JP3670859B2

JP3670859B2 - Light receiving position detection circuit

Info

Publication number: JP3670859B2
Application number: JP25404598A
Authority: JP
Inventors: 哲也吉冨; 孝染谷
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1998-09-08
Filing date: 1998-09-08
Publication date: 2005-07-13
Anticipated expiration: 2018-09-08
Also published as: JP2000089093A

Description

【０００１】
【発明の属する技術分野】
本発明は、カメラの自動焦点制御に用いる受光位置検出回路に関する。
【０００２】
【従来の技術】
図４は三角測距の原理を示す図面である。
【０００３】
図４において、発光体（１００）はカメラの特定位置に配置されたものであり、使用者がカメラを被写体に向けて発光操作を行った時、赤外線等の発光信号を被写体に対し出力する。発光信号は投光レンズ（１０１）を介して被写体に照射される。発光信号は被写体に到達すると反射するが、この反射信号は集光レンズ（１０２）を介して受光体（１０３）に到達する。被写体Ａ，Ｂは、発光信号が照射される対象であり、発光体（１００）に対し被写体Ａは被写体Ｂより遠い場所に存在するものとする。
【０００４】
発光信号が被写体Ａ（遠距離）に照射された場合、この時の反射信号は受光体（１０３）の左側に到達する。また、発光信号が被写体Ｂ（近距離）に照射された場合、この時の反射信号は受光体（１０３）の右側に到達する。即ち、反射信号を受ける集光レンズ（１０２）の位置が固定されている為、被写体と発光体（１００）との距離が近くなる程、受光体（１０３）に対する反射信号の到達位置は右方向に移動し、逆に被写体と発光体（１００）との距離が遠くなる程、受光体（１０３）に対する反射信号の到達位置は左方向に移動する。
【０００５】
この原理を利用し、反射信号が到達した受光体（１０３）の受光位置における電流を利用し、被写体に対する自動焦点制御の為の測距を実行している。
【０００６】
図３は基本的な受光位置検出回路を示す回路図である。
【０００７】
図３において、ＰＳＤ（Position Sensitive Light Detector）素子（２００）は、図４の反射信号を受光する受光体であり、抵抗成分を有する。例えば、反射信号がＰＳＤ素子（２００）の中間より左側の位置Ｘに到達した場合、位置Ｘで光電流が励起される。この光電流は位置ＸからＰＳＤ素子（２００）の左右端子までの各々の距離に反比例する形で分流される。これ故、位置Ｘを境にＰＳＤ素子（２００）の左側の抵抗値が右側の抵抗値より小さくなる為、ＰＳＤ素子（２００）の左端子の出力電流は右端子の出力電流より大きくなる。尚、ＰＳＤ素子（２００）の左右端子の出力電流の総和は受光位置に関わらず一定である。Ｉ−Ｖ変換器（２０１）はＰＳＤ素子（２００）の左端子の出力電流を抵抗値（２０２）に応じた電圧に変換するものである。また、Ｉ−Ｖ変換器（２０３）はＰＳＤ素子（２００）の右端子の出力電流を抵抗値（２０４）に応じた電圧に変換するものでる。カップリングコンデンサ（２０５）（２０６）は各々反射信号に対応する電圧のみを出力し周囲光に対応する電圧を除去するものである。増幅器（２０７）（２０８）は各々カップリングコンデンサ（２０５）（２０６）の出力を増幅する。比較回路（２０５）は増幅器（２０７）（２０８）の出力を比較するものである。比較回路（２０５）の出力はマイクロコンピュータ（図示せず）に供給される。即ち、比較回路（２０５）の出力がハイレベルの時、マイクロコンピュータは反射信号がＰＳＤ素子（２００）の左側に到達しているものと判断し、測距を行う為の制御信号を出力する。
【０００８】
