JP2008008647A - Photoelectric conversion device - Google Patents
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本発明は照度を電気信号に変換する光電変換装置に関し、特に照度に比例した電流を発生する複数の光電変換回路を備えた光電変換装置に関する。 The present invention relates to a photoelectric conversion device that converts illuminance into an electrical signal, and more particularly to a photoelectric conversion device that includes a plurality of photoelectric conversion circuits that generate a current proportional to illuminance.
照度に比例した電流を発生する光電変換回路を使った従来の光電変換装置は、光電変換回路で発生する電流を抵抗に流し込み、その抵抗の両端電圧を出力値とするものであった（例えば特許文献１参照）。しかし、この構成では出力電圧が照度に対して線形的に変化するため、照度範囲が広い場合、低照度側の分解能が低下する。例えば、薄暗い部屋の照度は約0.01（lx）であるのに対し、真夏の炎天下では約30000（lx）にも達し、その差は極めて大きい。このため、照度に対して線形的に変化する出力電圧によってリニア表示すると、薄暗い状態の照度の検出精度が極端に低下する。 A conventional photoelectric conversion device using a photoelectric conversion circuit that generates a current proportional to illuminance flows a current generated by the photoelectric conversion circuit into a resistor and uses a voltage across the resistor as an output value (for example, a patent) Reference 1). However, in this configuration, since the output voltage changes linearly with respect to the illuminance, the resolution on the low illuminance side decreases when the illuminance range is wide. For example, the illuminance of a dimly lit room is about 0.01 (lx), while it reaches about 30000 (lx) under the hot summer sun, and the difference is extremely large. For this reason, when linear display is performed with an output voltage that linearly changes with respect to illuminance, the detection accuracy of illuminance in a dim state is extremely lowered.
そこで、次式に示すようにダイオードの両端電圧Vfが流れ込む電流Iの対数に比例することを利用し、光電変換回路で発生した電流をダイオードに流し込んで、その電流値の対数に比例する電圧に変換する光電変換装置が知られている（例えば特許文献２参照）。
Vf=k×T／q×ln(I/Is) …(1)
ここで、kはボルツマン定数、Tは絶対温度、qは素電荷、Isはダイオードの飽和電流、lnはeを底とするlog関数である。
Therefore, using the fact that the voltage Vf across the diode flows in proportion to the logarithm of the current I as shown in the following equation, the current generated in the photoelectric conversion circuit is fed into the diode, and the voltage proportional to the logarithm of the current value is obtained. A photoelectric conversion device for conversion is known (see, for example, Patent Document 2).
Vf = k × T / q × ln (I / Is) (1)
Here, k is a Boltzmann constant, T is an absolute temperature, q is an elementary charge, Is is a diode saturation current, and ln is a log function with e as the base.
このような対数変換を行う光電変換装置によれば、高照度側に比べて低照度側の分解能を高めることができるため、薄暗い状態の照度も精度良く検出することが可能になる。 According to the photoelectric conversion device that performs such logarithmic conversion, it is possible to increase the resolution on the low illuminance side as compared with the high illuminance side, and thus it is possible to detect the illuminance in the dim state with high accuracy.
カメラなどでは露光前に照度を測定することは非常に重要である。照度により露光時間を調整しなければ、より適切な画像を得ることができないからである。この場合、構図のなかの或る１点の照度を測定するだけで露光時間を決めるよりは、構図のなかを複数箇所に分割しそれぞれの箇所で照度を測定し、それらを平均化した照度から露光時間を決めた方が、より最適な画像を得ることができる。そのためには、一つの光電変換回路しか有しない従来の光電変換装置では不十分であり、複数の光電変換回路が扱える光電変換装置が必要になってくる。 In cameras and the like, it is very important to measure illuminance before exposure. This is because a more appropriate image cannot be obtained unless the exposure time is adjusted by the illuminance. In this case, rather than determining the exposure time just by measuring the illuminance at a certain point in the composition, the composition is divided into a plurality of locations, the illuminance is measured at each location, and the averaged illuminance is calculated. A more optimal image can be obtained by determining the exposure time. For this purpose, a conventional photoelectric conversion device having only one photoelectric conversion circuit is insufficient, and a photoelectric conversion device that can handle a plurality of photoelectric conversion circuits is required.
