JP3104932B2 - Synchronous amplification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous amplifying device for synchronously amplifying a periodic detection signal, which is used in an object detecting device such as a photoelectric switch device in which photoelectric switches are sequentially arranged along an object conveying path. In particular, the present invention relates to a synchronous amplifying device having high DC operating point stability and a large dynamic range, and capable of eliminating saturation due to an excessive signal input in a short time.

[0002]

2. Description of the Related Art Conventionally, in a photoelectric switch device for detecting the presence or absence of a moving object, for example, the presence or absence of an object conveyed on a belt, by using photoelectric switches sequentially arranged along the belt, a photoelectric switch device is provided for each photoelectric switch. A signal detection unit that receives a periodically generated monitoring signal and generates a detection signal including information indicating the presence or absence of the object, a preamplifier that preamplifies the detection signal, and a preamplifier A main amplification unit for further amplifying the detected signal, a sample and hold unit for sampling and holding the amplified detection signal,
And a signal processing unit for converting the output signal of the sample hold unit into a binary signal and determining the presence or absence of the object based on the binary signal.

FIG. 5 is a block diagram showing an example of the structure of an object detecting means in the conventional photoelectric switch device.

In FIG. 5, reference numeral 51 denotes a photodiode (optical sensor); 52, a preamplifier; 53, an amplifying device;
4 is a sample and hold circuit, 55 is a binarization circuit, 56 is a microcomputer, 57 is a light emitting diode (LED), and 58 is an LED driving transistor.

The optical sensor 51 is connected to the signal detector, the preamplifier 52 is connected to the preamplifier, and the amplifier 53
Is the main amplifying section, and the sample and hold circuit 54 is the binarizing circuit 55 and the microcomputer 56 in the sample and hold section.
Respectively correspond to the signal processing units.

[0006] The object detecting means having the above-described structure generally performs the following operation.

First, when the microcomputer 56 generates a periodic LED drive signal to the LED drive transistor 58, the drive signal is transmitted to the LED drive transistor 58.
, And a monitoring signal composed of an optical signal is periodically projected from the LED 57 toward a detection object (not shown) based on the driving signal. At this time, the optical sensor 51 receives the periodic optical signal (monitoring signal) whose intensity changes depending on the presence or absence of the detection object, and has an amplitude corresponding to the amount of received light of the optical signal (monitoring signal). Generate a detection signal. Next, this detection signal is
After being amplified to a required amplitude by the preamplifier 52, the amplified signal is supplied to the amplifier 53. Subsequently, the detection signal is further amplified in the amplifying device 53,
It is supplied to the sample and hold circuit 54. In the sample and hold circuit 54, the amplified detection signal is sampled and held and converted into a hold signal.
Next, the hold signal is converted to a binary signal
After being converted into a binarized signal, the binarized signal is supplied to a microcomputer 56, and the microcomputer 56 analyzes the binarized signal to detect the presence or absence of the detection object.

[0008]

The conventional object detection means first amplifies a detection signal in a preamplifier 52, and then further amplifies the detection signal in an amplifying device 53 following the preamplifier 52 to obtain a required amplitude level. When the amplitude of the detection signal input to the amplifying device 53 is significantly increased, the amplifying device 53
Is saturated and the leading end of the waveform of the detection signal is crushed, and when the duty cycle of the detection signal is small, the amplifying device 53 is similarly saturated and the detection signal is Can not sufficiently follow the change of

If the tip of the detection signal is crushed due to the saturation of the amplifying device 53, it takes a long time to recover from the saturation state, and the signal width of the detection signal increases during the saturation. Accordingly, there is a problem that the detection position of the detection signal is shifted. Also, by inputting the detection signal having a small duty cycle,
When the amplification device 53 cannot sufficiently follow the change, the detection position of the detection signal is shifted as in the case described above, or the reference level of the output amplification signal is changed due to a change in the DC operating point of the amplification device 53. Fluctuates,
There is a problem that a detection error is introduced in the subsequent processing such as amplitude comparison of the output amplified signal.

Incidentally, in order to prevent the occurrence of the saturation state and the fluctuation of the DC operating point in the amplifying device 53, respectively, if the dynamic range of the amplifying device 53 is increased and the power supply voltage thereof is increased, It can be satisfied for the time being. However, it is not easy to obtain an amplifier 53 satisfying such conditions.
Even if it is obtained, there is a problem that the amplifying device 53 becomes considerably expensive.

