JP3910832B2 - Amplifier circuit and photoelectric switch device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an amplifier circuit, and more particularly to an amplifier circuit suitable for application to a photoelectric switch device or the like.
[0002]
[Prior art]
Photoelectric switch devices are used for the purpose of preventing accidents caused by inadvertent entry of humans into dangerous places in factories, etc., and for detecting the Service-to-Self who entered for crime prevention. . In a photoelectric switch device, a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode are arranged opposite to each other with a detection region interposed therebetween. If no object is present in the detection region, light emitted from the light-emitting element is received by the light-receiving element. If any object is present in the detection area, the light beam is blocked and the light from the light emitting element does not enter the light receiving element. For this reason, by monitoring the level of the photoelectric conversion current of the light receiving element, it is possible to detect the intrusion of an object into the detection region, and to issue an alarm or the like.
[0003]
Here, since light existing in the environment, that is, ambient light is sufficiently larger than the light emission level of the light emitting element, the light emitting element is generally driven by a pulse, and the original signal that appears superimposed on the ambient light signal on the output of the light receiving element is a high pass. Extraction is performed with a filter or the like. Further, since the level of the original signal is very small, a configuration is adopted in which a signal obtained by converting the photoelectric conversion current of the light receiving element into a voltage is amplified by a multistage amplifier circuit. In this case, each stage is coupled by a capacitor.
[0004]
In addition, since the detection region is one-dimensional only with a pair of light-emitting elements and light-receiving elements, when two-dimensional detection areas are required, for example, a plurality of pairs of light-emitting elements and light-receiving elements are arranged every several cm. If even one pair of rays is blocked, it is possible to detect that an object has entered. In this case, there is no problem as long as each pair does not interfere optically, but it is expensive to realize light input / output only between the paired light emitting element and light receiving element in the optical system in a practical apparatus. Difficult from the aspect. For this reason, a plurality of light emitting elements are caused to emit light sequentially at different timings, and this is dealt with by using a logic circuit that ignores even if a signal is detected by a light receiving element other than the light receiving element paired with the light emitting element.
[0005]
[Problems to be solved by the invention]
When a signal obtained by converting the photoelectric conversion current of the light receiving element into a voltage is amplified by a multistage amplifier circuit, a phenomenon occurs in which the signal oscillates in a tail. This phenomenon does not affect the detection accuracy when only one pair of light emitting element and light receiving element is used. However, as described above, a photoelectric switch in which a plurality of light emitting element and light receiving element pairs are arranged adjacent to each other. In the device, it causes malfunction. The reason is that even in a case where a pair of incoming / outgoing light beams are blocked and it is necessary to detect this blockage, by picking up signals from the other light emitting elements by crosstalk, the other light emitting elements can be detected. Even if the light emission timing can be suppressed by a logic circuit, the signal of the multistage amplifier is tailed. As a result, the signal of the pair of light emitting elements is cut off even at the timing of detecting its own signal. This is because the signal detected by the crosstalk has a tail in vibration, and thus the voltage due to the vibration of the tail is mistaken as an original signal. In order to increase detection accuracy, such malfunctions shorten the distance between the adjacent light emitting elements and the time from when the adjacent light emitting elements stop emitting light until the next light emitting element starts to emit light. It is more likely to occur.
[0006]
An object of the present invention is to provide an amplifying circuit capable of amplifying a signal having a low level even when it is amplified in multiple stages so that a phenomenon in which the signal oscillates is not generated.
[0007]
Another object of the present invention is to make it possible to prevent malfunction in a photoelectric switch device in which a plurality of pairs of light emitting elements and light receiving elements are arranged by analog signal processing.