図２はその種の光電変換装置の開発過程において本発明者が試作した一つの回路例を示す。同図に示す光電変換装置は、照度に比例した電流ii1〜iinを発生する複数の光電変換回路P1〜Pnと、アノードが基準電圧Vrに接続され、カソードが光電変換回路P1〜Pnに接続された複数のダイオードD1〜Dnと、複数のダイオードD1〜Dnのカソード電圧V1〜Vnを平均化する変換回路CNT1とから構成される。また、変換回路CNT1は、複数のバッファー回路BF1〜BFnと、同じ抵抗値の複数の抵抗R1〜Rnとで構成される。なお、光電変換回路P1〜Pnは、フォトダイオードやフォトトランジスタ等で構成される。 FIG. 2 shows an example of a circuit manufactured by the present inventor in the process of developing such a photoelectric conversion device. The photoelectric conversion device shown in the figure has a plurality of photoelectric conversion circuits P1 to Pn that generate currents ii1 to iin proportional to illuminance, an anode connected to the reference voltage Vr, and a cathode connected to the photoelectric conversion circuits P1 to Pn. The plurality of diodes D1 to Dn and a conversion circuit CNT1 that averages the cathode voltages V1 to Vn of the plurality of diodes D1 to Dn. The conversion circuit CNT1 includes a plurality of buffer circuits BF1 to BFn and a plurality of resistors R1 to Rn having the same resistance value. Note that the photoelectric conversion circuits P1 to Pn are configured by photodiodes, phototransistors, or the like.
図２の回路において、アノードを基準電圧Vrに接続した複数のダイオードD1〜Dnに、それぞれ光電変換回路P1〜Pnから出力される光の照度に比例した電流ii1〜iinを流し込むことによって、ダイオードD1〜Dnのカソードにそれらの電流ii1〜iinの対数に比例した電圧V1〜Vnを発生させることができる。また、それらの電圧V1〜Vnを、バッファー回路BF1〜BFnを通して抵抗R1〜Rnに加えることで、それらの電圧V1〜Vnの平均電圧Voを取り出すことができる。数式を用いて説明すると、以下のようになる。 In the circuit of FIG. 2, by flowing currents ii1 to iin proportional to the illuminance of light output from the photoelectric conversion circuits P1 to Pn into the plurality of diodes D1 to Dn having anodes connected to the reference voltage Vr, the diode D1 Voltages V1 to Vn proportional to the logarithm of the currents ii1 to iin can be generated at the cathode of ˜Dn. Further, by adding these voltages V1 to Vn to the resistors R1 to Rn through the buffer circuits BF1 to BFn, the average voltage Vo of these voltages V1 to Vn can be taken out. This will be described below using mathematical formulas.
光電変換回路P1〜Pnから出力される光の照度に比例した電流をii1〜iin、ダイオードD1〜Dnのカソード電圧をV1〜Vn、抵抗R1〜Rnの抵抗値をR、それらの抵抗R1〜Rnを流れる電流をi1〜in、変換回路CNT1の出力電圧をVoとすると、次式(2)、次式(3-1)〜(3-n)が成り立つ。
i1+i2+i3+……+in=0 …(2)
V1-Vo=R×i1 …(3-1)
V2-Vo=R×i2 …(3-2)
……
Vn-Vo=R×in …(3-n)
The current proportional to the illuminance of the light output from the photoelectric conversion circuits P1 to Pn is ii1 to iin, the cathode voltages of the diodes D1 to Dn are V1 to Vn, the resistance values of the resistors R1 to Rn are R, and the resistors R1 to Rn Where i1 to in and the output voltage of the conversion circuit CNT1 is Vo, the following equations (2) and (3-1) to (3-n) are established.
i1 + i2 + i3 + …… + in = 0… (2)
V1-Vo = R × i1 (3-1)
V2-Vo = R × i2 (3-2)
......
