JPS5964807A - Photoelectric transducing device for distance measurement - Google Patents

Abstract

PURPOSE:To attain a photoelectric transducing device for distance measurement which is not affected by a bias current by providing a filter circuit through which only modulation signal components of the output of a bipolar operational amplifying circuit pass. CONSTITUTION:A modulation light is converted to a current signal IA corresponding to the input light by a photoelectric transducer D. The current signal IA is converted to a voltage signal by the first operational amplifying circuit. The filter circuit consisting of a capacitor C1 and a resistance R1 is provided for the purpose of taking out a modulation signal. The output of the first operational amplifying circuit U1 has DC components cut by the capacitor C1 while it passes the filter circuit, and the whole of the modulation signal where VB is added to V0 is taken out. This modulation signal is amplified by the second operational amplifying circuit U2 furthermore and is outputted as VAC. Thus, the photoelectric transducing device which is not affected by the bias current is realized.

Description

[Detailed Description of the Invention] The present invention enables accurate photoelectric conversion without being affected by bias current even when a bipolar type operational amplifier circuit is used as an operational amplifier circuit that receives the output of a photoelectric conversion element. The present invention relates to a photoelectric conversion device for distance measurement.

In photometry circuits used in cameras, etc., it is necessary to amplify minute currents, so MO8 input type or FE type is used in the first stage.
A T input method is used. This is because the output current of the photoelectric conversion element is minute, so in order to accurately amplify the signal, the input impedance of the photometric circuit input stage is made high, and the magnitude of the bias current is ignored compared to that of the signal current. This is because it is necessary to make it as small as possible.

FIG. 1 is a circuit diagram showing an example of a conventional optical weight conversion device. In this device, the light to be converted is a photoelectric conversion element])
The current signal IA is converted into a current IA corresponding to the light \l by , and is input to an operational amplifier circuit consisting of an operational amplifier U1 and a feedback resistor R'', where the current signal IA is converted into a voltage signal \l.
converted to o.

Incidentally, the positive input terminal of the operational amplifier U1 is at the potential Vre
connected to f.

Here, if the bias current of the operational amplifier LJ1 is Is, the current flowing through the feedback resistor R out of the signal current [A is (IA-Is), and the operational amplifier circuit (operational amplifier U
+) output Vo is as shown in the following equation. Note that the symbols are used as they are as the resistance values (the same applies below).

Vo=-(lA-Is)Rf=(1) Therefore, for the true value -rA-R', 4-re -Rf becomes error X1.Now, considering the case where IA > In,
The effect of bias current on measurement accuracy is negligible. However, if an input stage with a large bias current Is is used or if the brightness is in a low brightness region, the rA ratio Is will have a very large effect on the measurement accuracy.

Figure 2 shows the bias current Is when the light to be converted is continuous light.
This is a dimensional diagram showing the influence of The offset voltage Vs (-Is - Rf) due to the bias current [B is the output Vo
Therefore, this Va is the measurement error and 4
7ru.

Generally, the signal current ■A handled by a photometric system is often less than several nA. Therefore, in order to accurately measure the signal current, it is necessary to use an operational amplifier circuit having an input stage in which the bias current Is is sufficiently smaller than the signal current IA.

In the case of the MOS input method or the FE type, it is easy to obtain a bias current Is of several pA or 1α, so it is possible to generate a signal proportional to the amount of light with an accuracy of 0.1% or less. becomes.

On the other hand, the use of ICs in Omi cameras' sequence controllers (-roll section or ΔF (J-1 to focus) arithmetic circuit section, etc.) is progressing, and from the viewpoint of the balance of the overall system, they are being integrated with analog arithmetic circuits, logic circuits, etc. , I21- are often used. Therefore, if the photometric device is a MOS type 4R device, the combination of a MOS type photometric system and a bipolar type signal amplification system,
The connection is difficult t1]. For this reason, it may be necessary to use separate chips or separate packages for both, resulting in a significant increase in cost. Furthermore, the space factor deteriorates, making it impossible to downsize the device. Or Wamp Tsubu, J2lkob
It is possible to use an advanced process such as i-MOS (IC), but the cost will be higher than that of a bipolar type.The bipolar type has a bias current on the order of n△, no matter how good the circuit is.

Therefore, as it is, it cannot be used as a photoelectric conversion device.

The present invention has been made in view of these points, and its purpose is to prevent the adverse effects of bias current from occurring even if a bipolar type arithmetic amplification circuit is used as an operational amplification circuit that receives the output of a photoelectric conversion element. The objective is to realize photoelectric conversion gE for distance measurement.

A photoelectric conversion device for distance measurement according to the present invention that achieves this object includes a modulation device that converts light toward or from a subject into modulated light, and a photoelectric conversion device that receives the light modulated by the modulation device. , a bipolar operational amplifier circuit that amplifies the output of the photoelectric conversion element, and a filter circuit that allows only the output of the operational amplifier circuit to pass through the modulation signal valve.