[0008]
[Means for Solving the Problems]
  A first amplifier circuit according to the present invention includes a first capacitor having one end connected to an input terminal to which an input signal from an input circuit is applied, and a signal component that does not include a signal component or has a phase opposite to that of the input signal. A second capacitor having one end connected to a compensation circuit including: a first input connected to the other end of the first capacitor and a second input connected to the other end of the second capacitor A connection point between the second amplifier and the second input; a dynamic amplifier; a first switch provided between a connection point between the first capacitor and the first input; and a reference voltage. And a second switch provided between the reference voltage and the reference voltage. According to the first amplifier circuit, the first and second switches are controlled to be closed except during a period in which the input signal is to be amplified. As a result, unnecessary signals are not amplified during the period when the first and second switches are closed, and the influence of the feedthrough of the switch can be reduced.Furthermore, the first amplifier circuit of the present invention includes a first resistor inserted between the first capacitor and the first input, and between the second capacitor and the second input. A second switch connected; a third switch connected between a connection point of the first resistor and the first input; and a reference voltage; the second resistor; and the second resistor A fourth switch connected between a connection point with the input and a reference voltage, and the third and fourth switches are controlled to open and close in synchronization with the first and second switches. As a result, the operation of amplifying other unnecessary signals during the period when the first to fourth switches are closed is further suppressed.
[0009]
According to a second amplifier circuit of the present invention, in the first amplifier circuit, the compensation circuit applies a fixed voltage having an impedance equivalent to an impedance when the input circuit side is viewed from the input terminal to the second capacitor. Configured to apply. Thereby, the voltage fluctuation amounts of the first and second capacitors when the first and second switches are opened can be made equal, and the influence of the switch feedthrough can be further reduced.
[0010]
The third amplifier circuit according to the present invention provides means for biasing the first and second inputs of the differential amplifier when the first and second switches are open in the first amplifier circuit. Is provided. Thereby, voltage fluctuations of the first and second capacitors when the first and second switches are opened can be suppressed.
[0011]
  According to a fourth amplifier circuit of the present invention, in the third amplifier circuit,The first and second switches are composed of PNP transistors,The means for providing a bias is a resistor, the resistor being connected to the first and second switches;With the same type, always closed PNP transistorIt is connected to a reference voltage via a switch. Thereby, voltage fluctuations of the first and second capacitors when the first and second switches are opened can be further suppressed.
[0013]
  First of the present invention5The amplifier circuit1In this amplifier circuit, a lateral PNP transistor in which two P diffusion layers are formed so that one of the switches surrounds the other is used as the switch. By using the inner P diffusion layer as the collector and the outer P diffusion layer as the emitter of the two P diffusion layers, the influence of feedthrough is further reduced.
[0014]
  On the other hand, in the photoelectric switch device of the present invention, a plurality of light emitting units are arranged on one side of the detection region, and a plurality of light receiving units corresponding to the light emitting units are arranged on the other side of the detection region. In the photoelectric switch device for detecting the presence or absence of an object entering the detection region by discriminating a signal obtained by amplifying the output of each light receiving unit by a multi-stage amplifier, at least the first-stage amplifier circuit in the multi-stage amplifier Second1By using this amplifier circuit, malfunction in the photoelectric switch device is prevented by analog signal processing.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a block diagram of an embodiment of a photoelectric switch device according to the present invention. The photoelectric switch device of this example includes a plurality of light emitting units 1-1 to 1-n, light receiving units 2-1 to 2-n corresponding to the light emitting units on a one-to-one basis, and analog provided for each light receiving unit. A processing circuit 3-1 to 3 -n, a logic circuit 4, an alarm device 5, and a timing circuit 6 that outputs timing signals T 1 to Tn to each unit are provided.
[0017]
As shown in FIG. 2, the timing circuit 6 constantly outputs timing signals T1 to Tn that are at a high level (H) in different periods. The timing signal Ti (i = 1 to n, hereinafter the same) output here is input to the light emitting unit 1-i, the analog processing circuit 1-i, and the logic circuit 4.
[0018]
Each light emitting unit 1-i includes a light emitting element such as a light emitting diode, a driving circuit for the light emitting element, and an optical system that emits light emitted from the light emitting element to the outside. They are arranged at intervals of about cm. The drive circuit of each light emitting unit 1-i drives the light emitting element in a pulsed manner during a period when the timing signal Ti is at a high level. As a result, pulsed emitted light generated by the light emitting element is radiated toward the detection region through the optical system.