Vn-Vo = R × in… (3-n)
上記の式(2)、式(3-1)〜(3-n)からi1〜inを消去すると、変換回路CNT1の出力電圧Voは以下のように与えられる。
Vo=(V1+V2+V3+……+Vn)/n …(4)
When i1 to in are eliminated from the above equations (2) and (3-1) to (3-n), the output voltage Vo of the conversion circuit CNT1 is given as follows.
Vo = (V1 + V2 + V3 + …… + Vn) / n… (4)
一方、ダイオードD1〜Dnの両端電圧は次の式で表される。
Vr-V1=Vt×ln(ii1/Is) …(5-1)
Vr-V2=Vt×ln(ii2/Is) …(5-2)
……
Vr-Vn=Vt×ln(iin/Is) …(5-n)
ここで、Vt=k×T／ｑ
On the other hand, the voltage across the diodes D1 to Dn is expressed by the following equation.
Vr-V1 = Vt × ln (ii1 / Is)… (5-1)
Vr-V2 = Vt × ln (ii2 / Is) (5-2)
......
Vr-Vn = Vt × ln (iin / Is)… (5-n)
Where Vt = k × T / q
式(5-1)〜(5-n)を式(1)に代入してV1〜Vnを消去し整理すると、
Vr-Vo=Vt×ln(n√(ii1×ii2×ii3×…×iin)/Is) …(6)
となり、変換回路CNT1の出力電圧Voは、光電変換回路P1〜Pnから出力される電流ii1〜iinの相乗平均の対数に比例した電圧となる。
Substituting Equations (5-1) to (5-n) into Equation (1) and erasing and organizing V1 to Vn,
Vr-Vo = Vt × ln ( n √ (ii1 × ii2 × ii3 ×… × iin) / Is) (6)
Thus, the output voltage Vo of the conversion circuit CNT1 is a voltage proportional to the logarithm of the geometric mean of the currents ii1 to iin output from the photoelectric conversion circuits P1 to Pn.
図２に示した光電変換装置によれば、照度に比例した電流ii1〜iinを発生する複数の光電変換回路P1〜Pnを備えているので、複数箇所の照度をそれぞれ独立に測定することが可能になる。また、各々の電流ii1〜iinをその電流値の対数に比例する電圧V1〜Vnに変換する複数のダイオードD1〜Dnを備えているため、各々の測定箇所の照度が小さい場合でも精度良く検出することができる。さらに、各々の電圧V1〜Vnの平均電圧Voを出力する変換回路CNT1を備えているため、各々の測定箇所の照度を平均化した照度を得ることができる。 According to the photoelectric conversion device shown in FIG. 2, since the plurality of photoelectric conversion circuits P1 to Pn that generate currents ii1 to iin proportional to the illuminance are provided, the illuminance at a plurality of locations can be measured independently. become. In addition, since it has a plurality of diodes D1 to Dn that convert each current ii1 to iin into voltages V1 to Vn that are proportional to the logarithm of the current value, even if the illuminance at each measurement point is small, it can be detected accurately. be able to. Furthermore, since the conversion circuit CNT1 that outputs the average voltage Vo of each of the voltages V1 to Vn is provided, the illuminance obtained by averaging the illuminance at each measurement location can be obtained.