しかし、ＰＳＤ素子（２００）はその構造上において抵抗層を有する為、反射信号の到達位置に応じた電流を出力する際、抵抗ノイズが発生する特性がある。特に、遠距離の被写体の場合、反射信号のレベルが弱くなるのに伴い、ＰＳＤ素子（２００）の出力電流のＳ／Ｎ比が劣化して測距精度が落ちる問題があった。
【０００９】
図２は従来の受光位置検出回路であり、ＰＳＤ素子の問題を解決したものである。一例としてフォトダイオードの数を８個とする。
図２において、フォトダイオード（１）〜（８）は図４の被写体からの反射信号を受光するものである。反射信号は、発光体と被写体との距離が遠くなる程、フォトダイオード（１）〜（８）の左方向に到達し、発光体と被写体との距離が近くなる程、フォトダイオード（１）〜（８）の右方向に到達する。Ｉ−Ｖ変換器（９）〜（１６）は、各々フォトダイオード（１）〜（８）を流れる電流を電圧に変換するものである。スイッチ回路（１７）〜（２３）の一端はＩ−Ｖ変換器（９）〜（１５）の出力と接続され、スイッチ回路（２４）〜（３０）の一端はＩ−Ｖ変換器（１０）〜（１６）の出力と接続される。スイッチ回路（１７）〜（２３）、（２４）〜（３０）の他端は各々カップリングコンデンサ（４０）（４１）と共通接続され、反射信号に対応する電圧のみが出力される。増幅器（４２）（４３）はカップリングコンデンサ（４２）（４３）の出力を増幅する。比較回路（３１）の−端子は増幅器（４２）の出力と接続され、＋端子は増幅器（４３）の出力と接続される。制御回路（３２）は、スイッチ回路（１７）〜（３０）の開閉を制御すると共に、比較回路（３１）の比較出力（バイナリ出力）を解読し、測距の為の制御信号を出力するものである。
【００１０】
以下、図２の動作について説明する。
【００１１】
使用者が発光操作を行い、発光信号が被写体に対して照射された後、被写体からの反射信号がフォトダイオード（１）〜（８）の何れかに到達すると、制御回路（３２）から出力される制御信号Ａに従って１４個のスイッチ回路が選択的に開閉される。詳しくは、先ず、スイッチ回路（２３）（３０）が閉じ、フォトダイオード（７）（８）の受光量に相当する電圧が比較回路（３１）に供給され比較される。次に、スイッチ回路（２２）（２９）が閉じ、フォトダイオード（６）（７）の受光量に相当する電圧が比較回路（３１）に供給され比較される。その後、スイッチ回路（２１）（２８）、（２０）（２７）、（１９）（２６）、（１８）（２５）、（１７）（２４）が順次閉じ、隣接するフォトダイオード（１）〜（８）の受光量に相当する電圧が左方向に移動しながら比較回路（３１）で比較される。比較回路（３１）から逐次出力される７ビットのバイナリデータは制御回路（３２）に供給され、制御回路（３２）は７ビットのバイナリデータを解読して、受光量が最大のフォトダイオードを示す制御信号Ｂを出力する。制御信号Ｂは測距信号として自動焦点回路（図示せず）に供給され、発光体と被写体との距離に応じた自動制御が行われる。
【００１２】
【発明が解決しようとする課題】
しかし、図２の場合、フォトダイオード（１）〜（８）の受光量に関して７回の比較動作を実行しなければならない為、自動焦点制御を実行する迄の時間が長くなってしまう問題があった。また、Ｉ−Ｖ変換器、スイッチ回路をフォトダイオード毎に設けなければならない為、集積化の際、素子数の増大に伴いチップ面積の大型化及びコスト高を招く問題があった。
【００１３】
【課題を解決するための手段】
本発明は、前記問題点を可決する為に創作されたものであり、発光体からの発光信号が被写体に照射された後、前記被写体からの反射信号を前記発光体と前記被写体との距離に応じた位置で受光する受光体を有し、前記受光体の受光位置を流れる電流に応じて前記発光体と前記被写体との間を測距する受光位置検出回路において、発光体と被写体との距離が特定距離未満の場合に対応する受光位置に配置された複数の第１受光素子と、発光体と被写体との距離が特定距離以上の場合に対応する受光位置に配置された単一の第２受光素子と、前記複数の第１受光素子を流れる電流を電圧に変換する複数の第１変換回路と、前記単一の第２受光素子を流れる電流を電圧に変換する単一の第２変換回路と、