JP4429240B2 - Optical sensor circuit and light receiving module - Google Patents

Description

  The present invention relates to an optical sensor circuit and a light receiving module that convert illuminance of visible light into an electrical signal, and in particular, an optical sensor circuit having spectral sensitivity characteristics close to human visual sensitivity characteristics, and a light receiving module including the optical sensor circuit. About.

  As the optical sensor for visible light, two sensors of a silicon photodiode and a CdS (cadmium sulfide) cell are typical. Silicon photodiodes are widely used in optical communications, optical receivers, optical sensors, and the like because they are small in size and have a high response speed. However, the spectral sensitivity characteristics of silicon photodiodes are very different from human visual sensitivity, and the sensitivity in the infrared region is increased. On the other hand, the CdS cell has a spectral sensitivity characteristic close to human visibility. Therefore, CdS cells have long been used as camera exposure meters and visible light sensors.

  The relationship (photoelectric sensitivity) between the amount of incident light and the photocurrent varies depending on the wavelength of incident light. This relationship between wavelength and photoelectric sensitivity is referred to as “spectral sensitivity characteristics”. The spectral sensitivity characteristic is represented by light receiving sensitivity (the ratio between the incident light quantity in watts (W) and the photocurrent in amperes (A)).

  In recent years, the use of substances with high environmental impact has become a problem. Therefore, the use of CdS cells mainly composed of cadmium sulfide is being restricted. For example, in July 2006, imports of products using cadmium, lead, hexavalent chromium and mercury will be banned after July 2006. On the other hand, silicon has a smaller environmental impact than cadmium sulfide. Therefore, there is an increasing demand for a sensor that is configured using a silicon photodiode and has a spectral sensitivity characteristic that is close to the human visual sensitivity characteristic.

  In recent years, backlights used in mobile phones, liquid crystal televisions, and the like have automatically adjusted their brightness (luminosity) according to the ambient brightness. Thereby, it becomes possible to suppress the consumption of the battery of the mobile phone. In addition, the visibility of the liquid crystal can be improved. For this reason, the demand for an illuminance sensor having a spectral sensitivity characteristic close to the visibility characteristic is increasing rapidly.

  FIG. 11 is a circuit diagram of a conventional photosensor circuit. FIG. 12 is a cross-sectional view showing the configuration of the silicon photodiode.

  Referring to FIGS. 11 and 12, the photosensor circuit 101 includes photodiodes PD1A, PD1B, and PD2B. By subtracting the photocurrent of the photodiode PD2B from the photocurrent of the photodiode PD1A, the spectral sensitivity characteristic of the photosensor circuit 101 can be brought close to the human visual sensitivity characteristic.

  As shown in FIG. 12, a buried N-type diffusion layer 112 and an N-type epitaxial layer 113 are formed on a P-type substrate 111. A P-type diffusion layer 114 is formed on the surface of the N-type epitaxial layer 113. A silicon oxide film 115 is formed so as to cover the surfaces of N type epitaxial layer 113 and P type diffusion layer 114. N-type epitaxial layer 113 is separated into a plurality of regions by P-type diffusion layer 116 and buried P-type diffusion layer 117.

  The photodiode PD1A includes a P-type diffusion layer 114 and an N-type epitaxial layer 113. Each of the photodiodes PD1B and PD2B includes a P-type substrate 111, a buried N-type diffusion layer 112, and an N-type epitaxial layer 113. The cathode of photodiode PD1A is connected to a power supply node having a potential of Vcc, and the anode is connected to node N5. Photodiode PD1B has a cathode connected to the power supply node and an anode connected to the ground node. The cathode of photodiode PD2B is connected to node N1, and the anode is connected to the ground node.

  The photodiode PD1A having a shallow PN junction mainly absorbs a short wavelength component of incident light. Each of the photodiodes PD1B and PD2B having a PN junction deeper than the photodiode PD1A absorbs a long wavelength component of incident light. Therefore, the wavelength at which the light receiving sensitivity reaches a peak in the spectral sensitivity characteristic is longer for the photodiodes PD1B and PD2B than for the photodiode PD1A.

  FIG. 13 is a diagram showing the spectral sensitivity characteristics of the photodiodes PD1A, PD1B, and PD2B in FIG.

  Referring to FIG. 13, curve PDA shows the spectral sensitivity curve of photodiode PD1A. A curve PDB shows the spectral sensitivity curves of the photodiodes PD1B and PD2B. The vertical axis of the graph indicates conversion efficiency, that is, light reception sensitivity.

  As shown by the curve PDB, the conversion efficiency in the photodiodes PD1B and PD2B peaks at a wavelength near 900 nm. On the other hand, as indicated by the curve PDA, the conversion efficiency of the photodiode PD1A peaks at a wavelength near 550 nm. In the curve PDA, in the wavelength range from 550 nm to around 1100 nm, the conversion efficiency decreases gradually.

FIG. 14 is a diagram illustrating human visibility characteristics.
Referring to FIG. 14, the human visibility characteristic (standard visibility characteristic) is indicated by a dashed curve. The visibility characteristic has a peak when the wavelength is around 550 nm. It is also shown that the human eye has sensitivity in the wavelength range of 400 nm to 700 nm.