[0019]
Each light receiving unit 2-i includes an optical system that receives light emitted from the light emitting unit 1-i, and a light receiving element such as a photodiode that generates a current corresponding to the intensity of the received light. For example, it is disposed at a distance of several centimeters at a position facing the light emitting unit 1-i across the detection region. The photoelectric current obtained by the light receiving element is output to the subsequent analog processing circuit 3-i.
[0020]
Each analog processing circuit 3-i includes an I / V conversion circuit that converts the photoelectric current output from the light receiving unit 2-i into a voltage, and a multistage amplifier that amplifies the output voltage of the I / V conversion circuit. The amplified output is output to the logic circuit 4. This multi-stage amplifier has a function of substantially amplifying only an input signal that appears during a period when the timing signal Ti is at a high level.
[0021]
The logic circuit 4 is a part that detects the intrusion of an object into the detection area by monitoring the output voltages of the plurality of analog processing circuits 3-1 to 3 -n. The alarm device 5 is driven to issue an alarm. The logic circuit 4 compares the output voltage of the analog processing circuit 3-i with, for example, a predetermined voltage every period when the timing signal Ti is at a high level, thereby determining whether or not the light emitted from the light emitting element 1-i is blocked. To detect.
[0022]
FIG. 3 is a block diagram showing a configuration example of the analog processing circuit 3-i. The analog processing circuit 3-i in this example includes an I / V conversion circuit 31 that converts the photoelectric current of the light receiving element 2-i into a voltage and a multistage amplifier 32. The amplifier 32 is an m-stage amplifier circuit 32. -1 to 32-m. Here, a capacitor is coupled between the I / V conversion circuit 31 and the first-stage amplifier circuit 32-1, and between the amplifier circuits 32-1 to 32-m. In addition, at least the first-stage amplifier circuit 32-1 among the amplifier circuits 32-1 to 32-m has a function of substantially amplifying only an input signal that appears during a period in which the timing signal Ti is at a high level. Of course, in addition to the first stage amplifier circuit 32-1, the other one, a plurality, or all of the amplifier circuits have a function of substantially amplifying only the input signal appearing in the period in which the timing signal Ti is at the high level. You may have it.
[0023]
According to the photoelectric switch device according to the present embodiment, the multistage amplifier 32 of the analog processing circuit 3-i substantially receives the light reception signal of the light receiving element 2-i only during the period during which the light emitting element 1-i emits light. Therefore, even if a signal from a light emitting element other than the light emitting element 1-i is picked up by crosstalk, the phenomenon that the signal detected by crosstalk is amplified and has a tail is eliminated. . This makes it possible to prevent malfunction in the photoelectric switch device in which a plurality of pairs of light emitting elements and light receiving elements are arranged by analog signal processing.
[0024]
Next, embodiments of the amplifier circuit according to the present invention will be described in detail. The amplifier circuit of this embodiment is used as the amplifier circuits 32-1 to 32-m that constitute the multistage amplifier 32 of the analog processing circuit 3-i in the above photoelectric switch device.
[0025]
(1) FirstPremiseExample
  FIG. 4A shows a first example of the amplifier circuit of the present invention.PremiseIt is a circuit diagram of an example. The amplifier circuit AMP1 in this example has a first capacitor C1 having one end connected to the input terminal IN, a compensation circuit HC, and a second capacitor having one end connected to the compensation circuit HC and having the same capacity as the first capacitor C1. Capacitor C2, a differential amplifier DAMP having a first input connected to the other end of the first capacitor C1 and a second input connected to the second capacitor C2, and the first capacitor C1 and the differential Connection of the first switch SW1 connected between the connection point a of the first input of the amplifier DAMP and the reference voltage Vref of the reference power source DC, and connection of the second capacitor C2 and the second input of the differential amplifier DAMP. A second switch SW2 connected between the point b and the reference voltage Vref is included. A resistor for applying an input bias is connected between the first and second inputs of the differential amplifier DAMP and the reference voltage Vref as necessary. Not.