前記複数の第１変換回路及び前記単一の第２変換回路の変換電圧を選択出力する選択回路と、前記選択回路から得られた一方の変換電圧が供給される第１加算回路と、前記選択回路から得られた他方の変換電圧が供給される第２加算回路と、前記第１加算回路及び前記第２加算回路から出力された２つの変換電圧を比較する比較回路と、前記比較回路の比較出力に応じて前記選択回路を制御すると共に、発光体と被写体との間の測距の為の制御信号を出力する制御回路と、を備え、前記特定距離は、発光体と被写体との間を測距可能な最大距離の中間となる距離、または、当該距離よりも短い距離であり、前記選択回路は、前記全受光素子の中間点を境とする、一方側の受光素子の受光量に相当する一方の変換電圧および他方側の受光素子の受光量に相当する他方の変換電圧を、前記第１加算回路および前記第２加算回路に供給するステップから、前記第１加算回路および前記第２加算回路の加算電圧のうち、一方の加算電圧が他方の加算電圧より大きくなると、前記一方の加算電圧を得るための前記一方側の受光素子または前記他方側の受光素子の中間点を境とする、一方側の受光素子の受光量に相当する一方の変換電圧および他方側の受光素子の受光量に相当する他方の変換電圧を、前記第１加算回路および前記第２加算回路に供給するステップまでを、少なくとも、前記一方側の受光素子または前記他方側の受光素子が前記単一の第２受光素子となるまで繰り返すことを特徴とする。
【００１６】
【発明の実施の形態】
本発明の詳細を図面を用いて具体的に説明する。
【００１７】
図１は本発明の受光位置検出回路を示す回路図である。尚、図１の素子の中で図２と同一素子に関しては同一番号を記す。
【００１８】
図１において、フォトダイオード（５）〜（８）は第１受光素子であり、発光体と被写体との距離が短くなる程、反射信号の到達位置は右方向に移動する。フォトダイオード（３３）は図２における４個のフォトダイオード（１）〜（４）に相当する第２受光素子である。比較的安価なカメラの自動焦点制御に関し、発光体（カメラ）と被写体との距離が近い人物等の撮影の場合、精度の高い焦点制御が要求されるが、発光体と被写体との距離が遠い風景等の撮影の場合、焦点制御を行っても焦点を特定距離で固定しても、視覚上の差異は無視できる程度である。そこで、比較的安価なカメラに限り、発光体と被写体との間が特定距離となる位置を境に、発光体と被写体との間が特定距離以上の場合の反射信号は１個のフォトダイオード（３３）で受光する構成とした。
【００１９】
Ｉ−Ｖ変換器（１３）〜（１６）は第１変換回路であり、フォトダイオード（５）〜（８）を流れる電流を電圧に変換するものである。Ｉ−Ｖ変換器（３４）は第２変換回路であり、フォトダイオード（３３）を流れる電流を電圧に変換するものである。スイッチ回路（３５）の一端はＩ−Ｖ変換器（３４）の出力と接続される。加算回路（３６）（３７）は、スイッチ回路の開閉に応じて導出された変換電圧を加算するものである。スイッチ回路（２１）（２２）（２３）（３５）の他端は加算回路（３６）の一入力と共通接続され、スイッチ回路（２７）（２８）（２９）（３０）の他端は加算回路（３７）の一入力と共通接続される。加算回路（３６）（３７）の出力は各々カップリングコンデンサ（４０）（４１）と接続され、反射信号に対応する電圧のみが抽出される。増幅器（４２）（４３）はカップリングコンデンサ（４０）（４１）の出力を増幅する。比較回路（３８）は増幅器（４２）（４３）の出力を比較するものである。制御回路（３９）はスイッチ回路（２１）〜（２３）（２７）〜（３０）（３５）の開閉を制御する制御信号Ａを出力すると共に、自動焦点制御の為の制御信号Ｂを出力するものである。
【００２０】