  The curves PDA and PDB shown in FIG. 14 correspond to the curves PDA and PDB shown in FIG. However, in FIG. 14, the peak intensity of each curve is normalized to 1. In order to bring the spectral sensitivity characteristic of the silicon photodiode close to the human visual sensitivity characteristic, it is necessary to reduce the sensitivity on the long wavelength side in the spectral sensitivity characteristic of the photodiode PD1A.

  NPN transistors QN1 and QN2 in FIG. 11 constitute a current mirror circuit. Similarly, NPN transistors QN3 and QN4 constitute a current mirror circuit. The current flowing through each of the NPN transistors QN3 and QN4 is equal to the current obtained by subtracting the current IB flowing through the photodiode PD2B from the current IA flowing through the photodiode PD1A, that is, (IA-IB). Thereby, the optical sensor circuit 101 can reduce the sensitivity of wavelengths of 800 nm or more.

  In FIGS. 13 and 14, a curve indicated by “(PDA) − (PDB) × α” indicates a change in (IA−IB) with respect to the wavelength of incident light. The constant α is a constant for bringing the spectral sensitivity curve close to human visibility characteristics, and is determined by the area ratio of the light receiving surfaces of the photodiodes PD1A and PD2B. Note that the intensity of the current IB is α times the intensity of the curve (PDB) shown in FIG.

Conventionally, many techniques for bringing the spectral sensitivity characteristic closer to the human visual sensitivity characteristic by reducing the sensitivity to wavelengths longer than 800 nm have been used. As an application example of such a technique, for example, there is a semiconductor optical sensor device disclosed in Japanese Patent Application Laid-Open No. 2004-119713 (Patent Document 1). In this semiconductor optical sensor device, two photodiodes are formed in a state where they are overlapped in the thickness direction of the semiconductor layer that is insulated and separated, thereby making it possible to obtain an output of spectral sensitivity characteristics with reduced influence of stray light.
JP 2004-119713 A

  As shown in FIG. 11, a reverse bias voltage is applied to the photodiode PD1A. The magnitude of the reverse bias voltage is equal to the magnitude obtained by subtracting the base-emitter voltage of the diode-connected NPN transistor QN3 from the magnitude of the power supply potential Vcc.

  A photodiode using a PN junction has a property of allowing a minute current to flow even when no light enters when a reverse bias voltage is applied. This minute current is called “dark current”. The dark current increases as the reverse bias voltage increases. Further, the dark current tends to increase by an order of magnitude when the temperature rises by 20 degrees.

  In the case of the optical sensor circuit 101 shown in FIG. 11, assuming that the power supply potential is Vcc and the base emitter voltage of the NPN transistor QN3 is Vbe, a reverse bias voltage having a magnitude of (Vcc−Vbe) is applied to both ends of the photodiode PD1A. Is done. As a result, a dark current is generated in the photodiode PD1A.

  At low illumination, the photocurrent flowing through the photodiode is reduced. In this case, the linearity of the output current of the photodiode is not satisfied due to the influence of the dark current. “Linearity of output current” refers to a linear change of output current with respect to light intensity. In short, when the illuminance is low, the signal output from the photodiode contains a lot of noise components.

  In the semiconductor optical sensor device disclosed in Japanese Patent Application Laid-Open No. 2004-119713 (Patent Document 1), a reverse bias voltage having a magnitude of (Vcc-2Vbe) is applied to the photodiode. Therefore, in this semiconductor photosensor device, dark current affects the output of the sensor. However, this method of reducing dark current is not disclosed in Japanese Patent Application Laid-Open No. 2004-119713 (Patent Document 1).

  The objective of this invention is providing the optical sensor circuit which can reduce the influence by dark current, and the light reception module using this optical sensor circuit.

  In summary, the present invention is an optical sensor circuit, comprising: a first light receiving element for detecting light; a second light receiving element that outputs a photocurrent according to the intensity of light; And a control circuit for changing an applied voltage applied to one light receiving element.

  Preferably, the first light receiving element is between a first node to which a first potential is applied and a second node to which a second potential having a potential different from the first potential by an applied voltage is applied. Connected to. The control circuit includes a first transistor having one end connected to the first node, the other end and the control electrode commonly connected to the third node, and one end connected to the second node, Is connected to the third node, the other end is connected to the fourth node, a current setting unit for setting a control current drawn from the third node according to the photocurrent, And an output unit that performs output processing in accordance with the detected current received from the node.

  More preferably, the ratio between the control current and the photocurrent is equal to the ratio between the area of the light receiving surface of the first light receiving element and the area of the light receiving surface of the second light receiving element.

  More preferably, the area of the light receiving surface of the second light receiving element is smaller than the area of the light receiving surface of the first light receiving element.

  More preferably, the optical sensor circuit further includes a third light receiving element having a photoelectric sensitivity to the wavelength of light different from that of the first light receiving element. The current setting unit changes the detection current according to the current flowing through the third light receiving element.

  More preferably, the optical sensor circuit further includes a third light receiving element whose light receiving surface is shielded from light. The current setting unit corrects the detected current according to the dark current flowing through the third light receiving element.

  Preferably, the first light receiving element and the second light receiving element have the same photoelectric sensitivity with respect to the wavelength of light.

