JP2008180522A - Photoelectric encoder and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive photoelectric encoder having excellent operation accuracy and little characteristic dispersion, even when a light receiving quantity is fluctuated. <P>SOLUTION: Since a negative feedback circuit 12 negatively feeds back a DC output of a differential amplifier 7 to the input side of diodes 5, 6 forming a logarithm compression section, this photoelectric encoder can reduce a DC offset of a light receiving signal based on a fluctuating light receiving signal itself. Hereby, the DC offset can be reduced surely even if dispersion of an optical system or dispersion of a circuit system exists. A feedback current is added from the negative feedback circuit 12 to a signal acquired by amplifying a light receiving signal output from photodiodes 1, 2 by amplifiers 3, 4 and input into the diodes 5, 6. Hereby, since the impedance of the diodes 5, 6 is lowered, the offset can be reduced, even when a coupling capacity is small especially at a low-speed operation time or the like and removal of an AC signal in the negative feedback circuit 12 is insufficient. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric encoder and an electronic device, and as an example, relates to a photoelectric encoder that detects a moving amount, a moving speed, a moving direction, and the like of a moving body using a light receiving element, and in particular, a printing device such as a copying machine or a printer. The present invention relates to a photoelectric encoder suitable for use in factory automation (FA) equipment.

  Conventionally, a light receiving circuit of a photoelectric encoder has been proposed in which the light receiving current output from the light receiving element is amplified and then logarithmically compressed, thereby suppressing the light amount dependency of the output signal (Patent Document 1 (Japanese Patent Laid-Open No. 2003-86227)). 2006-294682)).

  The photoelectric encoder includes a moving body 801 as shown by a solid line in FIG. 8 as an optical system and photodiodes 501 and 502 as light receiving elements. The moving body 801 has a transmission part 803 that transmits light from a light emitting element (not shown) and a non-transmission part 802 that does not transmit light, and the transmission part 803 and the non-transmission part 802 are arranged in a line. It can be moved. As the moving body 801 moves, the transmissive portions 803 and the non-transmissive portions 802 are alternately opposed to the photodiodes 501 and 502, and the light from the light emitting element is incident on the photodiodes 501 and 502. A state in which light from the light emitting element is not incident appears alternately in a cycle corresponding to the moving speed.

  As shown in FIG. 7A, the light receiving circuit of this photoelectric encoder receives light 510 and 520 by photodiodes 501 and 502, and amplifies the received light signals output from the photodiodes 501 and 502 by differential amplifiers 503 and 504. The diodes are compressed by the diodes 505 and 506. By this diode compression (logarithmic compression), the output amplitude can be ensured even when the amount of received light decreases or the SN ratio decreases. The signals that are diode-compressed by the diodes 505 and 506 are amplified by the differential amplifier 507, converted into a digital signal by the AD converter 513, and output. Here, as shown in FIG. 7B, if the two output signal waveforms 700A and 700B of the differential amplifier 507 are in an ideal state that is 180 degrees out of phase, the non-inverted output signal waveform 700A and the inverted phase The 50% duty can be maintained at the cross point with the output signal waveform 700B, and the AD converter 513 can obtain an ideal digital signal with a 50% duty.

  However, when the cross point of the non-inverted phase output signal waveform 700A and the inverted phase output signal waveform 700B is deviated as shown in FIG. The ratio gets worse. In addition, when the cross point between the non-inverted phase output signal waveform 700A and the inverted phase output signal waveform 700B is completely eliminated, the digital signal cannot be obtained at all, and the subsequent circuit connected to the encoder output operates. It will disappear.

  Therefore, in this conventional example, the peak value (maximum value) and the barrier value (minimum value) of the sine wave obtained from the received light signal are read, and the peak value and the barrier value are compared with the DC (direct current) voltage. It is disclosed that a DC offset value is obtained to cancel the offset of a received light signal (see Patent Document 2 (Japanese Patent Laid-Open No. 2004-317262)).

  Furthermore, in another conventional example, there is disclosed an offset cancel circuit of a differential amplifier that cancels a DC offset by negatively feeding back the DC output of the differential amplifier to the input side (Japanese Patent Laid-Open No. 58-111415). No.))). Furthermore, another conventional example discloses that a DC bias voltage is appropriately set by a current adjustment resistor that limits a current flowing through a light emitting diode (Japanese Patent Laid-Open No. 8-68666). )reference).

