JP2016111623A - Photosensor and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photosensor that prevents chattering.SOLUTION: A photosensor (1) comprises: a current control circuit (CC) that controls an inter-terminal current between first and second terminals (T1 and T2) of a light receiving element (11), depending on a potential at a circuit control terminal; a first current source (CS1) that generates a first current for raising the potential; and a second current source (CS2) that generates a second current for reducing the potential. A photocurrent of the light receiving element raises the potential, and the first current is increased, or alternatively, the second current is decreased, depending on the rise of the inter-terminal voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical sensor.

  In an electric product having an operation part driven by a motor, such as a digital camera and an ink jet printer, a sensor is used to detect an operation speed of the operation part. Such a sensor generally has three types of terminals: a power supply terminal, a sensor output terminal, and a GND terminal. For this reason, it is difficult to reduce the size of the sensor so as to adapt to the downsizing of the electrical product as described above. Further, in order to reduce the manufacturing process of the sensor and improve the yield, a light-saving optical sensor is required. In response to such demands, development of sensors with reduced terminals is underway.

  Patent Document 1 discloses an optical sensor using a two-terminal light-receiving element that detects a signal by changing a potential of the other terminal with respect to a fixed potential of one terminal by changing a circuit current during light input. Has been. In addition, a technique is disclosed in which chattering failure due to the influence of disturbance is suppressed by providing a hysteresis characteristic with the resistance value of an external resistor.

  Patent Document 2 discloses a technique for canceling a direct current component and a noise component included in both photocurrents by using a difference between photocurrents of two optical inputs having different 180 ° phases with respect to the optical sensor. .

  Patent Document 3 describes a comparator including a hysteresis control circuit.

JP2013-080892A (released on May 2, 2013) JP2013-247530A (released on December 9, 2013) JP 2006-229954 A (released August 31, 2006)

  However, the conventional optical sensor has insufficient hysteresis characteristics. Therefore, for example, in an optical sensor to which the technique described in Patent Document 2 is applied, there is a possibility that chattering may occur when the absolute value of the difference between two photocurrents having different phases is small.

  Moreover, the technique described in Patent Document 3 cannot be applied to a light receiving circuit in which a power supply terminal and an output terminal are common.

  The present invention has been made in view of the above problems, and an object thereof is to provide an optical sensor that prevents chattering.

  An optical sensor according to an aspect of the present invention is an optical sensor that includes a light receiving element having a first terminal and a second terminal, and detects a signal by changing a voltage between the first terminal and the second terminal. A current control circuit having a circuit control terminal and switching-controlling an inter-terminal current flowing between the first terminal and the second terminal in accordance with the potential of the circuit control terminal; and the potential of the circuit control terminal A first current source for generating a first current for increasing the voltage and a second current source for generating a second current for decreasing the potential of the circuit control terminal, and increases in response to light input to the light receiving element. The photocurrent increases the potential of the circuit control terminal, and the first current increases or the second current decreases as the voltage between the terminals increases.

  According to one embodiment of the present invention, chattering in detection by an optical sensor can be prevented.

It is a circuit diagram which shows the structure of the optical sensor which concerns on Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the optical sensor which concerns on Embodiment 2 of this invention. It is a circuit diagram which shows the structure of the optical sensor which concerns on Embodiment 3 of this invention. It is a circuit diagram which shows the structure of the optical sensor which concerns on Embodiment 4 of this invention. 7 is a graph showing the amplification factor with respect to the input current of the current mirror circuit when the driving voltage is low, where (a) is a case where the input side transistor size is different from the output side transistor size, and (b) is an input side transistor. It is a graph when the size and the transistor size on the output side are the same. (A) is a graph which shows the hysteresis characteristic of the conventional optical sensor, (b) is a graph which shows the hysteresis characteristic of the optical sensor which concerns on one Embodiment of this invention. (A) is a front view which shows the structure of the optical encoder using the optical sensor which concerns on one Embodiment of this invention, (b) is side perspective drawing which shows the structure of the said optical encoder. It is a figure which shows arrangement | positioning of the photodiode in case the optical sensor of FIG. 1 is used for the optical encoder of FIG. (A) is the waveform of the photocurrent of two photodiodes in the photosensor of FIG. 1, and (b) is the waveform showing the waveform of the current obtained by the difference between the two amplified photocurrents shown in (a). FIG. It is a graph which shows the electric current and output of the optical sensor which concern on Embodiment 2 of this invention.

Embodiment 1
Embodiment 1 according to the present invention will be described below with reference to FIGS. 1, 7, 8, and 9.

  FIG. 1 is a circuit diagram showing a configuration of an optical sensor 1 according to this embodiment. FIG. 7A is a front view showing a configuration of an optical encoder 101 using the optical sensor 1 according to the present embodiment. FIG. 7B is a side view showing the configuration of the optical encoder 101. FIG. 8 is a diagram showing the arrangement of photodiodes when the optical sensor 1 is used in the optical encoder 101. FIG. 9A is a waveform diagram showing waveforms of photocurrents of two photodiodes in the optical sensor 1. FIG. 9B is a waveform diagram showing a current waveform obtained by the difference between the amplified currents of the two photocurrents shown in FIG.

<Configuration of optical encoder>
As shown in FIG. 7A, the incremental optical encoder 101 includes a code wheel 102 that is a disk-like rotating body as a moving body, and a sensor body 103.

  The code wheel 102 has a substantially disk shape as a whole. A rotating shaft 104 is attached to the center of the code wheel 102. The code wheel 102 rotates in the direction of arrow S about the rotation shaft 104.

<Configuration of code wheel>
A plurality of slits 105 are formed in the code wheel 102 along the periphery. The slit 105 is formed so as to penetrate both sides of the code wheel 102 so that light can pass therethrough. A light blocking portion 106 that blocks light is formed between two slits 105 adjacent in the circumferential direction. Thereby, the plurality of slits 105 are arranged in a row in the circumferential direction with the light shielding portion 106 interposed therebetween. Therefore, the slits 105 and the light shielding portions 106 are alternately and continuously arranged in the moving direction (rotating direction) of the code wheel 102.

  Each slit 105 is formed so that the dimension (hereinafter referred to as “width dimension”) in the moving direction (direction of arrow S) of the code wheel 102 is equal. In addition, each light shielding portion 106 is formed so that the above width dimensions are equal. In addition, each slit 105 and each light shielding portion 106 are formed to have the same width dimension.

  One index pattern 107 that transmits light is formed at a predetermined reference position at the peripheral edge of the code wheel 102. This index pattern 107 is arranged inside the row of slits 105. The index pattern 107 is formed so that the width dimension is smaller than the width dimension of the slit 105 and the light shielding part 106.

<Configuration of sensor body>
As shown in FIG. 7B, the sensor body 103 has facing portions 103a and 103b formed so as to face each other with the outer peripheral portion of the code wheel 102 therebetween. A code wheel passage space is formed between the facing portions 103a and 103b.

  A light emitting unit 108 is disposed in the facing unit 103b. A light receiving portion 109 is disposed in the facing portion 103a. The light emitting unit 108 includes a light emitting element and a drive circuit that drives the light emitting element. The light emitting unit 108 is arranged such that the light emitting element emits light toward the code wheel 102.

  The light receiving unit 109 includes an optical sensor. The optical sensor includes a photoelectric conversion element that receives light from the light emitting element and outputs a photocurrent, and outputs a detection signal based on the output current from the photoelectric conversion element. The light receiving unit 109 is disposed so that the photoelectric conversion element can receive light from the light emitting element. Here, the light receiving unit 109 has two photoelectric conversion elements.