[0026]
An input signal Si from an external input circuit INC is input to the input terminal IN. The input circuit INC corresponds to the I / V conversion circuit 31 when the amplifier circuit AMP1 is used as the first stage amplifier circuit 32-1 of FIG. 3, and the amplifier circuit AMP1 is the second stage of FIG. When used as the subsequent amplifier circuits 32-2 to 32-m, it corresponds to the preceding amplifier circuit.
[0027]
The compensation circuit HC is a circuit that does not include a signal component or a circuit that includes a signal component having a phase opposite to that of the input signal Si. The compensation circuit HC including no signal component is realized as a circuit that supplies a fixed voltage Ve as shown in FIG. Here, the fixed voltage Ve is determined according to the reference voltage Vref and the type of the differential amplifier DAMP. For example, when the Vref is 5 V and the differential amplifier DAMP is composed of NPN transistors, the input range is 0.8 V to Since it is about 4.8V, the fixed voltage Ve is set to about 3V. Further, the compensation circuit HC including a signal component having a phase opposite to that of the input signal Si is realized as a negative phase input circuit GC as shown in FIG.
[0028]
The differential amplifier DAMP amplifies and outputs the voltage difference between the other ends of the first and second capacitors C1 and C2. The differential amplifier DAMP may be a one-output type that outputs only to one output terminal OUT as shown by a solid line in FIG. 4A, or two output terminals OUT1 as shown by a broken line. , OUT2 may be a two-output type that outputs two outputs of normal phase and reverse phase. For example, when this amplifier circuit AMP1 is used as the final stage amplifier circuit 32-m of FIG. 3, a two-input one-output differential amplifier DAMP may be used, and the other amplifier circuits 32-1 to 32-m-1 may be used. When using the differential amplifier DAMP having two inputs and two outputs, the amplifier circuit used in the previous stage when using the compensation circuit HC of FIG. 4C including a signal component having a phase opposite to that of the input signal Si. The negative phase output in the differential amplifier DAMP of the AMP 2-input 2-output type can be used.
[0029]
The first and second switches SW1 and SW2 are controlled to be opened and closed by a timing signal T supplied from an external timing circuit TM. The timing circuit TM generates a timing signal T that opens the first and second switches SW1 and SW2 while the amplifier circuit AMP1 should amplify the input signal Si of the input terminal IN, and closes the other periods. To do. This timing signal T corresponds to the timing signal Ti in the previous embodiment of the photoelectric switch device.
[0030]
  FIG. 5 is an operation time chart of the amplifier circuit AMP1 of FIG. In this operation time chart, the circuit that does not include the signal component shown in FIG. 4B is used as the compensation circuit HC, and the differential amplifier DAMP is a 2-input 1-output type. . Hereinafter, with reference to each figure,PremiseThe operation of the example amplifier circuit AMP1 will be described.
[0031]
First, the basic operation will be described. When the first and second switches SW1 and SW2 are closed, the first and second inputs of the differential amplifier DAMP are substantially equal to the reference voltage Vref regardless of the level of the input signal Si. No signal appears in. When the first and second switches SW1 and SW2 are opened, the one end side of the second capacitor C2 is the fixed voltage Ve, whereas the one end side of the first capacitor C1 varies depending on the input signal Si. A difference corresponding to the input signal Si is generated between the first input and the second input of the dynamic amplifier DAMP, and a signal obtained by amplifying the difference appears at the output terminal OUT. As a result, only the input signal that appears in the period to be originally amplified designated by the timing signal T is substantially amplified.