  By the way, for example, when the photoelectric encoder is used in an ink jet printer or the like, if the moving body is contaminated by ink mist or the like, the amount of received light decreases, the SN ratio decreases, and the operation accuracy deteriorates.

  On the other hand, in the photoelectric encoder described in Patent Document 1 described above, the light receiving current is amplified and logarithmically compressed to improve (suppress) the light quantity dependency. However, the amplification of the signal processing circuit unit is performed by the amplification. As a result, there is a problem that variation of characteristics increases and variation in characteristics increases.

  In the photoelectric encoder described in Patent Document 2, the DC voltage that is a reference for obtaining the DC offset of the received light signal varies depending on variations in the light receiving circuit, temperature characteristics, and the like. It is difficult to obtain a correlation between the fluctuation of the DC voltage and the SN variation of the received light signal by the optical system because the parameters that cause the difference are different.

  In the offset cancel circuit of the differential amplifier described in Patent Document 3 described above, the DC output of the differential amplifier is negatively fed back to the input side. However, in order to feed back only the DC component, an HPF (High Pass Filter) is used. The capacitance (capacitor) constant needs to be significantly increased. This results in an expensive circuit due to the capacitor.

Further, as described in the above-mentioned Patent Document 4, when the DC offset is removed by appropriately setting the DC bias voltage with the current adjusting resistor, the cost is increased due to the trimming process of the resistor, the circuit area increase, etc. Invite.
JP 2006-294682 A JP 2004-317262 A JP 58-11114 A JP-A-8-68666

  SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive photoelectric encoder that is excellent in operation accuracy even when the amount of received light varies and has little characteristic variation.

In order to solve the above problems, a photoelectric encoder of the present invention includes a light emitting element,
A plurality of light receiving elements arranged in one direction in a region where light from the light emitting element can reach,
A light-on portion that makes the light incident on the light receiving element when passing through a predetermined position corresponding to the light receiving element and the light when passing through a predetermined position corresponding to the light receiving element A photoelectric encoder that has a light-off portion that is not incident on the light source and detects the movement of the moving body in which the light-on portion and the light-off portion alternately pass the predetermined position when moving in the one direction. And
A logarithmic compression unit that logarithmically compresses a light reception signal output by the light receiving element with a diode and outputs a logarithm compression signal;
A differential amplifier to which the logarithmic compression signal is input from the logarithmic compression unit;
A negative feedback circuit connected between the output side of the differential amplifier and the input side of the logarithmic compression unit and negatively feeding back the DC output of the differential amplifier to the input side of the logarithmic compression unit It is characterized by.

  According to the photoelectric encoder of the present invention, the received light signal is input to the differential amplifier via the logarithmic compression unit, and the DC output of the differential amplifier is negatively fed back to the input side of the logarithmic compression unit by the negative feedback circuit. . Thereby, the DC offset of the received light signal can be reduced on the input side of the logarithmic compression unit.

  According to this invention, since the negative feedback circuit negatively feeds back the DC output of the differential amplifier to the input side of the logarithmic compression unit, the DC offset of the received light signal can be reduced based on the fluctuating received light signal itself, The DC offset can be reliably reduced even if there are variations in optical systems and circuit systems. Further, according to the present invention, the feedback current is added to the light receiving signal output from the light receiving element and input to the logarithmic compression unit, thereby reducing the impedance of the diode of the logarithmic compression unit. Even when the amount of received light is reduced when it is not sufficient, the offset can be reduced. In addition, by logarithmically compressing the received light signal with the diode, the dynamic range of signal processing for the received light signal can be widened, so that it can be used under various optical conditions.

  Therefore, according to the present invention, it is possible to realize a photoelectric encoder that is excellent in operation accuracy even when the amount of received light varies, and that is less expensive and less characteristic variation.

  The photoelectric encoder according to an embodiment includes a light reception signal amplifier that amplifies a light reception signal output from the light receiving element and outputs the amplified light reception signal to the logarithmic compression unit, and sets an amplification factor of the negative feedback circuit to that of the light reception signal amplifier. It was smaller than the amplification factor.

  According to this embodiment, the negative feedback circuit negatively feeds back the DC output of the differential amplifier to the input side of the logarithmic compression unit, but the signal input from the negative feedback circuit to the logarithmic compression unit is logarithmically compressed from the light receiving signal amplifier. It can be made smaller than the signal input to the unit. As a result, when the AC (alternating current) signal cannot be completely cut by the negative feedback circuit during low-speed operation, the output signal waveform of the differential amplifier can be prevented from being distorted. Can be prevented from disappearing.