  Preferably, the first and second light receiving elements are formed on the same semiconductor substrate. The first light receiving element has first and second light receiving surfaces provided on the main surface of the semiconductor substrate. The second light receiving element has a third light receiving surface provided on the main surface. When viewed from above the semiconductor substrate, the first and second light receiving surfaces are provided so as to sandwich the third light receiving surface from both sides.

  Preferably, the first and second light receiving elements are formed on the same semiconductor substrate. Each of the first and second light receiving elements is provided with a first N-type region, a P-type region provided on the surface of the first N-type region, and a surface of the P-type region. And a plurality of second N-type regions connected to each other.

  Preferably, the light receiving module includes any one of the above-described optical sensor circuits.

  According to the optical sensor circuit and the light receiving module of the present invention, the linearity of the current output from the photodiode can be improved by reducing the dark current of the photodiode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[Embodiment 1]
FIG. 1 is a diagram showing an application example of the optical sensor circuit of the present invention.

  Referring to FIG. 1, the light receiving module 50 includes an optical sensor circuit 1 and a signal processing circuit 2. The optical sensor circuit 1 outputs an electrical signal (signal S1) corresponding to the illuminance of visible light. The signal processing circuit 2 executes various processes according to the signal S1 received from the optical sensor circuit 1.

  The optical sensor circuit 1 includes photodiodes PD1A, PD2A, and PD2B that are light receiving elements. The photodiodes PD1A and PD2A correspond to the “first light receiving element” and the “second light receiving element” in the present invention, respectively. These photodiodes are silicon photodiodes.

  The photodiode PD1A detects light and outputs a current I1A. The photodiode PD2A outputs a current I2A (photocurrent) corresponding to the light intensity. The photodiode PD2B outputs a current I2B according to light.

  The optical sensor circuit 1 further includes a control circuit 4. The control circuit 4 changes the applied voltage to the photodiode PD1A according to the current I2A. When the applied voltage is applied, the photodiode PD1A outputs a current I1A when detecting light. The photoelectric sensitivity with respect to the wavelength of light is equal in the photodiodes PD1A and PD2A. Thereby, since the control circuit 4 can change an applied voltage according to the sensitivity of the photodiode PD1A, a noise component included in the current I1A, that is, a dark current can be reduced regardless of the wavelength of light.

  One end of the photodiode PD1A is connected to the power supply node. The potential of the power supply node is Vcc. The control circuit 4 changes the potential at the other end of the photodiode PD1A to change the applied voltage.

  Further, the control circuit 4 outputs a result obtained by subtracting the current I2B from the current I1A as the signal S1. Photodiode sensitivity with respect to the wavelength of light is different between the photodiode PD1A and the photodiode PD2B. As a result, the spectral sensitivity characteristic of the optical sensor circuit 1 can be brought close to the human visual sensitivity characteristic.

FIG. 2 is a circuit diagram of the photosensor circuit 1 of FIG.
Referring to FIG. 2, each of photodiodes PD1A, PD2A, PD2B is reverse-biased. The cathode of photodiode PD1A is connected to the power supply node, and the anode is connected to node N5. The cathode of the photodiode PD2A is connected to the node N1, and the anode is connected to the node N2. The cathode of photodiode PD2B is connected to node N1, and the anode is connected to the ground node. The potential of the ground node is GND.

  The control circuit 4 includes a current setting unit 6. Current setting unit 6 sets a control current drawn from node N6 in accordance with current I2A flowing through photodiode PD2A. Current setting unit 6 includes PNP transistors QP1 and QP2 and NPN transistors QN1 to QN7.

  The PNP transistors QP1 and QP2 constitute a current mirror circuit. PNP transistor QP1 has an emitter connected to the power supply node, and a base and a collector connected to node N1. PNP transistor QP2 has an emitter connected to the power supply node, a base connected to node N1, and a collector connected to node N3.

  NPN transistors QN1 to QN3 constitute a current mirror circuit. NPN transistor QN1 has a collector and a base commonly connected to node N2, and an emitter connected to a ground node. NPN transistor QN2 has a collector connected to node N3, a base connected to node N2, and an emitter connected to the ground node. NPN transistor QN3 has a collector connected to node N6, a base connected to node N2, and an emitter connected to the ground node.

  The current I6 flowing from the node N6 to the NPN transistor QN3 corresponds to the “control current” in the present invention. Note that the emitter area of the NPN transistor QN3 is set to 8 times the emitter area of the NPN transistor QN1.

  NPN transistors QN4, QN6 and QN7 constitute a current mirror circuit. NPN transistor QN4 has a collector connected to node N3, a base connected to node N3, and an emitter connected to the ground node. NPN transistor QN5 has a collector connected to the power supply node, a base connected to node N3, and an emitter connected to node N4. NPN transistor QN6 has a collector connected to node N5, a base connected to node N4, and an emitter connected to the ground node. NPN transistor QN7 has a collector connected to node N6, a base connected to node N4, and an emitter connected to the ground node.

  Here, the NPN transistor QN5 is provided to compensate for the base currents of the NPN transistors QN4, QN6, and QN7 to improve the accuracy of the current mirror circuit. When the NPN transistor QN5 is not provided, the magnitudes of the collector currents of the NPN transistors QN6 and QN7 are obtained by subtracting the base currents of the three transistors NPN transistors QN4, QN6, and QN7 from the collector current of the NPN transistor QN4. In the case of a current mirror circuit composed of about three transistors, the decrease in the accuracy of the collector current is small. However, for example, when a current mirror is constituted by 10 or more transistors, a base current compensating transistor such as the NPN transistor QN5 is required in order to prevent a decrease in the accuracy of the collector current.

