JPS5858609B2 - Photometering circuit for camera - Google Patents
Photometering circuit for cameraInfo
- Publication number
- JPS5858609B2 JPS5858609B2 JP13398877A JP13398877A JPS5858609B2 JP S5858609 B2 JPS5858609 B2 JP S5858609B2 JP 13398877 A JP13398877 A JP 13398877A JP 13398877 A JP13398877 A JP 13398877A JP S5858609 B2 JPS5858609 B2 JP S5858609B2
- Authority
- JP
- Japan
- Prior art keywords
- circuit
- photocurrent
- operational amplifier
- receiving element
- light receiving
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
- H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
- H03F3/087—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light with IC amplifier blocks
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Description
【発明の詳細な説明】
本発明は被写体の光量を測定するカメラ用測定回路に関
するものである。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a camera measurement circuit that measures the amount of light on an object.
従来の測光回路としては、演算増幅器の正負２つの入力
端子間に受光素子例えばシリコンブルーセルを接続し、
また演算増幅器の出力端子にブリーダ抵抗を接続し、こ
のブリーダ抵抗の分割点の電位を演算増幅器の負入力端
子に帰還させるようにし、演算増幅器の出力端子からシ
リコンブルーセルに入射した光量に応じた出力信号を得
るようにしたものが知られている。In a conventional photometric circuit, a light receiving element such as a silicon blue cell is connected between the positive and negative input terminals of an operational amplifier.
In addition, a bleeder resistor is connected to the output terminal of the operational amplifier, and the potential at the dividing point of this bleeder resistor is fed back to the negative input terminal of the operational amplifier. A device that obtains an output signal is known.
この測光回路では、帰還回路に抵抗を入れると、シリコ
ンブルーセルの光電流に比例した出力信号が得られるが
、カメラの撮影範囲は相当広範囲に広がっているため、
通常帰還回路にダイオードを入れて対数増幅することが
多い。In this photometric circuit, by inserting a resistor into the feedback circuit, an output signal proportional to the photocurrent of the silicon blue cell can be obtained, but since the camera's shooting range is quite wide,
Usually, a diode is inserted into the feedback circuit for logarithmic amplification.
前記シリコンブルーセルに光が入ると、光電流が発生し
、この光電流が対数変換用ダイオードを通って、ブリー
ダ抵抗の分割点に流れ込む。When light enters the silicon blue cell, a photocurrent is generated, which passes through the logarithmic conversion diode and flows into the dividing point of the bleeder resistor.
この光源流がダイオードを通るとき、電圧降下が生じる
から、光電流を対数変換した値に応じてブリーダ抵抗の
分割点の電位が決定される。When this light source flow passes through the diode, a voltage drop occurs, so the potential at the dividing point of the bleeder resistance is determined according to the logarithmically converted value of the photocurrent.
そこで、演算増幅器の出力端子には、ブリーダ抵抗の抵
抗値に応じて、その分割点の電位を増幅した出力電位が
現われる。Therefore, an output potential obtained by amplifying the potential at the dividing point appears at the output terminal of the operational amplifier in accordance with the resistance value of the bleeder resistor.
この測光回路では、ブリーダ抵抗の抵抗比によってその
ゲインが決定される。In this photometric circuit, the gain is determined by the resistance ratio of the bleeder resistor.
ところで、ブリーダ抵抗の分割点には、光電流が流れ込
むから、この光電流によってブリーダ抵抗の抵抗比が等
価的に変化する。By the way, since a photocurrent flows into the dividing point of the bleeder resistance, the resistance ratio of the bleeder resistance changes equivalently due to this photocurrent.
したがって、光電流の大きさによって演算増幅器のゲイ
ンが変化し、これが測光誤差となって現われる。Therefore, the gain of the operational amplifier changes depending on the magnitude of the photocurrent, and this appears as a photometric error.
ブリーダ抵抗のバイアス電流としては、通常１Ｏ−３Ａ
オ一ダー程度に設定されている。The bias current of the bleeder resistor is usually 1O-3A.
It is set to about one order.
光電流は、低輝度で１Ｏ−１１Ａオーダーであり、高輝
度で１０−’Ａオーダーである。The photocurrent is on the order of 10-11A at low brightness and on the order of 10-'A at high brightness.
したがって低輝度の場合には、光電流が流れ込んでもそ
の影響は殆ど無視することができるが、高輝度の場合に
は、１Ｏ−３Ａオーダーの電流が流れているブリーダ抵
抗の分割点に、１０−’Ａオーダーの光電流が流れ込む
ため、演算増幅器のゲインがかなり小さくなる。Therefore, in the case of low brightness, even if the photocurrent flows in, the effect can be almost ignored, but in the case of high brightness, 10- Since a photocurrent of the order of 'A flows in, the gain of the operational amplifier becomes considerably small.
