JPH0378612A - Signal processing circuit of distance measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a characteristic of an excellent S/N ratio by a low-voltage power source and to improve the precision of measurement of a distance by providing amplifiers amplifying information signals linearly and a time constant circuit controlling the quantity of an emitted light of a light-emitting circuit on a time basis. CONSTITUTION:A time constant circuit 10 is connected to a light-emitting circuit 1 and the quantity of an emitted light is so set thereby as to be proportional to a time (t). Amplifiers 9a and 9b amplifying outputs of amplifier circuits 4a and 4b are constructed of amplifying means of amplifying light information signals linearly, and the quantity of an incident light is amplified thereby linearly to a voltage value VD of an appropriate level being enough to secure a dynamic range of the circuits. When a distance to a target object is long or a reflectance thereof is small, for instance, a distance measurement timing signal is read in till the time shown at a distance measurement timing t3 and subjected to an arithmetic processing in an output waveform processing circuit 11 and a final distance measurement signal 13 is outputted, in this constitution.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a distance measuring device, and particularly to a signal processing circuit for a distance measuring device that measures the distance to a target object and is suitable for optical equipment such as a photographic camera. .

[Conventional technology]

Conventionally, various signal processing circuits have been proposed for distance measuring devices that measure the distance to a target object.
It is shown and explained in the figure. FIG. 3 is a block diagram of a signal processing circuit of a conventional distance measuring device.

In the figure, 11 is a light emitting circuit that drives a light emitting element (2), the light emitting circuit (11) and the light emitting element (2) constitute a light emitting means for emitting light toward a distance measuring object, and the light emitting element (2)
The light from the sensor is configured to be directed toward the object to be measured.

(3) is the target object (subject) to be measured, (4a
) and (4b) each have a light receiving element (5a) and a light receiving element (5b) that receive reflected light from the target object (3) and convert it into an electrical signal, and convert the light into a signal voltage and amplify it. In the circuit, the light receiving circuits (4a) and (4b) constitute a light receiving means for receiving reflected light from the target object (3) and photoelectrically converting it.

(6a) and (6b) are logarithmic compression circuits that input the outputs of the light receiving circuit (4a) and the light receiving circuit (4b), respectively, and logarithmically compress the outputs; (7) is the logarithmic compression circuit (6a);
, (6b) is an input, and a waveform processing circuit for calculating the output as distance information. (8) is a distance measurement signal.

Next, the operation will be explained. First, light emitted from the light emitting element (2) driven by the light emitting circuit fll hits the target object (3) and is reflected by the light receiving element (5a) (5).
Enter b). The light entering the light receiving elements (5a) and (5b) is converted into a signal voltage and amplified by the light receiving circuits (4a) and (4b), respectively. Next, the light receiving circuit (4a
) and (4b) are logarithmically converted by the next stage logarithmic compression circuits (6a) and (6b), respectively.

Here, the light intensity incident on each of the light receiving elements (5a) and (5b) varies by a factor of 1000 or more due to differences in distance to the target object (3), reflectance, etc., so the normal linear amplifier circuit However, it does not operate at low power supply voltages such as those using batteries.

Therefore, the circuit shown in FIG. 3 is a logarithmic compression circuit (6a
), (6b) are used to compress the signal, expand the dynamic range, operate with a low power supply voltage, and facilitate post-processing of the optical signal.

The outputs of the logarithmic compression circuits (6a) and (6b) are processed as distance information by a waveform processing circuit (7), and finally a ranging signal (8) is output from the output of the waveform processing circuit (7).

[Problem to be solved by the invention]

Since the signal processing circuit of a conventional ranging device is configured as described above, the optical signal amplified by the light receiving circuit is logarithmically compressed using a logarithmic compression circuit, and in principle, the optical signal is reduced from noise. The signal-to-noise ratio (signal-to-noise ratio S/N) is also compressed and worsens, making it impossible to distinguish weak reflected light from distant objects, resulting in poor long-distance performance. Furthermore, there is a drawback that the accuracy in processing the optical signal deteriorates, and as a result, the distance measurement accuracy decreases.

In view of the above points, this invention was made to solve these problems and eliminate such drawbacks.The purpose of this invention is to obtain a good signal-to-noise ratio with a low voltage power supply, and to improve distance measurement accuracy. It is an object of the present invention to provide a signal processing circuit for a distance measuring device that has a simple circuit configuration and is suitable for integrated circuit technology.

(Means for Solving the Problems) A signal processing circuit of a distance measuring device according to the present invention connects a timer circuit to a light emitting circuit, and temporally controls the amount of light emitted to emit an optical signal.

[For production]

The signal processing circuit of the distance measuring circuit according to the present invention performs waveform processing at an appropriate output level that can sufficiently guarantee the dynamic range of the circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings. FIG. 1 is a block diagram showing a signal processing circuit of a distance measuring device.

In the figure, (11~+31, (4a), (4
b), (5a), and (5b) are the same as those shown in the conventional example of FIG. 3, so their explanations will be omitted. (9a
) and (9b) are the light receiving circuits (4a) and (4b), respectively.
) constitutes an amplifying means that linearly amplifies the optical information signal from the light receiving means. 0 [ is a time constant circuit that is connected to the light emitting circuit fi+ and controls and varies the amount of light emitted according to time. 0υ is the amplifier (9a)
, (9b) are used as inputs, and a waveform processing circuit is used to calculate the input as distance information.
) is input, the output level is determined, and a signal is sent to the waveform processing circuit αU.The level determination circuit (2) is provided to notify the distance measurement determination timing. α heat is the final ranging signal.