しかしながら、式(6)から明らかなように、平均化された照度は、各々の測定箇所の照度の相乗平均になる。このため、例えば、n=2で、ii1=1、ii2=100とすると、その相乗平均は√(1×100)=10となる。光電変換回路から出力される電流は照度に比例しているため、2箇所の照度の中間値を表すのではなく、暗い側の照度に近い値となる。このため、正確な露光時間の設定が困難になるという問題があった。 However, as is clear from Equation (6), the averaged illuminance is a geometric mean of the illuminance at each measurement location. Therefore, for example, when n = 2, ii1 = 1, and ii2 = 100, the geometric mean is √ (1 × 100) = 10. Since the current output from the photoelectric conversion circuit is proportional to the illuminance, it does not represent the intermediate value of the illuminance at the two locations, but is close to the illuminance on the dark side. For this reason, there is a problem that it is difficult to set an accurate exposure time.
他方、図２の回路において、ダイオードD1〜Dnを抵抗R'に置換すれば、変換回路CNT1の出力電圧Voは、次式(7)に示されるように、光電変換回路から出力される光の照度に比例した電流ii1〜iinの相加平均値になる。
Vr-Vo=(ii1+ii2+ii3+…+iin)R'/n …(7)
On the other hand, if the diodes D1 to Dn are replaced with the resistors R ′ in the circuit of FIG. 2, the output voltage Vo of the conversion circuit CNT1 is the light output from the photoelectric conversion circuit as shown in the following equation (7). An arithmetic average value of currents ii1 to iin proportional to the illuminance is obtained.
Vr-Vo = (ii1 + ii2 + ii3 +… + iin) R '/ n… (7)
このため、前述と同様、n=2で、ii1=1、ii2=100とすると、その相加平均値は(1+100)/2=50.5となる。光電変換回路から出力される電流は照度に比例しているため、2箇所の照度のほぼ中間値を表すことになり、露光時間の設定が容易になる。しかしながら、前述したように照度の変動幅は10の6乗程度あるので、V1〜Vnの最大値を3Vとしても最小値は3μVとなり、実現は困難である。また、最小入力電流は0.1pA以下なので、3μVが扱えたとしても、検出抵抗R'は30MΩとなり、ICでは実現が難しい。 Therefore, as described above, when n = 2, ii1 = 1, and ii2 = 100, the arithmetic average value is (1 + 100) /2=50.5. Since the current output from the photoelectric conversion circuit is proportional to the illuminance, it represents an almost intermediate value of the illuminance at the two locations, and the exposure time can be easily set. However, as described above, since the fluctuation range of illuminance is about 10 6, even if the maximum value of V1 to Vn is 3V, the minimum value is 3 μV, which is difficult to realize. Also, since the minimum input current is 0.1 pA or less, even if 3 μV can be handled, the detection resistance R ′ is 30 MΩ, which is difficult to realize with an IC.
本発明はこのような事情に鑑みて提案されたものであり、その目的は、複数箇所の照度をそれぞれ独立に測定することができ、且つ、各々の測定箇所の照度が小さい場合でも精度良く検出でき、さらに各々の測定箇所の照度の相加平均値を出力する光電変換装置を提供することにある。 The present invention has been proposed in view of such circumstances, and its purpose is to be able to measure illuminance at a plurality of locations independently, and to detect accurately even when the illuminance at each measurement location is small. In addition, another object of the present invention is to provide a photoelectric conversion device that outputs an arithmetic mean value of illuminance at each measurement point.
本発明の光電変換装置は、照度に比例した電流を発生する複数の光電変換回路と、各々の前記光電変換回路で発生した電流をその電流値の対数に比例する電圧に変換する複数の非線形素子と、前記複数の非線形素子による変換で得られた電圧を入力し、前記複数の光電変換回路で発生した電流の相加平均値の対数に比例する電圧を出力する変換回路とを備えている。 The photoelectric conversion device of the present invention includes a plurality of photoelectric conversion circuits that generate current proportional to illuminance, and a plurality of nonlinear elements that convert the current generated in each of the photoelectric conversion circuits into a voltage proportional to the logarithm of the current value. And a conversion circuit for inputting a voltage obtained by the conversion by the plurality of nonlinear elements and outputting a voltage proportional to the logarithm of the arithmetic mean value of the current generated by the plurality of photoelectric conversion circuits.
