JP3363941B2 - Non-contact switch output circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact switch such as a photoelectric switch or a proximity switch, and more particularly to a gain control in its output circuit.

[0002]

2. Description of the Related Art Non-contact switches such as photoelectric switches and proximity switches are devices for non-contact detection of passage of an object by means of light, magnetism or the like, and FA (Factory Automa
It is widely used in fields such as For example, according to a photoelectric switch in which a light emitting element and a light receiving element are arranged on both sides of a component or work-in-process conveyance path, passage of the component or work-in-process can be detected as a light block.

Further, in this type of non-contact switch, it is necessary to control the gain according to the distance. For example, in the photoelectric switch, the output signal level (light receiving level) of the light receiving element is inversely proportional to the square of the distance from the light emitting element, as shown in FIG. When the output signal of the light receiving element is supplied to the circuit in the subsequent stage as it is or after being amplified with a constant gain, the circuit in the subsequent stage must process the signal whose level changes according to the distance. In order to prevent such a problem, when amplifying the output signal of the light receiving element, the gain related to the amplification is usually set according to the distance. For example, if the distance is doubled, the gain is set to 4 times. By doing this, it is possible to respond appropriately to the line scale, the type of production equipment, the size of the product, and other distance settings associated with factory design (for example, the distance settings between the light emitting element and the light receiving element according to the width of the transport path). Therefore, the processing in the circuit in the subsequent stage can be suitably executed.

FIG. 13 shows the configuration of a photoelectric switch and its output circuit according to a conventional example. In this figure, the light receiving element PD, the I / V conversion circuit 10, the amplifier section 1
2, a gain control circuit 14, a detection circuit 16 and a logic 18 are shown. The light receiving element PD is arranged at a certain distance from a light emitting element (not shown) such as an LED. The output signal of the light receiving element PD is obtained as a current and has an output characteristic inversely proportional to the square of the distance as shown in FIG. The I / V conversion circuit 10 is a circuit that converts the output of the light receiving element PD into a voltage, and includes an amplifier 20, a feedback resistor R ₁ and a coupling capacitor C ₁ as shown in FIG.

The amplifier section 12 has a structure in which a plurality of differential amplifiers 22 having the structure shown in FIG. 15 are connected in cascade. The differential amplifier 22 includes transistors TR ₁ and TR ₂ that are differentially connected, a current source 24 that supplies a current to the emitters of the transistors TR ₁ and TR ₂ , and a transistor TR _1.
And TR ₂ and load resistors R ₂ and R ₃ and input resistors R _{4 to} R _{7 of the} transistors TR ₁ and TR ₂ . At the bases of the transistors TR ₁ and TR ₂ , the output of the preceding circuit is differentially input ΔV via the input resistors R ₄ and R _5.
Applied as _B. The collector current of the transistor TR ₁ and TR ₂ are converted to by Ri voltage to the resistor R ₂ and R _3,
It is supplied to the circuit in the subsequent stage. When the differential amplifier 22 is used in the frontmost stage of the amplifier section 12, it is the output voltage of the input I / V conversion circuit 10, and when it is used in the last stage, the output destination is the detection circuit 16.

When the current of the current source 24 is expressed as I, the collector current I _out of the transistors TR ₁ and TR ₂ is
It is expressed by the following equation (1) using h _FE of these transistors TR ₁ and TR ₂ .

[0007]

[Equation 1] Therefore, by changing the current I of the current source 24,
The gain of the differential amplifier 22 can be adjusted. For example, if the current I is doubled, the current I _out and thus the output voltage of the differential amplifier 22 are doubled.

The gain control circuit 14 in this conventional example is a set of current sources 24 of each differential amplifier 22. That is, the gain control circuit 14 includes a current source 24 provided corresponding to each differential amplifier 22.

The current source 24, as shown in FIG.
It has a configuration in which the transistors TR ₃ and TR ₄ are differentially connected. The constant current I ₀ is supplied from the current source 26 to the emitters of the transistors TR ₃ and TR ₄ . Setting voltage V _R to the base of the transistor TR ₃ is, to the base of the transistor TR ₄ is constant bias voltage are respectively applied. Accordingly, holds the same relationship (Equation (2)) and (1) previously described in this current source 24, the collector current I of the transistor TR _3, using the _{h FE} of transistor TR ₃ and TR ₄ It can be expressed by the following equation (2).