[0032]
  Then thisPremiseThe example explains why a differential amplifier is used and two capacitors are used. By closing the first switch SW1 outside the period during which the amplifier circuit AMP1 amplifies the input signal Si, it is possible to prevent the input of the signal that causes the malfunction and the amplification itself. However, in general, a switch has a problem of feed-through in which a voltage for switching the switch flows through a parasitic capacitor of the switch element. For this reason, when the switch SW1 is closed, due to this feedthrough phenomenon, the potential at the point a of the first capacitor C1 fluctuates by ΔV as shown in the operation time chart of FIG. 5, which causes malfunction. Therefore, a differential amplifier DAMP is used as an amplifier, and a second capacitor C2 having the same capacity as the first capacitor C1 is connected to a second input having a polarity opposite to that of the first input to which the first capacitor C1 is connected. , And a second switch SW2 is provided between the point b and the reference voltage Vref, and the second switch SW2 is opened and closed simultaneously with the first switch SW1, and the operation time chart of FIG. As described above, the second capacitor C2 also causes a voltage fluctuation due to a feedthrough phenomenon having the same value as that of the first capacitor C1, and the voltage is canceled by the differential amplifier DAMP.
[0033]
(2) SecondPremiseExample
  thisPremiseAn example is the first shown in FIG.PremiseA compensation circuit HC1 shown in FIG. 4D is used as the compensation circuit HC in the example amplifier circuit AMP1. The fixed voltage Ve in the compensation circuit HC1 is the same as the fixed voltage Ve in FIG. The impedance Z is equal to the fixed voltage Ve and the second voltage so that the impedance when the fixed voltage Ve side is viewed from the second capacitor C2 is equivalent to the impedance when the input terminal IN side is viewed from the first capacitor C1. It is an impedance element inserted between the capacitor C2.
[0034]
  The first of FIG.PremiseIn the example, when the circuit of FIG. 4B is used as the compensation circuit HC, the first capacitor C1 is connected to the input circuit INC, while the second capacitor C2 is connected to the fixed voltage Ve. The impedance when the input terminal IN side is viewed from the first capacitor C1 does not necessarily match the impedance when the fixed voltage Ve side is viewed from the second capacitor C2. For this reason, when the first and second switches SW1 and SW2 are opened, a difference occurs in the voltage fluctuation amount of the first and second capacitors C1 and C2 due to the difference in impedance. Cannot be offset. In contrast, the bookPremiseIn the example, the impedance Z is equivalent to the impedance when the fixed voltage Ve side is viewed from the second capacitor C2 and the impedance when the input terminal IN side is viewed from the first capacitor C1. In addition, the voltage fluctuation amounts of the first and second capacitors C1 and C2 when the second switches SW1 and SW2 are switched become equal, and the voltage fluctuation due to feedthrough can be accurately canceled by the differential amplifier DAMP. .
[0035]
As the impedance Z, a circuit having the same configuration as the input circuit IN and not supplied with an input signal is ideal. However, since the circuit is complicated, the impedance of the input circuit IN is obtained by simulation or the like. It is preferably realized by a combination of a resistor and a capacitor.
[0036]
(3) ThirdPremiseExample
  FIG. 6 shows a third example of the amplifier circuit according to the present invention.PremiseFIG. 4 is a circuit diagram of an example, where the same reference numerals as those in FIG. 4A denote the same parts, and R1 and R2 are resistors for applying a bias to the first and second inputs of the differential amplifier DAMP. BookPremiseIn the example amplifier circuit AMP2, bias resistors R1 and R2 are connected in parallel to the first and second switches SW1 and SW2, and the resistor R1 starts when the first and second switches SW1 and SW2 are closed. And R2 to supply a bias to the first input and the second input of the differential amplifier DAMP.PremiseThis is different from the example amplifier circuit AMP1. Also, a differential amplifier composed of MOS type transistors has a large 1 / f noise and may not be suitable for amplification of minute voltages.PremiseIn the example, a differential amplifier composed of bipolar transistors is used as the differential amplifier DAMP. An example of a differential amplifier composed of bipolar transistors is shown in FIG. In FIG. 7, Q1 and Q2 are NPN transistors, R is a resistor, and I is a constant current source.