本発明の好ましい実施の形態にあっては、前記変換回路は、エミッタどうし及びコレクタどうしが互いに接続され、ベースに前記複数の非線形素子による変換で得られた電圧が入力される複数の第１のトランジスタと、エミッタが前記第１のトランジスタのエミッタに接続され、ベースとコレクタが互いに接続された第２のトランジスタと、前記複数の第１のトランジスタのコレクタ電流の和と概略同じ電流を前記第１のトランジスタのコレクタに流す回路とを備える。さらに、前記第２のトランジスタのエミッタ面積が、前記第１のトランジスタのエミッタ面積の総和に等しくされる。 In a preferred embodiment of the present invention, the conversion circuit includes a plurality of first transistors in which emitters and collectors are connected to each other, and voltages obtained by conversion by the plurality of nonlinear elements are input to a base. A transistor, an emitter connected to the emitter of the first transistor, a base and a collector connected to each other, and a current substantially the same as a sum of collector currents of the plurality of first transistors; And a circuit that flows through the collector of the transistor. Further, the emitter area of the second transistor is made equal to the sum of the emitter areas of the first transistor.
本発明によれば以下のような効果が得られる。 According to the present invention, the following effects can be obtained.
複数箇所の照度をそれぞれ独立に測定することができる。その理由は、照度に比例した電流を発生する複数の光電変換回路を備えているためである。 The illuminance at a plurality of locations can be measured independently. The reason is that a plurality of photoelectric conversion circuits that generate a current proportional to illuminance are provided.
各々の測定箇所の照度が小さい場合でも精度良く検出することができる。その理由は、照度に比例した電流をその電流値の対数に比例する電圧に変換する複数の非線形素子（例えばダイオード）を備えているためである。 Even when the illuminance at each measurement point is small, it can be detected with high accuracy. The reason is that a plurality of nonlinear elements (for example, diodes) that convert a current proportional to illuminance into a voltage proportional to the logarithm of the current value are provided.
カメラの露光制御に適用した場合、正確な露光時間の設定が可能になる。その理由は、複数の光電変換回路で発生した電流の相加平均値の対数に比例する電圧を出力する変換回路を備えているためである。 When applied to camera exposure control, an accurate exposure time can be set. This is because a conversion circuit that outputs a voltage proportional to the logarithm of the arithmetic mean value of the currents generated in the plurality of photoelectric conversion circuits is provided.
図１を参照すると、本発明の実施の形態にかかる光電変換装置は、照度に比例した電流ii1〜iinを発生する複数の光電変換回路P1〜Pnと、アノードが基準電圧Vrに接続され、カソードが光電変換回路P1〜Pnに接続された複数のダイオードD1〜Dnと、複数のダイオードD1〜Dnのカソード電圧V1〜Vnを入力し、複数の光電変換回路P1〜Pnで発生した電流ii1〜iinの相加平均値の対数に比例する電圧Voを出力する変換回路CNT2とから構成される。図２に示した光電変換装置と比較すると、変換回路CNT1の代わりに変換回路CNT2を備えている点が相違する。 Referring to FIG. 1, a photoelectric conversion apparatus according to an embodiment of the present invention includes a plurality of photoelectric conversion circuits P1 to Pn that generate currents ii1 to iin proportional to illuminance, an anode connected to a reference voltage Vr, and a cathode. Inputs a plurality of diodes D1 to Dn connected to the photoelectric conversion circuits P1 to Pn, and cathode voltages V1 to Vn of the plurality of diodes D1 to Dn, and currents ii1 to iin generated in the plurality of photoelectric conversion circuits P1 to Pn And a conversion circuit CNT2 that outputs a voltage Vo that is proportional to the logarithm of the arithmetic average value. Compared with the photoelectric conversion device shown in FIG. 2, the difference is that a conversion circuit CNT2 is provided instead of the conversion circuit CNT1.