<Operation of optical encoder>
In the optical encoder 101 configured as described above, when the code wheel 102 rotates in the direction indicated by the arrow S, the light emitted from the light emitting unit 108 passes through the slit 105 and the index pattern 107. When the light receiving unit 109 receives the light, a periodic pulse signal or a reference pulse signal is generated as a detection signal based on the photocurrent flowing through the photoelectric conversion element.

  The periodic pulse signal is a signal generated when light passes through the slit 105. By counting the pulse width of the periodic pulse signal, the rotation angle and rotation speed of the code wheel 102 can be obtained. On the other hand, the reference pulse signal is an origin detection signal generated when light passes through the index pattern 107.

<Configuration of optical sensor>
As shown in FIG. 1, the optical sensor 1 includes a light receiving element 11 and an external resistor R. This optical sensor 1 is used as the light receiving portion 109 of the sensor body 103 in the optical encoder 101 shown in FIGS. 7A and 7B.

  One end of the external resistor R is connected to a terminal T1 provided on the light receiving element 11 described later. The other end of the external resistor R is connected to a power supply line to which the power supply voltage Vcc is applied.

<Configuration of light receiving element>
The light receiving element 11 includes photodiodes PDA + and PDA−, resistors R1 and R2, transistors Tr1 to Tr4 (MOSFET: metal oxide field effect transistor), a first current mirror circuit CM1, a second current mirror circuit CM2, and a third. Current mirror circuit CM3, first current source CS1, and second current source CS2.

  The light receiving element 11 is a two-terminal light receiving element having a terminal T1 (first terminal) and a terminal T2 (second terminal). The terminal T2 is connected to GND. The light receiving element 11 changes the potential of the terminal T1 with respect to the fixed potential (GND potential) of the terminal T2 by changing the circuit current during light input, and outputs a detection signal. The optical sensor 1 detects this detection signal and detects the presence or absence of light input to the light receiving element 11. In the present embodiment, the detection signal is regarded as a high level if the potential of the terminal T1 is higher than a threshold potential, and is regarded as a low level if it is lower than the potential.

  Note that the potential of the terminal T2 may be changed with the potential of the terminal T1 as a fixed potential. In this case, the external resistor R is connected between the terminal T2 and GND.

  The photodiode PDA + is a photoelectric conversion element that receives input light and flows a photocurrent Ipa +. The photodiode PDA− is a photoelectric conversion element that receives input light and flows a photocurrent Ipa−. The anodes of these photodiodes PDA + and PDA− are grounded.

  As shown in FIG. 8, the arrangement pitch of the photodiode PDA + and the photodiode PDA− is half of the arrangement pitch of the plurality of slits 105. In other words, when light from the light emitting unit 108 passes through the slit 105 and is irradiated (input) to one photodiode PDA +, the light from the light emitting unit 108 is shielded by the light shielding unit 106 and irradiated to the other photodiode PDA−. Not. The reverse is also true. Therefore, when the code wheel 102 is rotating, the phases of the photocurrent Ipa + and the photocurrent Ipa− are shifted by 180 ° as shown in FIG.

  The first current mirror circuit CM1 has a pair of p-type transistors Tr11 and Tr12 (MOSFET: metal oxide film field effect transistor). The gate terminal of the transistor Tr11 is connected to the gate terminal of the transistor Tr12. The transistor Tr11 on the input side as a current mirror circuit has a drain terminal connected to the cathode of the photodiode PDA + and the gate terminal of the transistor Tr11, and a source terminal connected to the terminal T1. The transistor Tr12 on the output side as a current mirror circuit has a drain terminal connected to one end of the resistor R1 and the gate terminal (circuit control terminal) of the transistor Tr1, and a source terminal connected to the terminal T1.

  The second current mirror circuit CM2 has a pair of p-type transistors Tr21 and Tr22 (MOSFET). The gate terminal of the transistor Tr21 is connected to the gate terminal of the transistor Tr22. The transistor Tr21 on the input side as a current mirror circuit has a drain terminal connected to the cathode of the photodiode PDA- and the gate terminal of the transistor Tr21, and a source terminal connected to the terminal T1. The source terminal of the transistor Tr22 on the output side as a current mirror circuit is connected to the terminal T1.

  The third current mirror circuit CM3 has an n-type set of transistors Tr31 and Tr32 (MOSFET). The gate terminal of the transistor Tr31 is connected to the gate terminal of the transistor Tr32. The transistor Tr31 on the input side as a current mirror circuit has a drain terminal connected to the drain terminal of the transistor Tr22 and the gate terminal of the transistor Tr31, and a source terminal connected to the terminal T2. The transistor Tr32 on the output side as a current mirror circuit has a drain terminal connected to the drain terminal of the transistor Tr12 and a source terminal connected to the terminal T2.

  As is apparent from the above description, one end of the resistor R1 is connected to the drain terminal of the transistor Tr12. The other end of the resistor R1 and the source terminal of the n-type transistor Tr1 are connected to the terminal T2. The drain terminal of the transistor Tr1 is connected to the drain terminal of the p-type transistor Tr2 and the gate terminal of the n-type transistor Tr3. The transistor Tr2 has a source terminal connected to the terminal T1, and a gate terminal (circuit control terminal) connected to the gate terminal of the transistor Tr1. The transistors Tr1 and Tr2 are thus connected to form an inverter.

  The transistor Tr3 has a source terminal connected to the terminal T2, and a drain terminal connected to the source terminal of the n-type transistor Tr4. The transistor Tr4 has a drain terminal connected to the terminal T1, and a gate terminal connected to the gate terminal of the transistor Tr3 and one end of the resistor R2. The other end of the resistor R2 is connected to the terminal T1.

  The transistors Tr1 to Tr4 and the resistor R2 constitute a current control circuit CC (current control unit). The gate terminals (control terminals) of the transistors Tr1 and Tr2 function as control terminals (circuit control terminals) of the current control circuit CC. The current control circuit CC performs switching control of a current (current between terminals) flowing between the terminals T1 and T2 (current paths of the transistors Tr3 and Tr4) according to the potential of the control terminal.

  The first current source CS1 generates a first current I1 that increases as the voltage between the terminals T1 and T2 increases (that is, as the potential of the terminal T1 increases). The first current source CS1 has one end connected to the terminal T1 and the other end connected to one end of the resistor R1 and the gate terminal of the transistor Tr1. The first current I1 flows from the terminal T1 to one end of the resistor R1.

  The second current source CS2 generates a second current I2 that decreases as the voltage between the terminals T1 and T2 increases (that is, as the potential of the terminal T1 increases). The second current source CS2 has one end connected to one end of the resistor R1 and the gate terminal of the transistor Tr1, and the other end connected to the terminal T2. The second current I2 flows from one end of the resistor R1 into the terminal T2.

<Operation of optical sensor>
When the photodiode PDA + receives light, a photocurrent Ipa + flows through the photodiode PDA +. The photocurrent Ipa + is amplified by the first current mirror circuit CM1 (current amplification circuit), and is output from the output transistor Tr12 as the current IA +.

  On the other hand, when the photodiode PDA− receives light, a photocurrent Ipa− flows through the photodiode PDA−. The photocurrent Ipa− is amplified by the second current mirror circuit CM2 (current amplification circuit) and flows to the input side transistor Tr31 of the third current mirror circuit CM3 (current amplification circuit). As a result, the current IA− is output from the output side transistor Tr32 of the third current mirror circuit CM3.

  At this time, a part of the current IA + flows through the transistor Tr32 of the third current mirror circuit CM3 as the current IA-. That is, the output current IA− of the third current mirror circuit CM3 is subtracted from the output current IA + of the first current mirror circuit CM1.