  In the photoelectric encoder according to an embodiment, the current source of the light receiving signal amplifier and the current source of the negative feedback circuit are configured by the same current source.

  According to this embodiment, for example, by using a current mirror circuit or the like to share a current source between the light receiving signal amplifier and the negative feedback circuit, the characteristics of the negative feedback circuit vary depending on the power supply voltage and temperature. It becomes possible to prevent this.

  In one embodiment of the photoelectric encoder, the negative feedback circuit has two input portions connected by a coupling capacitor, and the two input portions include a Darlington connection.

  According to this embodiment, the input current in the negative feedback circuit can be reduced by a factor of the current amplification factor (hfe) by the Darlington connection of the input unit, and the DC offset increases by the presence of the negative feedback circuit. Can be prevented. Also, by connecting the Darlington connection part of the two input parts with a coupling capacitor, it is possible to introduce a capacitor at a location with high impedance, lower the cut-off frequency, attenuation of output amplitude due to feedback of AC component, waveform distortion Can be prevented. That is, by connecting a coupling capacitor to the Darlington connection portion, it is possible to obtain an effect of preventing the output amplitude from being attenuated and the waveform distortion by a factor of a current amplification factor (hfe).

  Further, in the electronic apparatus according to an embodiment, the provision of the photoelectric encoder enables cancellation of a DC offset in the optical system and the circuit system, and improves characteristics when SN is lowered.

  According to the photoelectric encoder of the present invention, since the negative feedback circuit negatively feeds back the DC output of the differential amplifier to the input side of the logarithmic compression unit, the DC offset of the received light signal is reduced based on the changing received light signal itself. Therefore, the DC offset can be surely reduced even if there are variations in the optical system and in the circuit system. Further, according to the present invention, the feedback current is added to the light receiving signal output from the light receiving element and input to the logarithmic compression unit, thereby reducing the impedance of the diode of the logarithmic compression unit. Even when the amount of received light decreases when it is not sufficient, the offset can be reduced. Further, by logarithmically compressing the received light signal with the diode, the dynamic range of signal processing for the received light signal can be widened, which is useful because it can be used under various optical conditions. Therefore, according to the present invention, it is possible to realize an inexpensive photoelectric encoder that has excellent operation accuracy even when the amount of received light varies, and has little characteristic variation.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 shows a circuit configuration of a first embodiment of the photoelectric encoder according to the present invention. The configuration of the optical system of the photoelectric encoder according to the first embodiment is the same as the configuration of the conventional example shown by the solid line in FIG.

  As shown in FIG. 1, in the first embodiment, photodiodes 1 and 2 as light receiving elements that receive signal lights 10 and 20 that have passed through a moving body from light emitting elements (not shown), Light receiving signal amplifiers 3 and 4 connected to the photodiodes 1 and 2, and diodes 5 and 6 as logarithmic compression units connected to the amplifiers 3 and 4. Further, the first embodiment includes a differential amplifier 7, a diode 5 is connected to the non-inverting input terminal of the differential amplifier 7, and a diode 6 is connected to the inverting input terminal of the differential amplifier 7. The differential amplifier 7 is connected to the AD converter 13.

  Further, the first embodiment is connected between the input side of the diodes 5 and 6 forming the logarithmic compression section and the output side of the amplifiers 3 and 4, and the DC output of the differential amplifier 7 is connected to the diodes 5 and 6 Is provided with a negative feedback circuit 12 for negative feedback on the input side. The negative feedback circuit 12 includes a differential amplifier 8, and an inverting input terminal of the differential amplifier 8 is connected to a first output line L 1 connected to a first output terminal of the differential amplifier 7. The non-inverting input terminal of the differential amplifier 8 is connected to a second output line L 2 connected to the second output terminal of the differential amplifier 7.

  The non-inverting output terminal of the differential amplifier 8 is connected to the connection line between the amplifier 3 and the diode 5, and the non-inverting output terminal of the differential amplifier 8 is connected to the connection line between the amplifier 4 and the diode 6. . A coupling capacitor 11 is connected between the first output terminal and the second output terminal of the differential amplifier 8.

  Since the basic operation of the photoelectric encoder of this embodiment is the same as that of the conventional example shown in FIGS. 8 and 7A, the description thereof will be omitted and the operation of the negative feedback circuit 12 will be mainly described.