変換回路CNT2は、特性の等しい複数の第１のトランジスタTR1〜TRnと、この複数の第１のトランジスタTR1〜TRnのエミッタ面積の総和に等しいエミッタ面積を有する第２のトランジスタTTと、定電流源ＳＳと、カレントミラー回路CMとから構成される。第１のトランジスタTR1〜TRnのエミッタどうし及びコレクタどうしは互いに共通電極に接続され、それらのベースにダイオードD1〜Dnのカソード電圧V1〜Vnが入力される。第２のトランジスタTTのエミッタは第１のトランジスタTR1〜TRnのエミッタと同じ電極に接続され、ベースとコレクタは互いに共通電極に接続されて、その共通電極から出力Voが取り出されるようになっている。定電流源SSは、複数の第１のトランジスタTR1〜TRnのエミッタと第２のトランジスタTTのエミッタに電流を流す手段である。カレントミラー回路CMは、複数の第１のトランジスタTR1〜TRnのコレクタ電流の和と概略同じ電流を第２のトランジスタTTのコレクタに流すために設けられている。 The conversion circuit CNT2 includes a plurality of first transistors TR1 to TRn having the same characteristics, a second transistor TT having an emitter area equal to the sum of the emitter areas of the plurality of first transistors TR1 to TRn, and a constant current source. It is composed of SS and a current mirror circuit CM. The emitters and collectors of the first transistors TR1 to TRn are connected to a common electrode, and the cathode voltages V1 to Vn of the diodes D1 to Dn are input to their bases. The emitter of the second transistor TT is connected to the same electrode as the emitters of the first transistors TR1 to TRn, the base and the collector are connected to a common electrode, and the output Vo is taken out from the common electrode. . The constant current source SS is means for flowing current to the emitters of the plurality of first transistors TR1 to TRn and the emitter of the second transistor TT. The current mirror circuit CM is provided to flow a current substantially the same as the sum of the collector currents of the plurality of first transistors TR1 to TRn to the collector of the second transistor TT.
本実施の形態にかかる光電変換装置において、アノードを基準電圧Vrに接続した複数のダイオードD1〜Dnに、それぞれ光電変換回路P1〜Pnから出力される光の照度に比例した電流ii1〜iinを流し込むと、ダイオードD1〜Dnのカソードにそれらの電流ii1〜iinの対数に比例した電圧V1〜Vnが発生する。そして、この発生した電圧V1〜Vnが変換回路CNT2に入力され、複数の光電変換回路P1〜Pnで発生した電流ii1〜iinの相加平均値の対数に比例する電圧Voが生成される。数式を用いて説明すると、以下のようになる。 In the photoelectric conversion device according to the present embodiment, currents ii1 to iin proportional to the illuminance of light output from the photoelectric conversion circuits P1 to Pn are respectively flowed into the plurality of diodes D1 to Dn whose anodes are connected to the reference voltage Vr. Then, voltages V1 to Vn proportional to the logarithms of the currents ii1 to iin are generated at the cathodes of the diodes D1 to Dn. The generated voltages V1 to Vn are input to the conversion circuit CNT2, and a voltage Vo proportional to the logarithm of the arithmetic average value of the currents ii1 to iin generated in the plurality of photoelectric conversion circuits P1 to Pn is generated. This will be described below using mathematical formulas.
基準電圧をVr、各ダイオードD1〜Dnのカソード電位をV1〜Vn、光電変換回路P1〜Pnの出力電流をii1〜iinとすると、次の式が成り立つ。
Vr-V1=Vt×ln(ii1/Is) …(8-1)
Vr-V2=Vt×ln(ii2/Is) …(8-2)
……
Vr-Vn=Vt×ln(iin/Is) …(8-n)
ここで、Vt=k×T／ｑ
Assuming that the reference voltage is Vr, the cathode potentials of the diodes D1 to Dn are V1 to Vn, and the output currents of the photoelectric conversion circuits P1 to Pn are ii1 to iin, the following equation is established.