  The amplification factor of the first current mirror circuit CM1 and the amplification factor of the second current mirror circuit CM2 are equal, for example, 20 times. On the other hand, the amplification factor of the third current mirror circuit CM3 is one. With this configuration, the amplification factor of the current IA + with respect to the photocurrent Ipa + is equal to the amplification factor of the current IA− with respect to the photocurrent Ipa−. In addition, since the transistors Tr31 and Tr32 constituting the third current mirror circuit CM3 are symmetric, the variation in the amplification factor in the third current mirror circuit CM3 due to the input current can be reduced. For the variation of the current mirror circuit due to the input current, see also Embodiment 4 described later.

  As shown in FIG. 9A, the photocurrents Ipa + and Ipa− include a direct current component due to the wraparound of light in the optical encoder 101 when the optical sensor 1 is mounted on the optical encoder 101. .

  The image of the light transmission region received by the optical sensor 1 (the light receiving unit 109) varies depending on the positional relationship between the light emitting unit 108 and the slit 105 and the index pattern 107 in the rotating code wheel 102. To do. When this fluctuation is received by the photodiodes PDA + and PDA− as a light sneak component, it appears as a direct current component in the photocurrents Ipa + and Ipa−.

  When the code wheel 102 is rotating, the currents IA + and IA− have waveforms similar to the waveforms of the photocurrents Ipa + and Ipa− shown in FIG. The currents IA + and IA− include DC components derived from DC components appearing in the photocurrents Ipa + and Ipa−, respectively. However, the current obtained by subtracting the current IA− from the current IA + becomes a current IA in which the DC component included in each output current is canceled as shown in FIG.

  The first current I1 merges with the current IA and flows into the resistor R1. On the other hand, the second current I2 branches from the current IA and flows to the second current source CS2. That is, the current IR1 obtained by adding the first current I1 to the current IA and subtracting the second current I2 flows through the resistor R1.

  When the current IR1 flows through the resistor R1, a potential difference is generated between both ends of the resistor R1. For this reason, the gate voltage (input voltage of the inverter) of the transistors Tr1 and Tr2 with respect to GND varies. The gate voltage is determined by the magnitude of the current IR1 flowing through the resistor R1. The resistance value of the resistor R1 is set so that the gate voltage exceeds the threshold voltage of the inverter when the current IR1 becomes equal to or greater than a certain value ITH.

  When the current value of the current IR1 exceeds ITH (when the gate voltage of the transistor Tr1 exceeds the threshold voltage), the transistor Tr1 is turned on. As a result, the transistors Tr3 and Tr4 are turned off, so that the current flowing between the terminals T1 and T2 via the current control circuit CC is reduced (eliminated). Therefore, since the current flowing through the external resistor R becomes small, the voltage drop from the power supply voltage Vcc by the external resistor R becomes small. Therefore, the potential of the terminal T1 rises and the voltage between the terminals T1 and T2 (2 terminals) rises.

  On the other hand, when the current value of the current IR1 falls below ITH (when the gate voltage of the transistor Tr1 falls below the threshold voltage), the transistor Tr1 is turned off. As a result, the transistors Tr3 and Tr4 are turned on, and the current flowing between the terminals T1 and T2 via the current control circuit CC increases. Therefore, since the current flowing through the external resistor R increases, the voltage drop from the power supply voltage Vcc due to the external resistor R increases. Therefore, the potential of the terminal T1 decreases, and the voltage between the two terminals decreases.

  The transistor Tr2 is turned on only during this transition period in order to increase the speed at which the transistor Tr1 is turned off and the transistors Tr3 and Tr4 are turned on.

  Thus, the voltage between the two terminals rises and falls according to the off / on of the transistors Tr3 and Tr4. Therefore, when the photodiode PDA + has an optical input (when Ipa + and IA + are large), the output voltage appearing at the terminal T1 becomes a high level voltage. When there is no light input to the photodiode PDA + (when Ipa + and IA + are small), the output voltage appearing at the terminal T1 becomes a low level voltage (but higher than GND). The optical sensor 1 can determine the presence or absence of light input to the photodiode PDA + by detecting the voltage at the terminal T1.

  For example, the first current source CS1 generates the first current I1 when the output voltage appearing at the terminal T1 is a high level voltage, and does not generate the first current I1 when the output voltage is a low level voltage. It can be said that the first current I1 of the first current source CS1 increases as the voltage between the terminals T1 and T2 increases.

  The second current source CS2 generates the second current I2 when the output voltage appearing at the terminal T1 is the low level voltage, and does not generate the second current I2 when the output voltage is the high level voltage. It can be said that the second current I2 of the second current source CS2 decreases as the voltage between the terminals T1 and T2 increases.

  With this configuration, the output voltage appearing at the terminal T1 has hysteresis characteristics.

  The second current I2 flowing out from one end (upper end) of the resistor R1 serves to reduce the current flowing through the resistor R1. Therefore, the second current I2 works to lower the potential of the control terminal of the current control circuit CC (the gate terminals of the transistors Tr1 and Tr2). That is, when the output voltage appearing at the terminal T1 shifts from the low level voltage to the high level voltage, the current IA needs to rise to a value obtained by adding the current value of the second current I2 to ITH.

  The first current I1 flowing into one end (upper end) of the resistor R1 serves to increase the current flowing through the resistor R1. Therefore, the first current I1 works to increase the potential of the control terminal of the current control circuit CC. That is, when the output voltage appearing at the terminal T1 shifts from the high level voltage to the low level voltage, the current IA needs to be reduced to a value obtained by subtracting the current value of the first current I1 from ITH.

  The current IA flowing into one end (upper end side) of the resistor R1 works to increase the current flowing through the resistor R1. Therefore, the current IA works to increase the potential of the control terminal of the current control circuit CC. Further, the current IA increases as the photocurrent Ipa + increases, and the photocurrent Ipa + increases according to the light input to the photodiode PDA + of the light receiving element 11. That is, it can be said that the photocurrent Ipa + that increases in response to the light input to the light receiving element 11 raises the potential of the control terminal of the current control circuit CC.

  The first current source CS1 does not generate the first current I1 after the output voltage appearing at the terminal T1 shifts from the high level voltage to the low level voltage. If the first current I1 continues to be generated after the output voltage appearing at the terminal T1 has shifted from the high level voltage to the low level voltage, the current IA required to shift the output voltage from the low level voltage to the high level voltage again. The value is reduced by the current value of the first current I1. That is, the hysteresis characteristic of the output voltage appearing at the terminal T1 decreases or disappears, and chattering is likely to occur.

  Similarly, the second current source CS2 does not generate the second current I2 after the output voltage appearing at the terminal T1 shifts from the low level voltage to the high level voltage. If the second current I2 continues to be generated after the output voltage appearing at the terminal T1 has shifted from the low level voltage to the high level voltage, the current IA required to shift the output voltage from the high level voltage to the low level voltage again. This is because the value is increased by the current value of the second current I2.

  Not limited to this, the first current source CS1 may increase the first current I1 in accordance with the increase in the output voltage appearing at the terminal T1, as described above. Further, the second current source CS2 may decrease the second current I2 in accordance with an increase in output voltage appearing at the terminal T1. When the output voltage appearing at the terminal T1 is a high level voltage, the first current I1 is configured to be larger than the second current I2. On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage, the second current I2 is configured to be larger than the first current I1.