An object of the present invention is to eliminate the above-mentioned problems, and an object of the present invention is to provide a large dynamic range and a high DC operating point stability at a low power supply voltage, and a saturation due to an excessive signal input. To provide a low-cost synchronous amplifier in which the DC operating point does not fluctuate due to the duty cycle of the detection signal.

[0012]

To achieve the above object, the present invention provides a direct connection type inverting amplifier circuit to which a periodic detection signal is supplied, and a connection between an input and an output of the direct connection type inverting amplifier circuit. And an AC feedback circuit including a switch for varying the amount of signal feedback, a DC feedback circuit including a first sample and hold circuit, and a second sample and hold circuit connected to the output side of the direct-coupled inverting amplifier circuit. The switch of the AC feedback circuit reduces the signal negative feedback amount during the supply period of the detection signal, increases the amplification gain in the direct-coupled inverting amplifier circuit, and reduces the signal negative feedback amount during the non-supply period of the detection signal. Is increased and the amplification gain in the direct-coupled inverting amplifier circuit is reduced, and the sampling of the first sample-and-hold circuit is performed as follows:
Sampling of the second sample and hold circuit is performed during a supply period of the periodic detection signal during a non-supply period of the detection signal. A means for setting a DC operation bias voltage of the inverting amplifier circuit is provided.

[0013]

According to the means, the AC feedback circuit reduces the amount of signal negative feedback during the supply period of the detection signal, increases the amplification gain in the direct connection type inverting amplifier circuit, and increases the signal gain during the non-supply period of the detection signal. The amount of negative feedback is increased, and the amplification gain in the direct-coupled inverting amplifier circuit is reduced. Therefore, the direct-coupled inverting amplifier circuit amplifies the detection signal with a large gain, and amplifies the noise component and the like supplied during the non-supply period of the detection signal with a small gain. It is possible to sufficiently eliminate the influence of the noise component and the like from the output amplified signal signal of the direct connection type inverting amplifier circuit,
Even if the detection signal is an asymmetric signal having ringing or distortion, the existence position can be detected correctly.

Further, according to the means, the DC feedback circuit extracts the fluctuation of the DC level at the output of the direct connection type inverting amplifier circuit, and feeds it back to the input of the direct connection type inverting amplifier circuit. In addition, the fluctuation of the DC level is effectively suppressed, and the fluctuation of the DC operating point of the direct connection type inverting amplifier circuit can be prevented. In this case, the fluctuation component of the DC level is further negatively fed back to the input of the direct-coupled inverting amplifier circuit through the AC feedback circuit, so that the signal negative feedback of the AC feedback circuit during the non-supply period of the detection signal. In conjunction with the increase in the amount, the DC level fluctuation component is controlled so as to disappear immediately, and as a result, the fluctuation of the DC operating point of the direct-coupled inverting amplifier circuit is quickly restored to the original DC level. Can be done. In the direct-coupled inverting amplifier circuit, if the change in the DC operating point can be quickly recovered, the direct-coupled inverting amplifier circuit can sufficiently follow the detection signal even if a detection signal with a small duty cycle is supplied. Further, even if the direct-coupled inverting amplifier circuit is saturated by the supply of the detection signal having a large amplitude, the saturation is immediately eliminated in a short time, and the detection position of the detection signal does not shift.

In addition, according to the above-mentioned means, the direct-coupled inverting amplifier circuit is constituted by an odd number stage (preferably three stages, but one stage is also possible) in which each amplification stage is DC-coupled. Since there is no separate DC bias circuit or differential circuit, the direct-coupled inverting amplifier can operate at high speed and can operate over a wide dynamic range. In addition, this direct connection type inverting amplifier circuit
Since there is no loop feedback circuit inside, high gain can be obtained.

Further, according to the means, since the DC feedback circuit and the AC feedback circuit are connected in parallel, the setting of stabilization of the DC operating point of the direct connection type inverting amplifier circuit by the DC feedback circuit; The magnitude of the AC signal gain by the AC feedback circuit can be set independently.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, a photoelectric switch device to which the synchronous amplifying device of the present invention is applied will be described.

FIG. 4 shows a photoelectric switch device to which the synchronous amplifying device of the present invention is applied. FIG. 4A shows the photoelectric switch device in which a plurality of photoelectric switches are arranged along an object transport belt. It is a schematic block diagram, (b) is a timing chart which shows the supply timing of the signal of each part in the said photoelectric switch apparatus.