  Control circuit 4 further includes an output unit 8. Output unit 8 performs output processing according to the detected current received from node N7.

  Output unit 8 includes NPN transistors QN8 and QN9. NPN transistor QN8 has a collector and a base both connected to node N7, and an emitter connected to the ground node. NPN transistor QN9 has a base connected to node N7 and an emitter connected to the ground node.

  NPN transistors QN8 and QN9 constitute a current mirror circuit. The current mirror circuit passes a current having the same magnitude as the detection current received from node N7 to NPN transistor QN9. This process corresponds to the “output process” of the present invention.

  The optical sensor circuit 1 further includes PNP transistors QP3 and QP4. These PNP transistors are provided for setting a reverse bias voltage to be applied to the photodiode PD1A.

  PNP transistor QP3 has an emitter connected to node N5, a base connected to node N6, and a collector connected to node N7. PNP transistor QP4 has an emitter connected to the power supply node, and a base and a collector commonly connected to node N6. The PNP transistor QP4 is diode-connected. That is, the PNP transistor QP4 is equivalent to a diode having an anode connected to the power supply node and a cathode connected to the node N6.

  The PNP transistor QP4 corresponds to the “first transistor” in the present invention, and the PNP transistor QP3 corresponds to the “second transistor” in the present invention. The power supply node corresponds to the “first node” in the present invention. Further, the nodes N5 to N7 correspond to the second to fourth nodes in the present invention, respectively. The difference between the potential Vcc (first potential) at the power supply node and the potential (second potential) at the node N5 is the magnitude of the reverse bias voltage (applied voltage) applied to the photodiode PD1A.

FIG. 3 is a cross-sectional view of the photodiodes PD1A, PD2A, and PD2B in FIG.
Referring to FIG. 3, buried N type diffusion layer 12 is formed on P type substrate 11. An N type epitaxial layer 13 (first N type region) is formed on the P type substrate 11. A P-type diffusion layer 14 (P-type region) is formed on the surface of the N-type epitaxial layer 13. A silicon oxide film 15 is formed so as to cover the surfaces of N type epitaxial layer 13 and P type diffusion layer 14.

  The N type epitaxial layer 13 is divided into a plurality of regions by the P type diffusion layer 16 and the buried P type diffusion layer 17. A ground potential is applied to the P-type diffusion layer 16 and the buried P-type diffusion layer 17 through the P-type substrate 11. On the other hand, a potential higher than the ground potential is applied to the N-type epitaxial layer 13. Thereby, each area | region is isolate | separated electrically.

  A photodiode PD1A is formed in one of the two regions separated from each other by the P-type diffusion layer 16 and the buried P-type diffusion layer 17, and photodiodes PD2A and PD2B are formed in the other region. Each of the photodiodes PD1A and PD2A includes a P-type diffusion layer 14 and an N-type epitaxial layer 13. The photodiode PD2B includes a P-type substrate 11, a buried N-type diffusion layer 12, and an N-type epitaxial layer 13. As described above, the photodiodes PD1A and PD2A are formed on the same semiconductor substrate.

  FIG. 3 shows a photodiode PD1B having the same configuration as the photodiode PD2B. Photodiode PD1B is connected between the power supply node and the ground node. Therefore, even if a current flows through the photodiode PD1B, this current only flows between the power supply node and the ground node, and does not directly contribute to the operation of the photosensor circuit 1. Therefore, the photodiode PD1B is not shown in the circuit diagram of FIG.

  In the case of a standard bipolar process, an N-type epitaxial layer is grown on a P-type substrate to form circuit elements. Therefore, the photodiode PD1B is formed even if unnecessary for circuit operation.

  The buried N-type diffusion layer 12 is deep from the surface of the semiconductor substrate. The deeper the PN junction, the longer the wavelength of light absorbed by the photodiode. A typical thickness of the N type epitaxial layer 13 is about 1 μm. Each of the photodiodes PD1B and PD2B exhibits a spectral sensitivity characteristic in which the light receiving sensitivity reaches a peak at a wavelength near 900 nm.

  The photodiode PD1A has a PN junction formed by a P-type diffusion layer 14 and an N-type epitaxial layer 13 formed near the surface of the semiconductor substrate. Since the PN junction exists near the surface of the semiconductor substrate, the peak wavelength of the spectral sensitivity characteristic of the photodiode PD1A is shorter than the peak wavelength of the spectral sensitivity characteristic of the photodiode PD1B. Specifically, the light receiving sensitivity of the photodiode PD1A has a peak at a wavelength near 550 nm. By adjusting the diffusion depth of the P-type diffusion layer 14, the peak wavelength of the photodiode PD1A is adjusted. Note that the peak wavelengths of the spectral sensitivity characteristics of the photodiodes PD2A and PD2B are the same as the peak wavelengths of the photodiodes PD1A and PD1B, respectively.

  FIG. 4 is a plan view showing light receiving surfaces of the photodiodes PD1A, PD1B, PD2A, and PD2B shown in FIG.