  Further, one of the first current I1 and the second current I2 may have a constant current value regardless of the inter-terminal voltage. For example, when the current value of the first current I1 is constant and the output voltage appearing at the terminal T1 is a high level voltage, the second current I2 is controlled to be smaller than the first current I1, and the output voltage appearing at the terminal T1 is When the voltage is a low level voltage, the second current I2 may be controlled to be larger than the first current I1. Conversely, when the current value of the second current I2 is constant and the output voltage appearing at the terminal T1 is a high level voltage, the first current I1 is controlled to be larger than the second current I2, and the output voltage appearing at the terminal T1 is controlled. When is a low level voltage, the first current I1 may be controlled to be smaller than the second current I2. As I1 and I2 ≧ 0, the component (I1-I2) that does not originate in the photocurrent out of the current flowing through the resistor R1 is negative when the output voltage appearing at the terminal T1 is a low level voltage, and the output voltage appearing at the terminal T1 It may be positive when is a high level voltage.

<Preventing a drop in response speed>
As described above, the transistors Tr1 and Tr2 constitute an inverter, so that the transistor Tr3 can perform a switching operation at a high speed. However, when the potential difference between the two terminals of the light receiving element 11 falls, the current decreases between the gate and drain of the transistor Tr2 because the potential difference gradually decreases after the transistor Tr3 performs the switching operation. For this reason, the response speed of the light receiving element 11 gradually decreases.

  Therefore, in order to avoid such inconvenience, the light receiving element 11 is provided with a resistor R2. As a result, the drop in the potential difference between the two terminals is assisted by the resistor R2, so that it is possible to prevent the response speed from being lowered.

  By the way, if each transistor in the detection signal generation unit of the light receiving element 11 is configured by a MOSFET, the operation threshold level of the transistor can be changed by adjusting the dose. For example, the operation threshold level of a transistor (a transistor Tr3 in the light receiving element 11) that generates a current to generate a potential difference between two terminals is set lower than 0.7V. This is because a device that receives the detection signal of the optical sensor 1 normally provides a threshold level at 0.7 V, which is a diode voltage.

  Thereby, the potential difference between the two terminals can be further increased. Therefore, the operating range of the light receiving element 11 can be expanded.

<Reduction of leakage current>
When a transistor with a low threshold level is used in the light receiving element 11, there is a concern that a leakage current is generated when the transistor Tr3 is turned off at a high temperature. When such a leak current occurs, there is a disadvantage that the potential difference between the two terminals decreases when the potential difference between the two terminals increases.

  Therefore, a transistor Tr4 that is cascade-connected to the transistor Tr3 is provided so as to avoid such an inconvenience. As a result, when the drain voltage of the transistor Tr3 is lowered, it is possible to reduce the off-state leakage current to 1/10 or more. Therefore, the leakage current when the transistor Tr3 is off can be greatly reduced. In particular, since the transistor Tr3 that performs the switching operation needs to be formed in a large size in order to flow a large current, the leak current tends to increase accordingly. Accordingly, it is possible to suppress a decrease in the potential difference between the two terminals when the potential difference between the two terminals increases.

  By the way, the transistor Tr1 may malfunction if a variation in the temperature characteristic of the threshold level is large. This is because the threshold level of the MOSFET decreases at a high temperature. On the other hand, if the resistance used for the current-voltage change is, for example, a diffused resistor, the resistance value increases at a high temperature, resulting in a large temperature characteristic in sensitivity.

  Therefore, the light receiving element 11 is composed of a resistor (for example, a polysilicon resistor) having a negative temperature characteristic in the resistor R1 (bias resistor) so as to avoid such inconvenience. As a result, it is possible to cancel the temperature characteristics of the transistor Tr1 that is a MOSFET and the temperature characteristics of the resistor R1. Therefore, fluctuations in temperature characteristics of the light receiving element 11 can be suppressed.

<Modification of circuit configuration>
Note that an optical sensor using a light receiving element in which one or both of the resistor R2 and the transistor Tr4 is omitted is also included in the technical scope of the present invention. In addition, an optical sensor using a light receiving element in which the photodiode PDA−, the second current mirror circuit CM2, and the third current mirror circuit CM3 are omitted is also included in the technical scope of the present invention. Alternatively, the transistor Tr1 may be omitted and a resistor connected instead, or the transistor Tr2 may simply be omitted. Further, instead of the first current mirror circuit CM1, a current amplifier circuit that amplifies the photocurrent Ipa + with a predetermined amplification factor and outputs the current IA + can be used. Similarly, instead of the second current mirror circuit CM2 and the third current mirror circuit CM3, a current amplifier circuit that amplifies the photocurrent Ipa− with a predetermined amplification factor and outputs the current IA− can be used. . Also, a diode (impedance element) connected in the forward direction with respect to the current IA can be used instead of the resistor R1 (resistance element, impedance element).

[Embodiment 2]
A second embodiment according to the present invention will be described with reference to FIGS. For convenience of explanation, members having the same functions as those described in the above embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of optical sensor>
FIG. 2 is a circuit diagram showing a configuration of the optical sensor 2 according to the present embodiment. As shown in FIG. 2, the optical sensor 2 includes a light receiving element 12 and an external resistor R. Similarly to the optical sensor 1 shown in FIG. 1, this optical sensor 2 is also used as the light receiving portion 109 of the sensor body 103 in the optical encoder 101 shown in FIGS. 7A and 7B. it can.

<Configuration of light receiving element>
Similar to the light receiving element 11 described above, the light receiving element 12 includes photodiodes PDA + and PDA−, resistors R1 and R2, transistors Tr1 to Tr4 (MOSFET), a first current mirror circuit CM1, a second current mirror circuit CM2, and a second current mirror circuit CM2. 3 current mirror circuit CM3, first current source CS1, and second current source CS2. The first current source CS1 includes a resistor R4 and a fifth current mirror circuit CM5. The second current source CS2 includes a resistor R3, a transistor Tr5, a fourth current mirror circuit CM4, and a sixth current mirror circuit CM6.

  The fourth current mirror circuit CM4 has a pair of p-type transistors Tr41 and Tr42 (MOSFET). The gate terminal of the transistor Tr41 is connected to the gate terminal of the transistor Tr42. The transistor Tr41 on the input side as a current mirror circuit has a drain terminal connected to the gate terminal of the transistor Tr41 and a source terminal connected to the terminal T1. The output-side transistor Tr42 as a current mirror circuit has a source terminal connected to the terminal T1. The threshold voltages of the transistors Tr41 and Tr42 are set to be lower than the threshold voltage of the transistor Tr3.

  The fifth current mirror circuit CM5 has a pair of p-type transistors Tr51 and Tr52 (MOSFET). The gate terminal of the transistor Tr51 is connected to the gate terminal of the transistor Tr52. The transistor Tr51 on the input side as a current mirror circuit has a drain terminal connected to the gate terminal of the transistor Tr51 and a source terminal connected to the terminal T1. The transistor Tr52 on the output side as a current mirror circuit has a drain terminal connected to one end of the resistor R1, and a source terminal connected to the terminal T1. The threshold voltages of the transistors Tr51 and Tr52 are set to be equal to or higher than the threshold voltage of the transistor Tr3.

  The sixth current mirror circuit CM6 has a set of n-type transistors Tr61 and Tr62 (MOSFET). The gate terminal of the transistor Tr61 is connected to the gate terminal of the transistor Tr62. The input-side transistor Tr61 as a current mirror circuit has a drain terminal connected to the gate terminal of the transistor Tr61 and the drain terminal of the transistor Tr42, and a source terminal connected to the terminal T2. The transistor Tr62 on the output side as a current mirror circuit has a drain terminal connected to one end of the resistor R1, and a source terminal connected to the terminal T2. The threshold voltages of the transistors Tr61 and Tr62 are set to be lower than the threshold voltage of the transistor Tr3.