[0010]

[Equation 2] If equation (2), since it is [Delta] V _B = _V R -V _B, the relationship of the set voltage _{V R} and the collector current I in current source 24 is almost exponential as shown in Figure 17. In other words, by adjusting the set voltage V _R, the current I, therefore the amplifier unit 12 which determines the gain of the differential amplifier 22
You can adjust the overall gain. Therefore, when installing the photoelectric switch in the line, by adjusting the set voltage V _R in accordance with the distance between the light emitting element and the light receiving element PD, irrespective of the distance how, to make the output level of the amplifier 12 to the constant Therefore, a signal suitable for the processing of the detection circuit 16 and the logic 18 can be obtained. Since the signal received by the light receiving element PD is modulated at the time of light emission, the detection circuit 16 detects the output of the amplifier unit 12. Logic 1
Reference numeral 8 is a circuit for performing a predetermined logical operation on the output of the detection circuit 16 and converting it into data.

[0011]

However, in a circuit having such a configuration, the relationship between the set voltage and the total gain of the amplifier section is not linear. As shown in FIG. 17, the current of each current source forming the gain control circuit has an exponential characteristic with respect to the set voltage, and the gain control based on this exponential characteristic is different for each differential amplifier. Therefore, if you try to set the total gain of the amplifier according to the distance,
As shown in, the set voltage must be changed nonlinearly with respect to the distance. Since the user usually adjusts the set voltage by adjusting the scale (control scale) such as a variable resistance, such a non-linear characteristic necessitates an unnatural adjustment work.

The present invention has been made to solve the above problems, and an object thereof is to realize a gain control that enables a user to perform a linear setting operation with respect to a distance.

[0013]

In order to achieve such an object, the present invention provides a light transmitted from an isolated location,
Detection means for receiving a radio signal such as magnetism and converting it into an electric signal, amplification means for amplifying this electric signal, and gain adjustment means for changing the gain of the amplification means so as to have a squared characteristic with respect to a set value, And a non-contact detection of an object that blocks a wireless signal.

According to the present invention, the amplifying means further comprises n (n: natural number) differential transistor pairs connected in series.
A stage differential amplifier, wherein the gain adjusting means has n current sources for respectively supplying currents according to set values to the common electrodes of the corresponding differential transistor pairs, and the current characteristics of the n current sources are The product has a squared characteristic with respect to a set value.

When n = 1 in the present invention,
The current source is configured to have a squared current characteristic with respect to the set value. Further, when n = 2 in the present invention, each of the current sources is configured to have a linear current characteristic with respect to the set value. In the present invention, when n = 3, one of the current sources has a linear current characteristic with respect to a set value, and the other two have root current characteristics with respect to the set value. Make up.

When n = 1, the current source is preferably constructed as follows. That is, the output current is exponential with respect to the differential input voltage including the first and second transistors that are differentially connected to input the potential difference between the control electrodes as the differential input voltage, and the coefficient including the temperature is multiplied. And a first, second, third and fourth active element whose output voltage has a logarithmic characteristic with respect to an input current and whose coefficient of the logarithm is the reciprocal of the coefficient. A first current supply circuit for supplying a current having a value according to the set value to the first and second active elements, and a constant current for the third and fourth
A second current supply circuit for supplying the active element,
The first transistor, the first active element and the second active element are connected so that the voltage applied to the control electrode of the transistor becomes the sum of the output voltage of the first active element and the output voltage of the second active element, The second transistor, the third active element and the fourth active element are connected so that the voltage applied to the control electrode of the two transistor becomes the sum of the output voltage of the third active element and the output voltage of the third active element, The output current of the output differential transistor pair is supplied to the common electrode of the one-stage differential amplifier.

The present invention may further include means for detecting the signal amplified by the amplifying means, and means for converting the detection result into digital data. The present invention can be applied to a production control device.

[0018]

In the present invention, wireless signals such as light and magnetism transmitted from isolated positions are received by the detecting means and converted into electric signals. This electric signal is amplified by the amplification means. The gain adjusting means adjusts the gain of the amplifying means. Therefore, by adjusting the gain, it is possible to obtain a signal having a constant level irrespective of the distance and suitable for a circuit in the subsequent stage, for example, the detection means. Further, in the present invention, since the gain adjusting means changes the gain so as to have a square characteristic with respect to the set value, when performing the gain setting according to the distance according to the detecting means, the relationship between the set value and the distance is shown. It is possible to obtain a non-contact switch that can be made linear and can set the gain without a feeling of strangeness.