  Referring to FIG. 4, the light receiving surface when viewed from above the surface of the semiconductor substrate is shown. The light receiving surface A1 is a light receiving surface common to the photodiodes PD1A and PD1B. The light receiving surface A2 is a light receiving surface common to the photodiodes PD2A and PD2B. The ratio of the area of the light receiving surface A1 to the area of the light receiving surface A2 is 8: 1. Note that the ratio of the current I6 (control current) and the current I2A (photocurrent) in FIG. 2 is determined by the ratio of the area of the light receiving surface A1 to the area of the light receiving surface A2. Further, by making the area of the light receiving surface A2 smaller than the area of the light receiving surface A1, the spectral sensitivity characteristic of the optical sensor circuit 1 can be brought close to the human visual sensitivity characteristic.

  With reference to FIG. 2 again, the operation of the optical sensor circuit 1 will be described. Currents I2A and I2B flow through the photodiodes PD2A and PD2B, respectively. The PNP transistors QP1 and QP2 constitute a current mirror circuit. A current of (I2A + I2B) flows through the collector of the PNP transistor QP1. Therefore, a current of (I2A + I2B) also flows through the collector of the PNP transistor QP2.

  NPN transistors QN1 to QN3 constitute a current mirror circuit. Since the collector current of NPN transistor QN1 is I2A, the collector current of NPN transistor QN2 is I2A. The collector current of NPN transistor QN3 is 8 × I2A.

  The collector current of the NPN transistor QN4 is obtained by subtracting the collector current (= I2A) of the NPN transistor QN2 from the collector current (I2A + I2B) of the PNP transistor QP2, and becomes I2B. Since NPN transistors QN4, QN6 and QN7 form a current mirror circuit, the collector currents of NPN transistors QN4, QN6 and QN7 are I2B.

  A current I1A flows through the photodiode PD1A. The collector current of the PNP transistor QP3 is (I1A-I2B) obtained by subtracting the collector current (= I2B) of the NPN transistor QN6 from the current I1A. By subtracting the photocurrent of the photodiode PD2B having a deep junction from the photocurrent of the photodiode PD1A, the sensitivity of the wavelength of 800 nm or more is lowered in the photosensor circuit 1. Therefore, the spectral sensitivity characteristic can be brought close to the visibility characteristic. That is, the current setting unit 6 adjusts the photoelectric sensitivity by changing the detection current received by the output unit 8 in accordance with the current flowing through the photodiode PD2B (third light receiving element).

  By adjusting the magnitude of the current I2B, the spectral sensitivity curve can be made closer to the human visual sensitivity characteristic. The magnitude of current I2B is determined, for example, by adjusting the area ratio of light receiving surfaces A1 and A2 shown in FIG. 3 and the ratio of collector currents of NPN transistors QN4 and QN6. By adjusting the spectral sensitivity characteristics, for example, the output current when the light of a 100 lux incandescent lamp is incident and the output current when the light of a 100 lux fluorescent lamp is incident can be made the same.

  A point to be noted in the present embodiment is that a current obtained by adding the collector current (current I2B) of the NPN transistor QN7 and the collector current (current I6) of the NPN transistor QN3 flows to the diode-connected PNP transistor QP4. is there. The relationship of I6 = 8 × I2A is established for the current I6. Further, as shown in FIG. 4, since the area ratio of the light receiving surfaces A1 and A2 is 8: 1, the relationship of I1A = 8 × I2A is established. That is, I6 = I1A. Therefore, the current flowing through the PNP transistor QP4 is (I1A + I2B). On the other hand, the current flowing through the PNP transistor QP3 is (I1A-I2B).

  When the base-emitter voltage of the PNP transistor QP4 is Vbe, the base potential of the PNP transistor QP3 is (Vcc-Vbe). Since a current larger than the current flowing through the PNP transistor QP4 does not flow through the PNP transistor QP3, the potential at the node N5 becomes higher than (Vcc−Vbe). Since the voltage applied to both ends of the photodiode PD1A is reduced to Vbe or less (specifically, about several mV to several tens mV), the dark current of the photodiode PD1A is reduced. Therefore, the optical sensor circuit 1 can improve the linearity at the time of low illumination.

  The reverse bias voltage applied to the photodiode PD1A will be described in more detail. The base-emitter voltages of the PNP transistors QP3 and QP4 are Vbe (QP3) and Vbe (QP4), respectively. In general, the base-emitter voltage is given according to equation (1).

Vbe = kT / q × ln (Ic / Is) (1)
Where k is the Boltzmann constant, T is the absolute temperature, Ic is the collector current of the transistor, and Is is the reverse saturation current.

When the collector currents flowing in the respective PNP transistors are the same, the base-emitter voltages Vbe (QP3) and Vbe (QP4) have the same value. Therefore, the potential difference between both ends of the photodiode PD1A becomes zero. When the emitter current of the PNP transistor QP4 is I and the collector current of the PNP transistor QP3 is I / 10, the difference between the base-emitter voltages Vbe (QP3) and Vbe (QP4) from the equation (1) is as follows: It is indicated by (2). This difference between the base-emitter voltages corresponds to the reverse bias voltage applied across the photodiode PD1A.
Vbe (QP4) -Vbe (QP3)
= KT / q * (ln (Ic (QP4) / Is) -ln (Ic (QP3) / Is))
= KT / q × ln (Ic (QP4) / Ic (QP3))
= KT / q × ln (10) (2)
In this case, Vbe (QP4) −Vbe (QP3) is about 60 mV. In practice, the collector current of the PNP transistor QP3 is approximately the same as or slightly smaller than the collector current of the PNP transistor QP4. Therefore, the reverse bias voltage applied to the photodiode PD1A is a value smaller than 60 mV.

