JPS631918A - Distance detector - Google Patents

Abstract

PURPOSE:To obtain a sharp photograph by preventing such as case that the remotest stage is passed over on the basis of noise, by providing an infinite distance judge circuit. CONSTITUTION:The sample holding circuit 5 of an infinite distance judge circuit holds the outputs V2+DELTAV2 of the logarithmic compression voltage converter circuit 16 of a photocurrent amplifying circuit when no pulse beam is incident upon. Constant voltage VA is added to said output by an adder circuit 6. When pulse light is incident upon, the output of the amplifying circuit comes to V2+DELTAV2. Next, a comparing circuit 7 compares the output V2+DELTAV2 with output V2+VA. When the relation of V2+DELTAV2<V2+VA is formed, this relation is regarded as an infinite distance and digital range finding output is set to the remotest shape and this result is latched to be outputted.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a semiconductor device detection device (PST): Po5i
tion 5 sensitive device).

(Prior Art) A distance detection device in which a semiconductor device detection device (hereinafter referred to as PSD) and a light projecting element are combined is known.

FIG. 4 is a schematic diagram showing the arrangement relationship between the light projecting section and the light receiving section of the distance detecting device.

FIG. 5 is a block diagram showing an example of a circuit configuration of a conventional distance detection device.

The light emitted from the light projecting element 4 is projected forward by the lens 3, and the reflected light from the object in front is formed by the lens 1 to form a reflected light spot on the PSD 2.

The circuit shown in FIG. 5 determines the distance to the object to be measured by calculating the position of the reflected light spot of the PSD 2.

Among the photocurrents from the PSD 2, pulsed photocurrents containing position information △■1. Only △■2 is connected to each charge current amplification circuit 1
．． The pulsed photocurrent extraction circuit 11.14 extracts the pulsed photocurrent of I[, and amplifies it with the amplifier circuit 12.15 (β△11.
βΔ12) is obtained.

This (β△r1.β△12) is converted into the logarithmic compression voltage conversion circuit 1
3.16, and the output is amplified by differential amplifier circuit 1.
7 performs differential amplification to obtain the following output.

Vref +K (Δ■1−ΔV2) This output is proportional to the reciprocal of the distance to the subject, so it is sampled and held in the sample and hold circuit 18 and input to the digital output circuit. The A/D conversion circuit 19 of the digital output circuit A/D converts this, and the decode launch circuit 20 outputs it as a digital output for zone focusing.

The output of current amplifier circuit I after logarithmic compression voltage conversion is v1+△
■1 - (AKT/Q) 12 n (I DC/ IS
)+'(AKT/Q) in ((I DC+β△r
+)/l5)1 ”= (A K T/ Q) A' n (I DC+
β△r+ /Is)・・・・・・・・・・・・■ However, A... Constant K... Portzmann's constant Q... Electron charge T... Absolute temperature rs... Diode's Reverse saturation current IDC: given by DC bias current. The same applies to V2+Δ■2.

The pulse photocurrent is Δl1= (△■1+△12) X (C+f-B/'t')
/2'C△12= (△■1+△I2) ρ...Distance to the object to be measured (problem to be solved by the invention) In the distance 1iIIIt detection device as described above, when the distance to the object to be measured is long, the output after differential amplification Vref +
K (△■1−△V2) varies greatly from distance measurement to measurement.

In the autofocus of compact cameras,
For distance measurement targets at infinity, due to depth of field,
The stopping position of the lens must always be at the farthest position, and even a one-step error is not allowed.

However, at present, when the noise generated by the arithmetic circuit and the noise generated by the sensor are combined, this limit is exceeded.

Of course, the best method is to suppress the noise generated by the arithmetic circuit and sensor as much as possible.

However, this requires an optimal arithmetic circuit, careful IC pattern design, and a special IC manufacturing process, which requires a lot of cost and time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a distance measuring device equipped with an infinity determination circuit that can solve the above-mentioned problems associated with infinite distance measurement.