When the amplifying means is realized as an n-stage differential amplifier in which n differential transistor pairs are connected in series,
The gain adjusting means of the present invention can be realized as n current sources. Each of these n current sources supplies a current corresponding to the set value to the common electrode of the corresponding differential transistor pair. Further, these n current sources are configured such that the product of the current characteristics has a squared characteristic with respect to the set value. With this configuration, the above-described operation can be realized by improving the conventional circuit or by combining the circuits having a relatively simple structure.

For example, current sources having square, linear, and root current characteristics with respect to the set value are prepared,
A current source having necessary characteristics may be selected from these current sources, and the selected current source may be provided corresponding to each stage of the differential amplifier which constitutes the amplifying means. Specifically, when the differential amplifier has one stage, a current source having a square characteristic is independently used and
When forming two stages, two current sources having linear characteristics may be combined, and when three stages are formed, two current sources having linear characteristics and one current source having root characteristics may be combined and used. In this way, the circuit designer only needs to select the configuration and combination of the current sources according to the number of stages of the differential amplifier, and the number of design steps and cost can be reduced.

The current source having the squared characteristic can be constructed without the temperature characteristic. This configuration has a pair of output differential transistors, four active elements, and two current supply circuits. The first current supply circuit supplies a current having a value according to the set value to the first and second active elements, and the second current supply circuit supplies a constant current to the third and fourth active elements. The first transistor, the first active element and the second active element are connected such that the voltage applied to the control electrode of the first transistor is the sum of the output voltage of the first active element and the output voltage of the second active element. , The second transistor, the third active element, and the fourth active element are connected such that the voltage applied to the control electrode of the second transistor is the sum of the output voltage of the third active element and the output voltage of the third active element. To be done.

Since the input current-output voltage characteristic of each active element is a logarithmic characteristic, the output voltage of the first active element changes logarithmically with respect to the input current having a value according to the set value.
Similarly, the output voltage of the second active element also changes logarithmically with respect to the input current having a value according to the set value. Therefore, the added value of the output voltage of the first active element and the output voltage of the second active element is proportional to the logarithm of the square of the set value. Therefore, the differential input voltage to the output differential transistor pair is also proportional to the logarithm of the square of the set value. On the other hand, the differential input voltage-output current characteristic of the output differential transistor pair is an exponential characteristic,
The output current of the output differential transistor pair, that is, the output current to the differential amplifier has a squared characteristic with respect to the set value. In this way, the square characteristic is realized.

In each active element, the temperature dependence of the input current-output voltage characteristic appears as a logarithmic coefficient. In the output differential transistor pair, the temperature dependence of the differential input voltage-output current characteristic appears as a coefficient of the differential input voltage. Since these coefficients are reciprocal of each other, the temperature term does not appear in the characteristic of the set value versus the output current to the differential amplifier in the above circuit configuration.

The present invention can be applied to a manufacturing control device.

[0025]

The preferred embodiments of the present invention will be described in detail below. The same components as those of the conventional example shown in FIGS. 12 to 18 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 shows the configuration of a photoelectric switch and its output circuit according to an embodiment of the present invention. The circuit shown in this figure is a gain control circuit 14 in the conventional example.
A gain control circuit 28 having a configuration described later.
It has a configuration replaced with.

The gain control circuit 28, the total gain of the formed amplifier unit 12 from a predetermined number of the differential amplifier 22, as shown in FIG. 2, is set to be square characteristic to the set voltage V _R. Figure 12 As described with reference to the change from the light receiving level of the light receiving element PD is inversely proportional to the square of the distance between the light emitting element, linearly with distance setting voltage V _R as shown in FIG. 3 If you let
The output signal level of the amplifier section 12 does not change depending on the distance. Therefore, the variable resistance scale (control scale) may be a linear scale with respect to the distance, and the user does not feel uncomfortable in the gain adjustment operation.

[0028] In order to obtain such an effect, the gain control circuit 28 for controlling the total gain of the amplifier portion 12 so as to be square characteristic to the set voltage V _R is essential. This embodiment is characterized by this gain control circuit 28.

Differential amplifiers 22 related to each stage of the amplifier section 12
Has a configuration as shown in FIG. 15, for example.
The gain control circuit 28 is configured as a set of current sources that supply emitter currents to the transistors TR ₁ and TR ₂ of each differential amplifier 22. Therefore, the configuration of the gain control circuit 28 is different depending on the number of stages of the amplifier section 12.

