JPH031626B2 - - Google Patents

Abstract

PURPOSE:To eliminate errors in the gain and frequency characteristics between channels, to decrease the number of parts, and to obtain a high-precision distance measurement signal by switching one variable gain amplifier through switching operation based upon a distance measurement timing signal. CONSTITUTION:Switch circuits 10a-10c turn on and off photodetecting circuits 5a and 5b and a gain control circuit 7 according to the timing output of a level decision circuit 9. Irradiation light from a light emitting element 2 is reflected by a body 3 to enter photodetecting elements 4a and 4b. Their photodetection outputs are led in the variable gain amplifier 6 through the photodetecting circuits 5a and 5b in operation states and amplified with the gain corresponding to the output of a control circuit 7, and both amplification outputs are supplied to a waveform processing circuit 8. The processing circuit 8 processes both amplification levels to output final distance information.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a signal processing circuit for a distance measuring device.
In particular, the present invention relates to a signal processing circuit for a distance measuring device suitable for optical equipment such as a photographic camera that measures the distance to a target object (subject).

[Prior Art] FIG. 1 is a schematic block diagram showing an example of a signal processing circuit of a conventional distance measuring device.

First, the configuration of a signal processing circuit of a conventional distance measuring device will be explained with reference to FIG. In FIG. 1, a light emitting circuit 1 drives a light emitting element 2 to emit light, and the light is emitted from a target object (subject) to be measured.
It is configured to irradiate towards 3. The reflected light from the target object 3 is transmitted to light receiving elements 4a and 4.
The signal is converted into an electric signal at step b, and further amplified at light receiving circuits 5a and 5b. Light receiving circuits 5a and 5b
The outputs of are respectively applied to variable gain amplifiers 6a and 6b whose gains are variable and amplified. Here, the gain control circuit 7 is a control circuit that changes the gains of the variable gain amplifiers 6a and 6b as a function of time. Variable gain amplifier 6
The outputs of a and 6b are given to a waveform processing circuit 8, and the waveform processing circuit 8 simultaneously calculates these inputs as distance information when receiving a distance measurement timing signal, which will be described later. Further, the output of the variable gain amplifier 6b is also given to the level determination circuit 9 at the same time, and the level determination circuit 9 rises from the low level to the high level when the output level of the variable gain amplifier 6b exceeds a predetermined threshold. A distance measurement timing signal is generated and applied to the waveform processing circuit 8. When the waveform processing circuit 8 receives this ranging timing signal, it calculates the distance information from the variable gain amplifiers 6a and 6b described above and outputs the result as final ranging information representing the measured distance to the target object.

FIG. 2 is a waveform diagram for explaining the operation of the signal processing circuit of the conventional distance measuring device shown in FIG.

Next, the operation of the signal processing circuit of the conventional distance measuring device shown in FIG. 1 will be explained with reference to FIG.

First, light emitted from the light emitting element 2 driven by the light emitting circuit 1 hits the target object 3, is reflected, and enters the light receiving elements 4a and 4b. and,
The light entering the light-receiving elements 4a and 4b is targeted to an electric signal, respectively, and the light-receiving circuits 5a and 5b
is amplified. The signals amplified by the light receiving circuits 5a and 5b are amplified by variable gain amplifiers 6a and 6b at the next stage, respectively. The gains of the variable gain amplifiers 6a and 6b are varied as a function of time by the gain control circuit 7 as described above, but here, as shown in FIG. 2a, for example, the gain G (vertical axis) Consider the case where t increases in proportion to time t (horizontal axis) (other time functions may be used). The light receiving circuits 5a and 5 input to the variable gain amplifiers 6a and 6b.
Each signal from b is input as a constant amount if the state of the target object 3 is constant. For example, consider a case where the distance to the target object 3 to be measured is medium and the reflectance from the subject is medium, that is, the amount of incident light is medium. FIG. 2b is a graph in which the vertical axis represents the output levels of variable gain amplifiers 6a and 6b, and the horizontal axis represents time t. When the above-mentioned amount of incident light is medium, the variable gain amplifier 6a
and 6b increase linearly as shown in FIG. 2a, so the outputs of variable gain amplifiers 6a and 6b increase with linear characteristics as shown by LM in FIG. 2b.