  According to this embodiment, since the negative feedback circuit 12 negatively feeds back the DC output of the differential amplifier 7 to the input side of the diodes 5 and 6 forming the logarithmic compression unit, based on the fluctuating received light signal itself, DC offset can be reduced. Therefore, according to this embodiment, it is possible to reliably reduce the DC offset even if there are variations in the optical system and variations in the circuit system. In this embodiment, the diode 5 that forms a logarithmic compression section by adding a feedback current from the negative feedback circuit 12 to the signal obtained by amplifying the light reception signal output from the photodiodes 1 and 2 as the light receiving elements by the amplifiers 3 and 4. , 6. As a result, the impedances of the diodes 5 and 6 in the logarithmic compression section are lowered, so that the offset can be reduced even when the coupling capacitance is small and the removal of the AC signal in the negative feedback circuit 12 is not sufficient particularly during low-speed operation. It becomes. That is, when the capacity of the coupling capacitor 11 is not sufficient, the negative feedback circuit 12 serves as an attenuator (signal attenuator). As described above, when the moving body operates at a low speed, although the AC signal removal in the negative feedback circuit 12 is not sufficient as compared with the case where the moving body operates at a high speed, the amplification factor of the received light signal decreases, so that the received light signal is reduced. The DC offset can be improved.

  Further, in this embodiment, the logarithm compression of the light reception signal by the diodes 5 and 6 can widen the dynamic range of signal processing for the light reception signal, so that it can be used under various optical conditions.

  In this embodiment, the cutoff frequency by the coupling capacitor 11 that the negative feedback circuit 12 has for cutting the AC signal is set to 6.3 kHz as an example to reduce the cost increase due to the coupling capacitor 11. ing. Correspondingly, in this embodiment, the amplification factor of the negative feedback circuit 12 is made smaller than the amplification factors of the light receiving signal amplifiers 3 and 4. As an example, the amplification factor of the negative feedback circuit 12 during normal operation is set to one fifth of the amplification factor of the light receiving signal amplifiers 3 and 4.

  In this case, for example, when the amplification factor of the amplifiers 3 and 4 is A, the amplification factor of the negative feedback circuit 12 is A / 5, and the current input to the diodes 5 and 6 is caused by the negative feedback of the negative feedback circuit 12. , (A− (1/5) A) times = (4/5) A times the input current I to the amplifiers 3 and 4, that is, the current (I input to the diodes 5 and 6 when there is no negative feedback) It is about 80% of xA). In this way, by reducing the output signal of the negative feedback circuit 12, signal attenuation and waveform distortion can be suppressed at a frequency lower than the cutoff frequency 6.3 kHz set as an example.

  However, as in the above example, the feedback current during normal operation is 1/5 of the current output from the amplifiers 3 and 4, but not only when the SN decreases but also when the absolute value of the received light amount decreases. The ratio of the feedback current is higher than 1/5. This is beneficial because the DC offset removal rate increases when the conditions become worse.

  Next, FIG. 2 shows an example of an electronic circuit that realizes the first embodiment. In FIG. 2, PNP transistors 33 and 34 correspond to the amplifiers 3 and 4 in FIG. 1, and diodes 35A and 35B and 36A and 36B correspond to the diodes 5 and 6 in FIG. 2 constitutes the differential amplifier 7 of FIG. 1, and the circuit 42 constitutes the negative feedback circuit 12 of FIG. The AD converter 43 in FIG. 2 corresponds to the AD converter 13 in FIG.

  In the circuit shown in FIG. 2, light reception signals from the photodiodes 1 and 2 are amplified by the PNP transistors 33 and 34 at a current amplification factor hfe. This light-amplified received light signal is voltage-converted by the diodes 35A, 35B and 36A, 36B. The voltage-converted received light signal is input to the differential amplifier 37 and output from the first and second output lines L1 and L2 of the differential amplifier 37 as a voltage signal. The voltage signals output from the first and second output lines L1 and L2 are respectively input to the Darlington connection portion constituting the two input portions D1 and D2 connected by the coupling capacitor C1 of the negative feedback circuit 42. The In this negative feedback circuit 42, the voltage signal from the first output line L1 is converted into a current signal and fed back from the feedback line L3 to the connection point P1 between the PNP transistor 33 and the diodes 35A and 35B, and from the second output line L2. Is fed back from the feedback line L4 to the connection point P2 between the PNP transistor 34 and the diodes 36A and 36B. In the feedback of the current signal, the AC signal of the current signal is cut by the coupling capacitor C1. The current signals fed back to the connection points P1 and P2 are converted into voltages by the diodes 35A and 35B and 36A and 36B, and then input to the differential amplifier 37.