本発明は上記欠点を解決するもので、光電流の影響を防
止して演算増幅器のゲインを一定に保つようにしたカメ
ラ用測光回路を提供することを目的とするものである。SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and it is an object of the present invention to provide a photometry circuit for a camera that prevents the influence of photocurrent and keeps the gain of an operational amplifier constant.
本発明のカメラ用測光回路は、ブリーダ抵抗の分割点と
演算増幅器の負入力端子を接続した負帰還回路に、電圧
ホロワ回路を挿入して光電流を吸収し、それにより分割
点には光電流を対数変換した電位だけが現われるように
したことを特徴とするものである。The photometric circuit for cameras of the present invention absorbs photocurrent by inserting a voltage follower circuit into the negative feedback circuit that connects the dividing point of the bleeder resistor and the negative input terminal of the operational amplifier. This feature is characterized in that only the potential obtained by logarithmically transforming the voltage appears.
したがって、分割点には光電・流が流れ込むことがない
から、演算増幅器のゲインが一定に保たれ、その出力端
子には入射光量に対応した出力電位が現われる。Therefore, since no photocurrent or current flows into the dividing point, the gain of the operational amplifier is kept constant, and an output potential corresponding to the amount of incident light appears at its output terminal.
以下、図面を参照して本発明の実施例について詳細に説
明する。Embodiments of the present invention will be described in detail below with reference to the drawings.
演算増幅器１０の正入力端子には、一定の基準電位Ｖｒ
ｅｆが印加されるまたその正負２つの入力端子間に受光
素子１１が接続されている。A constant reference potential Vr is connected to the positive input terminal of the operational amplifier 10.
A light receiving element 11 is connected between the two positive and negative input terminals to which ef is applied.
この受光素子１１としては、シリコングルーセルのよう
な光起電力素子が用いられる。As this light receiving element 11, a photovoltaic element such as silicon glue cell is used.
演算増幅器１０の出力端子には、抵抗１２．１３からな
るブリーダ抵抗１４が接続されている。A bleeder resistor 14 consisting of resistors 12 and 13 is connected to the output terminal of the operational amplifier 10.
このブリーダ抵抗１４の分割点Ｐと、演算増幅器１０の
負入力端子間を接続した負帰還回路には、演算増幅器１
５の負入力端子と出力端子とを短絡している電圧ホロワ
回路１６と、対数変換用ダイオード１７とが挿入されて
いる。The negative feedback circuit connected between the division point P of the bleeder resistor 14 and the negative input terminal of the operational amplifier 10 includes an operational amplifier 1
A voltage follower circuit 16 that short-circuits the negative input terminal and output terminal of No. 5 and a logarithmic conversion diode 17 are inserted.
この電圧ホロワ回路１６は、出力電圧が入力電圧に等し
くなるように作動する。This voltage follower circuit 16 operates so that the output voltage is equal to the input voltage.
つぎに上記構成の本発明の作用について説明する。Next, the operation of the present invention having the above configuration will be explained.
受光素子１１に被写体からの光が入射すると、その光量
に応じた光電流が流れる。When light from a subject enters the light receiving element 11, a photocurrent flows depending on the amount of light.
この光電流は、ダイオード１７を通り、ここでは対数変
換され、電圧ホロワ回路１５に入る。This photocurrent passes through a diode 17, where it is logarithmically transformed and enters a voltage follower circuit 15.
この電圧ホロワ回路１６は、回路の絶縁を図るためのも
ので、増幅作用がないから、Ｐ点に光電流に関連した電
位が生じ、この電位が演算増幅器１０で増幅される。This voltage follower circuit 16 is intended to insulate the circuit and has no amplifying effect, so a potential related to the photocurrent is generated at point P, and this potential is amplified by the operational amplifier 10.
Ｐ点の電位をｖＬとし、演算増幅器１０の出力電位をＶ
ｏとすれば、
となる。Let the potential at point P be vL, and let the output potential of the operational amplifier 10 be V.
If o, then it becomes.
ここでＲ１は抵抗１２の抵抗値を、またＲ２は抵抗１３
の抵抗値をそれぞれ表わしている。Here, R1 is the resistance value of resistor 12, and R2 is the resistance value of resistor 13.
represents the resistance value of each.
ところで、ダイオード１１の電圧降下をＶＤとすれは、
（１）式はつぎのようになる。By the way, if the voltage drop of the diode 11 is VD, then
Equation (1) is as follows.