Next, the operation will be explained with reference to FIG.

FIG. 2 is a graph explaining the operation of the circuit of FIG. 1. Fig. 2 fa) shows the change in the emitted light lp with respect to time t, and Fig. 2 (bl shows the change in the output of the amplifiers (9a) and (9b) with respect to time t. (C1 represents the change in the output of the level judgment circuit with respect to time t. In Fig. 2 (bl), Vo indicates the voltage value set in the level judgment circuit LM indicates "distance" LS indicates "long distance", and in FIG. 2 fcl, H indicates high level and L indicates low level.

First, a light emitting element (2
) hits the target object (subject) (3), is reflected and enters the light receiving elements (5a) and (5b), respectively. The light received by the light receiving elements (5a) and (5b) is converted into a signal and amplified by the light receiving circuits (4a) and (4b), respectively. Each optical signal amplified by the light receiving circuits (4a) and (4b) is sent to the next stage amplifier (9a).
, (9b).

Next, the operation of the time constant circuit α connected to the light emitting circuit +11 will be explained. Let us now assume that the amount of light emitted from the light emitting circuit (1) changes as shown in FIG.
Although the case where the change in the amount of emitted light is proportional to time is shown as an example, other time functions may be used.

Each optical signal from the light receiving circuits (4a) and (4b) input to the amplifiers (9a) and (9b) enters as a constant amount if the state of the target object (3) is constant. .

First, consider a case where the distance to the target object (subject) (3) to be measured is medium and the subject reflectance is about ``medium.'' In this case, the outputs of the amplifiers (9a) and (9b) are
It changes as shown in the characteristic "LM" in the figure (bl).

Here, the output of the amplifier (9b) is output to the level judgment circuit (2).
When the voltage V, set in Fig. 2 is reached, FC+
As shown in , the output of the level determination circuit (2) is at a high level “II” so that the signal is output at the distance measurement timing t2.
”, and this output is used by the waveform processing circuit a that creates distance measurement information.
Send it to t+. That is, the amount of incident light by the amplifiers (9a) and (9b) is set to a voltage value V that is an appropriate level that can sufficiently guarantee the dynamic range of the circuit.

linearly amplified up to Then, the ranging timing signal is read at a time indicated by t1 in the figure.

Next, if the target object (subject) (3) is to be processed at a short distance and its reflectance is large, an amplifier (9a) is used.

The output of the amplifier (9b) changes as shown in the characteristic LL of bl in FIG. C
1, the ranging timing signal is read at the time indicated by t in the figure.

Next, when the distance to the target object (subject) (3) is long or the reflectance is small, a distance measurement timing signal is read at a time indicated by distance measurement timing t in the figure.

As a result of the signals at these timings, the outputs of the amplifiers (9a) and (9b) are processed as distance measurement information in the waveform processing circuit 0υ, and are output as the final distance measurement signal α.

In this way, by operating the amplifiers (9a) and (9b) linearly regardless of the distance and reflectance of the target object (subject) (3), there is no need to consider the dynamic range of the circuit, so low voltage A good S/N ratio characteristic can be obtained from the power supply, and distance measurement accuracy can be improved.

In the above embodiment, the level determination circuit (2) is inserted into the circuit system of the amplifier (9b), but it may also be inserted into the circuit system of the amplifier (9a). They can also be provided corresponding to both circuit systems 9a) and (9b), respectively.

Further, in the above embodiment, the light receiving circuit (4a).

(4b) and amplifier (9a), (9b) is 2
Although the present invention has been explained by taking as an example a circuit system having two or more sets, the present invention is not limited thereto, and the same effect can be obtained in the case of a circuit system having two or more sets.

〔Effect of the invention〕

As explained above, according to the present invention, since the amplifier is operated in a line system, there is no need to consider the dynamic range of the circuit, regardless of the distance or reflectance of the target object (subject). With voltage power supply, signal-to-noise ratio S
Since good characteristics of /N can be obtained and distance measurement accuracy can be improved, the practical effect is extremely large.

In addition, the circuit structure becomes simple, and especially when applied to an integrated circuit, manufacturing becomes easy and suitable for mass production, and it is extremely effective in that cost amplifiers can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a signal processing circuit of a distance measuring device according to an embodiment of the present invention, FIG. 2 is a graph explaining the operation of the circuit in FIG. 1, and FIG. 3 is a signal processing circuit of a conventional distance measuring device. FIG. 2 is a block diagram showing an example of a processing circuit. In the figure, (1) is a light emitting circuit, (2) is a light emitting element, (
3) is the target object, (4a) and (4b) are the light receiving circuits,
(5a), (5b) are light receiving elements, (9a), (9b
) is an amplifier, α[ is a time constant circuit, αυ is a waveform processing circuit, (
2) is a level determination circuit, and α is a final ranging signal. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] A distance measuring device for measuring the distance to a target object, comprising: a light emitting means for emitting light toward the target object to be measured; a light receiving means for receiving reflected light from the target object and photoelectrically converting the received light; 1. A signal processing circuit for a distance measuring device, comprising: amplifying means for linearly amplifying an optical information signal from the means; and a time-setting circuit for temporally controlling the amount of light emitted from the light emitting circuit.