  In the circuit of FIG. 2, the current source I1 and the current source I2 of the negative feedback circuit 43 are configured from the same current source using a current mirror circuit or the like, so that negative feedback is caused depending on the power supply voltage and temperature. It is possible to prevent the circuit characteristics from fluctuating. Here, in order to set the amplification factor of the negative feedback circuit 42 to one fifth of the amplification factor of the light receiving signal amplifiers 33 and 44, the current from the current source I2 is set to one fifth of the current from the current source I1.

  Further, in the circuit of FIG. 2, since the input portions D1 and D2 of the negative feedback circuit 42 are configured by Darlington connection portions, if the current amplification factor of the transistors at the Darlington connection portions is hfe, Can be reduced to (1 / hfe), and the presence of the negative feedback circuit 42 can prevent the DC offset from increasing. In addition, by connecting the Darlington connection part of the two input parts D1 and D2 with a coupling capacitor C1, it is possible to introduce a capacitor at a location with high impedance, lower the cut-off frequency, and cut AC components down to the low frequency range. It is possible to prevent attenuation of output amplitude and waveform distortion due to feedback.

(Circuit simulation)
Next, the results of circuit simulation using the circuit of FIG. 2 are shown in FIGS. 3A and 3B. In FIG. 3A, the horizontal axis is time, and the vertical axis is current. In this simulation, incident light to the photodiodes 1 and 2 is turned on and off at 10 kHz due to movement of the moving body, and SN is reduced to 1/10 of normal operation.

  In FIG. 3A, a signal S1A is an output signal of the transistor 33, and a signal S1B is an output signal of the transistor 34. The duty ratio of these signals S1A and S1B is 25%. 3A, a signal C1A is an output signal of the transistor 38, and a signal C1B is an output signal of the transistor 39. 3B, the horizontal axis is time, the vertical axis is voltage, the signal S3A is an output signal to the first output line L1 of the differential amplifier 37, and the signal S3B is the second output of the differential amplifier 37. This is an output signal to the line L2. In FIG. 3B, a signal S7 is an output signal of the AD converter 43. The duty ratio of the signal S7 is 36%, and the duty ratio is improved from the duty ratio 25% of the signals S1A and S1B.

  On the other hand, as a comparative example, FIGS. 4A and 4B show the results of circuit simulation in the case where the negative feedback circuit 42 is not provided. In FIG. 4A, signals S10A and S10B are output signals of the transistors 33 and 34. 4B, signals S3A and S3B are output signals to the first and second output lines L1 and L2 of the differential amplifier 37, and a signal S70 is an output signal of the AD converter 43. The duty ratio of the signal S70 is 20%, and the duty ratio is deteriorated from the duty ratio 25% of the signals S10A and S10B.

  Further, FIG. 5 shows a simulation result of the duty ratio (output duty ratio) of the output signal of the AD converter 43 when the duty ratio (input duty ratio) of the output signals of the transistors 33 and 34 is changed. The point where the input duty ratio is 25% corresponds to FIGS. 3A, 3B, 4A, and 4B. A characteristic K1 in FIG. 5 indicates the characteristic of the circuit in FIG. 2, and a characteristic K2 in FIG. 5 indicates a characteristic of the circuit that does not have the negative feedback circuit 42 in FIG. Comparing the characteristics K1 and K2, it can be seen that the output feedback ratio is improved by having the negative feedback circuit 42, and the effect of the negative feedback circuit 42 increases as the input duty ratio decreases.

  In general, the post-stage circuit after the AD converter 43 can operate normally if the cycle is constant even if the duty ratio is, for example, 80%: 20%. Therefore, the minimum operation condition is that there is a cross point between the two received light signals, and the simulation result of the characteristic K1 in FIG. 5 means that normal operation is possible even if the SN ratio decreases to the limit. It is extremely useful in practice.

(Second embodiment)
Next, FIG. 6 shows the configuration of a circuit system according to a second embodiment of the photoelectric encoder of the present invention. The second embodiment includes the photodiodes 1 and 2, the light receiving signal amplifiers 3 and 4, the diodes 5 and 6, the differential amplifier 7, the AD converter 13, and the negative feedback circuit 12 of the first embodiment shown in FIG. 1. Two circuit systems are provided.