  One end of the resistor R3 is connected to the drain terminal of the transistor Tr41. The other end of the resistor R3 is connected to the terminal T2. One end of the resistor R4 is connected to the drain terminal of the transistor Tr51. The other end of the resistor R4 is connected to the terminal T2.

  The n-type transistor Tr5 has a drain terminal connected to the gate terminal of the transistor Tr62, a source terminal connected to the terminal T2, and a gate terminal connected to one end of the resistor R1. The threshold voltage at which the transistor Tr5 is turned on is the same as the threshold voltage at which the transistor Tr1 is turned on.

<Operation of optical sensor>
Since the operation for detecting light is the same as that in the first embodiment, a description thereof will be omitted. Below, operation | movement of 1st current source CS1 and 2nd current source CS2 in this embodiment is demonstrated.

  First, when the output voltage appearing at the terminal T1 is a low level voltage, the first current source CS1 does not generate the first current I1. The fifth current mirror circuit CM5 is turned off when the output voltage appearing at the terminal T1 is a low level voltage, and therefore does not output the first current I1.

  On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage, the second current source CS2 generates the second current I2. The fourth current mirror circuit CM4 is turned on even when the output voltage appearing at the terminal T1 is a low level voltage, and outputs a current. The current output from the fourth current mirror circuit CM4 is input to the sixth current mirror circuit CM6. The transistor Tr5 is turned off when the output voltage appearing at the terminal T1 is at a low level (when the current IR1 is less than ITH). For this reason, the sixth current mirror circuit CM6 is turned on and outputs a second current I2 that flows from one end (upper end) of the resistor R1 to the terminal T2.

  Next, when the output voltage appearing at the terminal T1 is a high level voltage, the first current source CS1 generates the first current I1. The fifth current mirror circuit CM5 is turned on when the output voltage appearing at the terminal T1 is a high level voltage, and outputs a first current I1 flowing from the terminal T1 to one end (upper end) of the resistor R1.

  On the other hand, when the output voltage appearing at the terminal T1 is a high level voltage, the second current source CS2 does not generate the second current I2. The transistor Tr41 of the fourth current mirror circuit CM4 is turned on when the output voltage appearing at the terminal T1 is a high level voltage. The current output from the fourth current mirror circuit CM4 is input to the sixth current mirror circuit CM6. However, the transistor Tr5 is turned on when the output voltage appearing at the terminal T1 is a high level voltage (when the current IR1 is greater than ITH). For this reason, the transistor Tr62 is turned off. Therefore, the sixth current mirror circuit CM6 does not output the second current I2.

  With this configuration, the output voltage appearing at the terminal T1 has the same hysteresis characteristic as that described in the first embodiment. The second current I2 flowing out from one end (upper end) of the resistor R1 decreases the current flowing through the resistor R1, that is, lowers the potential of the control terminal of the current control circuit CC (the gate terminals of the transistors Tr1 and Tr2). Work like that. The first current I1 flowing into one end (upper end) of the resistor R1 works to increase the current flowing through the resistor R1, that is, to increase the potential of the control terminal of the current control circuit CC.

  The current values of the first current I1 and the second current I2 are the amplification factor of the fourth current mirror circuit CM4, the fifth current mirror circuit CM5, and the sixth current mirror circuit CM6, and the resistance values of the resistors R3 and R4. It can be changed appropriately by setting. However, the resistor R1 is grounded by being connected to the terminal T2, and no negative current is generated. Therefore, it is preferable to make the current value of the first current I1 larger than the current value of the second current I2.

  FIG. 10 is a diagram illustrating the current IR1 flowing through the resistor R1 and the output voltage appearing at the terminal T1 in the optical sensor 2. The horizontal axis indicates time. When the current value of the current IR1 exceeds ITH, the output voltage appearing at the terminal T1 changes from the low level voltage (L) to the high level voltage (H), and when it falls below ITH, the output voltage appearing at the terminal T1 becomes the high level voltage. It changes from (H) to low level voltage (L). As shown in FIG. 10, when the output voltage appearing at the terminal T1 is a high level voltage (H), the current IR1 flowing through the resistor R1 is obtained by adding the current value of the first current I1 to the current IA. On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage (L), the current IR1 flowing through the resistor R1 is obtained by subtracting the second current I2 from the current IA. “Hysteresis” in the figure matches the value of I1 + I2. However, as described above, since no negative current is generated in the resistor R1, the current IR1 does not become less than zero.

The pulse duty ratio between the high level and the low level of the output voltage appearing at the terminal T1 is determined by the magnitudes of the first current I1, the second current I2, and ITH. For example, when the following expression is satisfied, the pulse duty ratio is 50%.
ITH = (I1-I2) / 2
Note that the fourth current mirror circuit CM4 and the fifth current mirror circuit CM5 are preferably composed of transistors having the same structure. Here, the same structure means that the structures of the gate, the drain, and the source are the same. At this time, it can be said that the first current source CS1 and the second current source CS2 include switching elements having the same structure.

  With this configuration, the characteristics of the corresponding transistors constituting these circuits change in a similar manner with respect to process variations or temperature changes.

  In the above-described embodiment, an example in which the first current source CS1 and the second current source CS2 include transistors (MOSFETs) having the same structure has been described. However, in implementing the present invention, not only a transistor but also any switching element can be used.

[Embodiment 3]
A third embodiment according to the present invention will be described with reference to FIG. For convenience of explanation, members having the same functions as those described in the above embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of optical sensor>
FIG. 3 is a circuit diagram showing a configuration of the optical sensor 3 according to the present embodiment. As shown in FIG. 3, the optical sensor 3 includes a light receiving element 13 and an external resistor R. Similarly to the optical sensor 1 shown in FIG. 1, the optical sensor 3 is also used as the light receiving unit 109 of the sensor body 103 in the optical encoder 101 shown in FIGS. 7A and 7B. it can.

<Configuration of light receiving element>
As with the light receiving element 11 described above, the light receiving element 13 includes photodiodes PDA + and PDA−, resistors R1 and R2, transistors Tr1 to Tr4 (MOSFET), a first current mirror circuit CM1, a second current mirror circuit CM2, and a second current mirror circuit CM2. 3 current mirror circuit CM3, first current source CS1, and second current source CS2. The first current source CS1 includes a resistor R4 and a fifth current mirror circuit CM5. In the present embodiment, the second current source CS2 includes a transistor Tr6, a fourth current mirror circuit CM4, and a sixth current mirror circuit CM6.

  The n-type transistor Tr6 has a gate terminal connected to the gate terminal of the transistor Tr3, a drain terminal connected to the drain terminal of the transistor Tr41 on the input side of the fourth current mirror circuit CM4, and a source terminal connected to the terminal T2. ing. Further, the threshold voltage at which the transistor Tr6 is turned on is the same as the threshold voltage at which the transistor Tr3 is turned on.

  The current control circuit CC (current control unit) includes a transistor Tr3 (first switching element) provided on a path of an inter-terminal current that flows between the terminal T1 and the terminal T2. The second current source CS2 includes a transistor Tr6 (second switching element) that controls the second current I2. It can be said that the gate terminal (first control terminal) of the transistor Tr3 and the gate terminal (second control terminal) of the transistor Tr6 are connected. That is, the transistor Tr3 and the transistor Tr6 are mirror-connected.

  Note that a resistor may be provided between the drain terminal of the transistor Tr41 and the drain terminal of the transistor Tr6.