In FIG. 4, reference numeral 40 denotes an object conveying belt;
1-A to 41-D are photoelectric switches, 42-A to 42-42
-D is a photodiode (optical sensor), 43-A to 4
3-D is a light emitting diode (LED), 44 is a synchronous circuit,
Reference numeral 45 denotes a transport object.

A plurality of photoelectric switches 41-A to 41-D are arranged at predetermined intervals, for example, at equal intervals along the object transport belt 40.
A to 41-D are optical sensors 42-A to 42-, respectively.
D and LEDs 43-A to 43-D. The optical sensors 42-A to 42-D and the LEDs 43-A to 43-D are arranged facing the object conveyance belt 40, and sensing light (monitoring light) intermittently projected from the optical sensors 42-A to 42-D. ) Is irradiated on the transport object 45 being transported on the object transport belt 40, and the reflected light from the transport object 45 is received by the LEDs 43-A to 43-D. The synchronizing circuit 44 controls the signal generation timing of each of the photoelectric switches 41-A to 41-D, and sequentially moves the optical sensors as the conveyed object 45 conveyed on the object convey belt 40 moves. 42
-A to 42-D so that the intermittent sensing light is sequentially projected.

The operation of the photoelectric switch device having the above configuration will be described with reference to the timing chart of FIG.

First, when the object transport belt 40 is driven to move in the direction of the arrow, the transport object 45 is moved at a predetermined time interval.
Are sequentially conveyed on the belt 40. Here, the time when the first transport object 45 is moved near the first photoelectric switch 41-A is T ₁ , and the time when the transport object 45 is moved near the next photoelectric switch 41-B is T _2. , them to said conveying body 45 is further succeeding photoelectric switches 41-C T ₃ time moved to the vicinity of, the time the transfer object 45 is moved in the vicinity of the end of the photoelectric switches 41-D and T ₄ if the conveying speed of the belt 40 is constant, since each interval between the photoelectric switches 41-a through 41-D to be next phase equal, from time T ₁ to time T _2, the time T
From ₂ to time T _3, none of the time interval from time T ₃ to time T ₄ becomes [Delta] T.

[0023] Now, at the time T _1, is supplied the control signal from the synchronization circuit 44 to the photoelectric switch 41-A, the came with the photoelectric switch 41-A in response to the control signal L
Sensing light L _SA is projected from the ED43-A toward the conveying object 45. At this time, the light reflected by the transport object 45 is received by the optical sensor 42-A. Then, at a time T _2, the photoelectric switch 4
1-A is transmitted light L _TA respect succeeding photoelectric switch 41-B is supplied from the photoelectric switch 41-B that has received the transmission light L _TA to the transfer object 45 from LED 43-B of the accessory The sensing light L _SB is projected toward the sensor. At this time, the transport object 45 is also detected by the optical sensor 42-B.
The reflected light reflected at is received. Subsequently, at the time T _3, transmitted light L _TB thereto from said photoelectric switch 41-B with respect to succeeding photoelectric switches 41-C is supplied, the photoelectric switch 41-C which has received the transmission light L _TB Projects the sensing light L _SC from the attached LED 43-C toward the transport object 45. Also in this case, the optical sensor 4
In 2-C, the light reflected by the transport object 45 is received. Further, at the time T _4, it the succeeding from the photoelectric switch 41-C photoelectric switches 41-D
Against transmission light L _TC is supplied, by projecting the sensing light L _SD said photoelectric switch 41-D which has received the transmission light L _TC is toward the conveyance object 45 from LED 43-D of the accessory, at the same time, light The sensor 42-D receives the reflected light reflected by the transport object 45.

As described above, each of the photoelectric switches 41-B
Through 41-D are the preceding photoelectric switches 41-A through 41-D.
Receiving the transmitted light L _{TA to} L _TC from the -C, the sensing light L _{SB to} L _SD is projected toward the transport object 45, and at the same time, the next photoelectric switch 41- Transfer light L _{TB to} L _TC to C to 41-D
Are supplied, each of the photoelectric switches 41-A to 41-A to 41-A
From -D, 41-A, 41-B, 41-C, 41-D
, The sensing light L _{SA to} L _SD shifted by time ΔT
Are projected toward the transport object 45, respectively.

The sensing light L _{SA to} L _SD
Are reflected by the corresponding photoelectric switches 41-A to 41-D one after another, and the received reflected light is converted into an electrical detection signal. Processing such as amplification is performed by the synchronous amplifying device or the like according to the present invention.
5, an output indicating the presence or absence of conveyance is obtained.

