JP3093415B2 - Distance detection device and distance detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active distance detecting device used for an optical device such as a camera, and more particularly to an active distance detecting device provided at a place where a pulse reflected light from a distance measuring object is formed. A semiconductor optical position detector (PSD) for outputting first and second currents corresponding to positions, and a pair of pulsed lights for receiving each current output of the PSD and extracting a variation in the current output due to the pulse reflected light A current extraction circuit,
The present invention relates to a distance detection device including a pair of logarithmic conversion circuits that logarithmically convert these extracted pulsed photocurrents, and a differential circuit that obtains a distance detection signal by calculating a difference between both logarithmically converted voltage outputs. Things.

[0002]

2. Description of the Related Art In an active distance detecting device, a pulse light is emitted from an LED to an object whose distance is to be detected, and reflected light from the object is received and collected on a PSD 2 shown in FIG. You. PSD corresponding to the focus position on PSD2
Currents I ₁ and I ₂ are extracted from both ends of the LED ₂ respectively, and from these currents, pulsed light currents of reflected light due to light emission of the LEDs are extracted by the pulsed light current extraction circuits 4 a and 4 b. The extracted reflected light current intensities are ΔI ₁ and ΔI ₂ , are logarithmically compressed by the logarithmic conversion circuits 6a and 6b, respectively, and the resulting difference between the voltages V ₁ and V ₂ is calculated by the differential circuit 8 and output Vou.
t is obtained.

FIG. 2 shows an example of a conventional pulsed photocurrent sampling circuit and logarithmic conversion circuit. The collector of the NPN transistor 10 is connected to one end of the PSD, the emitter of the transistor 10 is connected to the GND terminal, the capacitor 12 is connected between the base of the transistor 10 and the GND terminal. Connected to output terminal. The collector of the transistor 10 is connected to the inverting input terminal of the amplifier 16 via the amplifier 18 and NP.
It is connected to the base of N transistor 20. A reference voltage Vref is applied to the non-inverting input terminal of the amplifier 16,
The base potential of the transistor 20 is fixed at the reference voltage Vref. A current mirror circuit is formed by the transistors 22, 24, and 26. A diode 28 is connected between the collector of the transistor 24 and the GND terminal.
An output voltage is taken out from the anode of the diode 28 via the buffer amplifier 30. FIG.
Are included in the distance detection device of FIG.

The operation of the distance detecting device shown in FIGS. 1 and 2 will be described. In a steady state, an external photocurrent from PSD ₂ flows as I ₁ and I ₂ to transistor 10 of each pulsed photocurrent extracting circuit. When the collector current of the transistor 10 and I _1, the base potential Vbe is a potential represented by the following formula. Vbe = (kT / q) ln (I 1 / Is) where, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge, Is is the reverse saturation current. Capacitor 12
Accumulates a charge corresponding to the base potential Vbe.

In this state, when the switch 14 is opened and the light emitting LED emits light in a pulsed manner at the same time, the reflected light (pulse light current) ΔI ₁ by the LED is superimposed on the external light current I ₁ flowing constantly. that is, the transistor 10 is the base potential Vbe is fixed by the capacitor 12, I ₁ or more current does not flow, [Delta] I ₁ is the transistor 20
Flows into the base and is separated. This ΔI ₁ is amplified by hfe times by the transistor 20, and becomes an output logarithmically compressed by the logarithmic conversion diode 28. This relationship is shown by the following equation. V ₁ = (kT / q) ln (ΔI ₁ · hfe / Is) (1)

Assuming that the output of the other pulsed photocurrent sampling circuit and logarithmic conversion circuit is V ₂ , V ₂ = (kT / q) ln (ΔI ₂ · hfe / Is) (2) When these outputs V ₁ and V ₂ are input to the differential amplifier of the differential circuit 18, the output Vout _{is, Vout = V 1 -V 2 =} (kT / q) ln (ΔI 1 · hfe / ΔI 2 · hfe) (3), and the ratio of the signal current is obtained as the output Vout. In FIG. 2, ΔI ₁ (ΔI ₂ ) is multiplied by A by the amplifier 18, but the amplification factor A is omitted in the description for simplicity.