(Means for Solving the Problems) In order to solve the above problems, the distance measuring device according to the present invention projects pulsed light toward the object to be measured, and forms a spot of reflected light on the semiconductor device detection device. The pulsed photocurrent from the light spot taken out from both terminals of the semiconductor device detection device is amplified and taken out by a charge current amplification circuit, and the difference is taken to generate a digital output corresponding to the distance to the distance measurement target. In the distance detection device obtained,
If the output of either one of the charging current amplifying circuits does not rise above a certain level of voltage during optical pulse projection, an infinity determination circuit is provided to determine that the object to be measured is in a region corresponding to infinity. When this is done, one digital output corresponding to the infinite range is output.

The output of the pulsed photocurrent amplification circuit determined by the infinity determination circuit may be the output of a photoelectric amplification circuit that detects the output of the semiconductor device detection device on the side close to the means for projecting the pulsed light. . Further, the infinity determination circuit is
a sample hole l: circuit that samples and holds the output of the pulsed photocurrent amplification circuit before pulsed light projection; an adder circuit that adds a constant voltage to the output of the sample and hold circuit and outputs the result; an output of the adder circuit and the pulse; a comparison circuit that compares the output with the output of the photocurrent amplifier circuit and outputs the output;
It is comprised of a circuit that inputs the output of the comparison circuit to a decoder section of the digital distance measurement output circuit and makes the output of the digital distance measurement output circuit infinite, and a circuit that launches and outputs the output of the comparison circuit. be able to.

(Example) The present invention will be described in more detail below with reference to the drawings and the like.

FIG. 1 is a block diagram showing an embodiment of the main parts of a distance detecting device to which an infinity determination circuit according to the present invention is added.

The arrangement relationship between the light projecting section and the light receiving section is basically the same as the configuration shown in FIG. 4 described above, and the distance calculation circuit section is basically the same as the configuration shown in FIG. 5.

In the autofocus of compact cameras, so-called zone focusing is often allowed.

In other words, objects located within a certain distance are photographed at the same lens position.

At the same lens position as the one used to photograph the subject at infinite distance, we will also photograph a subject at a distance of about 9 m. case).

In other words, it is safe to assume that all objects at a distance of 9 meters or more are at infinity.

The circuit shown in FIG. 1 is constructed based on the above concept.

The sample hold circuit 5 of the infinity determination circuit receives the output V2+△V of the logarithmic compression voltage conversion circuit 16 of the charge current amplification circuit ■.
2 is sampled and held when no pulsed light is incident (that is, the output is V2).

The adder circuit 6 of the infinity determination circuit adds -constant voltage VA to this.

When pulsed light is incident, the output of the charging current amplification circuit ■ is V
2+△■2.

The comparator circuit 7 of the infinity determination circuit compares the above ■2+Δ■2 with the output v2+VA of the adder circuit 6.

(2) When the relationship 2+Δv2<V2+VA holds true, this is regarded as infinite distance, and the digital distance measurement output is set as the farthest stage.

At the same time, launch and output this result.

■2+△v2>V2+VA In this case, normal distance measurement results are output.

The output of the charging current amplifying circuit II which detects the output of the PSD located close to the light projecting means as the output of the charging current amplifying circuit determined by the infinity determination circuit (charging current amplifying circuit ■ in Fig. 5); The reason for this is as follows. In other words, from the shape of the output Vref +K (△■1 - △V2) of the differential amplifier 17, the output increases and passes the farthest stage when △Vl - increases, or △■2 - low 2 - This is the case.

If ΔV, - increases, it cannot be distinguished from the case of finite distance, so it is better to monitor the case of Δ■2→decrease.

FIG. 2 is a circuit diagram showing an embodiment of the sample and hold circuit 5. In FIG.

The operational amplifier 51 uses a bipolar I/Rangis low input type, and the operational amplifier 52 uses an FET input type.

In the sample mode, the operational amplifier 51 is operated,
In the hold' mode, the operating current of the operational amplifier 51 is cut off by a control signal (timing control), so that v2 held in the hold capacitor 53 is outputted via the operational amplifier 52.

This output ■2 is connected to a normal adder circuit 6 (see Figure 1) to add V.
A is added.