In the above description, each photoelectric switch 4
In 1-A to 41-D, LEDs 43-A to 43-43
Although it has been described that the sensing light L _{SA to} L _SD projected from −D is received only by its own optical sensors 42-A to 42-D, actually, as shown by the dotted line in FIG.
The sensing light L _{SA to} L _SD projected from each of the LEDs 43-A to 43-D is reflected and scattered not only at the transport object 45 but also at various places. Are received as interference light by optical sensors other than the optical sensors 42-A to 42-D. In this case, each of the optical sensors 42-A to 42-A to 42
The detection signals respectively detected in -D will be composed of a regular detection signal supplied periodically and many interference signals supplied between the regular detection signals.

Next, an embodiment of the synchronous amplifying device according to the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the synchronous amplifying device according to the present invention.

In FIG. 1, 1 is a direct-coupled inverting amplifier circuit,
1A to 1C are amplification transistors, 2 is an AC feedback circuit, 3 is a DC feedback circuit, 4 is an input coupling capacitance, 5 is a signal input terminal, 6 is a signal output terminal, 7 is a first sample and hold circuit, and 8 is a bias voltage. A generating circuit, 8A is a differential amplifier circuit, 10 is a reference voltage source, 11 is a second sample and hold circuit, 12 is a comparator circuit, 12A is a differential amplifier circuit, 13 is an output terminal of the comparator circuit, 15 is a timing generator circuit, 16 is a preamplifier, 17 is a photodiode (optical sensor), 1
8 is a light emitting diode (LED), 19 is an LED drive circuit, 20 is a switch, 21 and 24 are sampling switches, and 22 and 23 are feedback resistors.

The direct-coupled inverting amplifier circuit 1 is composed of a circuit in which three amplifier stages including the transistors 1A to 1C are directly coupled and a DC bias supply circuit between the amplifier stages is omitted. The direct-coupled inverting amplifier 1 includes an AC feedback circuit 2 and a DC feedback circuit 3 between the input and output terminals.
Are connected in parallel, the input terminal is connected to a signal input terminal 5 via an input coupling capacitor 4, and the output terminal is directly connected to a signal output terminal 6.
Connected to each other. The AC feedback circuit 2 includes a switch 20 and two feedback resistors 22 and 23. One of the feedback resistors 22 is always connected and the other feedback resistor 23 is connected.
Are selectively inserted and connected by the switch 20. The DC feedback circuit 3 comprises a first sample-and-hold circuit 7, a bias voltage generation circuit 8, and a reference voltage source 10 , wherein the first sample-and-hold circuit 7 includes a series-connected sampling switch 24 and a shunt switch. The reference voltage source 10 is composed of a DC power supply and a potentiometer connected in parallel. Further, the bias voltage generating circuit 8 includes a differential amplifier circuit 8A, a feedback capacitor and a feedback resistor, and the feedback capacitor is provided between an inverting input and an output of the differential amplifier circuit 8A. The feedback resistors are connected in series to the output of 8A.

The second sample and hold circuit 11 connected to the signal output terminal 6 comprises a sampling switch 21 and a shunt capacitance connected in series, and a comparison circuit 12 connected to the output side of the second sample and hold circuit 11. Has a differential amplifier circuit 12A. The optical sensor 17 is connected to the signal input terminal 5 via the preamplifier 16, and the LED drive output terminal of the timing generation circuit 15 is connected to the LED 18 via the LED drive circuit 19. The switch 20 and the sampling switch 24 are of a normally-closed contact type that is driven to an off state only when the timing signal generated by the timing generation circuit 15 is supplied.
The sampling switch 21 is of a normally open contact type that is driven to an ON state only when a timing signal generated by the timing generation circuit 15 is supplied.

FIG. 2 is a signal waveform diagram showing signal waveforms and supply timings of various parts in the apparatus of the embodiment shown in FIG.

In FIG. 2, (a) is a drive signal waveform of the LED 18 (point A in FIG. 1), (b) is a timing signal waveform (points B, C and D in FIG. 1), and (c) is an input detection signal. The waveform (point E in FIG. 1) and (d) are the waveforms of the output detection signal (F in FIG. 1).
Point), (e) is the hold signal waveform (point G in FIG. 1),
(F) is a comparison output signal waveform (point H in FIG. 1).

Then, the timing generation circuit 15
As shown in (a) and (b), a timing signal corresponding to the generation timing of the drive signal of the LED 18 is generated, and these timing signals are supplied to the switch 20 and the two sampling switches 21 and 24.