<Operation of optical sensor>
Since the operation for detecting light is the same as that in the first embodiment, a description thereof will be omitted. Below, operation | movement of 1st current source CS1 and 2nd current source CS2 in this embodiment is demonstrated.

  First, when the output voltage appearing at the terminal T1 is a low level voltage, the first current source CS1 does not generate the first current I1. The fifth current mirror circuit CM5 is turned off when the output voltage appearing at the terminal T1 is a low level voltage, and therefore does not output the first current I1.

  On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage, the second current source CS2 generates the second current I2. The transistor Tr3 of the current control circuit CC is turned on when the output voltage appearing at the terminal T1 is a low level voltage, and generates an inter-terminal current. At this time, the transistor Tr6 is similarly turned on. Therefore, the fourth current mirror circuit CM4 and the sixth current mirror circuit CM6 are turned on. The current output from the fourth current mirror circuit CM4 is input to the sixth current mirror circuit CM6. The sixth current mirror circuit CM6 to which a current is input from the fourth current mirror circuit CM4 outputs a second current I2 that flows from one end (upper end) of the resistor R1 to the terminal T2.

  Next, when the output voltage appearing at the terminal T1 is a high level voltage, the first current source CS1 generates the first current I1. The fifth current mirror circuit CM5 is turned on when the output voltage appearing at the terminal T1 is a high level voltage, and outputs a first current I1 flowing from the terminal T1 to one end (upper end) of the resistor R1.

  On the other hand, when the output voltage appearing at the terminal T1 is a high level voltage, the second current source CS2 does not generate the second current I2. The transistor Tr3 of the current control circuit CC is turned off when the output voltage appearing at the terminal T1 is a high level voltage. At this time, the transistor Tr6 is similarly turned off. Therefore, the fourth current mirror circuit CM4 is turned off. Therefore, the sixth current mirror circuit CM6 does not output the second current I2.

  With this configuration, the output voltage appearing at the terminal T1 has the same hysteresis characteristic as that described in the first embodiment. The second current I2 flowing out from one end (upper end) of the resistor R1 decreases the current flowing through the resistor R1, that is, lowers the potential of the control terminal of the current control circuit CC (the gate terminals of the transistors Tr1 and Tr2). Work like that. The first current I1 flowing into one end (upper end) of the resistor R1 works to increase the current flowing through the resistor R1, that is, to increase the potential of the control terminal of the current control circuit CC.

  The second current source CS2 in this embodiment includes a transistor Tr6 whose gate terminal is connected to the gate terminal of the transistor Tr3 and whose source terminal is connected to the terminal T2 similarly to the source terminal of the transistor Tr3. The low level voltage of the terminal T1 (output detection A) is determined by the current flowing through the transistor Tr3. In the optical sensor 3, the second current I2 is controlled by the transistor Tr6 mirror-connected to the transistor Tr3. As a result, the second current I2 can be controlled in synchronization with the switching control of the transistor Tr3 without being affected by variations in the characteristics (manufacturing process) of the characteristics of the transistors Tr1, Tr2, and the like. Therefore, the hysteresis characteristic can be stabilized.

  In addition, when switching control of the 2nd electric current I2, the structure controlled using the switching element which carries out switching control of the electric current between the terminals of the current control circuit CC can be considered. For example, in the light receiving element 13 shown in FIG. 3, the transistor Tr6 is omitted, and the drain terminal of the transistor Tr41 is connected to the drain terminal of the transistor Tr3. With this configuration, when the output voltage appearing at the terminal T1 is a high-level voltage, the second current I2 is controlled to be off like the inter-terminal current. On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage, the second current I2 is on-controlled in the same manner as the inter-terminal current.

  In the above embodiment, the switching element provided on the current path between the terminals in the current control circuit CC and the switching element that controls the switching of the second current in the second current source CS2 are respectively transistors (MOSFETs). An example is shown. However, in implementing the present invention, not only a transistor but also any switching element can be used.

[Embodiment 4]
Embodiment 4 which concerns on this invention is demonstrated based on FIG.4, FIG.5 and FIG.6. For convenience of explanation, members having the same functions as those described in the above embodiment are denoted by the same reference numerals and description thereof is omitted.

<Configuration of optical sensor>
FIG. 4 is a circuit diagram showing a configuration of the optical sensor 4 according to the present embodiment. FIG. 5A is a graph showing the amplification factor with respect to the input current when the drive voltage is low when the input-side transistor size and the output-side transistor size are different in the current mirror circuit. As shown in FIG. 4, the optical sensor 4 includes a light receiving element 14 and an external resistor R. This optical sensor 4 is also used as the light receiving portion 109 of the sensor body 103 in the optical encoder 101 shown in FIGS. 7A and 7B, similarly to the optical sensor 1 shown in FIG.

<Configuration of light receiving element>
As with the light receiving element 11 described above, the light receiving element 14 includes photodiodes PDA + and PDA−, resistors R1 and R2, transistors Tr1 to Tr4 (MOSFET), a first current mirror circuit CM1, a second current mirror circuit CM2, and a second current mirror circuit CM2. 3 current mirror circuit CM3, first current source CS1, and second current source CS2. The first current source CS1 includes a resistor R4 and an eighth current mirror circuit CM8. The second current source CS2 includes a transistor Tr6 and a seventh current mirror circuit CM7.

  The seventh current mirror circuit CM7 has a pair of p-type transistors Tr71 and Tr72 (MOSFET). The gate terminal of the transistor Tr71 is connected to the gate terminal of the transistor Tr72. The input side transistor Tr71 as a current mirror circuit has a drain terminal connected to the gate terminal of the transistor Tr71 and a source terminal connected to the terminal T1. The transistor Tr72 on the output side as a current mirror circuit has a source terminal connected to the terminal T1 and a drain terminal connected to the cathode of the photodiode PDA +. The threshold voltages of the transistors Tr71 and Tr72 are set to be lower than the threshold voltage of the transistor Tr3.

  The eighth current mirror circuit CM8 has a set of n-type transistors Tr81 and Tr82 (MOSFET). The gate terminal of the transistor Tr81 is connected to the gate terminal of the transistor Tr82. The transistor Tr81 on the input side as a current mirror circuit has a drain terminal connected to the gate terminal of the transistor Tr81 and a source terminal connected to the terminal T2. The transistor Tr82 on the output side as a current mirror circuit has a source terminal connected to the terminal T2 and a drain terminal connected to the cathode of the photodiode PDA +. The threshold voltages of the transistors Tr81 and Tr82 are set higher than the threshold voltage of the transistor Tr3.

  That is, it can be said that the second current source CS2 includes a circuit that generates the second current I2 with the voltage between the terminals T1 and T2 lower than the threshold voltage at which the first current source CS1 generates the first current I1. .

  Note that a resistor may be provided between the drain terminal of the transistor Tr71 and the drain terminal of the transistor Tr6.

<Operation of optical sensor>
Since the operation for detecting light is the same as that in the first embodiment, a description thereof will be omitted. Below, operation | movement of 1st current source CS1 and 2nd current source CS2 in this embodiment is demonstrated.

  First, when the output voltage appearing at the terminal T1 is a low level voltage, the first current source CS1 does not generate the first current I1. The eighth current mirror circuit CM8 is turned off when the output voltage appearing at the terminal T1 is a low level voltage, and therefore does not output the first current I1.

  On the other hand, when the output voltage appearing at the terminal T1 is a low level voltage, the second current source CS2 generates the second current I2. The transistor Tr3 is turned on when the output voltage appearing at the terminal T1 is a low level voltage, and generates an inter-terminal current. At this time, the transistor Tr6 is similarly turned on. Therefore, the seventh current mirror circuit CM7 is turned on and outputs a second current I2 that flows into the cathode side of the photodiode PDA +.