[0007]

Since the transistor 20 has a parasitic capacitance, this affects the rise of the circuit. Therefore, it is necessary to flow the current Ii (hereinafter referred to as idle current) even in the steady state. When the equation (3) is rewritten in consideration of the idle current Ii, the following equation (4) is obtained. Vout = (kT / q) ln {(ΔI ₁ · hfe ₁ + Ii) / (ΔI ₂ · hfe ₂ + Ii)} (4) When Vout is 1 in the logarithm (ΔI ₁ = ΔI ₂ = 0) Vout
= 0, indicating infinite distance. Therefore, in a range where ΔI × hfe is sufficiently large with respect to Ii, equations (3) and (4) are almost the same. However, when hfe is small, even if the pulsed photocurrent has a certain magnitude, the output is The value is closer to infinity. Therefore, in equation (4), ΔI
₁ , ΔI ₂ , hfe ₁ , hfe ₂ are better the larger,
The smaller i is, the better. However, if Ii is too small, it does not serve as an idle current, so there is a limit in reducing Ii.

A first object of the present invention is to improve the distance measurement accuracy by preventing an idle current required only in a steady state from flowing through the transistor 20 for extracting a pulsed light current during distance measurement. A second object of the present invention is to enable a distance to an object to be accurately detected without being affected by hfe and Ii.

[0009]

In order to prevent an idle current required only in a steady state from flowing through the transistor 20 during distance measurement, the method according to the present invention employs a method as shown in FIG. The base potential of the first transistor 20 for extracting the pulsed photocurrent into which the current output of the PSD flows into the base is fixed to a constant potential and the first transistor 2
A small current (idle current) Ii is supplied to the collector of 0, and at the time of distance measurement, the idle current Ii is supplied to another transistor 32 so that only the fluctuation due to the pulse reflected light is supplied to the first transistor 20. Then, the collector current of the first transistor 20 is detected.

In order to realize the method of the present invention, the present invention relates to a pulsed photocurrent extracting circuit comprising a first transistor for extracting a pulsed photocurrent in which the base potential is fixed to a constant potential and the current output of the PSD flows into the base. 20, a detection circuit 22, 24, 26 for detecting the collector current of the first transistor 20, a second transistor 32 connected in parallel with the first transistor 20 on the detection circuit side, The switch 36 is connected to the base of the second transistor 32 and is connected to a potential that turns off the second transistor 32 in a normal state, and is opened in distance measurement. The switch 36 is opened in a normal state and the base of the first transistor 20 in distance measurement. And a switch circuit including a switch 34 connected to the same potential.

In order to accurately detect the distance to the object without being affected by hfe or Ii, the present invention employs a logarithmic conversion circuit as shown in FIG. A resistor circuit 40 for converting the pulsed photocurrent extracted by the pulsed photocurrent extraction circuit into a voltage, and a voltage v
Amplifying circuit 44 including an operational amplifier for inputting and amplifying o
46, 48, 50 and 52, and conversion circuits 56 and 58 for converting the amplified voltage into logarithmic values.

[0012]

FIG. 3 shows a first embodiment. This circuit shows one of two sets of a pulse photocurrent sampling circuit and a logarithmic conversion circuit of the distance detecting device shown in FIG.
Each set has the same configuration. The same parts as those in FIG. 2 are denoted by the same reference numerals. NPN transistor 1 at one end of PSD
0 is connected, the emitter of the transistor 10 is connected to the GND terminal, the capacitor 12 is connected between the base of the transistor 10 and the GND terminal, and connected to the output terminal of the amplifier 16 via the switch 14. I have. The collector of the transistor 10 is connected to the inverting input terminal of the amplifier 16 via the amplifier 18 and the NP for extracting the pulsed photocurrent.
It is connected to the base of N transistor 20. A reference voltage Vref is applied to the non-inverting input terminal of the amplifier 16,
The base potential of the transistor 20 is fixed at the reference voltage Vref. A current mirror circuit is formed by the transistors 22, 24, and 26. A diode 28 is connected between the collector of the transistor 24 and the GND terminal.
An output voltage is taken out from the anode of the diode 28 via the buffer amplifier 30.

An NPN transistor 3 is connected to a node between the collector of the transistor 20 and the collector of the transistor 22.
2, the emitter of the transistor 32 is connected to the GND terminal, the base of the transistor 32 is connected to the non-inverting input terminal of the amplifier 16 via the switch 34, and the base of the transistor 32 is connected to the switch 36.
To the GND terminal. Switch 14,
The switches 34 and 36 operate in synchronization, and the switches 14 and 36 have the same phase and the switch 34 has the opposite phase.