FIG. 4 shows the configuration of the gain control circuit 28 in the case where the number of stages of the amplifier section 12, that is, the number of cascaded differential amplifiers 22 is one. The gain control circuit 28 shown in FIG.
2 has a square-law characteristic current source 30 for supplying an emitter current to the differential transistor pair.

The square-law current source 30 has differentially connected transistors TR ₃ and TR ₄ as shown in FIG. A current source 26 having a current value I ₀ is connected to the emitters of the transistors TR ₃ and TR ₄ . The voltage V _B1 is applied to the bases of the transistors TR ₃ and TR ₄ , respectively.
And V _B2 are applied. The transistor TR ₃ is supplied from the square characteristic current source 30 to the differential amplifier 22.
Is the collector current I of

The square characteristic current source 30 has a variable resistor R ₈ for generating the set voltage V _R. The user
By linear scale operates the variable resistor R ₈ which dumped for the distance, as appropriate, to generate a set voltage V _R with a linear value for the distance. Setting voltage V _R is applied to the base of the transistor TR ₅ of the collector grounded, it is supplied with current from the current source 32 to the transistor TR _5. Therefore, the emitter of the transistor TR ₅ appears substantially equal voltage setting voltage _{V R.} This voltage is applied to the base of the transistor TR ₆ . The emitter of the transistor TR ₆ is grounded via the resistor R9. Therefore, the collector current I of the transistor TR _6
1 is a current proportional to the set voltage V _R.

Collector current I of transistor TR _6
1 is input to the current mirror circuit 34. The two output side transistors of the current mirror circuit 34 are the anode of the diode D ₁ and the transistor TR _{7 respectively.}
Connected to the emitter. Therefore, the diode D ₁
A current I ₁ proportional to the set voltage V _R is supplied to the transistor TR ₇ .

The cathode of the diode D ₁ and the collector of the transistor TR ₇ are grounded, and the anode of the diode D ₁ is connected to the base of the transistor TR ₇ . The emitter of the transistor TR ₇ is connected to the base of the transistor TR ₃ . Therefore, when the voltage across the diode _{D 1} expressed _{V F1,} the base-emitter voltage of the transistor TR ₃ and _{V F2,} the base potential _{V B1} of the transistor TR ₃ is expressed as follows.

V _B1 = V _F1 + V _F2 (3) The square characteristic current source 30 has a diode D ₂ and a transistor TR ₈ on the other hand. The same current I ₂ is supplied from the current sources 36 and 38 to the anode of the diode D ₂ and the emitter of the transistor TR ₈ , respectively. Cathode of diode D ₂ and transistor TR ₈
Is grounded, and the anode of the diode D ₂ is connected to the base of the transistor TR _{8 and} the anode of the transistor TR _8.
Since the emitters of ₈ are connected to the base of the transistor TR ₄ , respectively, the base potential V _B2 of the transistor TR ₄ is expressed as follows.

V _B2 = V _F3 + V _F4 (4) where V _F3 is the voltage across the diode D ₂ and V _F4 is the base-emitter voltage of the transistor TR ₈ .

Therefore, the differential input ΔV to the differential transistor pair composed of the transistors TR ₃ and TR _4
B can be represented as follows:

ΔV _B = V _B1 −V _B2 (5) By the way, the current-voltage characteristic of the diode can be expressed by the following equation.

V _F = − (kT / q) ln (I _D / I _s ) ... (6) where V _F is the voltage across the diode and I _D is the current, to distinguish it from the output of the current source 30. The subscript D is attached. Also, _{I s} is the dark current. When this relationship is applied to four diodes of the diode D ₁ , the base-emitter diode of the transistor TR ₃ , the diode D ₂ and the base-emitter diode of the transistor TR ₈ , the following relational expressions (7) to (10) are applied. ) Is obtained.

V _F1 = − (kT / q) ln (I ₁ / I _s ) ... (7) V _F2 = − (kT / q) ln (I ₁ / I _s ) ... (8) V _F3 = − ( _{kT / q) ln (I 2} / I s) ... (9) V F4 = - ( a _{kT / q) ln (I 2} / I s) ... (10) this relationship in equation (3) and (4) By substituting, the following equations (11) and (12) are obtained.