  That is, in the second embodiment, the first circuit system including the photodiodes 61 and 62, the light receiving signal amplifiers 63 and 64, the diodes 65 and 66, the differential amplifier 67, the AD converter 73, and the negative feedback circuit 72. And a second circuit system including photodiodes 81 and 82, received light signal amplifiers 83 and 84, diodes 85 and 86, a differential amplifier 87, an AD converter 93, and a negative feedback circuit 92. The negative feedback circuit 72 of the first circuit system includes a differential amplifier 68 and a coupling capacitor 71 connected between the first output terminal and the second output terminal of the differential amplifier 68. The negative feedback circuit 92 of the second circuit system includes a differential amplifier 88 and a coupling capacitor 91 connected between the first output terminal and the second output terminal of the differential amplifier 88.

  The photodiodes 61 and 62 correspond to the photodiodes 1 and 2, the light receiving signal amplifiers 63, 64 and 83 and 84 correspond to the light receiving signal amplifiers 3 and 4, and the differential amplifiers 67 and 87 correspond to the differential amplifier 7. It corresponds to. The AD converters 73 and 93 correspond to the AD converter 13, and the negative feedback circuits 72 and 92 correspond to the negative feedback circuit 12.

  In the second embodiment, in addition to the moving body 801 indicated by the solid line in FIG. 8 and the photodiodes 501 and 502 corresponding to the photodiodes 61 and 62 as the light receiving elements, the photo as the light receiving element indicated by the one-dot chain line in FIG. Diodes 81 and 82 are provided.

  In the first optical system for the first circuit system, the signal lights 10A and 20A that have passed through the moving body from the light emitting element (not shown) are 180 ° out of phase. In the second optical system for the second circuit system, the signal lights 10B and 20B that have passed through the moving body from the light emitting element (not shown) are out of phase by 180 °. The signal light 10A of the first optical system and the signal light 10B of the second optical system are 90 ° out of phase, and the signal light 20A of the first optical system and the signal light 20B of the second optical system are out of phase. It is 90 ° off.

  In the second embodiment, signal light 10A, 10B having a phase difference of 90 ° and signal light 20A, 20B having a phase difference of 90 ° are received by photodiodes 61, 81, 62, 82 as light receiving elements. The moving direction of the moving body is detected.

  The second embodiment includes a negative feedback circuit 102 connected between the first circuit system and the second circuit system. The negative feedback circuit 102 includes a differential amplifier 98 and a coupling capacitor 101. The differential amplifier 98 has a non-inverting input terminal connected to the first output line L21 of the differential amplifier 67 of the first circuit system and an inverting input terminal of the first differential amplifier 87 of the second circuit system. It is connected to the output line L23. The coupling capacitor 101 is connected between the first output terminal and the second output terminal of the differential amplifier 98. The differential amplifier 98 has a first output terminal connected to the output terminal of the light receiving signal amplifier 63 of the first circuit system, and a second output terminal output from the light receiving signal amplifier 83 of the second circuit system. Connected to the terminal.

  The negative feedback circuit 102 includes a DC output of the differential amplifier 67 of the first circuit system and a DC output of the differential amplifier 87 of the second circuit system of the diode 65 that forms a logarithmic compression unit of the first circuit system. Negative feedback is performed to the input side of the diode 85 forming the logarithmic compression unit of the input side and the second circuit system. As a result, the DC offset between the received light signals having a phase difference of 90 ° can be reduced, so that the output signal waveform S73 of the AD converter 73 of the first circuit system and the output signal waveform S93 of the AD converter 93 of the second circuit system can be reduced. The phase difference accuracy of 90 ° can be improved, and the moving amount and moving speed detection accuracy of the moving body can be improved even at high speed or when the SN ratio is deteriorated.

  In the first and second embodiments described above, the case where the DC offset between received light signals having a phase difference of 180 ° or 90 ° has been described, but the phase difference such as 45 ° other than 180 ° and 90 ° may be reduced. The present invention can also be applied when reducing the DC offset between the received light signals. Furthermore, in the above-described embodiment, the photoelectric encoder itself is provided with a moving body. However, the moving body is not necessarily provided in the photoelectric encoder, and the present invention is also applied when the moving body is provided on the electronic device side. Is possible.