  Next, when the output voltage appearing at the terminal T1 is a high level voltage, the first current source CS1 generates the first current I1. The eighth current mirror circuit CM8 is turned on when the output voltage appearing at the terminal T1 is a high level voltage, and outputs the first current I1 flowing out from the cathode side of the photodiode PDA +.

  On the other hand, when the output voltage appearing at the terminal T1 is a high level voltage, the second current source CS2 does not generate the second current I2. The transistor Tr3 is turned off when the output voltage appearing at the terminal T1 is a low level voltage. At this time, the transistor Tr6 is similarly turned off. Therefore, the seventh current mirror circuit CM7 is turned off. Therefore, the seventh current mirror circuit CM7 does not output the second current I2.

  With this configuration, the output voltage appearing at the terminal T1 has the same hysteresis characteristic as that described in the first embodiment. The second current I2 flowing into the cathode side of the photodiode PDA + reduces the current flowing through the transistor Tr11. Therefore, the second current I2 works to decrease the current flowing through the transistor Tr12 and the resistor R1, that is, to lower the potential of the control terminal of the current control circuit CC (the gate terminals of the transistors Tr1 and Tr2). Further, the first current I1 flowing out from the cathode side of the photodiode PDA + increases the current flowing through the transistor Tr11. Therefore, the first current I1 works to increase the current flowing through the transistor Tr12 and the resistor R1, that is, to increase the potential of the control terminal of the current control circuit CC.

  When the optical sensor is used as an optical encoder, the pulse duty ratio by turning on / off the light is often used at 50%. In this case, the hysteresis characteristic of the output voltage appearing at the terminal T1 with respect to the change in the current IA is that the output voltage appearing at the terminal T1 shifts from the low level voltage to the high level voltage and the high voltage shifts from the high level voltage to the low level voltage. It is desirable that they are equivalent. That is, it is desirable that the magnitude of the first current I1 when the output voltage appearing at the terminal T1 is a high level voltage is equal to the magnitude of the second current I2 when it is a low level voltage.

  In the current mirror circuit, when the drive voltage (drain-source voltage) is low, the amplification factor may vary depending on the input current. Since the first current mirror circuit CM1 needs to amplify a minute photocurrent Ipa +, it preferably has an amplification factor of 10 times or more. However, when the amplification factor is large, the influence due to the variation of the amplification factor depending on the input current is also large.

  FIG. 5B is a graph showing the amplification factor with respect to the input current when the drive voltage is low when the input-side transistor size and the output-side transistor size are the same in the current mirror circuit. As shown in FIG. 5B, when the transistor size on the input side and the transistor size on the output side of the current mirror circuit are the same, the variation in the amplification factor is small. The transistor size means (channel width W) / (channel length L). However, in actual use, in order to reduce the chip size, the two transistors of the current mirror circuit are set to different transistor sizes. As shown in FIG. 5A, when the transistor size on the input side is different from the transistor size on the output side, the variation in the amplification factor becomes large.

  When the output voltage appearing at the terminal T1 is a low level voltage, the first current mirror circuit CM1 is operated with a low driving voltage. At this time, the first current I1 is not generated and the second current I2 is generated. When the second current I2 flows into the cathode side of the photodiode PDA +, the first current mirror circuit CM1 amplifies the difference ((Ipa +) − I2) between the photocurrent Ipa + and the second current I2 with an amplification factor α. . That is, the photocurrent Ipa + and the second current I2 can be amplified with the same amplification factor α. As a result, it is possible to suppress variations in the value of the photocurrent Ipa +, which is a threshold for switching by the current control circuit CC, due to fluctuations in the amplification factor. Therefore, variation in the hysteresis characteristic of the output voltage appearing at the terminal T1 can be suppressed.

The first current I1 generated when the output voltage appearing at the terminal T1 is a high level voltage is amplified by the first current mirror circuit CM1 together with the photocurrent Ipa +. When the amplification factor of the first current mirror circuit CM1 is α, the output current of the first current mirror circuit CM1 is α ((Ipa +) − I2 + I1). Thus, the current IR1 flowing through the resistor R1 is as follows.
IR1 = α ((Ipa +) − I2 + I1) − (IA−)
The product of the amplification factor of the second current mirror circuit CM2 and the amplification factor of the third current mirror circuit CM3 is also set to α. (IA −) = α (Ipa−). Therefore, the photocurrent Ipa + and the first current I1 work to increase the voltage between the terminals T1 and T2. On the other hand, the photocurrent Ipa− and the second current I2 work to lower the voltage between the terminals.

  FIG. 6A is a graph showing the hysteresis characteristic of the output voltage of the conventional photosensor. FIG. 6B is a graph showing hysteresis characteristics of the output voltage of the photosensor 4 according to the present embodiment. The left vertical axis represents the output voltage appearing at the terminal T1, and the right vertical axis (downward) represents two amplified photocurrents. The horizontal axis shows the amplified photocurrent Ipa +. Here, for simplicity, the graph is drawn with amplified Ipa− as a reference (constant).

  As shown in FIG. 6 (a), the conventional photosensor has an output appearing at the terminal T1 in a region where the amplified photocurrent IA + is larger than the amplified photocurrent IA− (a region to the right of 5.0 mA). The voltage does not have hysteresis characteristics.

  On the other hand, as shown in FIG. 6B, the photosensor 4 according to the present embodiment has the amplified photocurrent α · Ipa + greater than or equal to the amplified photocurrent α · Ipa−. The output voltage appearing at the terminal T1 has hysteresis characteristics. Then, the hysteresis on the positive side of the difference in photocurrent ((Ipa +) − (Ipa−)) and the hysteresis on the negative side in the difference of photocurrent can be made comparable.

[Modification]
In any of the above-described embodiments, an example in which one optical sensor includes one light receiving element has been described. However, one optical sensor may include two light receiving elements. For example, the photodiodes are arranged so that the phase is shifted by 90 ° between the photocurrent of the photodiode of the first light receiving element and the photocurrent of the second photodiode. The light receiving element A includes two photodiodes PDA + and PDA−, and the light receiving element B includes two photodiodes PDB + and PDB−. The light receiving element A and the light receiving element B have respective output terminals (corresponding to the terminal T1). The light receiving element A and the light receiving element B can have the same configuration. Four photodiodes PDA +, PDB +, PDA−, and PDB− are arranged in this order along the moving direction of the slit of the code wheel. Thereby, the optical sensor can determine the rotation direction of the code wheel by detecting which light receiving element has the phase of the photocurrent advanced. Further, one optical sensor may include three or more light receiving elements. The optical sensor requires a plurality of terminals (corresponding to the terminal T1) for supplying power to each light receiving element and detecting the output of each light receiving element, and a terminal for supplying a reference potential (GND) to each light receiving element. To do. That is, the number of terminals required by the optical sensor is obtained by adding 1 to the number of light receiving elements included in the optical sensor.

  Note that the optical sensor according to one embodiment of the present invention can be applied not only to a rotary encoder but also to a linear encoder. The optical sensor according to one embodiment of the present invention can be used as a sensor such as a smoke sensor, a proximity sensor, or a distance measuring sensor.

  The optical encoder including the optical sensor according to one embodiment of the present invention can be applied to an electronic device including a movable part that can rotate or translate, for example. The optical encoder detects the rotation or movement of the movable part. Examples of the electronic device including such an optical encoder include a digital camera, a multifunction device, a printer, a portable device, and a stepping motor.