Next, the operation of the embodiment shown in FIG. 3 will be described. In a steady state, switches 14 and 36 are closed and switch 34 is open. The operation in this state is the same as that in the steady state of the circuit in FIG. 2, and the idle current Ii flows through the transistor 20. During the distance measurement operation, switches 14 and 36
Opens, and the switch 34 closes. When the switch 14 is opened, the pulse photocurrent component ΔI ₁ is extracted, ΔI ₁ flows into the base of the transistor 20, and the value multiplied by hfe is logarithmically compressed by the diode 28, and the output voltage V ₁
Is output as Attention is paid to the circuit of the transistor 32 in this state. When the switch 36 is opened and the switch 34 is closed in synchronization therewith, the base of the transistor 32 is connected to the non-inverting input terminal of the amplifier 16 and is fixed to the reference voltage Vref. That is, in the steady state, the base potential of the transistor 20 becomes equal to the potential of Vref due to the virtual short circuit in the amplifier 16, but when the switch 34 is closed, the base potential of the transistor 32 also becomes equal to Vref.
A current equal to the collector current of 0 (that is, the idle current Ii) is the current of the transistor 32, and the current flowing through the transistor 20 is a component of only ΔI × hfe.

In the circuit shown in FIG. 3, the input pulse photocurrent ΔI ₁
The relational expression between the output voltage Vout and the output voltage Vout is obtained by adding the relational expression for the transistor 32 to the expression (4). Vout = (kT / q) ln {(ΔI ₁ · hfe ₁ + Ii−Ii) / (ΔI _2. hfe ₂ + Ii−Ii)} = (kT / q) ln (ΔI ₁ · hfe ₁ ) / (ΔI ₂ · hfe ₂ ) (5) That is, the idle current Ii can be canceled,
It is possible to reduce the error of the distance measurement output.

FIG. 4 shows an embodiment of a logarithmic conversion circuit which is not affected by the transistor hfe and the idle current Ii.
This is used as the logarithmic conversion circuits 6a and 6b in FIG. In FIG. 4, the resistance 40
, A constant current I is supplied to the constant current source 42. Across the resistor 40, respectively resistance is connected to respective input terminals of the differential amplifier 48 via a resistor 44, 46 of the R _1. The non-inverting input terminal of the differential amplifier 48 has a resistance value R ₂
Is the reference voltage Vref through the resistor 50 is applied, an inverting input terminal of the differential amplifier 48 is connected to the output point A by the resistor 52 of the resistance value R _2. Logarithmic compression amplifier 56 the output terminal of the differential amplifier 48 via a resistor 54 of resistance R ₃
, And a reference voltage Vref is applied to a non-inverting input terminal of the amplifier 56. A transistor 58 is connected between the inverting input terminal and the output terminal of the amplifier 56 for logarithmic conversion, and the base of the transistor 58 is connected to the GND terminal.

Next, the operation of the embodiment shown in FIG. 4 will be described. When the constant current I flows through the resistor 40 having the resistance value r, a potential difference v ₀ of r · I is generated between both ends of the resistor 40. The v ₀ is a differential amplifier of the differential amplifier 48, Va = Vref- a _{(R 2 / R 1) v} 0 ...... (6). This output voltage Va is logarithmically compressed by the amplifier 56 and is expressed by the following equation (7). Vout = Vref− (kT / q) ln (Il / Is) = Vref− (kT / q) ln (Va / Is · R ₃ ) (7) By substituting equation (6) into equation (7), the output voltage Vout is expressed by Vout = Vref- (kT / q) ln {(Vref- (R 2 / R 1) v 0) / is · R 3} (8). Here, Vout is changed from Vout ₁ to Vout ₂ by Δ
When changes by _{Vout, ΔVout = Vout 2 -Vout 1} = [Vref- (kT / q) ln {(Vref- (R 2 / R 1) v 02) / Is · R 3}] - [Vref- ( kT / q) ln {(Vref- (R 2 / R 1) v 01) / Is · R 3}] = (kT / q) ln {(Vref- (R 2 / R 1) v 01) / Is · _{R 3} - (kT / q} ) ln {(Vref- (R 2 / R 1) v 02) / Is · R 3} = (kT / q) ln {(Vref- (R 2 / R 1) v 01 ) / (Vref− (R ₂ / R ₁ ) v ₀₂ )} (9) In the equation (9), all the items affected by the characteristics of the transistor are canceled, so that a more accurate distance measuring operation can be performed even in a long distance measurement or when the reflected light intensity is low.