  In addition, electronic devices such as copiers, printers, and other electronic devices such as FA (factory automation) devices are equipped with the photoelectric encoder of the above embodiment, so that DC offset can be canceled and characteristics can be improved when SN decreases. It becomes.

It is a figure which shows the structure of the circuit system of 1st Embodiment of the photoelectric encoder of this invention. It is a circuit diagram which shows an example of the electronic circuit which implement | achieves the said 1st Embodiment. FIG. 3 is a circuit simulation result of the electronic circuit of FIG. 2 and shows waveforms of output signals S1A, S1B, C1A, and C1B of transistors 33, 34, 38, and 39. FIG. 3 is a circuit simulation result of the electronic circuit of FIG. 2 and shows waveforms of output signals S3A and S3B of a differential amplifier 37 and an output signal S7 of an AD converter 43. It is a circuit simulation result when it does not have the negative feedback circuit 42 (comparative example), and is a diagram showing waveforms of output signals S10A and S10B of transistors 33, 34, 38, and 39. FIG. 7 is a circuit simulation result when the negative feedback circuit 42 is not provided (comparative example), and shows the waveforms of the output signals S30A and S30B of the differential amplifier 37 and the output signal S70 of the AD converter 43. In the electronic circuit of FIG. 2 and the above comparative example, the simulation result of the duty ratio (output duty ratio) of the output signal of the AD converter 43 when the duty ratio (input duty ratio) of the output signals of the transistors 33 and 34 is changed. FIG. It is a figure which shows the structure of the circuit system of 2nd Embodiment of the photoelectric encoder of this invention. It is a figure which shows the structure of the light receiving circuit of the photoelectric encoder of a prior art example. It is a wave form diagram which shows the ideal state in which the two output signal waveforms 700A and 700B of the differential amplifier 507 of the photoelectric encoder of the conventional example are 180 degrees out of phase. It is a wave form diagram which shows the state from which the phase difference of the two output signal waveforms 700A and 700B of the differential amplifier 507 of the photoelectric encoder of the said prior art example has shifted | deviated from 180 degrees. It is a schematic diagram which shows the example of arrangement | positioning of the mobile body and light receiving element of a photoelectric encoder.

Explanation of symbols

1, 2, 61, 62, 81, 82 Photodiode 3, 4, 63, 64, 83, 84 Light receiving signal amplifier 5, 6, 35A, 35B, 36A, 36B, 65, 66, 85, 86 Diode 7,8 , 37, 67, 68, 87, 88, 98 Differential amplifier 10, 20, 10A, 20A, 10B, 20B Signal light 11, C 1, 71, 91, 101 Coupling capacity 12, 42, 72, 92, 102 Negative Feedback circuit 13, 73, 93 AD converter 33, 34 PNP transistor 35A, 35B, 36A, 36B Diode D1, D2 Input section

Claims (5)

A light emitting element;
A plurality of light receiving elements arranged in one direction in a region where light from the light emitting element can reach,
A light-on portion that makes the light incident on the light receiving element when passing through a predetermined position corresponding to the light receiving element and the light when passing through a predetermined position corresponding to the light receiving element A photoelectric encoder that has a light-off portion that is not incident on the light source and detects the movement of the moving body in which the light-on portion and the light-off portion alternately pass the predetermined position when moving in the one direction. And
A logarithmic compression unit that logarithmically compresses a light reception signal output by the light receiving element with a diode and outputs a logarithm compression signal;
A differential amplifier to which the logarithmic compression signal is input from the logarithmic compression unit;
A negative feedback circuit connected between the output side of the differential amplifier and the input side of the logarithmic compression unit and negatively feeding back the DC output of the differential amplifier to the input side of the logarithmic compression unit A photoelectric encoder characterized by The photoelectric encoder according to claim 1,
A light receiving signal amplifier that amplifies a light receiving signal output from the light receiving element and outputs the amplified signal to the logarithmic compression unit;
A photoelectric encoder characterized in that an amplification factor of the negative feedback circuit is made smaller than an amplification factor of the light receiving signal amplifier. The photoelectric encoder according to claim 2,
A photoelectric encoder, wherein a current source of the light receiving signal amplifier and a current source of the negative feedback circuit are constituted by the same current source. The photoelectric encoder according to claim 1,
The negative feedback circuit is
A photoelectric encoder having two inputs connected by a coupling capacitor, the two inputs including a Darlington connection.   The electronic device provided with the photoelectric encoder as described in any one of Claims 1 thru | or 4.

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