したがってブリ・−ダ抵抗１４の抵抗比が演算増幅器１
０のゲインとなり、分割点Ｐの電位がこれに比例して増
幅される。Therefore, the resistance ratio of the bleeder resistor 14 is
The gain becomes 0, and the potential at the dividing point P is amplified in proportion to this.
この場合に、光電流が分割点Ｐを通って抵抗１３に流れ
ると、ブリーダ抵抗１４に流れるバイアス電流が減少す
るから、等何曲にそのゲインが減少することになる。In this case, when the photocurrent flows through the dividing point P to the resistor 13, the bias current flowing to the bleeder resistor 14 decreases, so that the gain decreases to a certain degree.
しかし、帰還回路に電圧ホロワ回路１６が接続されてい
るから、光電流が吸収され、Ｐ点には電位のみが現われ
る。However, since the voltage follower circuit 16 is connected to the feedback circuit, the photocurrent is absorbed and only the potential appears at point P.
したがって、バイアス電流が、光電流によって変化しな
いため、演算増幅器１０のゲインが一定になる。Therefore, since the bias current does not change depending on the photocurrent, the gain of the operational amplifier 10 remains constant.
なお、測光範囲が小さい場合は、ダイオード１７の代わ
りに、抵抗を入れ、光電流に比例した出力信号を得るよ
うにすることができる。Note that if the photometry range is small, a resistor may be inserted in place of the diode 17 to obtain an output signal proportional to the photocurrent.
上記構成を有する本発明によれは、帰還回路に電圧ホロ
ワ回路を接続したから、光電流の大きさにより演算増幅
器のゲインが変動するのを防止し、測光精度を高めるこ
とができる。According to the present invention having the above configuration, since the voltage follower circuit is connected to the feedback circuit, it is possible to prevent the gain of the operational amplifier from varying due to the magnitude of the photocurrent and improve the photometry accuracy.
図面は本発明の測光回路を示す回路図である。
１０・・・・・・演算増幅器、１１・・・・・・受光素
子、１４・・・・・・ブリーダ抵抗、１６・・・・・・
電圧ホロワ回路、１７・・・・・・対数変換用ダイオー
ド、Ｐ・・・・・・分割点。The drawing is a circuit diagram showing a photometric circuit of the present invention. 10... operational amplifier, 11... light receiving element, 14... bleeder resistor, 16...
Voltage follower circuit, 17...Diode for logarithmic conversion, P...Dividing point.
Claims (1)
続し、また出力端子にブリーダ抵抗を接続するとともに
、このブリーダ抵抗の分割点の電位を負入力端子に負帰
還させてなる測光回路において、前記演算増幅器の帰還
回路に電圧ホロワ回路を挿入して、前記受光素子の光電
流の大きさに関係なく演算増幅器のゲインを一定に保つ
ようにしたことを特徴とするカメラ用測光回路。 ２ ＠記帰還回路にダイオードを接続して受光素子の光
電流を対数増幅するようにしたことを特徴とする特許請
求の範囲第１項記載のカメラ用測光回路。 ３ 前記帰還回路に抵抗を接続して受光素子の光電流に
比例した出力電位が得られるようにしたことを特徴とす
る特許請求の範囲第１項記載のカメラ用測光回路。[Claims] 1. A light receiving element is connected between the positive and negative input terminals of the operational amplifier, and a bleeder resistor is connected to the output terminal, and the potential at the dividing point of the bleeder resistor is negatively fed back to the negative input terminal. In the photometry circuit, a voltage follower circuit is inserted into the feedback circuit of the operational amplifier so that the gain of the operational amplifier is kept constant regardless of the magnitude of the photocurrent of the light receiving element. photometering circuit. 2. The photometry circuit for a camera according to claim 1, wherein a diode is connected to the feedback circuit to logarithmically amplify the photocurrent of the light receiving element. 3. The camera photometry circuit according to claim 1, wherein a resistor is connected to the feedback circuit to obtain an output potential proportional to the photocurrent of the light receiving element.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13398877A JPS5858609B2 (en) | 1977-11-08 | 1977-11-08 | Photometering circuit for camera |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13398877A JPS5858609B2 (en) | 1977-11-08 | 1977-11-08 | Photometering circuit for camera |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5466836A JPS5466836A (en) | 1979-05-29 |
| JPS5858609B2 true JPS5858609B2 (en) | 1983-12-26 |
Family
ID=15117748
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP13398877A Expired JPS5858609B2 (en) | 1977-11-08 | 1977-11-08 | Photometering circuit for camera |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5858609B2 (en) |
-
1977
- 1977-11-08 JP JP13398877A patent/JPS5858609B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5466836A (en) | 1979-05-29 |
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