JP2831217B2 - Distance measuring circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-amount detecting distance measuring circuit which emits light from a camera, detects the amount of reflected light from a subject, and measures the distance to the subject.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional light detection type distance measuring circuit. In the figure, Q1 is an SPD (silicon photo diode) for detecting the amount of light reflected from the subject, the cathode of which is a power supply VCC, and the anode of which is a transistor Q.
3, and the base of Q6 and the collector of transistor Q2. A current corresponding to the light L incident on the silicon photodiode Q1 flows from the anode into the bases of the transistors Q3 and Q6 and the collector of the transistor Q2.

The base of the transistor Q2 is connected to a control circuit 10
Of the transistors Q14, Q16 and the hold capacitor C1, and the emitter thereof is connected to GND (ground) via the resistor R1. Q
Reference numerals 3, Q4 and Q5 denote transistors constituting a circuit for keeping the input terminal voltage constant. The emitter of the transistor Q3 is connected to the power supply VCC, and the collector is connected to the base of the transistor Q4 and the constant current source 1. Transistor Q
4 has the collector connected to GND and the emitter connected to the transistor Q5.
Is connected to the constant current source 2 and the transistor Q
5 has a collector connected to VCC, an emitter connected to the constant current source 3 and the emitter of the transistor Q6, and forms a negative feedback circuit so that the voltage (input terminal voltage) between the emitter and the base of the transistor Q3 is constant. ing.

The collector of the transistor Q6 has a superimposed constant current I ₄ for increasing the response speed of the transistor Q6.
Current source 4 for supplying the current and the cathode of a logarithmic compression diode Q7 for logarithmically compressing the input current since the current range of the input current is wide, the input side transistor Q8 of the differential amplifier 11 of the control circuit 10 and the transistor Q of the comparator 12
26 bases. The anode of the compression diode Q7 is connected to the power supply VCC.

The emitter of the transistor Q8 is the emitter of the transistor Q9 and the constant current source 5, and the collector is the collector and base of the transistor Q11 and the transistor Q13.
And the first together with Q11 and Q13
Of the current mirror circuit. Transistor Q
The base of 9 is connected to the cathode of a diode Q10 for generating a reference voltage. The anode of diode Q10 is connected to power supply VCC. The collector of the transistor Q9 is connected to the collector and base of the transistor Q12 and the base of the transistor Q14.
Together with Q12 and Q14, a second current mirror circuit is formed.

The collector of the transistor Q13 is connected to the collector and base of the transistor Q15 and the transistor Q16.
To form a third current mirror circuit. The collector of the transistor Q16 is connected to the collector of the transistor Q14, the base of the transistor Q2, and the hold capacitor C1, and the three current mirror circuits output the connection line 14 as an output.
A control circuit 10 having the bases of the transistors Q8 and Q9 as inputs is formed.

The transistors Q11, Q12, Q1
3, the emitters of Q14 have resistors R2, R3,
R4 and R5 are connected, and the other ends of these resistors are connected to the power supply VCC. Also, the transistor Q1
5, the emitter of Q16 is connected to GND.

Now, in a steady state (a state in which the silicon photodiode Q1 receives only steady light without emitting light for distance measurement from the camera side), a constant current is supplied to operate the control circuit 10. . Negative feedback is applied to the input side via the transistor Q2 so that the base voltage of the transistor Q8 becomes equal to the base voltage of the transistor Q9, so that both base currents become the same current. That is, the compression diode Q
The current flowing through 7 is the same as that of the reference diode Q10.

[0009] At this time, the current flowing through the transistor Q6 is next I _4, the sum of the base current of the base current and Q3 of the transistor Q6 at the time and Ic. Further, a current generated in the silicon photodiode Q1 by the steady light is defined as Ia, and a collector current of the transistor Q2 is defined as Ib. Now, if Ib <Ia + Ic, the base current of the transistor Q6 increases as the current of Ia + Ic−Ib, so that the current flowing through the compression diode Q7 increases, the voltage between the anode and cathode of the transistor Q7 increases, and the base voltage of the transistor Q8 increases. Go down. For this reason, the collector current of the transistor Q8 decreases, and the collector current of the transistor Q9 increases, so that the first and third current mirror currents become smaller than the second current mirror current, and the collector current of the transistor Q14 becomes smaller than the collector current of the transistor Q16. And the base current of the transistor Q2 increases, so that Ib
Works in a direction to increase the current value of.

