the light receiving element is a component in which a direct current component due to dark current, disturbance 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 for a large change in DC component, and a device using a low voltage such as a battery as a power source can have a large dynamic range. 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
It is given to the input terminal of the voltage conversion circuit, the output voltage of this current / voltage conversion circuit and the reference voltage are compared by the comparison circuit, and the output is given to the buffer circuit while being held by the voltage holding circuit via the rectification circuit. The output voltage of the buffer circuit is applied to the input terminal of the current / voltage conversion circuit via a resistor, and the differential voltage between the output voltage output to the output terminal of the current / voltage conversion circuit and the reference voltage is differentially amplified. The signal amplified by and processed by the output terminal is output.

(Function) The output voltage of the current / voltage conversion circuit to which the current output of the light receiving element is given is compared with the reference voltage by the comparison circuit, and the output voltage of the buffer circuit is controlled by the output, and the output voltage of this buffer circuit is changed to the resistor. Since it is given to the input terminal of the current / voltage conversion circuit connected to the light receiving element via the light receiving element, if the output voltage of the current / voltage conversion circuit differs from the reference voltage, the current input to the current / voltage conversion circuit by the output voltage of the buffer circuit. By changing the magnitude of the output voltage so that the output voltage becomes the reference voltage.
Then, the output of the comparison circuit is given to the buffer circuit via the rectifier circuit and the output is held by the voltage holding circuit, so the impedance changes due to the change in the amount of light received by the light receiving element, and the output at the output end of the current / voltage conversion circuit. When the voltage changes, if the output of the comparison circuit is the reverse voltage of the rectifier circuit, the output held in the voltage holding circuit is continuously given to the buffer circuit, and the current / voltage conversion is performed according to the impedance change of the light receiving element. The output voltage of the circuit changes. Furthermore, since the differential voltage between the output voltage of this current / voltage conversion circuit and the reference voltage is amplified and output by the differential amplifier circuit, only the AC component corresponding to the impedance change of the light receiving element is output as a signal to the output terminal. It

(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 the signal processing device of the present invention, FIG. 2 is a diagram for explaining the operation when the amount of light received by the phototransistor is small, and FIG.
It is a figure explaining operation | movement when the light-receiving amount of a phototransistor is large.

First, referring to FIG. The configuration will be described. 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 second 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 the third operational terminal
It is connected to the non-inverting input terminal of the operational amplifier 15. The inverting input terminal of the third operational amplifier 15 and the first operational amplifier 10
Reference voltage circuit 16 whose non-inverting input terminal outputs the reference voltage V _S
It is connected to the. Further, the output terminal of the third operational amplifier 15 is connected to the cathode of the diode 17, and the anode of the diode 17 is connected to the second operational amplifier 13 via the resistor 18.
Connected to the non-inverting input of. The non-inverting input terminal of the second 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 output terminal. Furthermore, the fourth operational amplifier 14
The inverting input terminal of is connected to the reference voltage circuit 16 via the resistor 21, and is connected to the output terminal via the resistor 22. Further, the output terminal of the fourth operational amplifier 14 is connected to the output terminal 23.

In such a configuration, the first operational amplifier 10 to which the reference voltage V _S is applied to the non-inverting input terminal and the resistor 11 form a current / voltage conversion circuit, and the second operational amplifier 13 forms a buffer circuit. A comparison circuit is formed by the third operational amplifier 15 to which the output voltage of 10 and the reference voltage V _S are given, and a rectification circuit is formed by the diode 17,
A voltage holding circuit is formed by a parallel connection body of a capacitor 19 and a resistor 20 to which a reference voltage V _S is applied at one end, and a differential amplifier circuit is formed by the fourth operational amplifier 14 and resistors 21 and 22. 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 oppose 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 of the second operational amplifier 13 via the resistor 20, and the output terminal becomes the reference voltage V _S. Therefore, from the power supply terminal to the second operational amplifier 13
A current flows toward the output terminal of the first operational amplifier 10, the potential of the inverting input terminal of the first op-amp 10 is higher than the reference voltage V _S , and the first operational amplifier 10 tries to become the output voltage of the “L” level. And
A current I ₁ flows from the inverting input end to the output end through the resistor 11, and the potential of the output end is set according to the power supply value.
Since this output voltage is lower than the reference voltage V _S , the output of the third operational amplifier 15 becomes the “L” level, the diode 17 becomes conductive, and the output of the third operational amplifier 15 becomes the resistor 18 and the capacitor 19.
And the capacitor 19 is charged through the diode 17 in the forward direction. Therefore, the non-inverting input terminal of the second operational amplifier 13 has a potential difference V _e across the capacitor 19 from the reference voltage V _S.
Given only a low voltage, across the reference voltage V _S voltage difference V _e
A low voltage is output, and the current I ₂ flowing through the resistor 12 is increased. 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 a white background, the reflected light becomes strong, and the phototransistor 2 receives the amount of light received at the level p in FIG. 2B. Then, the impedance of the phototransistor 2 decreases and the flowing current I ₃ increases, so that the potential of the inverting input terminal of the first operational amplifier 10 tries to rise and the resistance is increased.
The current I ₁ flowing through 11 increases and the output voltage at the output end decreases. Then, the output terminal of the third operational amplifier 15 becomes "L" level, this output is integrated by the capacitor 19, the potential difference V _e across the capacitor 19 increases, and the second 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 third operational amplifier 15 outputs the "H" level, but the diode 16 blocks the current to the capacitor 19. Therefore, the potential difference V _e across the capacitor 19 does not change as shown in FIG. 2 (e), the output voltage of the second operational amplifier 13 does not change, 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. 2 (d).
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 the output terminal 23 of FIG. ), Only the AC component 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.

