JPH0341484Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention is a semiconductor position detection element (hereinafter referred to as
The present invention relates to a dark current component removal device for a semiconductor position detection element that removes a dark current component from a position signal output from a position signal output from a semiconductor position detection element (hereinafter referred to as PSD).

Conventional technology PSD outputs one pair of output signals for one-dimensional position detection and two pairs of output signals for two-dimensional position detection, depending on the position of the light spot incident on the light receiving surface.
They are configured to output each.

To explain the operation using a PSD for one-dimensional position detection as an example, in FIG. When the current signals I _{1 and I 2} , which are a pair of output signals of the PSD 22, are input at a position at a distance l ₁ from one end and _{a distance l 2 from} the _{other end} , ...(1-1) There is a relationship as follows.

Therefore, the position of the light spot in this case is d/(l ₁ + l ₂ ) = (l ₂ - l ₁ )/2(l ₁ +l ₂ ) = (I ₁ - I ₂ )/2(I ₁ +I ₂ ) ...(1-2).

The above equation (1-2) is calculated by a conventional device having the configuration shown in FIG. i.e. PSD
The pair of output signals of 22 are subtracted from each other by the calculation means 23, and as a result, (I ₁ -I ₂ ) is obtained. Similarly, (I ₁ +
I ₂ ) is calculated, and these two results are divided by the dividing means 2.
5 to obtain (I ₁ -I ₂ )/(I ₁ +I ₂ ), and based on this, the light spot position is detected.

Problems with the Prior Art However, in reality, even when a light spot is incident, a dark current i _b is output at the same time, and this dark current is added to the output signals I ₁ and I ₂ , respectively.
Since each i _b /2 is included, the above equation (1-2) is d/(l ₁ + l ₂ ) = (I ₁ − I ₂ )/2 (I ₁ + I ₂ + i _b )
(2-1) Therefore, there is a problem that the conventional device having the above configuration cannot accurately detect the position.

In addition, the dark current i _b changes according to temperature changes, and its value differs for each element, so even if temperature correction is to be performed, a correction circuit with a specific constant is required for each element. Its implementation is difficult because it requires

Purpose of the invention This invention was made in view of the above-mentioned circumstances, and aims to provide a device that automatically removes dark current components in order to accurately detect the position of a light spot.

Structure of the invention The device for removing dark current components of a semiconductor position detection element according to this invention is a device for removing a dark current component from a semiconductor position detection element.
a first subtraction means for subtracting the paired position signals from each other;
an adding means for adding the position signals to each other; a first sample and hold means for holding an output signal output from the adding means when the semiconductor position detecting element receives light; a second sample and hold means for holding the output signal output from the addition means when the addition is performed; a second subtraction means for calculating the difference between the outputs of the first and second sample and hold means; and a first subtraction means. The structure further comprises: a division means for dividing the output signal of the means by an output signal of the second subtraction means; and a control means for controlling the timing of signal holding by the first sample and hold means and the second sample and hold means. This is the characteristic of

Effect This device is constructed as described above, so the first
The sample and hold means samples and holds the position signal including the dark current, and the second sample and hold means samples and holds only the dark current. and,
Since the second subtraction means subtracts the respective output signals of the first sample and hold means and the second sample and hold means, the dark current component is removed.
Accurate detection can be performed.

Embodiments Hereinafter, embodiments of this invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a dark current component removing device according to an embodiment of this invention, and FIG. 2 is a time chart of signals in the same device. Note that this invention is not limited to the embodiment shown in the figures.

In Figure 1, 1 is for one-dimensional position detection.
In PSD, corresponding to the position of the incident light spot,
This is a conventionally known device that outputs a position signal from a pair of output ends 2 and 3. 4 is a first subtraction means, and 5 is an addition means, each of which is preferably a differential amplifier circuit or an addition circuit using an operational amplifier. 6 is a first sample and hold means, and 7 is a second sample and hold means, the input ends of which are connected to the output end of the addition means 5. 8 is a second subtraction means, one of its inputs is connected to the output terminal of the first sample and hold means 6;
The other input terminals are respectively connected to the output terminals of the second sample and hold means 7, and the output terminals are
It is connected to one input terminal of the dividing means 9 at the subsequent stage.
The other input terminal of the dividing means 9 is connected to the first subtracting means 4.
The output end of is connected.

Reference numeral 10 denotes a control means, which includes an oscillation circuit 11 that outputs a signal of a constant frequency, and a first sample and hold means 6.
A first one-shot pulse circuit 12 is connected to outputs a one-shot pulse that determines sample timing, and a second one-shot pulse circuit is connected to second sample hold means 7 and outputs a one-shot pulse that determines sample timing. It is composed of a circuit 13.