  On the other hand, in the case of the photodiode PD1A in the optical sensor circuit 101 (conventional example) in FIG. 11, a reverse bias voltage of Vcc-Vbe (QN3) is applied to both ends of the photodiode PD1A. If Vcc is 5V and Vbe (QN3) is about 0.6V, a reverse bias voltage of 4.4V is applied across the photodiode PD1A in the conventional example.

  The collector current (= I1A-I2B) of the PNP transistor QP3 is a current output to the outside of the optical sensor circuit 1 by the NPN transistors QN8 and QN9. This current is amplified or voltage-converted, for example, by the signal processing circuit 2 of FIG.

  In order to reduce the reverse bias voltage applied to both ends of the photodiode PD1A, the photodiodes PD1A and the photodiode PD2A need to have the same photoelectric sensitivity with respect to the wavelength of light. Further, the area ratio of the light receiving surfaces of the photodiodes PD1A and PD2A and the ratio of the photocurrents output from the photodiodes PD1A and PD2A must be the same. Therefore, it is necessary for light to uniformly enter the light receiving surface of each photodiode.

FIG. 5 is a diagram showing an example of the arrangement of the light receiving surfaces of the photodiodes.
Referring to FIG. 5, light receiving surfaces A11 and A12 are light receiving surfaces common to photodiodes PD1A and PD1B, and correspond to “first and second light receiving surfaces” in the present invention, respectively. The light receiving surface A2 is a light receiving surface common to the photodiodes PD1A and PD1B, and corresponds to the “third light receiving surface” in the present invention.

  The light receiving surfaces A11 and A12 are provided so as to sandwich the light receiving surface A2 from both sides when viewed from above the semiconductor substrate. The light receiving surfaces A11, A12, A2 are arranged symmetrically with respect to the axis X on the main surface of the semiconductor substrate and the axis Y perpendicular to the axis X. Note that the light receiving surfaces A11, A12, and A2 may be symmetric with respect to only one of the axes X and Y.

FIG. 6 is a diagram illustrating another example of the arrangement of the light receiving surfaces of the photodiodes.
Referring to FIG. 6, light receiving surfaces A21 and A22 are light receiving surfaces common to photodiodes PD2A and PD2B. The light receiving surfaces A1, A21, A22 are arranged symmetrically with respect to the point P1.

  By arranging the light receiving surface as shown in FIGS. 5 and 6, the operation of the circuit can be stabilized even when the light incident on the photodiode is uneven, that is, when the amount of incident light is not uniform.

FIG. 7 is a diagram for explaining the effect of the optical sensor circuit 1.
Referring to FIG. 7, the horizontal axis represents illuminance, and the vertical axis represents the output current of photodiode PD1A. Compared to the conventional example (the optical sensor circuit 101 in FIG. 11), in the present invention, the reverse bias voltage applied to both ends of the photodiode PD1A is reduced, thereby reducing the dark current. As shown in FIG. 7, according to the present invention, the linearity of the output current at the time of low illuminance can be improved as compared with the conventional example.

  In the optical sensor circuit 1 of FIG. 1, the PNP transistor may be replaced with a P-channel MOSFET, and the NPN transistor may be replaced with an N-channel MOSFET.

[Embodiment 2]
The optical sensor circuit of the second embodiment is different from the optical sensor circuit of the first embodiment in that dark current compensation is performed. By applying dark current compensation, the photosensor circuit of Embodiment 2 can operate stably even at low illuminance or at high temperatures. Since the configuration of the light receiving module including the optical sensor circuit according to the second embodiment is the same as that shown in FIG. 1, the following description will not be repeated.

FIG. 8 is a circuit diagram of the photosensor circuit of the second embodiment.
Referring to FIG. 8, optical sensor circuit 1A differs from optical sensor circuit 1 of FIG. 2 in that it further includes a photodiode PD3A whose light receiving surface is shielded. The optical sensor circuit 1A is different from the optical sensor circuit 1 of FIG. 1 in that a control circuit 4A is provided instead of the control circuit 4.

  The control circuit 4A is different from the control circuit 4 in that a current setting unit 6A is included instead of the current setting unit 6. The current setting unit 6A is different from the current setting unit 6 in that it further includes a dark current compensation unit 21. Since the configuration of the other parts of photosensor circuit 1A is the same as that of photosensor circuit 1, the following description will not be repeated.

  The photodiode PD3A is provided for dark current compensation. The configuration of the photodiode PD3A is the same as that of the photodiode PD1A shown in FIG. However, the light receiving surface of the photodiode PD3A is covered with the light shielding film 22. The light shielding film 22 is a metal film, for example.