Here, the operation of the synchronous amplifying device of this embodiment will be described with reference to the signal waveform diagram of FIG.

First, when no optical signal (sensing light) is detected by the optical sensor 17 and no signal is supplied to the signal input terminal 5 (when no signal is input), a bias voltage is generated in the direct-coupled inverting amplifier circuit 1. The DC bias voltage is supplied from the circuit 8. The DC bias voltage is obtained by supplying the voltage V ₁ obtained from the reference voltage source 9 via the differential amplifier circuit 8 A of the bias voltage generating circuit 8. The direct-coupled inverting amplifier circuit 1 is supplied by the supply of the DC bias voltage.
DC operating point when no signal input at transistors 1A to 1C each amplifier stage is selected set to be the reference level that matches the value of the voltage V _1.

Here, when the timing generation circuit 15 generates an LED drive signal as shown in FIG.
Upon receiving the LED drive signal, the LED 18 generates a periodic optical signal (sensing signal) toward a detection object (not shown). Next, the reflected light signal (sensing signal) from the detected object is detected by the optical sensor 17, and the optical sensor 17 transmits a detection signal in response to the detection. Next, this detection signal is amplified by the preamplifier 16 and
A signal input terminal 5 as an input detection signal as shown in FIG.
Supplied to Subsequently, the input detection signal is supplied to the direct-coupled inverting amplifier circuit 1 after the DC component is cut in the input coupling capacitor 5. Directly coupled inverting amplifier circuit 1, the input detection signal and a high gain amplifier, and sends the output detection signal as shown in FIG. 2 (d) to the voltages V ₁ and the reference level to the signal output terminal 6.

Next, the output detection signal is supplied to a second sample-and-hold circuit 11. In the second sample-and-hold circuit 11, a normally open contact-type sampling switch 21 from the timing generation circuit 15 shown in FIG. 2B, the output detection signal is sampled and held in synchronization with the supply of the detection signal (timing signal) because it is driven to the ON state when the timing signal is supplied as shown in FIG. A hold signal as shown in FIG. Subsequently, this hold signal
The voltage V ₂ obtained by the reference voltage source 10 (where V ₁ > V
₂₎ together are supplied to the differential amplifier circuit 12A of the comparison circuit 12, the voltage V ₂ and the amplitude level is compared in the differential amplifier circuit 12A. As a result of this comparison, the output terminal 13 of the comparison circuit outputs the voltage V
A comparison output signal as shown in FIG. 2F consisting of only the signal portion exceeding ₂ is obtained.

Incidentally, a part of the output detection signal obtained at the signal output terminal 6 is negatively fed back to the input terminal of the direct connection type inverting amplifier 1 via the AC feedback circuit 2. In this case, the AC feedback circuit 2 is turned off when the normally closed contact type switch 20 is supplied with the timing signal from the timing generation circuit 15, and the feedback resistor 23 is disconnected from the AC feedback circuit 2 at that time. Since the series resistance value of the AC feedback circuit 2 increases, the amount of negative feedback of the AC feedback circuit 2 decreases in synchronization with the supply of the timing signal (detection signal). As a result, the direct connection type The AC signal gain of the inverting amplifier circuit 1 increases. On the other hand, when the timing signal (detection signal) is not supplied, the switch 20 is kept on, and the feedback resistor 23 is connected to the AC feedback circuit 2.
And the series resistance of the AC feedback circuit 2 is reduced, so that the amount of negative feedback of the AC feedback circuit 2 is increased. As a result, the AC signal gain of the direct-coupled inverting amplifier circuit 1 is reduced. Decrease.

In this case, as shown in FIG. 2C, even if the noise signals n ₁ , n _2, etc. are superimposed on the input detection signal at a portion deviating from the supply timing of the detection signal. since the AC signal gain of the direct-type inverting amplifier circuit 1 with respect to the noise signal n _1, n _2, etc. is less than the AC signal gain for the detection signal, the noise signal n _1,
The amplification degree such as n ₂ is limited, and as shown in FIG.
The levels of the noise signals n ₁ , n _2, etc. decrease to a level that is not noticeable in the output detection signal. Also, for example,
Even when the level of the superimposed noise signals n ₁ , n _2, etc. is considerably large, the amplification degree is limited, so that the noise signals n ₁ , n
Waveforms such as ₂ are not clipped, and the DC operating point of the direct-coupled inverting amplifier circuit 1 does not change due to the clipping of the waveform.