[0037]
  Figure 8PremiseAn operation time chart of the example amplifier circuit AMP2 is shown. When the first and second switches SW1 and SW2 are closed, a bias is supplied to the first and second inputs of the differential amplifier DAMP from the reference voltage Vref through the first and second switches SW1 and SW2. The When the first and second switches SW1 and SW2 are opened, if the bias resistors R1 and R2 are not connected, the first and second capacitors C1 and C2 are connected to the bases of the transistors Q1 and Q2. As the current flows, the potentials at the points a and b greatly decrease as shown by the broken lines in FIG. 8, and the first and second capacitors C1 and C1 are deviated from the operating voltage range or due to the difference in the flowing current. A difference in the voltage of the electrode on the rear end side of C2 may cause a malfunction.
[0038]
  In contrast, the bookPremiseIn the example, the resistors R1 and R2 having the same value are connected in parallel to the first and second switches SW1 and SW2, so that when the first and second switches SW1 and SW2 are opened, the bias current is changed to the resistor R1. And the voltage at the first and second inputs of the differential amplifier DAMP is the first to a value determined by the drop voltage due to the current flowing through the resistors R1 and R2, as shown by the solid line in FIG. And, it gradually changes with a time constant determined by the second capacitors C1 and C2 and the resistors R1 and R2. Accordingly, it is possible to prevent the voltage at the first and second inputs of the differential amplifier DAMP from deviating from the operating voltage range or to make a difference between the voltages at the rear end electrodes of the first and second capacitors C1 and C2. The cause of malfunction can be removed. Note that, by setting the time constant to be sufficiently larger than the cutoff frequency of the next stage, the fluctuation of the voltage does not affect the output.
[0039]
(4) FourthPremiseExample
  FIG. 9 shows a fourth example of the amplifier circuit according to the present invention.PremiseIt is a circuit diagram of an example, and the same numerals as FIG. BookPremiseThe amplifier circuit AMP3 in the example is connected in series with a resistor R1 and a switch SW3 in parallel with the first switch SW1, and connected in series with a resistor R2 and a switch SW4 in parallel with the second switch SW2. ThreePremiseThis is different from the example amplifier circuit AMP2. Here, the resistance R1 and the resistance R2 are the thirdPremiseThe resistors R1 and R2 in the example are bias resistors, and the switches SW3 and SW4 are normally closed switches. The switches SW1 to SW4 are all of the same type. BookPremiseIn the example, the switches SW1 to SW4 are configured by PNP transistors for the purpose of reducing the feedthrough.
[0040]
  A switch using a PNP transistor generates a voltage even when the collector current is not flowing in the closed state. For this reason, the voltages at points a and b when the switches SW1 and SW2 are closed are actually the voltage difference between the switches SW1 and SW2 added to the reference voltage Vref. Therefore, there are no switches SW3 and SW4 in FIG.PremiseIn the example, the voltage fluctuation amount at the points a and b when the switches SW1 and SW2 are opened is not only the voltage generated when the bias current flows through the resistors R1 and R2, but also the voltage difference between the switches SW1 and SW2. It will be added. If this fluctuation amount is large, there is a risk of affecting the normal operation after the next stage.
[0041]
  In contrast, the bookPremiseIn the example, since switches SW3 and SW4 similar to the switches SW1 and SW2 are connected in series to the resistors R1 and R2, the voltages at the ends of the resistors R1 and R2 in the state where the switches SW1 and SW2 are closed are expressed as point a and It can be set in advance to be the same as the voltage at point b. Therefore, the voltage fluctuation amount at the points a and b when the switches SW1 and SW2 are opened is the third value.PremiseCompared to the example, the voltage difference between the switches SW1 and SW2 can be reduced, and the influence on the next stage is reduced accordingly.