[0018]

According to the present invention, the base potential of the transistor for extracting the pulsed light current from which the current output of the PSD flows into the base is fixed to a constant potential, and an idle current is supplied to the collector of the transistor. By flowing the current to another transistor, only the fluctuation due to the pulsed reflected light flows to the pulsed light current extracting transistor, and the collector current of the pulsed light current extracting transistor at that time is detected, so the logarithmic conversion circuit In this case, an accurate distance measuring operation can be performed without the influence of the idle current. In the present invention, further, as a configuration of the logarithmic conversion circuit, the pulse photocurrent extracted by the pulse photocurrent extraction circuit is converted into a voltage by a resistor circuit, and the voltage is amplified by an amplifier circuit including an operational amplifier, and the amplified voltage is amplified. Since the voltage is converted to a logarithmic value, the influence of hfe of the transistor in the logarithmic conversion circuit is eliminated, and a more accurate ranging operation can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a distance detection device to which the present invention is applied.

FIG. 2 is a circuit diagram showing a conventional pulsed photocurrent sampling circuit and a logarithmic conversion circuit.

FIG. 3 is a circuit diagram showing a pulsed photocurrent sampling circuit and a logarithmic conversion circuit in the first embodiment.

FIG. 4 is a circuit diagram illustrating a logarithmic conversion circuit according to a second embodiment.

[Explanation of symbols]

 2 PSD 4a, 4b Pulsed photocurrent sampling circuit 6a, 6b Logarithmic conversion circuit 8 Differential circuit 20 First transistor 32 Second transistor 34, 36 Switch 40 Resistance 48, 56 Operational amplifier

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01C 3/06 G01S ⁷ /48-7/51 G01S 17/00-17/95 G01B 11/00

Claims (3)

(57) [Claims] 1. A semiconductor optical position detector which is provided at a position where a pulse reflected light from a distance measuring object is imaged and outputs first and second currents corresponding to an image forming position, and a semiconductor optical position detector. A pair of pulsed light current extraction circuits that receive each current output of the detector and extract a variation in the current output due to the pulse reflected light, and a pair of logarithmic conversion circuits that logarithmically convert these extracted pulsed light currents, A differential circuit that obtains a distance detection signal by obtaining a difference between the logarithmically converted two voltage outputs, wherein the pulsed photocurrent sampling circuit has a base potential fixed to a constant potential and the semiconductor A first transistor for extracting a pulsed photocurrent into which a current output of the optical position detector flows into a base, a detection circuit for detecting a collector current of the first transistor, and a parallel circuit with the first transistor A second transistor mutually connected on the detection circuit side, a switch connected to a base of the second transistor, connected to a potential that turns off the second transistor in a steady state, and opened during distance measurement; And a switch circuit including a switch connected to the same potential as the base of the first transistor during normal distance measurement and distance measurement. 2. A semiconductor optical position detector is provided at a position where a pulse reflected light from a distance measuring object is formed, and first and second currents are supplied from the semiconductor optical position detector in accordance with the image forming position. In the distance detection method of extracting a variation due to the pulse reflected light from each of the current outputs and obtaining a distance detection signal by calculating the difference between the variations of the two voltage outputs after logarithmically converting these extracted pulsed photocurrents, In order to extract the fluctuation due to the pulsed reflected light from the current output of the semiconductor optical position detector, the base potential of the first transistor into which the current output of the semiconductor optical position detector flows into the base is fixed to a constant potential. A small current is caused to flow through the collector of one transistor, and this small current is caused to flow through another transistor during distance measurement, so that the first transistor has a variation due to pulse reflected light. A distance detection method for detecting the collector current of the first transistor at that time. 3. A semiconductor optical position detector which is provided at a position where a pulse reflected light from a distance measuring object is formed and outputs first and second currents corresponding to the image forming position, and a semiconductor light position detector. A pair of pulsed light current extraction circuits that receive each current output of the detector and extract a variation in the current output due to the pulse reflected light, and a pair of logarithmic conversion circuits that logarithmically convert these extracted pulsed light currents, A differential circuit that obtains a distance detection signal by obtaining a difference between the fluctuations of both voltage outputs that have been logarithmically converted, wherein the logarithmic conversion circuit includes a pulsed light extracted by the pulsed light current extraction circuit. A distance comprising: a resistor circuit for converting a current into a voltage; an amplifier circuit including an operational amplifier for inputting and amplifying the voltage; and a conversion circuit for converting the amplified voltage to a logarithmic value. detection apparatus.