Here, the output level of the variable gain amplifier 6b is
Voltage threshold set by level judgment circuit 9
When reaching V _D (time t ₁ ), the level judgment circuit 9
outputs a ranging timing signal that rises from low level to high level and sends it to the waveform processing circuit 8.
In response to this, the waveform processing circuit 8 calculates the outputs of the variable gain amplifiers 6a and 6b, and outputs a final ranging signal.

Next, when the distance to the target object 3 is short and its reflectance is large, the amount of incident light is large, and the output level of the variable gain amplifiers 6a and 6b has a linear characteristic as shown by LL in FIG. 2b. increases with time
The threshold V _D is reached at t ₂ . At this time, the level determination circuit 9 outputs a distance measurement timing signal, and the final distance measurement signal can be obtained from the waveform processing circuit 8 as described above.

Further, when the distance to the target object is long or the reflectance is small, the amount of incident light is small and the output level of the variable gain amplifiers 6a and 6b is
It increases with a linear characteristic as shown by LS in Figure b, and reaches the threshold value V _D at time _t3 . At this time, the level determination circuit 9 outputs a distance measurement timing signal, and the final distance measurement signal can be obtained from the waveform processing circuit 8 as described above.

That is, the variable gain amplifiers 6a and 6b linearly amplify the amount of incident light to a voltage value V _D that is an appropriate level that can sufficiently guarantee the dynamic range of the circuit. Then, when the threshold value V _D is reached, a ranging timing signal is generated and a final ranging signal is obtained.

However, the conventional distance measuring device described above uses a plurality of signal processing systems (two systems in the above example), that is, a light receiving circuit and a variable gain amplifier, in order to improve measurement accuracy, but the gain between each signal processing system is It is difficult to completely eliminate errors in frequency characteristics.
The drawback was that it was not possible to obtain highly accurate calculation results due to slight errors.

[Summary of the Invention] Therefore, the main object of the present invention is to use a plurality of light receiving circuits as before, but by configuring it so that only one variable gain amplifier is required by switching a switch. It is an object of the present invention to provide a highly accurate signal processing circuit for a distance measuring device that is not affected by errors between signal processing systems and has a small number of parts.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

[Embodiment of the Invention] FIG. 3 is a schematic block diagram showing an embodiment of the invention.

The example shown in FIG. 3 is the same as the schematic block diagram shown in FIG. 1 above, except for the following points.
That is, each output of the light receiving circuits 5a and 5b is
It is applied to a single variable gain amplifier 6 , and the output of the variable gain amplifier 6 is applied as a single input to a waveform processing circuit 8 and also to a level determination circuit 9 . The output of the level judgment circuit 9 is
When the input is below a certain threshold value V _D , it is at low level, and when it exceeds V _D , it outputs a timing signal that rises from low level to high level.
The switch circuits 10a, 10b, and 10c are for switching the light receiving circuits 5a, 5b and the gain control circuit 7 into an operating state or a non-operating state, respectively, based on the above-mentioned timing signal output from the level determination circuit 9. .

To explain in more detail, the switch circuit 10a
is the light receiving circuit 5a when the input to the level determination circuit 9 does not reach the threshold and its output is low level.
The switch circuit 10b is set to be in the operating state and switched to the non-operating state when the threshold value is reached and a high-level timing signal is generated. The light receiving circuit 5b is set to be in a non-operating state and switched to an operating state when a high-level timing signal is generated, and the switch circuit 10c is set to switch the gain control circuit 7 to a non-operating state when the output of the level measuring circuit 9 is at a low level.
is set to be in an active state, and switched to a non-active state when a high-level timing signal is generated.

FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to FIG.