使用者が発光操作を行い、発光信号が被写体に対して照射された後、被写体からの反射信号がフォトダイオード（３３）（５）〜（８）の何れかに到達すると、最初に、制御信号Ａに従ってスイッチ回路（２７）〜（３０）（３５）が一律に閉じ、加算回路（３６）にはフォトダイオード（３３）の受光量に相当する変換電圧が供給され、加算回路（３７）には４個のフォトダイオード（５）〜（８）の受光量に相当する変換電圧が供給され加算される。この時の加算回路（３６）（３７）の２加算出力は比較回路（３８）でその大小が比較される。例えば、加算回路（３７）の加算電圧の方が大きい場合、比較回路（３８）がローレベルを出力し、制御回路（３９）はこの時の比較結果に応じて反射信号がフォトダイオード（５）〜（８）の何れかの位置に到達していることを示す制御信号Ａを出力し直す。
【００２１】
次に、制御信号Ａに従ってスイッチ回路（２１）（２２）（２９）（３０）が閉じ、加算回路（３６）には２個のフォトダイオード（５）（６）の受光量に相当する変換電圧が供給され、加算回路（３７）には２個のフォトダイオード（７）（８）の受光量に相当する変換電圧が供給され加算される。この時の加算回路（３６）（３７）の２加算出力は比較回路（３８）でその大小が比較される。例えば、加算回路（３６）の加算電圧の方が大きい場合、比較回路（３８）がハイレベルを出力し、制御回路（３９）はこの時の比較結果に応じて反射信号がフォトダイオード（５）（６）の何れかの位置に到達していることを示す制御信号Ａを出力し直す。
【００２２】
最後に、制御信号Ａに従ってスイッチ回路（２１）（２８）が閉じ、加算回路（３６）にはフォトダイオード（５）の受光量に相当する変換電圧が供給され、加算回路（３７）にはフォトダイオード（６）の受光量に相当する変換電圧が供給される。この時の加算回路（３６）（３７）の２出力は比較回路（３８）でその大小が比較される。例えば、加算回路（３７）の出力電圧の方が大きい場合、比較回路（３８）がローレベルを出力し、制御回路（３９）はこの時の比較結果に応じて反射信号がフォトダイオード（６）に到達していることを示す制御信号Ｂを出力する。制御信号Ｂは測距信号として自動焦点回路（図示せず）に供給され、発光体と被写体との距離に応じた自動制御が行われる。
【００２３】
尚、最初の比較の際、加算回路（３６）の出力電圧の方が大きい場合は、反射信号はフォトダイオード（３３）に到達していることになり、制御回路（３９）によるスイッチ回路の開閉制御は１回で済む。
【００２４】
以上より、発光体と被写体との間が特定距離である位置を境に、発光体と被写体との間が特定距離以上の場合の反射信号を１個のフォトダイオード（３３）で受光する構成とし、更に、フォトダイオードを逐次比較選択する構成とした。これにより、フォトダイオードの受光量を比較する回数が従来の７回から１回若しくは３回に減り、カメラ使用者の発光操作から焦点制御までの時間を短縮できる、といった作用効果を奏する。
【００２５】
尚、本発明の実施の形態においては、第１受光素子数を４個に設定したが、これに限定されることなく５個以上であっても何ら差し支えない。また、第１受光素子と第２受光素子との境を発光体と被写体との間の中間位置に設定したが、これに限定されることなく中間位置より被写体寄りの位置に設定しても何ら差し支えない。
【００２６】
【発明の効果】
本発明によれば、第１及び第２受光素子の受光量を比較する回数が従来より減る為、カメラ使用者の発光操作から焦点制御までの時間を短縮できる利点が得られる。
【図面の簡単な説明】
【図１】本発明の受光位置検出回路を示す回路図である。
【図２】従来の受光位置検出回路の一具体例を示す回路図である。
【図３】従来の受光位置検出回路の他の具体例を示す回路図である。
【図４】三角測距の原理を示す図である。
【符号の説明】
（５）〜（８）（３３）フォトダイオード
（１３）〜（１６）（３４）Ｉ−Ｖ変換器
（２１）〜（２３）（２７）〜（３０）（３５）スイッチ回路
（３６）（３７）加算回路
（３８）比較回路
（３９）制御回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light receiving position detection circuit used for automatic focus control of a camera.
[0002]
[Prior art]
FIG. 4 shows the principle of triangulation.