V _B1 = −2 (kT / q) ln (I ₁ / _Is ) (11) V _B2 = −2 (kT / q) ln (I ₂ / _Is ) (12) Substituting into equation (5), ΔV _B = −2 (kT / q) ln {(I ₁ / I _s ) / (I ₂ / I _s )} = − 2 (kT / q) ln (I ₁ / I ₂ ) = (kT / q) ln {(I ₂ / I ₁ ) ² } (13)

It is clear from this equation that the differential input ΔV _B to the differential transistor pair formed by the transistors TR ₃ and TR ₄ is the square of the current I ₁ that is linear with respect to the set voltage V _R. It is proportional to the logarithm. The output current I of this differential transistor pair includes the exponential term of the differential input ΔV _B , as expressed by the above-mentioned equation (2). Substituting the differential input ΔV _B represented by the equation (13) into the equation (2) under the assumption that h _FE is sufficiently larger than 1, the relation as the equation (14) is obtained. You can

[0043] _{I = I 0 / {1+ (} I 2 / I 1) 2} ... (14) What is represented by the formula, the first, current I, linear with respect to the set voltage _{V R} That is, it is approximately proportional to the square of the current I ₁ . Therefore, the current I is fed to the differential amplifier 22.
Is supplied to the amplifier unit 12, the total gain of the one-stage amplifier unit 12 can be made a square characteristic with respect to the set voltage V _R. This represents the realization of the characteristics of FIGS. 2 and 3 described above.

Secondly, it is apparent from the equation (14) that the output current I image temperature characteristic of the square characteristic current source 30 is not provided. That is, since the coefficient kT / q included in Expression (13) cancels out the coefficient q / kT in the exponential term of Expression (2), the term of temperature T does not appear in Expression (14).

As described above, according to the present embodiment, when the gain adjustment is performed so that the output signal level of the one-stage amplifier section 12 becomes constant regardless of the distance, the sense of discomfort associated with the setting of the resistor R ₈ is given. Can be prevented. In addition, the current I can be stabilized in temperature. In addition, as the diodes D ₁ and D ₂ , a transistor T is used.
It is preferable to short-circuit the base and collector of a transistor having the same characteristics as R ₇ and TR ₈ before use.

FIG. 6 shows the configuration when the number of stages of the amplifier section 12 is two. That is, the two differential amplifiers 22 are connected in series via the coupling capacitors C ₂ and C ₃ , and the two linear characteristic current sources 40 are used as the current sources of the differential amplifiers 22. The gain control circuit 28 is composed of these linear characteristic current sources 40.

The linear characteristic current source 40 has its output current I
There is a current source having a linear characteristic with respect to the set voltage V _R, it has a configuration as shown in Figure 7, for example. The linear characteristic current source 40 in this figure has a resistor R ₈ for setting the set voltage V _R. The user sets the set voltage V _R by operating the resistor R ₈ . Set voltage V
_R is applied to the base of the transistor TR ₅ whose collector is grounded. The transistor TR ₅ is supplied with current from the resistor R ₁₀ (or the current source 32 similar to FIG. 5).
The emitter voltage of the transistor TR ₅ , and thus the set voltage V
_R is applied to the base of the transistor TR _6, the emitter of the transistor TR ₆ is grounded through a resistor R _9. Therefore, the collector current _{I 3} of the transistor TR ₆ is a value inversely proportional to the resistance _{R 9} is proportional to the set voltage _{V R.}

Collector current I of transistor TR _6
3 is input to the current mirror circuit 42. The output side transistor of the current mirror circuit 42 is further connected to the input side of the current mirror circuit 44. Therefore, the output current of the current mirror circuit 44 becomes linear with respect to the set voltage V _R. This, if supplied to the differential amplifier 22 corresponding as a current I, can be linearly set the gain of the differential amplifier 22 with respect to the set voltage V _R.

FIG. 8 shows the configuration when the number of stages of the amplifier section 12 is three. That is, the three differential amplifiers 22 are connected in series via the coupling capacitors C ₂ and C ₃ and C ₄ and C ₅ , and the two route characteristic current sources 46 are used as the current sources of the differential amplifiers 22. And one linear characteristic current source 40 is used. The gain control circuit 28 uses these route characteristic current sources 4
6 and a linear characteristic current source 40. Although the current source corresponding to the final stage differential amplifier 22 is the linear characteristic current source 40 in this figure, the first stage or the second stage may be the linear characteristic current source 40. The configuration shown in FIG. 7 can be used as the linear characteristic current source 40.