Vr-V1 = Vt × ln (ii1 / Is) (8-1)
Vr-V2 = Vt × ln (ii2 / Is)… (8-2)
......
Vr-Vn = Vt × ln (iin / Is)… (8-n)
Where Vt = k × T / q
また、第１のトランジスタTR1〜TRnのエミッタ電圧をV、各コレクタ電流をi1〜inとすると、次の式が成り立つ。
V-V1=Vt×ln(i1/Is) …(9-1)
V-V2=Vt×ln(i2/Is) …(9-2)
……
V-Vn=Vt×ln(in/Is) …(9-n)
Further, when the emitter voltages of the first transistors TR1 to TRn are V and the collector currents are i1 to in, the following equation is established.
V-V1 = Vt × ln (i1 / Is)… (9-1)
V-V2 = Vt × ln (i2 / Is)… (9-2)
......
V-Vn = Vt × ln (in / Is)… (9-n)
式(2-1)〜(2-n)と式(3-1)〜(3-n)とから、i1とi2〜inとの電流比は、ii1とii2〜iinとの電流比に等しいという以下の式(10-2)〜(10-n)が導出できる。
i2=(ii2/ii1)×i1 …(10-2)
i3=(ii3/ii1)×i1 …(10-3)
……
in=(iin/ii1)×i1 …(10-n)
From formulas (2-1) to (2-n) and formulas (3-1) to (3-n), the current ratio between i1 and i2 to in is equal to the current ratio between ii1 and ii2 to iin. The following equations (10-2) to (10-n) can be derived.
i2 = (ii2 / ii1) × i1… (10-2)
i3 = (ii3 / ii1) × i1 (10-3)
......
in = (iin / ii1) × i1… (10-n)
一方、第１のトランジスタTR1〜TRnのコレクタと第２のトランジスタTTのコレクタはカレントミラー回路CMに接続されているため、第１のトランジスタTR1〜TRnのコレクタ電流の総和(i1+i2+…+in)と、第２のトランジスタTTのコレクタ電流とは等しくなる。また、第２のトランジスタTTのエミッタ面積は、第１のトランジスタTR1〜TRnのエミッタ面積の総和に等しい。従って、次の式が成り立つ。
V-Vo=Vt×ln((i1+i2+i3+…+in)/(n×Is)) …(11)
On the other hand, since the collectors of the first transistors TR1 to TRn and the collector of the second transistor TT are connected to the current mirror circuit CM, the sum of collector currents (i1 + i2 +... + In of the first transistors TR1 to TRn). ) Is equal to the collector current of the second transistor TT. The emitter area of the second transistor TT is equal to the sum of the emitter areas of the first transistors TR1 to TRn. Therefore, the following equation holds.
V-Vo = Vt × ln ((i1 + i2 + i3 +… + in) / (n × Is))… (11)
この式(11)に、i1=(ii1/ii1)×i1…式(10-1)と、式(10-2)〜(10-n)を代入して、さらに式(2-1)と式(3-1)をあわせると、以下の式が得られる。
Vr-Vo=Vt×ln((ii1+ii2+ii3+…+iin)/(n×Is)) …(12)
すなわち、第２のトランジスタTTのコレクタ電位Voは、光電変換回路P1〜Pnの出力電流ii1〜iinの相加平均値を対数に変換した電圧となる。
In this equation (11), i1 = (ii1 / ii1) × i1 Equation (10-1) and Equations (10-2) to (10-n) are substituted, and Equation (2-1) and Combining equation (3-1) yields the following equation:
Vr-Vo = Vt × ln ((ii1 + ii2 + ii3 +… + iin) / (n × Is))… (12)
That is, the collector potential Vo of the second transistor TT is a voltage obtained by converting the arithmetic average value of the output currents ii1 to iin of the photoelectric conversion circuits P1 to Pn into a logarithm.