[0003]
In FIG. 4, the light emitter (100) is disposed at a specific position of the camera. When the user performs a light emission operation with the camera facing the subject, a light emission signal such as infrared rays is output to the subject. The light emission signal is applied to the subject through the light projecting lens (101). The light emission signal is reflected when it reaches the subject, but this reflection signal reaches the light receiver (103) via the condenser lens (102). The subjects A and B are objects to which the light emission signal is irradiated, and it is assumed that the subject A exists in a place farther than the subject B with respect to the light emitter (100).
[0004]
When the light emission signal is applied to the subject A (a long distance), the reflected signal at this time reaches the left side of the photoreceptor (103). Further, when the light emission signal is applied to the subject B (short distance), the reflected signal at this time reaches the right side of the photoreceptor (103). That is, since the position of the condensing lens (102) that receives the reflected signal is fixed, the arrival position of the reflected signal with respect to the light receiving body (103) becomes the right direction as the distance between the subject and the light emitting body (100) decreases. Conversely, as the distance between the subject and the light emitter (100) increases, the arrival position of the reflected signal with respect to the light receiver (103) moves to the left.
[0005]
Using this principle, distance measurement is performed for automatic focus control on the subject using the current at the light receiving position of the photoreceptor (103) where the reflected signal arrives.
[0006]
FIG. 3 is a circuit diagram showing a basic light receiving position detection circuit.
[0007]
In FIG. 3, a PSD (Position Sensitive Light Detector) element (200) is a light receiver that receives the reflected signal of FIG. 4 and has a resistance component. For example, when the reflected signal reaches the position X on the left side of the middle of the PSD element (200), the photocurrent is excited at the position X. This photocurrent is shunted in a manner that is inversely proportional to the distance from the position X to the left and right terminals of the PSD element (200). Therefore, since the resistance value on the left side of the PSD element (200) becomes smaller than the resistance value on the right side at the position X, the output current at the left terminal of the PSD element (200) becomes larger than the output current at the right terminal. Note that the sum of the output currents of the left and right terminals of the PSD element (200) is constant regardless of the light receiving position. The IV converter (201) converts the output current at the left terminal of the PSD element (200) into a voltage corresponding to the resistance value (202). The IV converter (203) converts the output current at the right terminal of the PSD element (200) into a voltage corresponding to the resistance value (204). Each of the coupling capacitors (205) and (206) outputs only a voltage corresponding to the reflected signal and removes a voltage corresponding to the ambient light. The amplifiers (207) and (208) amplify the outputs of the coupling capacitors (205) and (206), respectively. The comparison circuit (205) compares the outputs of the amplifiers (207) and (208). The output of the comparison circuit (205) is supplied to a microcomputer (not shown). That is, when the output of the comparison circuit (205) is at a high level, the microcomputer determines that the reflected signal has reached the left side of the PSD element (200) and outputs a control signal for distance measurement.
[0008]
However, since the PSD element (200) has a resistance layer on its structure, there is a characteristic that resistance noise is generated when a current corresponding to the arrival position of the reflected signal is output. In particular, in the case of a long-distance subject, as the level of the reflected signal becomes weak, there is a problem that the S / N ratio of the output current of the PSD element (200) is deteriorated and the ranging accuracy is lowered.
[0009]
FIG. 2 shows a conventional light receiving position detection circuit which solves the problem of the PSD element. As an example, the number of photodiodes is eight.
In FIG. 2, photodiodes (1) to (8) receive reflected signals from the subject shown in FIG. The reflected signal reaches the left of the photodiodes (1) to (8) as the distance between the light emitter and the subject increases, and the photodiode (1) to (8) increases as the distance between the light emitter and the subject decreases. Reach right (8). The IV converters (9) to (16) convert currents flowing through the photodiodes (1) to (8) into voltages, respectively. One ends of the switch circuits (17) to (23) are connected to the outputs of the IV converters (9) to (15), and one ends of the switch circuits (24) to (30) are connected to the IV converter (10). To the output of (16). The other ends of the switch circuits (17) to (23) and (24) to (30) are commonly connected to the coupling capacitors (40) and (41), respectively, and only the voltage corresponding to the reflected signal is output. The amplifiers (42) and (43) amplify the outputs of the coupling capacitors (42) and (43). The negative terminal of the comparison circuit (31) is connected to the output of the amplifier (42), and the positive terminal is connected to the output of the amplifier (43). The control circuit (32) controls opening and closing of the switch circuits (17) to (30), decodes the comparison output (binary output) of the comparison circuit (31), and outputs a control signal for distance measurement It is.