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

FIG. 3 is an electrical configuration diagram showing an embodiment of the present invention (the same parts as in FIG. 1 are given the same reference numerals). In the figure, CP is a modulation means that converts DC light into modulated light. As the modulation means CP, for example, a Siemens star (a rotating disk in which a large number of radial slits are formed) that converts continuous light into pulsed light is used. Operational amplifier U1
The output Vo of the first operational amplifier circuit consisting of nine resistors Rf, Rf, etc. passes through a filter circuit, which is a series circuit, to an operational amplifier U2 and a feedback resistor R? The signal is input to a second operational amplifier circuit consisting of.

The operation of the device configured as described above will be explained as follows.

The continuous light is changed into pulsed light by the modulation means CP. This modulated light is converted by a photoelectric conversion element into a current signal IA corresponding to the input light.

Incidentally, as this photoelectric conversion element, for example, a photodiode or a phototransistor is used.

Also, there is a type of photodiode C, F"S l)
It can also be applied to semiconductor device detectors called . However, this P
The SD outputs a pair of current signals that vary depending on the position of the incident light spot (changes depending on the subject distance).
As shown in Japanese Patent Application No. 08 and Japanese Patent Application No. 56-178583, it is necessary to use this method for each of a pair of currents. The current signal IA is converted into a voltage 4rr by a subsequent first operational amplifier circuit.

The voltage signal vo at this time is -(lA-) as in equation (1).
Is) Rf roars. FIG. 4(a) is a diagram showing the output waveform of this first operational amplifier circuit.

The DC potential is \lo, but the reference potential \1r
Va (=ra ・R
f) is included. If Vo is directly amplified directly, it will be affected by the bias current Is and will contain an error, but in the circuit of the present invention, in order to extract a modulation signal that includes not only \10 but also Vs, a capacitor is used. iJ'C
A filter circuit composed of I and a resistor R1 is provided. While the output of the first operational amplifier circuit passes through the filter circuit, the capacitor IJ-CIT-DC component is cut off, and a modulated signal in which Va is added to Vo is extracted in its entirety. This modulation signal is further amplified by the subsequent second operational amplifier circuit and output as V'AC. FIG. 4(b) is a dimensional diagram showing the output waveform of this second operational amplifier circuit. It can be seen that the modulation waveform is completely amplified. At this time, VAC is given by the following equation, assuming that the capacitance of capacitor C1 is sufficiently large.

V A C-'R2(\10+Ve)/R+=Rz
((IA-Is)Rf +Ze-Rf)/R+ =R2・Rf-rA/R+ (2) In this way, if J: is used in the device of the present invention, charging conversion without the influence of bias current is possible. After all, accurate distance measurement becomes possible. Furthermore, since the influence of the bias current is eliminated, a bipolar type transistor circuit with a large bias current can be used in the input stage of the operational amplifier circuit. Therefore, it becomes possible to use one-deep IC and one package. Furthermore, since the influence of the offset voltage of the operational amplifier can also be removed, if a bipolar operational amplifier with a small offset voltage is used, a photometric circuit without offset adjustment can be realized. M.O.
When using an 8-type amplifier, the offset voltage is several tens of meters.
Since the voltage is about V, it is generally difficult to realize a circuit without adjustment.

In the above description, a Siemenster is used as the modulation means. However, in the case of an active type ΔF, it is also possible to modulate the light emission. Further, as a filter circuit for extracting a modulated signal, the case has been explained using a series circuit of a capacitor C1 and a resistor R1, which has the simplest circuit configuration, as an example, but it is not limited to kneading, and as long as only a modulated signal can be extracted, It can be anything. Further, the output signal VAC can be converted into direct current and used as necessary.

As described above, according to the present invention, it is possible to realize a photoelectric conversion device for distance measurement that is not affected by bias current. Therefore, it is possible to use a bipolar derivational amplifier circuit with a large bias current, making it possible to integrate it into one depth and into one package, improving compatibility with other circuits, and realizing cost reduction and downsizing of the device. .

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional photoelectric conversion device, Figure 2 is a circuit diagram showing an example of a conventional photoelectric conversion device.
FIG. 3 is an explanatory diagram showing the influence of the bias current, FIG. 3 is a J-circuit diagram showing one embodiment of the present invention, and FIG. 4 is an explanatory diagram of the operation of the circuit shown in FIG. D...Photoelectric conversion cable CP...Modulation means Rf
, R2...Feedback resistance tJ+, U2...Operation amplifier C1...'Ndenza R+...Resistance special 91 Applicant: Konishiroku Photo Industry Co., Ltd. Ne1 (1 other person)

Claims (4)

[Claims] (1) A modulation means that converts light to or from the subject into modulated light, a photoelectric conversion element that receives the light modulated by the modulation means, and a bipolar operational amplifier circuit that amplifies the output of the photoelectric conversion element. and a filter circuit that allows only the modulation signal valve to pass among the output of the operational amplifier circuit. (2) The photoelectric conversion device for distance measurement according to claim 1, wherein a light emitting circuit of a light source that modulates the light irradiated onto the subject in a pulse form is used as the modulation means. (3) The photoelectric conversion device for distance measurement according to claim 1, wherein a Siemenster that modulates reflected light from a subject in a pulse shape is used as the modulation means. (4) Claim 1, characterized in that the filter circuit is a series circuit of a conductor and a resistor.
A photoelectric conversion device for distance measurement according to items 1 to 3.