The circuit shown in FIG. 3 is a circuit diagram showing an embodiment of an addition sample and hold circuit in which the sample and hold circuit 5 and the addition circuit 6 of the circuit shown in FIG. 1 are integrated.

The operational amplifier 56 uses a bipolar transistor input type, and the operational amplifier 57 uses an FET input type.

The base of a transistor 59 is connected to the output of the operational amplifier 57, and the emitter of the transistor 59 is connected to a constant current source via a resistor 60.

By making the resistor 60 capable of generating voltage VA and performing the same operation as described above, it is possible to obtain an output of V2 +VA.

(Effects of the Invention) As described in detail above, the distance detection device according to the present invention projects pulsed light toward a distance measurement target, forms a spot of reflected light on the semiconductor device detection device, and detects the semiconductor device. In a distance detection device, the pulsed photocurrents from the optical spot taken out from both terminals of the device are amplified and taken out by charging current amplification circuits, and the difference is calculated to obtain a digital output corresponding to the distance to the distance measurement target,
If the output of either the photoelectric or current amplifying circuit does not rise above a certain voltage when the optical pulse is projected, an infinity determination circuit is provided to determine that the object to be measured is in a region corresponding to infinity. When the distance is determined, one digital output corresponding to the infinite range is output.

Therefore, in infinite distance measurement without input, it is possible to prevent the farthest stage from being missed due to various noises.

By using the distance detection device for camera autofocus, it is expected that clear photographs can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a distance detection device to which an infinity determination circuit according to the present invention is added. FIG. 2 is a circuit diagram showing an embodiment of the sample and hold circuit. FIG. 3 is a circuit diagram showing an embodiment of the addition sample and hold circuit. FIG. 4 is a schematic diagram showing the arrangement relationship between the light projecting section and the light receiving section of the distance m detecting device. FIG. 5 is a block diagram showing an example of a circuit configuration of a conventional distance detection device. □ 1... Light receiving lens 2... Semiconductor device detection device (PSD) 3... Projection lens 4... Light projecting element 5... Sample hold circuit 6... Addition circuit 7... Comparison circuit 8... Latch circuit 11.14... Pulse photocurrent extraction circuit 12.1.5.
...Amplifier □ 13.16...Logarithmic compression voltage conversion circuit 17...Differential amplifier circuit 1.8...Sample and hold circuit. 19... A/D conversion circuit 20... Decode launch circuit 5, -1, 52i 56. ．． 57... operational amplifier 5
3.58...Hold capacitor 59...Transistor 60...Resistance Patent applicant Hamamatsu Photonics Co., Ltd. Chi-Non Co., Ltd.

Claims (3)

[Claims] (1) Project a pulsed light toward a distance measurement target, form a reflected light spot on a semiconductor device detection device, and generate a pulsed photocurrent by the light spot taken out from both terminals of the semiconductor device detection device. In a distance detection device that obtains a digital output corresponding to the distance to the object to be measured by amplifying and extracting the current by a current amplification circuit and taking the difference, the output of either one of the photocurrent amplification circuits is present when a light pulse is projected. If the voltage does not rise above a certain level, an infinity determination circuit is provided that assumes that the object to be measured is in an area corresponding to infinity, and when it is deemed to be in the area, outputs one digital output corresponding to the infinity area. A distance detection device characterized in that it is configured to. (2) The output of the pulsed photocurrent amplification circuit judged by the infinity judgment circuit is the output of a photocurrent amplification circuit that detects the output of the semiconductor device detection device on the side close to the means for projecting the pulsed light. A distance detection device according to claim 1. (3) The infinity determination circuit includes a sample and hold circuit that samples and holds the output of the pulsed photocurrent amplification circuit before pulsed light projection, and an addition circuit that adds a constant voltage to the output of the sample and hold circuit and outputs the result. a comparison circuit that compares and outputs the output of the adder circuit and the output of the pulsed photocurrent amplification circuit, and inputs the output of the comparison circuit to the decoder section of the digital distance measurement output circuit to output the digital distance measurement output. 2. The distance detecting device according to claim 1, comprising: a circuit that outputs an infinite distance; and a circuit that latches and outputs the output of the comparison circuit.