JPH0328709A - Signal processing circuit for distance measuring instrument - Google Patents

Abstract

PURPOSE:To improve an SN ratio and distance measurement accruacy even when a light signal is weak by providing a light emitting means, a light receiving means, amplifying circuits, an operational amplifier, and subtracting circuits. CONSTITUTION:A light emitting circuit 1 and a light emitting element 2 constitute the light emitting means and light from the light emitting element 2 irradiates a target body 3. Light receiving circuits 4a and 4b constitute the light receiving means and have light receiving elements 5a and 5b which photodetect reflected light beam from the object body 3 and convert them into electric signals, and light is converted into a signal voltage, which is amplified. The amplifying circuits 6a and 6b input and amplify the outputs of the light receiving circuits 4a and 4b. The subtracting circuits 9a and 9b subtract noise voltages from a light information signal from the light receiving means. The operational amplifier 10 holds the noise voltages in the absence of a signal and a capacitor 11 holds the output voltage of the operational amplifier 10. A switch 12 turns on and off the light emitting circuit 1 and a switch 13 turns on and off the operational amplifier 10. A waveform processing circuit 7 input and process the outputs of the subtracting circuits 9a and 9b as distance information.

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 distances in target object trenches.
It is shown and explained in the figure.

In the figure, (1) is a light emitting circuit that drives a light emitting element (2), and this light emitting circuit (1) and light emitting element (2) are connected to a distance measuring object (hereinafter referred to as a target object) (3). The light emitting device (2) is configured to emit light from the light emitting device (2), and the light from the light emitting device (2) is configured to be directed toward a target object. (3) is a target object (subject) to be measured; (4a)
The buttons (4b) each have a light receiving element (5a) & 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 to increase the signal voltage. Each of these light receiving circuits (4a), (4
b) constitutes a light receiving means for receiving reflected light from the target object (3) and photoelectrically converting it.

(6a) t=> and (6b) are the light receiving circuit (4a
)> and the output of the light receiving circuit (4b) as inputs, and an amplification circuit that amplifies the output; (7) is each amplification circuit (6a) (
This is a waveform processing circuit which takes the output of 6b) as an input and calculates the output as distance information.

In a circuit constructed in this way, first the light emitting circuit (1
The light emitted from the light emitting element (2) driven by the
), enter (5b). Then, this light receiving element (5a
) (5b) are sent to the light receiving circuits (4a) and 5b, respectively.
(4b), it is converted into a signal voltage and amplified. next,
The signal amplified by the light receiving circuits (4a) and (4b) is
Each of the signals is amplified by amplifying circuits (6a) and (6b) in the next stage.

[Problem to be solved by the invention]

Since the signal processing circuit of a conventional distance measuring device is constructed as described above, the light intensity incident on each light receiving element becomes a weak signal due to differences in distance to the target object, reflectance, etc. When amplification is performed using a normal amplification circuit, noise is generated and it becomes difficult to amplify only the true optical signal, resulting in a poor signal-to-noise ratio (S/N ratio). Since the noise generated by circuit D and the amplification circuit is added to the optical signal voltage, the distance measurement performance deteriorates as a result, especially when the optical signal is weak (for example, at a long distance or when the subject reflectance is low). There was a problem with that.

This invention was made to solve the above-mentioned problems, and even when the optical signal is weak, the signal-to-noise ratio (S/
It is an object of the present invention to provide a signal processing circuit for a distance measuring device that can improve the N ratio) and improve the distance measurement accuracy.

[Means for Solving the Problems J] The signal processing circuit of the distance measuring device according to the present invention provides a switch in the light emitting circuit to create a no-signal state, and converts the noise voltage at the time of no signal to an operational amplifier with a capacitor. Along with remembering
The difference between this noise voltage and the optical signal voltage at the time of optical signal is subtracted by a subtraction circuit, and this difference voltage is input to the waveform processing circuit at the subsequent stage.

[Effect]

The noise voltage storage circuit according to the present invention includes an operational amplifier and a capacitor, and stores the noise voltage level when there is no signal.

[Embodiment] Hereinafter, an embodiment of the present invention will be explained with reference to the drawings. 1st
The figure is a block diagram showing one embodiment of a signal processing circuit of a distance measuring device according to the present invention.