If Ib> Ia + Ic, the base current of the transistor Q6 is reduced by the amount of Ib- (Ia + Ic), so that the current flowing through the compression diode Q7 is reduced and the voltage between the anode and cathode of the transistor Q7 is reduced. The base voltage of Q8 increases. For this reason, the collector current of the transistor Q8 increases, and the collector current of the transistor Q9 decreases, so that the first and third current mirror currents become larger than the second current mirror current, and the collector current of the transistor Q14 becomes larger than the collector current of the transistor Q16. And the base current of the transistor Q2 decreases, so that the current value of Ib decreases. That is, in the steady state, the collector current Ib of the transistor Q2 is equal to the steady current of the silicon photodiode Q1 and the transistor Q2.
3. Balanced with base current of Q6 (Ib = Ia + Ic)
Work like that.

Next, the emitter of the transistor Q26 serving as the input transistor of the comparator 12 is connected to the emitter of the transistor Q27 and the constant current source 6, and the collector is connected to the collector and base of the transistor Q29 and the base of the transistor Q17. Transistor Q2
A fourth current mirror circuit is constituted together with Q9 and Q17. The base of transistor Q27 is a constant current source 7 is connected for supplying a constant current I ₇ comprising the cathode of diode Q28 for generating a reference voltage and the reference current, the anode is connected to VCC. Also, the transistor Q
The collector of 27 is connected to the collector and base of transistor Q30 and the base of transistor Q18.
A fifth current mirror circuit is formed together with the transistors Q30 and Q18. The collector of the transistor Q17 is connected to the collector and base of the transistor Q19 and the base of the transistor Q20.
A sixth current mirror circuit is configured together with the transistors 19 and Q20.

The collector of the transistor Q20 is connected to the collector of the transistor Q18 and the base of the transistor Q21. The three current mirror circuits have the collector of the transistor Q21 as an output terminal, the base of the transistor Q26 as an input terminal, and the transistor Q27. Are formed using the base voltage of the comparator as a reference voltage. The transistors Q29, Q30, Q17, Q1
The emitter of 8 is connected to VCC. The emitters of the transistors Q19, Q20, Q21 are connected to GND.

In the steady state described above, the constant current source 5 is controlled by the switching control signal from the switching control signal supply circuit 20.
Is ON, and the constant current sources 6 and 7 are OFF at this time.
b = Ia + Ic, and the silicon photodiode Q
The stationary photocurrent generated in 1 is absorbed by the collector of Q2. At this time, the current flowing through the compression diode Q7 is only the base current of the transistor Q8. Next, the constant current source 5 is turned off and the constant current sources 6 and 7 are turned on by the switching control signal from the circuit 20. The feedback circuit is turned off because the bias current of the control circuit 10 is turned off, but the state in which the steady current is absorbed by the collector of the transistor Q2 remains unchanged because the hold capacitor C1 holds the voltage at the time of feedback. At this time, the base current of the transistor Q8 is 0
Therefore, theoretically, the current flowing through the compression diode Q7 becomes zero.

In this state, light is emitted from the camera to the object, the light reflected on the object is incident on the silicon photodiode Q1, and a reflected light current corresponding to the light amount is added to the steady-state photocurrent, and the input point is changed. (A). Since Q2 absorbs only the stationary photocurrent, the reflected photocurrent flows into the base of the transistor Q6, and the current multiplied by the current amplification factor h _fe by the transistor Q6 flows through the collector of the transistor Q6 and the compression diode Q7. This current is only a current obtained by multiplying the reflected light current by h _fe , and the voltage between the anode and the cathode is a logarithmically compressed voltage thereof.

This current is Id, and the voltage is Vd.
Further, the voltage generated in the transistor Q28 and Ve by the constant current I _7. When Vd <Ve, the base voltage of the transistor Q26 is higher than the base voltage of the transistor Q27, so that the collector current of the transistor Q26 becomes larger than the collector current of the transistor Q27.
The collector current of the transistor Q20 is
8 is smaller than the collector current of transistor Q2.
1 is turned off.

If Vd> Ve, the base voltage of the transistor Q26 is lower than the base voltage of the transistor Q27, so that the collector current of the transistor Q26 becomes smaller than the collector current of the transistor Q27. Since the current becomes larger than the collector current, the transistor Q21 is turned on.

[0017] Here, to detect the reflected light current I _in for generating a light quantity detection silicon photo diode Q1 is reflected by the current value of the constant current I ₇ and I ₇ = h _fe × I _in If the photocurrent is greater than I _in , the transistor Q
21 is ON, and transistor Q21 is OFF if it is small.
I do. That is, when the transistor Q21 is turned on, the distance to the subject is at a short distance level, and the transistor Q21 is turned on.
Is turned off, it can be detected that the distance to the subject is at a long distance level.

[0018]

However, in the circuit shown in FIG. 2, each of the control circuit 10 and the comparator 12 requires a differential amplifier, so that many circuit elements are required.
There is a problem that the chip area is increased even in the case of the IC, and the cost is increased. An object of the present invention is to provide a distance measuring circuit that solves such a problem.