  By shielding the light receiving surface A11 shown in FIG. 5 with a metal film, a photodiode PD3A having the same configuration as the photodiode PD1A can be formed. However, in this case, the area of the light receiving surface of the photodiode PD1A is halved compared to the first embodiment. That is, the ratio of the light receiving surface of the photodiode PD1A to the light receiving surface of the photodiode PD2A is 4: 1. As a result, the collector current flowing through the NPN transistor QN3 is four times the collector current flowing through the NPN transistor QN1. That is, in the photosensor circuit 1A, the emitter size of the NPN transistor QN3 is half of the emitter size of the NPN transistor QN3 in the photosensor circuit 1.

  Further, the current flowing through the photodiode PD1A is halved as compared with the first embodiment. The collector current of each of NPN transistors QN6 and QN7 also needs to be half of the collector current in the first embodiment. Therefore, the emitter size of NPN transistor QN4 is set to twice the emitter size of NPN transistor QN4 in the first embodiment.

  The dark current compensation unit 21 includes a PNP transistor QP5 and NPN transistors QN10 and QN11.

  The emitter of PNP transistor QP5 is connected to the anode of photodiode PD3A, the base is connected to node N6, and the collector is connected to node N7. NPN transistor QN10 has a collector and a base commonly connected to node N7, and an emitter connected to the ground node. NPN transistor QN11 has a collector connected to node N5, a base connected to node N7, and an emitter connected to the ground node. NPN transistors QN10 and QN11 constitute a current mirror circuit.

  A dark current flowing through the photodiode PD3A is assumed to be IDARK. The dark current IDARK flows through the PNP transistor QP5 and the NPN transistor QN10. At this time, the dark current IDARK also flows through the NPN transistor QN11. The collector of the NPN transistor QN11 is connected to the anode of the photodiode PD1A. The collector current (detection current) flowing through the NPN transistor QN8 is equal to the current obtained by subtracting the dark current IDARK from the current flowing through the photodiode PD1A. The dark current generated in the photodiode PD1A is cancelled. That is, the current setting unit 6A corrects the detected current according to the dark current IDARK that flows through the photodiode PD3A (third light receiving element).

  The light receiving area of the photodiode PD3A may be 1 / N of the area of the photodiode PD1A, and the emitter area of the NPN transistor QN11 may be N times that of the NPN transistor QN10 (N is a natural number). In this case, since the area of the photodiode PD3A can be reduced, the area of the photosensor circuit can be reduced. In this case, the dark current flowing through the photodiode PD3A is 1 / N times the dark current IDARK described above. Therefore, the emitter area ratio of NPN transistors QN10 and QN11 is set to 1: N. Since the current flowing through the NPN transistor QN11 is N times the current flowing through the NPN transistor QN10, a current obtained by subtracting the dark current from the current generated in the photodiode PD1A can be obtained.

  As described above, according to the second embodiment, the dark current generated in the photodiode can be canceled. Therefore, according to the second embodiment, dark current can be reduced not only at low illuminance but also at high temperatures, and the linearity of output current can be improved.

[Embodiment 3]
Since the circuit configuration of the photosensor circuit of the third embodiment is similar to the circuit configuration of photosensor circuit 1 shown in FIG. 1, the following description will not be repeated. The configuration of the light receiving module including the photosensor circuit according to the third embodiment is the same as the configuration shown in FIG. The optical sensor circuit of the third embodiment is different from the first embodiment in the configuration of a photodiode having a shallow PN junction.

  FIG. 9 is a cross-sectional view illustrating a configuration of a photodiode included in the photosensor circuit according to the third embodiment.

  Referring to FIG. 9, a plurality of N-type diffusion layers 31 (a plurality of second N-type regions) are formed in a strip shape in each of P-type diffusion layers 14 (P-type regions) of photodiodes PD1A and PD2A. Is done. In this respect, the photodiodes PD1A and PD2A shown in FIG. 9 are different from the photodiodes PD1A and PD2A shown in FIG.

  The configuration of the other parts of the photodiodes PD1A and PD2A is the same as that shown in FIG. Further, the configuration of the photodiode PD1B shown in FIG. 9 is the same as the configuration shown in FIG. Therefore, the following description regarding these configurations will not be repeated.

  The plurality of N-type diffusion layers 31 are short-circuited with the P-type diffusion layer 14. When light enters, carriers generated near the surface of the semiconductor substrate are absorbed by the plurality of N-type diffusion layers 31. In the third embodiment, the sensitivity on the short wavelength side can be made lower than that in the first embodiment. Thereby, the spectral sensitivity characteristic of the optical sensor circuit can be brought close to the human visual sensitivity characteristic.

  Note that the sensitivity of the short wavelength region can be lowered as the area of the N-type diffusion layer 31 is larger, so that the spectral sensitivity characteristic can be made closer to the visibility characteristic. However, when the N-type diffusion layer 31 is formed as one region instead of a strip, the resistance of the P-type diffusion layer 14 is reduced by a pinch phenomenon (a phenomenon in which the resistance channel is narrowed by diffusing the N-type layer into the P-type resistor). Becomes larger. When the resistance of the P-type diffusion layer 14 increases, the response of the photodiodes PD1A and PD2A is delayed. By arranging the plurality of N-type diffusion layers 31 in a strip shape, it is possible to prevent the response speed of the photodiode from decreasing.