[0010]
The operation of FIG. 2 will be described below.
[0011]
After the user performs a light emission operation and the light emission signal is applied to the subject, when the reflection signal from the subject reaches any one of the photodiodes (1) to (8), the light is output from the control circuit (32). The 14 switch circuits are selectively opened and closed according to the control signal A. Specifically, first, the switch circuits (23) and (30) are closed, and a voltage corresponding to the amount of light received by the photodiodes (7) and (8) is supplied to the comparison circuit (31) for comparison. Next, the switch circuits (22) and (29) are closed, and a voltage corresponding to the amount of light received by the photodiodes (6) and (7) is supplied to the comparison circuit (31) for comparison. Thereafter, the switch circuits (21), (28), (20), (27), (19), (26), (18), (25), (17), and (24) are sequentially closed, and adjacent photodiodes (1) to (1) to (24) are closed. The voltage corresponding to the amount of received light in (8) is compared by the comparison circuit (31) while moving in the left direction. The 7-bit binary data sequentially output from the comparison circuit (31) is supplied to the control circuit (32), and the control circuit (32) decodes the 7-bit binary data to indicate the photodiode having the maximum light receiving amount. A control signal B is output. The control signal B is supplied as a distance measurement signal to an automatic focus circuit (not shown), and automatic control according to the distance between the light emitter and the subject is performed.
[0012]
[Problems to be solved by the invention]
However, in the case of FIG. 2, since the comparison operation must be executed seven times with respect to the received light amounts of the photodiodes (1) to (8), there is a problem that the time until the automatic focus control is executed becomes long. It was. Further, since an IV converter and a switch circuit must be provided for each photodiode, there is a problem in that the chip area is increased and the cost is increased as the number of elements is increased during integration.
[0013]
[Means for Solving the Problems]
The present invention was created to pass the problem, and after the light emission signal from the light emitter is irradiated to the subject, the reflected signal from the subject is set to the distance between the light emitter and the subject. A distance between the light emitter and the subject in a light receiving position detection circuit that has a light receiver that receives light at a corresponding position and measures a distance between the light emitter and the subject according to a current flowing through the light receiving position of the light receiver. A plurality of first light receiving elements arranged at a light receiving position corresponding to the case where the distance is less than a specific distance, and a single second light receiving element arranged at a light receiving position corresponding to the case where the distance between the light emitter and the subject is equal to or greater than the specific distance . A light receiving element, a plurality of first conversion circuits that convert currents flowing through the plurality of first light receiving elements into voltages, and a single second conversion circuit that converts currents flowing through the single second light receiving elements into voltages The plurality of first conversion circuits and the single first A selection circuit for selectively outputting the converted voltage of the converter circuit, a first adder circuit for one of the conversion voltage obtained from said selecting circuit is supplied, converts the voltage on the other derived from the selection circuit is supplied a second adder circuit that includes a comparator circuit for comparing the two converted voltage outputted from the first adder circuit and said second adder circuit, controls the selection circuit in response to the comparison output of the comparator circuit, A control circuit that outputs a control signal for ranging between the illuminant and the subject, and the specific distance is a distance that is an intermediate distance between the illuminant and the subject, Or, the distance is shorter than the distance, and the selection circuit uses one conversion voltage corresponding to the amount of light received by one light receiving element and the other light receiving element as a boundary at an intermediate point of all the light receiving elements. The other conversion voltage corresponding to the amount of received light is When one of the addition voltages of the first addition circuit and the second addition circuit becomes larger than the other addition voltage from the step of supplying to the one addition circuit and the second addition circuit, the one addition voltage To the conversion voltage corresponding to the amount of light received by the light receiving element on one side and the amount of light received by the light receiving element on the other side, with the intermediate point between the light receiving element on one side or the light receiving element on the other side as a boundary. Up to the step of supplying the corresponding other conversion voltage to the first addition circuit and the second addition circuit, at least the one light receiving element or the other light receiving element is the single second light receiving element. It repeats until it becomes .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be specifically described with reference to the drawings.