次に本実施の形態の効果を説明する。 Next, the effect of this embodiment will be described.
本実施の形態によれば、複数箇所の照度をそれぞれ独立に測定することができ、且つ、各々の測定箇所の照度が小さい場合でも精度良く検出でき、さらに各々の測定箇所の照度の相加平均値を出力することができる。 According to the present embodiment, the illuminance at a plurality of locations can be measured independently, can be detected accurately even when the illuminance at each measurement location is small, and the arithmetic average of the illuminance at each measurement location A value can be output.
また本実施の形態によれば、ダイオードD1〜Dnのカソード電位V1〜Vnが安定した時点から数μs程度の短時間で、光電変換回路P1〜Pnの出力電流ii1〜iinの相加平均値を対数に変換した電圧Voを得ることができる。その理由は、複数の第１のトランジスタTR1〜TRnと第２のトランジスタTTとは一種の差動増幅器によるホロワであり、対数に圧縮されたものを一旦元のリニアに伸長して加算後再び圧縮する場合のような応答の遅れがないためである。 Further, according to the present embodiment, the arithmetic average value of the output currents ii1 to iin of the photoelectric conversion circuits P1 to Pn is obtained in a short time of about several μs after the cathode potentials V1 to Vn of the diodes D1 to Dn are stabilized. The voltage Vo converted into logarithm can be obtained. The reason is that the plurality of first transistors TR1 to TRn and the second transistor TT are a follower by a kind of differential amplifier, and the logarithmically compressed one is expanded to the original linear once and added and then compressed again. This is because there is no delay in response as in the case of doing.
以上本発明の実施の形態について説明したが、本発明は以上の実施の形態にのみ限定されず、その他各種の付加変更が可能である。例えば、図１の回路では、複数ある光電変換回路P1〜Pnの全ての電流ii1〜iinの相加平均値を対数に変換した電圧Voを生成したが、各第１のトランジスタTR1〜TRnのベースと対応するダイオードD1〜Dnのカソードとの間にスイッチング素子を挿入してそのオン、オフを制御すること等により、任意の数の光電変換回路のグループ毎にその電流の相加平均値を対数に圧縮した電圧を順次求めるようにしても良い。 Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various other additions and modifications can be made. For example, in the circuit of FIG. 1, the voltage Vo is generated by converting the arithmetic average value of all the currents ii1 to iin of the plurality of photoelectric conversion circuits P1 to Pn into logarithms, but the bases of the first transistors TR1 to TRn are generated. Logarithmically calculate the arithmetic average value of the current for each group of photoelectric conversion circuits by inserting a switching element between the corresponding diode D1 to Dn and the cathode of the corresponding diode D1 to Dn and controlling on / off thereof, etc. Alternatively, the compressed voltage may be obtained sequentially.
P1〜Pn…光電変換回路
D1〜Dn…ダイオード
TR1〜TRn…第１のトランジスタ
TT…第２のトランジスタ
SS…定電流源
CM…カレントミラー回路
CNT1、CNT2…変換回路
BF1〜BFn…バッファー
R1〜Rn…抵抗
P1 to Pn: Photoelectric conversion circuit
D1-Dn ... Diode
TR1 to TRn: 1st transistor
TT ... second transistor
SS: Constant current source
CM: Current mirror circuit
CNT1, CNT2 ... Conversion circuit
BF1 ~ BFn ... buffer
R1 ~ Rn ... resistance
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| JPS5946521A (en) * | 1982-09-08 | 1984-03-15 | Canon Inc | Light measuring circuit |
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| JP2012084790A (en) * | 2010-10-14 | 2012-04-26 | Canon Inc | Photoelectric conversion device |
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