In the drawings, the same reference numerals as those in the prior art are the same, and the explanation will be omitted. In the figure, (9a) and (9b) are amplifiers (1) that receive the outputs of the amplifier circuits (6a) and (6b), respectively, and subtract the noise voltage from the optical information signal from the light receiving means. It consists of an arithmetic circuit. (10) is an arithmetic amplifier to maintain the noise voltage when there is no signal, and (1) is a capacitor to maintain the output voltage of the arithmetic amplifier (10). , (12) is a switch for turning on and off the light emitting circuit (1), and (13) is a switch for turning on and off the operational amplifier (10).Waveform processing circuit (7) Multiplication circuit ( 9g) Use each output of (9b) as input, and calculate the input as distance information.

Next, the operation of this signal processing circuit will be explained with reference to FIG. Fig. 2 is an explanatory diagram of the operation of Fig. 1. In Fig. 2(a), the horizontal axis shows time and the vertical axis shows the on/off state of the switch (12), which turns on the light emitting circuit (1). , turn off. When the switch (12) is on, it corresponds to a signal, and when it is off, it corresponds to a no signal. Switch (13) is switch (1
It operates in the opposite way to 2), when it is on it corresponds to no signal, and when it is off it corresponds to when there is a signal. In Fig. 2(b), the horizontal axis is t, and the vertical axis is the output Vo2 of the amplifying circuit (6a) (same for the amplifying circuit (6b)).
a) (or Vo2(b)). It also represents the output Vol of the computation unit [1].

In Fig. 2(c), the horizontal axis is t, the vertical axis is the subtraction circuit (9a),
(9b) Output vo3(a.), (Output Vo3(b)
(same as above). Here, Vo3
(a) = Vo2 (a) − Vol
-11) Vo3 (b) = Vo2 (h)
Let it be Vol-(2).

1. At time to, the switch (12) is turned off and the switch (13) is turned on. The light emitting circuit (1) is inactive, and the operational intensifier (10) is active.

Since the light emitting circuit (1) does not operate, there is no optical signal, and some noise is generated at the output of the amplification circuit (6b) (it also occurs at the output of the amplification circuit 6a, but for the sake of explanation, it is Width circuit 6b
(The explanation will focus on Let this voltage be Vo]. This noise voltage Vol enters the input of the operational amplifier 11 (10) and is held as an output in the capacitor C (11.).

Next, at time t1, the switch (12) is turned off, and the switch (13) is turned off. The light emitting circuit (1) is activated, and the operational amplifier (lO) is inactivated. At the time of this signal, the output of the amplifier circuit 6b (6a) is Vo2b (Vo28),
It is input to the subtraction circuit (9b). The signal Vo2b includes some noise. Here, in the subtraction circuit (9b), Vo2
Perform the calculation of b − Vol, that is, Vo2b − Vol = Vo3(b)
−(3)(Vo2a−Vol)=V
o3(a) ...(4).

(See CC diagram) As can be seen from equations (3) and (4), the noise voltage generated when there is no signal is removed.

[Effects of the invention] As described above, according to the present invention, regardless of the distance and reflectance of the target object (subject), the signal-to-noise ratio (S/ Since it is possible to obtain a better characteristic of N ratio) and to improve distance measurement accuracy, the practical effect is extremely large. In addition, the circuit structure is simple, and especially when applied to an integrated circuit, it is easy to manufacture, suitable for mass production, and extremely effective in preventing cost increases.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a signal processing circuit of a distance measuring device according to the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1,
FIG. 3 is a block diagram of a signal processing circuit of a conventional distance measuring device. In the figure, (1)...Light-emitting circuit, (2)...Light-emitting element, (3)...Target object (subject), (4m) (4b
)...Light emitting circuit, (5a), (5b)-light receiving element, (9a), (9b) = subtraction circuit, (10)
... Arithmetic amplifier, (11) ... Capacitor, (12)
, (13)...Switch. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A distance measuring device for measuring a 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; an amplification means for amplifying the optical information signal from the means; an arithmetic amplifier for storing the voltage of the light emitting means when the light is not emitted; and a subtraction means for subtracting the voltage when the light is emitted and the voltage when the light is not emitted. 1. A signal processing circuit for a distance measuring device, comprising: a circuit.