[0017]
FIG. 1 is a circuit diagram showing a light receiving position detection circuit of the present invention. 1 that are the same as those in FIG. 2 are denoted by the same reference numerals.
[0018]
In FIG. 1, photodiodes (5) to (8) are first light receiving elements, and the arrival position of the reflected signal moves to the right as the distance between the light emitter and the subject decreases. The photodiode (33) is a second light receiving element corresponding to the four photodiodes (1) to (4) in FIG. Regarding automatic focus control of a relatively inexpensive camera, in the case of shooting a person or the like whose distance between the light emitter (camera) and the subject is close, high-precision focus control is required, but the distance between the light emitter and the subject is long. In the case of shooting landscapes or the like, visual differences are negligible whether focus control is performed or the focus is fixed at a specific distance. Therefore, only in a relatively inexpensive camera, the reflected signal when the distance between the light emitter and the subject is equal to or greater than the specific distance from the position where the distance between the light emitter and the subject is a specific distance is one photodiode ( 33).
[0019]
The IV converters (13) to (16) are first conversion circuits, and convert currents flowing through the photodiodes (5) to (8) into voltages. The IV converter (34) is a second conversion circuit, and converts the current flowing through the photodiode (33) into a voltage. One end of the switch circuit (35) is connected to the output of the IV converter (34). The adder circuits (36) and (37) add conversion voltages derived in accordance with opening and closing of the switch circuit. The other ends of the switch circuits (21), (22), (23), and (35) are commonly connected to one input of the adder circuit (36), and the other ends of the switch circuits (27), (28), (29), and (30) are added. Commonly connected to one input of the circuit (37). The outputs of the adder circuits (36) and (37) are connected to the coupling capacitors (40) and (41), respectively, and only the voltage corresponding to the reflected signal is extracted. The amplifiers (42) and (43) amplify the outputs of the coupling capacitors (40) and (41). The comparison circuit (38) compares the outputs of the amplifiers (42) and (43). The control circuit (39) outputs a control signal A for controlling opening / closing of the switch circuits (21) to (23) (27) to (30) (35) and also outputs a control signal B for automatic focus control. Is.
[0020]
After the user performs a light emission operation and the light emission signal is applied to the subject, when the reflected signal from the subject reaches any one of the photodiodes (33), (5) to (8), first, the control signal According to A, the switch circuits (27) to (30) (35) are uniformly closed, a conversion voltage corresponding to the amount of light received by the photodiode (33) is supplied to the addition circuit (36), and the addition circuit (37). A conversion voltage corresponding to the amount of light received by the four photodiodes (5) to (8) is supplied and added. The two addition outputs of the adder circuits (36) and (37) at this time are compared in magnitude by the comparator circuit (38). For example, when the addition voltage of the addition circuit (37) is larger, the comparison circuit (38) outputs a low level, and the control circuit (39) outputs the reflected signal to the photodiode (5) according to the comparison result at this time. The control signal A indicating that the position has reached any one of (8) is output again.
[0021]
Next, the switch circuits (21), (22), (29), and (30) are closed according to the control signal A, and the adder circuit (36) has a conversion voltage corresponding to the amount of light received by the two photodiodes (5) and (6). And a conversion voltage corresponding to the amount of light received by the two photodiodes (7) and (8) is supplied and added to the adder circuit (37). The two addition outputs of the adder circuits (36) and (37) at this time are compared in magnitude by the comparator circuit (38). For example, when the addition voltage of the addition circuit (36) is larger, the comparison circuit (38) outputs a high level, and the control circuit (39) outputs the reflected signal to the photodiode (5) according to the comparison result at this time. The control signal A indicating that the position has reached any one of (6) is output again.
[0022]
Finally, the switch circuits (21) and (28) are closed according to the control signal A, a conversion voltage corresponding to the amount of light received by the photodiode (5) is supplied to the adder circuit (36), and a photovoltage is supplied to the adder circuit (37). A conversion voltage corresponding to the amount of light received by the diode (6) is supplied. The two outputs of the adder circuits (36) and (37) at this time are compared in magnitude by the comparator circuit (38). For example, when the output voltage of the adder circuit (37) is larger, the comparison circuit (38) outputs a low level, and the control circuit (39) outputs the reflected signal to the photodiode (6) according to the comparison result at this time. A control signal B indicating that it has reached is output. The control signal B is supplied as a distance measurement signal to an automatic focus circuit (not shown), and automatic control according to the distance between the light emitter and the subject is performed.