[0042]
(5)Of the present inventionExample
  FIG. 10 shows an amplifier circuit according to the present invention.oneFIG. 4 is a circuit diagram of the embodiment, where the same reference numerals as those in FIG. 4 denote the same parts, SW5 and SW6 are switches, and R3 and R4 are resistors. In the amplifier circuit AMP4 of this embodiment, resistors R3 and R4 are inserted between the first capacitors C1 and C2 and the first and second inputs of the differential amplifier DAMP, and the resistors R3 and the differential amplifier DAMP are connected. The switch SW5 is connected between the connection point c with the input 1 and the reference voltage Vref, and the switch SW6 is connected between the connection point d between the resistor R4 and the second input of the differential amplifier DAMP and the reference voltage Vref. And the firstPremiseThis is different from the example amplifier circuit AMP1.
[0043]
  Generally, there is a contradictory relationship between the on-resistance of the switch element and the parasitic capacitance. That is, in order to reduce the on-resistance, it is necessary to increase the size, which increases the parasitic capacitance. The first of FIG.PremiseIn the example, unnecessary signals are blocked by the switches SW1 and SW2, but when the on-resistance values of the switches SW1 and SW2 are large, signal input cannot be completely blocked. For this reason, if the switch element is enlarged and the on-resistance value is reduced, the parasitic capacitance is increased and the feedthrough is increased. If the feedthrough is the same at both inputs of the differential amplifier DAMP, it is canceled out. However, since this is not actually caused by variations in the two switches SW1 and SW2, it cannot be completely removed.
[0044]
In contrast, in this embodiment, resistors R3 and R4 are inserted between the capacitors C1 and C2 and the next input, and between the points c and d on the rear end side of the resistors R3 and R4 and the reference voltage Vref. Furthermore, since the switches SW5 and SW6 that are opened and closed simultaneously with the first and second switches SW1 and SW2 are provided, even if the on-resistance value of each switch is somewhat large, as shown in the operation time chart of FIG. In addition, the signal passing through the first switches SW1 and SW2 when the switch is turned on is once reduced and then further reduced by the resistors R3 and R4 and the switches SW5 and SW6 in the subsequent stage. As a result, a sufficient signal suppression effect can be obtained without enlarging the size of each switch and reducing the on-resistance.
[0045]
  ThisThe fruitThe example is the firstPremiseAs an example, the second through fourthPremiseAn example can also be assumed. For example, the third of FIG.PremiseWhen applied to the example, bias resistors R1 and R2 are connected in parallel to the switches SW5 and SW6 as shown by the broken lines in FIG.
[0046]
  Next, each of the aboveAssumptions andAn embodiment of a switch element suitable for the switches SW1 to SW6 used in the amplifier circuit of the embodiment will be described.
[0047]
When realizing the switch element in a semiconductor device, it is desirable that the parasitic capacitance is as small as possible and the parasitic capacitance is small in order to avoid feedthrough. Therefore, in this embodiment, as shown in the plan view of FIG. 12A and FIG. 12B showing the cross section along the line XX of FIG. 12, the N-type epitaxial layer separated by isolation diffusion is used. A PNP transistor having a lateral structure in which two P diffusion layers are formed so that one side surrounds the other is used as a switching element. Usually, the inside of the two P diffusion layers is an emitter and an outer side. Is the collector, but in this embodiment, the inner P diffusion layer is used as the collector and the outer P diffusion layer is used as the emitter. Thereby, the capacitance between the base and the collector is reduced, and a switching element with a small influence of feedthrough is obtained.
[0048]
FIG. 13 shows a circuit diagram when the switch element of this embodiment is applied to the switch SW1. In this case, the switching signal is turned on at a low level L and turned off at a high level H. A timing signal Ti is used as the switching signal. The other switches SW2 to SW6 can be similarly realized.
[0049]
In the above embodiments of the amplifier circuit, the application to the amplifier circuit in the photoelectric switch device is taken as an example, but the amplifier circuit of the present invention can be applied to various devices other than the photoelectric switch device.
[0050]
【The invention's effect】
As described above, according to the present invention, even when a low level signal is amplified in multiple stages, an amplifier circuit capable of amplifying the signal so as not to cause a vibrational tailing phenomenon can be obtained. In addition, malfunction in the photoelectric switch device in which a plurality of pairs of light emitting elements and light receiving elements are arranged can be prevented by analog signal processing.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of a photoelectric switch device according to the present invention.