[0019]

In order to achieve the above object, according to the present invention, there is provided a photoelectric conversion element, and a stationary photocurrent absorption device for absorbing a stationary photocurrent flowing through the photoelectric conversion element when no light is emitted from the camera side. Means, a control circuit provided on the output side of the photoelectric conversion element, the control circuit controlling the steady-state photocurrent absorption means so that the steady-state photocurrent absorption means absorbs the steady-state photocurrent in response to a change in the steady-state photocurrent; A comparator that holds the control result, and a signal that is provided at the output side of the photoelectric conversion element and compares the signal current of the photoelectric conversion element due to the reflected light from the subject when the light is emitted from the camera side with a reference value to measure the distance measurement signal. A light amount detection type distance measuring circuit that emits light from the camera side, detects the amount of reflected light from the object, and measures the distance to the object.
An output of the differential amplifier, the output of the photoelectric conversion element being provided to a first input terminal and the reference value being provided to a second input terminal, is commonly connected to the output portions of the control circuit and the comparator. Switching means for switching the reference value given to the second input terminal of the amplifier between the steady light mode and the signal light mode and switching the operation of the output section is provided.

[0020]

In the stationary light mode, the output of the control circuit operates,
The output of the comparator becomes inactive. In this state,
The output of the differential amplifier is supplied to the steady-state photocurrent absorbing means through the output section of the control circuit, and serves to absorb the steady-state photocurrent of the photoelectric conversion element. Next, in the ranging mode in which light is emitted from the camera side, the output section of the control circuit becomes inactive, and the output section of the comparator is activated. For this reason, the differential amplifier functions as a comparator together with the output section, and outputs a ranging signal. At this time, since the control state of the control circuit in the steady light mode is held by the holding means, the steady photocurrent component is absorbed by the absorbing means and does not affect the comparator.

[0021]

FIG. 1 shows an embodiment of the present invention. In this figure, the same parts as those of the conventional circuit of FIG. In FIG. 1, the emitter of the transistor Q8 is connected to the constant current source 5 together with the emitter of the transistor Q9, and the collector is connected to the collector and base of the transistor Q11, the base of the transistor Q13 and the base of the transistor Q17,
A current mirror circuit is configured together with Q11, Q13, and Q17. The base of the transistor Q9 is connected to the collector of the transistor Q23 and the cathode of the diode Q10. The power supply VCC is connected to the anode of the diode Q10.
It is connected to the.

The base of the transistor Q23 is connected to the collector and base of the transistor Q22, the constant current source 8, and the bases of the transistors Q24 and Q25. The resistor R8 is connected to the emitter of the transistor Q23, and the other end of the resistor R8 is connected to GND. Also,
The collector of transistor Q9 is the collector and base of Q12, the base of transistor Q14 and transistor Q1.
8 and a second current mirror circuit together with Q14 and Q18.

The collector of the transistor Q13 is the collector and base of the transistor Q15 and the transistor Q16.
And the bases of the transistors Q15, Q1
6 together with a third current mirror circuit. The collector of the transistor Q16 is connected to the collector of the transistor Q14, the base of the transistor Q2, and the hold capacitor C1.
A control circuit 10 having the bases of the transistors Q8 and Q9 as inputs is formed. Note that the collector of the transistor Q17 is connected to the collector and base of the transistor Q19 and the base of the transistor Q20, and constitutes a fourth current mirror circuit together with the transistors Q19 and Q20. The collector of transistor Q20 is connected to the collector of transistor Q18 and the base of transistor Q21.

Transistors Q11, Q12, Q17, Q
The 18 emitters have resistors R2, R3, R6, R
7 are connected, and the other ends of these resistors are connected to a power supply VCC.
It is connected to the. The emitter of the transistor Q13 is connected to the collector of the transistor Q24 and the resistor R4, and the emitter of the transistor Q14 is connected to the collector of the transistor Q25 and the resistor R5.
The other ends of these resistors R4 and R5 are connected to VCC. Also, transistors Q15, Q16, Q19, Q2
The emitters of 0, Q22, Q24, and Q25 are connected to GND (ground).

The transistors Q13 to Q16 form an output section of the control circuit 10, and the transistors Q17 to Q17
Reference numeral 21 denotes an output unit of the comparator 12. The constant current source 8 is turned on or off in response to a switching signal from the switching control signal supply circuit 20.
When the photometry / ranging start switch of the camera is turned on, the constant current source 8 is turned off from the circuit 20 in order to set the camera to a steady light state at first.
A control signal for turning on the constant current source 8 is supplied to the constant current source 8 for performing distance measurement after a while.

In this embodiment, the switching point is only one point of the constant current source 8. In the conventional example (FIG. 2), a constant current source 5 and
The constant current sources 6 and 7 are switching locations, and there are many switching locations. In this regard, the present embodiment is simplified.