The route characteristic current source 46 has its output current I
There is a current source having a first power property of 2 minutes the set voltage V _R, has a structure as shown for example in FIG. The route characteristic current source 46 in this figure is provided on the output side of the current mirror circuit 44 of the linear characteristic current source 40 shown in FIG. 7, and further the transistors TR ₉ , TR ₁₀ and TR.
₁₁ , a diode D _{3 and a} current source 48 are provided.

The current source 48 supplies a constant current I ₄ to the transistor TR ₉ . Therefore, the base-emitter voltage V _F5 of the transistor TR ₉ can be expressed as follows.

V _F5 = − (kT / q) ln (I ₄ / I _s ) ... (15) When the output current of the current mirror circuit 44 is I ₅ , the current from the output side transistor of the current mirror circuit 44 is The base-emitter voltage V _F6 of the supplied transistor TR ₁₀ can be expressed as follows.

[0053] _{V F6 = - (kT / q} ) ln (I 5 / I s) ... (16) the base of the transistor TR ₉ is connected to the emitter of the transistor _{TR 10,} the base of the transistor _{TR 10} is the transistor _{TR 11} The base potential V _B3 of the transistor TR ₁₁ can be expressed as follows.

[0054] _{V B3 = V F5 + V F6} ... (17) , while the emitter of the transistor _{TR 11} is connected to the anode of the diode _{D 3,} the cathode of the diode _{D 3} is grounded. Therefore, the transistor TR
_When the collector current of ₁₁ is I, the voltage V _F7 across the diode D ₃ and the base-emitter voltage V _F8 of the transistor TR ₁₁ can be expressed as follows.

V _F7 = − (kT / q) ln (I / I _s ) (18) V _F8 = − (kT / q) ln (I / I _s ) (19) Base potential V of the transistor TR _{11 From} these relationships, _B3 can be expressed as V _B3 = V _F7 + V _F8 (20). The above equation (17) and this equation (2
The right side of (0) is connected with an equal sign, and equations (15), (16), (1
By substituting 8) and (19), the following equation is obtained. _{- (kT / q) ln (} I 4 / I s) - (kT / q) ln (I 5 / I s) = - (2kT / q) ln (I / I s) ... (21) deforming the equation Then, the coefficient of kT / q disappears and I _s also disappears. Therefore, I ₄ I ₅ = I ² (22)

Here, since the current source 48 is a constant current source, it can be seen that the current I is proportional to the current I ₄ , and thus the square root of the set voltage V _R. In other words, by using the circuit of FIG. 9, a characteristic of the route for setting the voltage V _R, it is possible to set the gain of the corresponding differential amplifier 22.

FIG. 10 shows an example in which the detection circuit 16 is constructed by an integration method. The detection circuit 16 includes the amplifier unit 1
The output of 2 is input through the amplifier 50. The output of the amplifier 50 is input to the limiter 52 via the capacitor C ₆ , is subjected to amplitude limitation, and then is input to the sample hold circuit 54. The sample hold circuit 54 samples the input signal at the light emission timing of the light emitting element given by the synchronization signal. The signal sampled and held by the sample hold circuit 54 is input to the comparator 56 having a hysteresis characteristic.

FIG. 11 shows the operation of the detection circuit 16 shown in FIG. As shown in this figure, when the output of the light receiving element PD synchronized with the light emission timing is sampled at the light emission timing indicated by the synchronization signal and the output of the sample hold circuit 54 exceeds the reference value of the comparator 56, the comparator 56 outputs. The output changes to H, and the detection circuit 16 can also be configured by a counter.

Further, the present invention can be applied to other types of non-contact sensors and various manufacturing control devices equipped with the sensors.

[0060]

As described above, according to the present invention,
Since the gain adjusting means for changing the gain of the amplifying means according to the set value is provided, the level of the output signal of the amplifying means can be set to a constant level regardless of the distance, and it is suitable for the circuit in the subsequent stage, for example, the detecting means. The signal is obtained. According to the present invention, in particular, since the characteristic of the gain adjusting means is the squared characteristic with respect to the set value, when performing the gain setting according to the distance related to the detecting means, the relationship between the set value and the distance is made linear. Thus, a non-contact switch capable of gain setting without any discomfort can be obtained.