The first one-shot pulse circuit 12 is triggered by the rising edge of the clock signal CK output from the oscillation circuit 11 to output a one-shot pulse, and the second one-shot pulse circuit 13 is triggered by the falling edge of the clock signal CK. Outputs a one-shot pulse when triggered.

14 is an LED drive circuit, and LED 15 serves as a light source.
The clock signal CK is connected to the clock signal CK to blink the LED 15 according to the cycle of the clock signal CK.

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

The LED 15, which is a light source, blinks in response to a clock signal CK, and a spot enters the PSD 1 when turned on. That is, the LED 15 is lit while the clock signal CK is at "Hi" level, and is off while the clock signal CK is at "Lo" level.

When the LED 15 lights up and the light spot enters the PSD 1, the PSD 1 converts the pair of position signals I ₁ and I ₂ into a dark current.
Output with i _b . That is, one output terminal 2 outputs an output signal of (I ₁ +i _b /2), and the other output terminal 3 outputs an output signal of (I ₂ +i _b /2).

(I ₁ +i _b /2) and (I ₂ +i _b /2) are the addition means 5
The result is (I ₁ +I ₂ +i _b ), which is sampled by the first sample and hold circuit 6 and held until the next sampling timing.

The timing at which the pulse is sampled by the first sample and hold circuit 6 is the timing at which the PSD 1 receives light, that is, the timing at which the LED 15 lights up. At the rising edge of the clock signal CK, the first one-shot pulse circuit 12 samples the one-shot pulse for the first time. It is determined by outputting to the hold circuit 6.

Next, when the clock signal CK becomes the "Lo" level, the LED 15 turns off. At this time, dark current i _b /2 is generated from each output terminal 2 and 3 of PSD 1.
is output. Therefore, i _b is output from the adding means 5, and the second sample and hold circuit 7 is triggered by the fall of the clock signal CK and samples i _b by the one shot pulse output from the second one shot pulse circuit 13. Hold i _b until the next one-shot pulse.

The sample was held by the first sample holding means 6 (I ₁
+I ₂ +i _b ) and i _b held by the second sample hold means 7 are subtracted by the second subtraction means 8, resulting in (I ₁ +I ₂ ).

In other words, dark current component i _b is removed by this subtraction.

Then, (I ₁ + I ₂ ) is input to the division means 9 together with (I ₁ − I ₂ ) output from the first subtraction means 4, and the division means 9 calculates (I ₁ − I ₂ )/(I ₁ + I ₂ ). is calculated,
The light spot position can be determined without being affected by dark current i _b .

In the above embodiment, the light source is made to blink by the control means 10, and the respective sample and hold means are controlled in synchronization with this, but the blinking of the light source is detected by, for example, a phototransistor. It is also possible to adopt a configuration in which each sample hold means is controlled accordingly.

Effects of the invention This invention comprises: a first subtraction means for mutually subtracting a pair of position signals output from a semiconductor position detection element; an addition means for mutually adding the position signals;
a first sample and hold means for holding an output signal output from the addition means when the semiconductor position detection element receives light; and an output signal output from the addition means when the semiconductor position detection element receives light. a second sample and hold means for holding a second sample and hold means; a second subtraction means for calculating the difference between the outputs of the first and second sample and hold means; A dark current component removal device for a semiconductor position detection element, comprising: a division means for dividing by; and a control means for controlling the timing of signal holding by the first sample and hold means and the second sample and hold means. As a result, the dark current component of the PSD can be reliably removed, and the position of the light spot can be detected accurately.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a dark current component removal device according to an embodiment of this invention, Fig. 2 is a time chart for explaining the operation of the device, Fig. 3 is an explanatory diagram for explaining the operation of the PSD, FIG. 4 is a block diagram of a conventional example. Explanation of symbols: 1... Semiconductor position detection device (PSD), 4... First subtraction means, 5... Addition means,
6...First sample hold means, 7...Second sample hold means, 8...Second subtraction means, 9...
...Division means, 10...Control means.

Claims (1)

[Scope of utility model registration request] a first subtraction means for mutually subtracting a pair of position signals output from the semiconductor position detection element; an addition means for mutually adding the position signals; a first sample and hold means for holding an output signal;
A second sample and hold means holds the output signal output from the addition means when the light is applied to the semiconductor position detection element, and the difference between the outputs of the first sample and hold means and the second sample and hold means is calculated. Controls the timing of signal holding of the second subtraction means for calculating, the division means for dividing the output signal of the first subtraction means by the output signal of the second subtraction means, and the first sample hold means and the second sample hold means. What is claimed is: 1. A dark current component removal device for a semiconductor position detection element, comprising: a control means for removing a dark current component from a semiconductor position detection element.