White part w with the phototransistor 2 facing the barcode surface
When the received light amount of the large level p'of FIG. 3 (b) is received, 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 the voltage increases. Therefore, the output terminal of the third operational amplifier 15 becomes "L" level, and the potential difference across the capacitor 19 is generated.
V _e ′ increases as shown in FIG. 3 (e), and the second operational amplifier
13 output voltage drops, and increasing the current I _'2 that flows through the resistor 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 across the capacitor 19 is reached.
As V _e ′ increases, the output voltage of the second operational amplifier 13 decreases and the current I ′ ₂ increases as shown in FIG. 3 (c). Then, the phototransistor 2 Scanning the bar code, increases the impedance of the phototransistor 2 is the amount received by the black portion y is reduced, 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 ′ across the capacitor 19 does not change, and the 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 causes the third voltage with respect to the reference voltage V _S.
As shown in FIG. 3D, the signal is output as a high voltage signal, and the differential voltage between this output voltage and the reference voltage V _S is amplified by the fourth operational amplifier 14 and output to the output terminal 23. As described above, only the AC component corresponding to the change in impedance of the phototransistor 2 is output as a signal. And
The voltage of the signal of only the AC component output to the output terminal 23 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 third 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 terminal of the second 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 terminal 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 third operational amplifier 15 outputs the "H" level, the output is integrated, the capacitor 19 is charged through the diode 17, and the second operational amplifier 13 outputs a voltage higher than the reference voltage V _S. . Then, the potential of the inverting input terminal of the first operational amplifier 10 decreases, the current I ₁ ″ flowing through the resistor 11 also decreases, and the output voltage of the output terminal of the first operational amplifier 10 matches the reference voltage V _S.

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 as the potential of the inverting input terminal of 10 decreases, and the output voltage of the output terminal increases, and the output terminal of the third operational amplifier 15 becomes “H” level. The output is integrated by the capacitor 19 to increase the potential difference V _e across the capacitor 19 and output a higher output voltage to the output terminal of the second operational amplifier 13. As a result, the current I ₂ ″ flowing through the resistor 12 increases. Then, the potential of 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, so that the output voltage of the output terminal does not change and coincides with the reference voltage V _S. It is still done.

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 third operational amplifier 15 outputs the "L" level but is blocked by the diode 17 so that the potential difference V _e ″ across the capacitor 19 does not change and the output voltage of the second operational amplifier 13 does not change. The black portion y of the bar code is output to the output terminal of the first operational amplifier 10 as a signal having a voltage lower than the reference voltage V _S , and the output voltage and the reference voltage V _S
The voltage difference between the output voltage and 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 to the output terminal 23 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 because it does not require a large dynamic range because only the AC component corresponding to the change in the 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 the signal processing device of the present invention, FIG. 2 is a diagram for explaining the operation when the amount of light received by the phototransistor is small, and FIG. 3 is a phototransistor. FIG. 4 is a diagram for explaining the operation when a large amount of light is received, FIG. 4 is a circuit diagram of another embodiment of the signal processing device of the present invention, and FIG. 5 is a conventional AC coupling type signal processing. FIG. 6 is a circuit diagram of the apparatus, and FIG. 6 is a diagram for explaining the operation of FIG. 2: Phototransistor, 10: First operational amplifier, 11,12,18,20,21,22: Resistance, 13: Second operational amplifier, 14: Fourth operational amplifier, 15: Third operational amplifier, 16: Reference Voltage circuit, 17: diode, 19: capacitor, 23: 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, and a current output of the light receiving element is applied to an input terminal of a current / voltage conversion circuit, and an output voltage of the current / voltage conversion circuit. And a reference voltage are compared by a comparison circuit,
The output is supplied to the buffer circuit while being held by the voltage holding circuit via the rectifier circuit, and the output voltage of the buffer circuit is supplied to the input terminal of the current / voltage conversion circuit via a resistor, A signal processing device, wherein a differential voltage between the output voltage and the reference voltage output to an output terminal is amplified by a differential amplifier circuit and a processed signal is output from an output terminal. 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 holding circuit is formed by applying the reference voltage to the input end, the capacitor and the resistor are connected in parallel, one end of the parallel connection body is connected to the input end of the buffer circuit, and the other end is the reference voltage. The signal processing device according to claim 1, wherein the signal processing device is formed by giving