According to the present invention, when the n-stage differential amplifier in which n differential transistor pairs are connected in cascade is used as the amplifying means, the gain adjusting means is used as the n current sources corresponding to the respective stages. Since the product of the current characteristics is squared with respect to the set value, the above effect can be realized by improving the conventional circuit or by combining the circuits having a relatively simple structure. For example, square, linear,
If each of the current sources having the root current characteristic is prepared, the circuit designer has only one square-characteristic current source for the first stage and two linear characteristic current sources for the second stage.
It is sufficient to select the configuration and combination of the current sources in accordance with the number of stages of the differential amplifier, such as combining two individual current sources with linear characteristics and one current source with root characteristics in three stages. As a result, design man-hours and costs can be reduced.

According to the present invention, when the differential amplifier is provided in one stage, the corresponding current sources have a differential configuration, and two active elements are provided at the control terminals of each transistor according to the differential configuration. Since the active elements related to the same control terminal are connected in series and driven by the same current, the current source having the square characteristic can be configured to have no temperature characteristic.

According to the present invention, each of the above effects can be
It can be obtained in the production control device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a photoelectric switch and an output circuit thereof according to an embodiment of the present invention.

FIG. 2 is a diagram showing a total gain control characteristic in this embodiment.

FIG. 3 is a diagram showing an effect of this embodiment.

FIG. 4 is a block diagram showing the configuration of the main part of this embodiment when the amplifier unit has a one-stage configuration.

FIG. 5 is a circuit diagram showing a configuration of a squared characteristic current source.

FIG. 6 is a block diagram showing a configuration of a main part of this embodiment when the amplifier unit has a two-stage configuration.

FIG. 7 is a circuit diagram showing a configuration of a linear characteristic current source.

FIG. 8 is a block diagram showing a main configuration of this embodiment when the amplifier unit has a three-stage configuration.

FIG. 9 is a circuit diagram showing a configuration of a route characteristic current source.

FIG. 10 is a block diagram showing a configuration of a detection circuit.

FIG. 11 is a timing chart showing the operation of the detection circuit.

FIG. 12 is a diagram showing a change in a light receiving level depending on a distance.

FIG. 13 is a block diagram showing a configuration of a photoelectric switch and its output circuit according to a conventional example.

FIG. 14 is a circuit diagram showing a configuration of an I / V conversion circuit.

FIG. 15 is a circuit diagram showing a configuration of an amplifier section in a conventional example.

FIG. 16 is a circuit diagram showing a configuration of a gain control circuit in a conventional example.

FIG. 17 is a diagram showing a gain control characteristic in a conventional example.

FIG. 18 is a diagram showing a problem of the conventional example.

[Explanation of symbols]

10 I / V conversion circuit 12 Amplifier section 16 Detection circuit 18 Logic 22 Differential amplifier 28 Gain control circuit 30 Square characteristic current source 26, 32, 36, 38, 48 Constant current source 34, 42, 44 Current mirror circuit 40 Linear characteristic Current source 46 Root characteristic current source PD Transistors TR ₃ and TR ₄ forming a differential amplifier at each stage of the light receiving elements TR ₁ and TR ₂ amplifier section Transistor TR ₆ forming a square characteristic current source Voltage-current converting transistor TR ₇ TR ₁₁ current - voltage converting transistor _D 1 to D ₃ current - current _I 2 corresponding to the voltage conversion diode _{R 8} setting voltage _V for _R setting resistor _{V R} set voltage _{I 1} set voltage _{V R, I 4} constant current I output current _V F1 of ₅ current mirror circuit _{44, V F3,} V _F7 diode _D 1 ends in to D ₃ voltage _{V F2 V F4} ~V _F6, V _F8 transistor _TR 7 ~
Base-emitter voltage V _{B1 of} TR ₁₁ and V _B2 base potential I of transistors TR ₃ and TR ₄ Output current of each current source forming a gain control circuit

Claims (2)

(57) [Claims] 1. A detection means for receiving a radio signal such as light or magnetism transmitted from an isolated position and converting the radio signal into an electric signal.
Amplifying means for amplifying the electrical signal, a gain adjusting means for adjusting the gain of the amplifying means in accordance with the set value, the output circuit of <br/> contactless switch with amplification means, the differential transistor pair With n (n: own
Number of differential amplifiers connected in cascade.
The product of the current characteristics of the current source of each differential amplifier
An output circuit of a non-contact switch characterized by having a square characteristic . 2. A control device comprising an output circuit of the non-contact switch according to claim 1.