[0027] serves as a constant current source 5 and 6 of the constant current source 5 is conventional circuit (FIG. 2), I ₅ is flowing at all times. In the steady state, the constant current source 8 is turned off, the collector current of the transistor Q23 is set to 0, the current flowing through the diode Q10 is set to only the base current of the transistor Q9, and the collector currents of the transistors Q24 and Q25 are also set to 0. Q13, Q14, Q15, Q16 operate,
Transistor Q so that the steady current of silicon photodiode Q1 is absorbed by the collector of transistor Q2.
The same operation as the conventional circuit is performed so as to control the base voltage of the second circuit.

Next, when the constant current source 8 is turned on, the collector currents of the transistors Q24 and Q25 flow, the emitter voltages of the transistors Q13 and Q14 are reduced by R4 and R5, the transistors Q13 and Q14 are turned off, and the transistors Q15 and Q16 are turned off. Also turns off the transistor Q
14, the collector of Q16 is cut off and the control circuit 10
Is turned off, and the state in which the steady current is absorbed by the collector of the transistor Q2 remains unchanged because the hold capacitor C1 holds the voltage at the time of feedback.

In this state, light is emitted from the camera to the subject, and the light reflected by the subject is incident on the silicon photodiode Q1, and a reflected light current corresponding to the amount of light flows into the base of the transistor Q6. Q6
The current multiplied by h _fe flows through the collector of the transistor Q6 and the compression diode Q7. The current flowing through the compression diode Q7 is only a current obtained by multiplying the reflected light current by h _fe , and the voltage between the anode and the cathode is a logarithmically compressed voltage thereof. This current is Id, and the voltage is Vd. Further, the Ve voltage which is generated in the diode Q10 the collector current I ₂₃ of the transistor Q23.

If Vd <Ve, the transistor Q
8 is higher than the base voltage of the transistor Q9, the collector current of the transistor Q11 becomes larger than the collector current of the transistor Q12.
Becomes larger than the second current mirror current, and the collector current of the transistor Q20 becomes larger than the collector current of the transistor Q18, so that the transistor Q21 is turned off.

When Vd> Ve, the base voltage of the transistor Q8 is lower than the base voltage of the transistor Q9, so that the collector current of the transistor Q11 becomes smaller than the collector current of the transistor Q12, and the first and fourth current mirror currents become smaller. Since the current becomes smaller than the second current mirror current and the collector current of the transistor Q20 becomes smaller than the collector current of the transistor Q18, the transistor Q21 is turned on. This is exactly the same as the operation of the comparator 12 in the conventional circuit of FIG.

[0032] Here, the current value of the reflected light current collector of the transistor Q23 to be detected at I _in current I ₂₃ which generates a light quantity detection silicon photo diode Q1 h
By adjusting the resistance value so that _fe × I _in , if the reflected light current is larger than I _in , the distance to the subject is at a short distance level, and if the transistor Q21 is turned off, the distance to the subject is at a long distance. Can be detected.

[0033]

As described above, according to the present invention, since the differential amplifier of the control circuit and the comparator is also used, the number of elements in the circuit can be reduced, and the O of the current source can be reduced.
Since the control of N and OFF can be reduced from two places to one place, the control can be made simpler than the control of the conventional circuit.
Even in the case of C, the chip size can be reduced, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a distance measuring circuit embodying the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Control circuit 11 Differential amplifier 12 Comparator C1 Hold capacitor Q1 Silicon photodiode Q13-Q16 Transistor which constitutes the output part of a control circuit Q17-Q21 Transistor which constitutes the output part of a comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01C 3/00-3/32 G01B 11/00-11/30 G02B 7/32 G03B 13/36

Claims (1)

(57) [Claims] 1. A photoelectric conversion element, a stationary photocurrent absorption means for absorbing a stationary photocurrent flowing through the photoelectric conversion element when no light is emitted from the camera side, and the stationary photocurrent absorption means provided on an output side of the photoelectric conversion element. A control circuit that controls the steady-state photocurrent absorbing unit so that the photocurrent absorbing unit absorbs the steady-state photocurrent in response to the change in the steady-state photocurrent; a holding unit that holds a control result thereof; and A comparator that is provided on the output side and outputs a distance measurement signal by comparing a signal current of the photoelectric conversion element due to light reflected from the object with a reference value when light is emitted from the camera side, and emits light from the camera side. In a light quantity detection type distance measuring circuit which detects a light quantity reflected from a subject and measures a distance to the subject, an output of the photoelectric conversion element is provided to a first input terminal, and a reference value is provided to a second input terminal. A given output of the differential amplifier is connected in common to the respective output sections of the control circuit and the comparator, and a reference value given to a second input terminal of the differential amplifier is switched between a steady light mode and a signal light mode, and A distance measuring circuit comprising switching means for switching an operation of an output unit.