FIG. 2 is a diagram illustrating a timing signal output from a timing circuit of the photoelectric switch device according to the present invention.
FIG. 3 is a block diagram illustrating a configuration example of an analog processing circuit 3-i.
FIG. 4 shows first and second amplifier circuits of the present invention.PremiseIt is a circuit diagram of an example.
FIG. 5 shows the first of the present inventionPremiseIt is an operation | movement time chart of the amplifier circuit concerning an example.
FIG. 6 shows a third embodiment of the present invention.PremiseIt is a circuit diagram of the amplifier circuit concerning an example.
FIG. 7 is a circuit diagram showing an example of a differential amplifier composed of bipolar transistors.
FIG. 8 shows the third of the present inventionPremiseIt is a figure which shows the operation | movement time chart of the amplifier circuit concerning an example.
FIG. 9 shows the fourth aspect of the present invention.PremiseIt is a circuit diagram of the amplifier circuit concerning an example.
FIG. 10 shows the present invention.oneIt is a circuit diagram of the amplifier circuit concerning an Example.
FIG. 11 shows the present invention.oneIt is a figure which shows the operation | movement time chart of the amplifier circuit concerning an Example.
FIG. 12 is a diagram showing a structure of a switch element used in the amplifier circuit of the present invention.
13 is a circuit diagram when the switch element of FIG. 12 is applied to a switch SW1.
[Explanation of symbols]
1-1 to 1-n: Light emitting part
2-1 to 2-n: light receiving part
T1 to Tn: Timing signal

Claims (6)

A first capacitor having one end connected to an input terminal to which an input signal from the input circuit is applied, and one end connected to a compensation circuit that does not include a signal component or includes a signal component that is opposite in phase to the input signal. A second capacitor; a differential amplifier having a first input connected to the other end of the first capacitor and a second input connected to the other end of the second capacitor; and the first capacitor; A first switch provided between a connection point of the first input and a reference voltage; and provided between a connection point of the second capacitor and the second input and a reference voltage. A second switch; a first resistor inserted between the first capacitor and the first input; and a second resistor connected between the second capacitor and the second input. Resistance, a connection point between the first resistance and the first input, and a reference voltage Third and switch, and a fourth switch connected between the connection point and the reference voltage and the second input and the second resistor, the first and which is connected between the An amplifier circuit in which the second switch is controlled to be closed except during a period in which the input signal is to be amplified, and the third and fourth switches are controlled to open and close in synchronization with the first and second switches .   2. The amplifier circuit according to claim 1, wherein the compensation circuit applies a fixed voltage having an impedance equivalent to an impedance when the input circuit is viewed from the input terminal to the second capacitor.   2. The amplifier circuit of claim 1, further comprising means for biasing the first and second inputs of the differential amplifier when the first and second switches are open. The first and second switches are composed of PNP transistors, and the means for biasing is a resistor, the resistor being the same type as the first and second switches, and a normally closed PNP. 4. The amplifier circuit according to claim 3, wherein the amplifier circuit is connected to a reference voltage via a switch by a transistor . As the switch, a PNP transistor having a lateral structure in which two P diffusion layers are formed on the basis of the separated N-type epitaxial layer and one of which surrounds the other is used, and the two P diffusion layers are used. amplifier circuit of claim 1, wherein the use collector, the outer P diffusion layer as the emitter inside the P diffusion layer of the. A plurality of light emitting units are arranged on one side of the detection region, a plurality of light receiving units corresponding to the light emitting units on the other side of the detection region are arranged, and outputs of the respective light receiving units are configured in a multistage configuration. In the photoelectric switch device that detects whether or not an object has entered the detection region by discriminating a signal amplified by the amplifier, the amplification circuit according to claim 1 is provided in at least a first-stage amplification circuit in the multistage amplifier. A photoelectric switch device characterized by being used.

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