First, light emitted from the light emitting element 2 driven by the light emitting circuit 1 hits the target object 3, is reflected, and enters the light receiving elements 4a and 4b. However, the light receiving circuits 5a and 5b are
0a and 10b are set so that only the light receiving circuit 5a is in an operating state, and only the light that enters the light receiving element 4a is converted into an electrical signal and amplified by the light receiving circuit 5a. The signal amplified by this light receiving circuit 5a is given to a variable gain amplifier 6 and amplified. This variable gain amplifier 6 is the same as the variable gain amplifiers 6a and 6b in the conventional example shown in FIG. 1, and the gain of this variable gain amplifier 6 is as follows.
As mentioned above, the gain control circuit 7 (level determination circuit 9
Since the output of is still at a low level, it is increased as a function of time by the gain control circuit 7 (at this time the gain control circuit 7 is active). And here, as in the conventional signal processing circuit shown in FIG. 2a, the gain G changes over time t.
Consider a case in which the time function increases in proportion to (other time functions may be used). And this variable gain amplifier 6
If the target object 3 is in a constant state, the optical signal from the light receiving circuit 5a is input as a constant amount. FIG. 4a is a graph showing the relationship between the output level (vertical axis) of the variable gain amplifier 6 and time t (horizontal axis), which increases linearly in the same way as the gain changes. 4c, d, and g are graphs showing whether the light receiving circuits 5a, 5b and the gain control circuit 7 are in an operating state (on) or a non-operating state (off), respectively. In the state where the variable gain amplifier output is increasing, the light receiving circuit 5a is in an operating state, the light receiving circuit 5b is in an inactive state, and the gain control circuit 7 is in an operating state. here,
When the output level of the variable gain amplifier 6 reaches V D, which is an appropriate level that can sufficiently guarantee the dynamic range of the circuit set by the level judgment circuit 9 (time t ₁ ), the level judgment circuit 9 changes the level from the low level to V _D (time t 1 ). Timing signal rising to high level (4th
Figure b) is output. (In other words, the dynamic range of the circuit is guaranteed in this state.) Here,
As the level determination circuit 9 outputs a high-level timing signal, the light receiving circuit 5a becomes inactive after _t1 , as shown in FIG. 4c, d, and e.
The light receiving circuit 5b is switched to an operating state, and the gain control circuit 7 is switched to a non-operating state. In this state, the gain of the variable gain amplifier 6 is fixed to the gain immediately before t ₁ , and since the light receiving circuit 5b is in the operating state, the light receiving circuit 5b
An optical signal enters from the input terminal and is amplified by the variable gain amplifier 6. That is, the waveform processing circuit 8 is as shown in FIG.
As shown in FIG. 1, the final ranging information at t ₁ can be output by calculating the output level of the variable gain amplifier 6 immediately before t 1 and the output level of the variable gain amplifier 6 immediately after _{t 1 .}

In addition, in the above-mentioned embodiment, 5 is used as the light receiving circuit.
Although the circuit system having two channels a and 5b has been described, the same effects as in the above-mentioned embodiments can be obtained even in the case of two or more channels.

[Effects of the Invention] As described above, in the present invention, a plurality of variable gain amplifiers, which were conventionally required, can be used to amplify and calculate a plurality of optical input signals with one by switching a switch based on a ranging timing signal. With this configuration, it is possible to eliminate errors in gain and frequency characteristics between channels, which have been difficult to adjust in the past, and to obtain an inexpensive and highly accurate signal processing circuit for a distance measuring device with a small number of parts.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the configuration of a signal processing circuit of a conventional distance measuring device. FIG. 2 is a waveform diagram showing the operation of the signal processing circuit of the conventional distance measuring device shown in FIG. FIG. 3 is a schematic block diagram showing one embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3. In the figure, 1 is a light emitting circuit, 2 is a light emitting element, and 3 is a light emitting circuit.
is a target object, 4a, 4b are light receiving elements, 5a, 5b
is a light receiving circuit, 6, 6a, 6b are variable gain amplifiers,
7 is a gain control circuit, 8 is a waveform processing circuit, 9 is a level determination circuit, and 10a, 10b, and 10c are switch circuits.

Claims (1)

[Scope of Claims] 1. A signal processing circuit for a distance measuring device that measures the distance to a target object, comprising: a light emitting unit that irradiates light to the target object; and a light emitting unit that receives reflected light from the target object. a plurality of light receiving means for converting into electrical signals; a single variable gain amplifying means for amplifying the output signal from the light receiving means; a gain control means for changing the gain of the variable gain amplifying means as a function of time; level determining means for generating a timing signal when the output level of the variable gain amplification means reaches a predetermined threshold; and setting the light receiving means and the gain control means in an operating state or a non-operating state based on the timing signal. switching means for switching; and waveform processing for calculating the output of the variable gain amplification means immediately before the generation of the timing signal and the output of the variable gain amplification means immediately after the generation of the timing signal and outputting a ranging signal representing the distance to the target object. A signal processing circuit for a distance measuring device, comprising means.