[0023]
When the output voltage of the adder circuit (36) is larger at the time of the first comparison, the reflected signal has reached the photodiode (33), and the switch circuit is opened and closed by the control circuit (39). Only one control is required.
[0024]
As described above, a single photodiode (33) receives the reflected signal when the distance between the light emitter and the subject is equal to or greater than the specific distance at the position where the distance between the light emitter and the subject is a specific distance. In addition, the photodiodes are sequentially compared and selected. As a result, the number of times that the amount of light received by the photodiode is compared is reduced from 7 times to 1 time or 3 times, and the time from the camera user's light emission operation to focus control can be shortened.
[0025]
In the embodiment of the present invention, the number of first light receiving elements is set to four. However, the number is not limited to this, and may be five or more. In addition, the boundary between the first light receiving element and the second light receiving element is set to an intermediate position between the light emitter and the subject, but the present invention is not limited to this, and it may be set to a position closer to the subject than the intermediate position. There is no problem.
[0026]
【The invention's effect】
According to the present invention, since the number of times of comparing the received light amounts of the first and second light receiving elements is reduced as compared with the prior art, there is an advantage that the time from the light emission operation of the camera user to the focus control can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a light receiving position detection circuit of the present invention.
FIG. 2 is a circuit diagram showing a specific example of a conventional light receiving position detection circuit.
FIG. 3 is a circuit diagram showing another specific example of a conventional light receiving position detection circuit.
FIG. 4 is a diagram illustrating the principle of triangulation.
[Explanation of symbols]
(5) to (8) (33) Photodiode (13) to (16) (34) IV converter (21) to (23) (27) to (30) (35) Switch circuit (36) ( 37) Adder circuit (38) Comparison circuit (39) Control circuit

Claims

A light-receiving body that receives a reflected signal from the subject at a position corresponding to a distance between the light-emitting body and the subject after the light-emitting signal from the light-emitting body is applied to the subject; In a light receiving position detection circuit that measures a distance between the light emitter and the subject according to a flowing current,
A plurality of first light receiving elements disposed at a light receiving position corresponding to a case where the distance between the light emitter and the subject is less than a specific distance ;
A single second light receiving element disposed at a light receiving position corresponding to a case where the distance between the light emitter and the subject is equal to or greater than a specific distance ;
A plurality of first conversion circuits for converting currents flowing through the plurality of first light receiving elements into voltages;
A single second conversion circuit for converting a current flowing through the single second light receiving element into a voltage;
A selection circuit that selectively outputs conversion voltages of the plurality of first conversion circuits and the single second conversion circuit;
A first adder circuit for one of the conversion voltage obtained from said selecting circuit is supplied,
A second adding circuit for converting voltage of the other derived from the selection circuit is supplied,
A comparison circuit for comparing two conversion voltages output from the first addition circuit and the second addition circuit;
A control circuit that controls the selection circuit according to the comparison output of the comparison circuit and outputs a control signal for ranging between the light emitter and the subject ,
The specific distance is a distance between the maximum distance that can be measured between the light emitter and the subject, or a distance shorter than the distance,
The selection circuit includes:
One conversion voltage corresponding to the amount of light received by the light receiving element on one side and the other conversion voltage corresponding to the amount of light received by the light receiving element on the other side with the intermediate point of all the light receiving elements as a boundary. And supplying to the second adder circuit,
When one of the addition voltages of the first addition circuit and the second addition circuit is larger than the other addition voltage, the light receiving element on one side or the other side for obtaining the one addition voltage One conversion voltage corresponding to the amount of light received by the light receiving element on one side and the other conversion voltage corresponding to the amount of light received by the light receiving element on the other side, with the intermediate point of the light receiving element as a boundary, Up to the step of supplying to the second addition circuit,
A light receiving position detecting circuit, which is repeated until at least the one light receiving element or the other light receiving element becomes the single second light receiving element .