FIG. 10 is a diagram for explaining the effect of the third embodiment.
Referring to FIG. 10, curves B1 and B2 respectively show the sensitivity of the photosensor circuit when there is no carrier absorption and the sensitivity of the photosensor circuit when there is carrier absorption. Further, FIG. 9 shows a standard visibility curve.

  When the curves B1 and B2 are compared, the sensitivity in the presence of carrier absorption is lower than that in the absence of carrier absorption, particularly at a wavelength shorter than 480 nm. In other words, the sensitivity characteristic approaches the visibility characteristic by performing carrier absorption.

  As described above, according to the third embodiment, by forming a plurality of strip-shaped N-type diffusion layers in the P-type diffusion layer on the surface of the semiconductor substrate, it is possible to obtain a sensitivity characteristic closer to the visibility characteristic. Become.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a figure which shows the example of application of the optical sensor circuit of this invention. FIG. 2 is a circuit diagram of the photosensor circuit 1 in FIG. 1. FIG. 3 is a cross-sectional view of the photodiodes PD1A, PD2A, and PD2B in FIG. FIG. 3 is a plan view showing light receiving surfaces of the photodiodes PD1A, PD1B, PD2A, and PD2B of FIG. It is a figure which shows an example of arrangement | positioning of the light-receiving surface of a photodiode. It is a figure which shows another example of arrangement | positioning of the light-receiving surface of a photodiode. It is a figure explaining the effect by the optical sensor circuit. 6 is a circuit diagram of an optical sensor circuit according to a second embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of a photodiode included in the photosensor circuit according to Embodiment 3. FIG. It is a figure explaining the effect by Embodiment 3. FIG. It is a circuit diagram of the conventional photosensor circuit. It is sectional drawing which shows the structure of a silicon photodiode. It is a figure which shows the spectral sensitivity characteristic of photodiode PD1A of FIG. 12, PD1B, PD2B. It is a figure which shows a human visual sensitivity characteristic.

Explanation of symbols

  1, 1A, 101 photo sensor circuit, 2 signal processing circuit, 4, 4A control circuit, 6, 6A current setting unit, 8 output unit, 11, 111 P-type substrate, 12, 112 buried N-type diffusion layer, 13, 113 N-type epitaxial layer, 14,114 P-type diffusion layer, 15,115 silicon oxide film, 16,116 P-type diffusion layer, 17,117 buried P-type diffusion layer, 21 dark current compensation unit, 22 light-shielding film, 31 N type diffusion layer, 50 light receiving module, A1, A2, A11, A12, A21, A22 light receiving surface, B1, B2 curve, N1 to N7 nodes, P1 point, PD1A, PD1B, PD2A, PD2B, PD3A photodiode, QN1 QN11 NPN transistor, QP1-QP5 PNP transistor, X and Y axes.

Claims (6)

A first light receiving element (PD1A) for detecting light;
A second light receiving element (PD2A) that outputs a photocurrent (I2A) corresponding to the intensity of the light;
A control circuit (4) for changing an applied voltage applied to the first light receiving element (PD1A) according to the photocurrent (I2A);
The first light receiving element (PD1A) includes a first node (VCC) and a second node (N5) having a potential different from the potential of the first node (VCC) by the applied voltage. Connected to
The control circuit (4) includes a first voltage (Vbe (QP4)) that changes according to the photocurrent (I2A), a voltage smaller than the first voltage (Vbe (QP4)), and the photocurrent. A second voltage (Vbe (QP3)) that changes in accordance with (I2A) is generated, and between the first voltage (Vbe (QP4)) and the second voltage (Vbe (QP3)) A voltage corresponding to the voltage difference is applied to the first light receiving element (PD1A) as the applied voltage,
The second voltage (Vbe (QP3)) changes in the same direction as the change direction of the first voltage (Vbe (QP4)) according to the photocurrent (I2A).
The control circuit (4)
A first transistor (QP4) having one end connected to the first node (VCC) and the other end and a control electrode commonly connected to a third node (N6);
A second transistor (QP3) having one end connected to the second node (N5), a control electrode connected to the third node (N6), and the other end connected to a fourth node (N7) )When,
A current setting unit (6) for setting a control current (I6) drawn from the third node (N6) according to the photocurrent (I2A);
An optical sensor circuit comprising: an output unit (8) that performs an output process according to a detection current received from the fourth node (N7) . The ratio between the control current (I6) and the photocurrent (I2A) is the ratio between the area of the light receiving surface of the first light receiving element (PD1A) and the area of the light receiving surface of the second light receiving element (PD2A). The optical sensor circuit of claim 1 , wherein The optical sensor circuit according to claim 2 , wherein an area of a light receiving surface of the second light receiving element (PD2A) is smaller than an area of a light receiving surface of the first light receiving element (PD1A). The photosensor circuit is:
A third light receiving element (PD1B) having a photoelectric sensitivity to the wavelength of the light different from that of the first light receiving element (PD1A);
The optical sensor circuit according to claim 1 , wherein the current setting unit (6) changes the detection current in accordance with a current flowing through the third light receiving element (PD1B). The photosensor circuit is:
A third light receiving element (PD3A) whose light receiving surface is shielded;
The optical sensor circuit according to claim 1 , wherein the current setting unit (6A) corrects the detection current in accordance with a dark current flowing through the third light receiving element (PD3A). Receiving module including a light sensor circuit according to any one of claims 1-5.

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