[Summary]
An optical sensor according to aspect 1 of the present invention includes a light receiving element (11 to 14) having a first terminal (terminal T1) and a second terminal (terminal T2), and is provided between the first terminal and the second terminal. An optical sensor for detecting a signal by changing a voltage between terminals, having a circuit control terminal (gate terminals of the transistors Tr1 and Tr2), and depending on the potential of the circuit control terminal, a first terminal, a second terminal, A current control circuit (CC) that performs switching control of the current between terminals flowing between the first current source (CS1) that generates a first current (I1) that raises the potential of the circuit control terminal, and the circuit control terminal A second current source (CS2) that generates a second current (I2) that lowers the potential of the light receiving element, and a photocurrent (Ipa +) that increases in response to light input to the light receiving element is a potential of the circuit control terminal. To increase the voltage across the terminals Correspondingly, the first current is increased, or the second current decreases.

  According to said structure, the said voltage between terminals becomes a low level or a high level according to the presence or absence of the said current between terminals. When the inter-terminal voltage is at a high level, the potential of the circuit control terminal is raised by the first current. Therefore, the threshold value of the photocurrent necessary for shifting to the low level is lowered. On the other hand, when the voltage between the terminals is at a low level, the potential of the circuit control terminal is lowered by the second current. Therefore, the threshold value of the photocurrent necessary for shifting to the high level becomes high. Thereby, a large hysteresis characteristic can be given to the voltage change between the terminals with respect to the optical input. Therefore, chattering in the detection of the optical sensor can be prevented.

  In the optical sensor according to aspect 2 of the present invention, in the aspect 1, the first current increases as the inter-terminal voltage increases, and the second current decreases as the inter-terminal voltage increases. May be.

  The first current lowers the threshold of the photocurrent necessary for shifting the inter-terminal voltage to a high level or a low level. On the other hand, the second current increases the threshold of the photocurrent necessary for shifting the inter-terminal voltage to a high level or a low level. According to said structure, the width | variety of the hysteresis of a photocurrent can be enlarged regarding the transition to any state.

  Note that the first current and the second current may change stepwise as the voltage between the terminals increases. For example, the first current may be generated only when the inter-terminal voltage is at a high level, and the second current may be generated only when the inter-terminal voltage is at a low level.

  In the optical sensor according to aspect 3 of the present invention, in the above aspect 1 or 2, the second current source generates the second current at the terminal voltage lower than the threshold voltage at which the first current source generates the first current. It may be a configuration.

  According to the above configuration, since the threshold voltages of the first current source and the second current source are different, for example, when the inter-terminal voltage is at a low level, the first current source does not generate the first current, The two current sources can generate a second current.

  In the optical sensor according to aspect 4 of the present invention, in the above aspects 1 to 3, the first current source and the second current source may each include a transistor having the same structure.

  According to said structure, the characteristic of each transistor of a 1st current source and a 2nd current source changes similarly with respect to the dispersion | variation in the characteristic by a manufacturing process, or a temperature change, for example. Therefore, the fluctuations of the first current and the second current can be made comparable. Therefore, the hysteresis at the time of shifting the inter-terminal voltage to a high level or a low level can be made comparable. Thereby, for example, when the optical input changes in a sin cycle, the duty ratio of the output of the optical sensor can be stabilized (for example, the high level ratio in the inter-terminal voltage is set to 50%).

  In the optical sensor according to aspect 5 of the present invention, in the aspect 2, the magnitude of the first current when the inter-terminal voltage is at a high level and the magnitude of the second current when the inter-terminal voltage is at a low level. An equal configuration may be used.

  According to said structure, the hysteresis at the time of shifting the said inter-terminal voltage to a high level or a low level can be made comparable. Thereby, for example, when the optical input changes in a sin cycle, the ratio of the high level in the inter-terminal voltage can be set to 50%.

  In the optical sensor according to aspect 6 of the present invention, in the above aspects 1 to 5, the current control circuit includes a first switching element (transistor Tr3) provided on the path of the current between the terminals, and the second current source is , The second switching element (transistor Tr6) for controlling the second current, the first control terminal of the first switching element (the gate terminal of the transistor Tr3) is the second control terminal of the second switching element (the gate of the transistor Tr6) Terminal) may be connected.

  According to said structure, it can be said that the 1st switching element and the 2nd switching element are mirror-connected. Since the first switching element and the second switching element can be controlled by the same potential, the switching control of the current between the terminals by the first switching element and the switching control of the second current by the second switching element are synchronized. be able to. Therefore, it is possible to stabilize the hysteresis characteristics against variations in voltage at the control terminals (first control terminal and second control terminal) due to the manufacturing process.

  An optical sensor according to aspect 7 of the present invention may include a current amplification circuit (first current mirror circuit CM1) that amplifies the difference between the photocurrent and the second current in the above aspects 1 to 6. Good.

  According to the above configuration, the photocurrent and the second current are amplified with the same amplification factor. Thereby, the dispersion | variation in the value of the photocurrent used as the threshold value which a current control circuit switches due to the fluctuation | variation of the amplification factor of a current amplifier circuit can be suppressed. The output current of the current amplifier circuit works to increase the voltage between the terminals.

  An optical sensor according to an aspect 8 of the present invention is an optical sensor that includes a light receiving element having a first terminal and a second terminal, and detects a signal by changing a voltage between the first terminal and the second terminal. A current control circuit having a circuit control terminal (the gate terminals of the transistors Tr1 and Tr2) and switching-controlling the inter-terminal current flowing between the first terminal and the second terminal in accordance with the potential of the circuit control terminal. (CC), an impedance element (resistor R1) connected between the second terminal and the circuit control terminal and receiving a current that increases in response to light input to the light receiving element, and an increase in the voltage between the terminals. A first current source (CS1) that generates a first current (I1) that increases in response to the current flowing in the impedance element, and decreases in response to an increase in the inter-terminal voltage, and flows in the impedance element. A second current source for generating a second current (I2) to reduce and a (CS2).

  The impedance element may be a resistance element or a diode.

  An electronic device according to an aspect 9 of the present invention includes the optical sensor according to any one of the above aspects 1 to 8.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  The present invention can be used for an optical sensor or an electronic device including the optical sensor.

1 to 4 Optical sensors 11 to 14 Light receiving elements 101 Optical encoder 102 Code wheel 103 Sensor body 105 Slit CC Current control circuits CM1 to CM8 First to eighth current mirror circuits CS1 First current source CS2 Second current source

Claims (5)

An optical sensor comprising a light receiving element having a first terminal and a second terminal, and detecting a signal by varying a voltage between terminals between the first terminal and the second terminal,
A current control circuit that has a circuit control terminal and performs switching control of an inter-terminal current flowing between the first terminal and the second terminal according to the potential of the circuit control terminal;
A first current source for generating a first current for raising the potential of the circuit control terminal;
A second current source for generating a second current for lowering the potential of the circuit control terminal,
The photocurrent that increases in response to light input to the light receiving element raises the potential of the circuit control terminal,
The optical sensor according to claim 1, wherein the first current increases or the second current decreases as the voltage between the terminals increases.   2. The optical sensor according to claim 1, wherein the magnitude of the first current when the inter-terminal voltage is high is equal to the magnitude of the second current when the inter-terminal voltage is low. The current control circuit includes a first switching element provided on a path of the current between the terminals,
The second current source includes a second switching element that controls the second current,
The optical sensor according to claim 1, wherein the first control terminal of the first switching element is connected to the second control terminal of the second switching element.   The optical sensor according to claim 1, further comprising a current amplification circuit that amplifies a difference between the photocurrent and the second current.   An electronic apparatus comprising the optical sensor according to claim 1.

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