On the other hand, when a large-level detection signal is input, the direct-coupled inverting amplifier circuit 1 is once in a saturated state, but when the supply timing of the detection signal ends, the feedback amount of the AC feedback circuit 2 is reduced. Immediately increases the amount of negative feedback to the direct-coupled inverting amplifier circuit 1, and the negative feedback acts to cancel the saturation of the direct-coupled inverting amplifier circuit 1. Saturation is eliminated, and an operation delay of the direct connection type inverting amplifier circuit 1 with respect to the detection signal can be prevented.

Further, when this synchronous amplifying device is applied to a photoelectric switch device as in the present embodiment, the synchronous amplifying device merely determines the presence or absence of a detection signal. The synchronous amplifying device only needs to have a small dynamic range, and the power supply voltage of the synchronous amplifying device can be reduced. In addition, since the AC signal gain of the direct-coupled inverting amplifier circuit 1 changes in synchronization with the detection signal, the signal band characteristic of the direct-coupled inverting amplifier circuit 1 has the same discrete spectrum as the detection signal. In particular, since the signal band can be narrowed without dulling the signal waveform when amplifying a pulse signal, a synchronous amplifier having excellent S / N can be obtained.

Next, a part of the output detection signal obtained at the output signal terminal 6 is negatively fed back to the input of the direct-coupled inverting amplifier 1 via the DC feedback circuit 3. In this negative feedback, the output detection signal is first supplied to the first sample and hold circuit 7, but the sampling switch 24
Is configured to be driven to the ON state when the timing signal is not supplied, so that the first sample and hold circuit 7 has a reference level when the output detection signal is not supplied, that is, the detection signal is present. The reference level component of the period not to be extracted is extracted. Then, the reference level components this that extracted is supplied to the non-inverting input of the differential amplifier circuit 8A, the voltages V ₁ from a reference voltage source 10 is supplied to its inverting input to the differential amplifier circuit 8A In the differential amplifier circuit 8A, the reference level component and the voltage V
₁ is compared with the level, and the comparison output voltage is taken out from the output of the differential amplifier circuit 8A. Subsequently, the comparison output voltage is negatively fed back to the input terminal of the direct-coupled inverting amplifier circuit 1 via a feedback resistor. In this case, the comparison output voltage is a reference level (the voltage V _{1) of the} output detection signal. ) And have such a magnitude and polarity as to compensate for the variation.

Here, when the DC operating point of each amplifying stage of the direct connection type inverting amplifier circuit 1 fluctuates from the set value for some reason, the reference level of the output detection signal also fluctuates due to the fluctuation. However, as described above, the fluctuation of the reference level is detected as the comparison output voltage in the differential amplifier circuit 8A when the detection signal is not supplied, and the detected comparison output voltage is used as the direct-coupled inverting amplifier circuit. 1, the direct connection type inverting amplifier circuit 1
DC operating point will be returned to its set value,
At the same time, the reference level of the output detection signal is immediately returned to the original level. Therefore, the DC operating point of the direct-coupled inverting amplifier circuit 1 is always kept constant, and the stability of the DC operating point is significantly increased.

As is well known, the DC operating point stability of the direct-coupled inverting amplifier circuit 1 is, as is well known, the magnitude of the gain of the DC feedback circuit 3, and in this embodiment, the differential amplifier circuit 8A of the DC feedback circuit 3 Depends on the magnitude of the DC gain. Here, a feedback capacitance is coupled between the inverting input and the output of the differential amplifier circuit 8A, and its DC gain (for example, about 100 to 120 db) is changed to its AC gain (for example, about 80 db).
Since it is configured to be considerably larger than
If the differential amplifier circuit 8A having the above configuration is used for the DC feedback circuit 3, the DC operating point of the direct-coupled inverting amplifier circuit 1 can be sufficiently stabilized.

In this case, the stabilization of the DC operating point of the direct connection type inverting amplifier circuit 1 is determined by the circuit setting of the DC feedback circuit 3, and the AC signal gain and signal gain frequency characteristics of the direct connection type inverting amplifier circuit 1 are as described above. The stabilization and the characteristics can be independently set since they are determined by the circuit setting of the AC feedback circuit 2. Further, since the differential amplifier circuit 8A mainly performs only the processing of the DC component,
A low-speed differential amplifier circuit 8A can be used.

Further, the synchronous amplifying device of this embodiment is similar to that of FIG.
The present invention is not limited to the case where the detection signal as shown in FIG. 4C is supplied. For example, a detection signal including many interference signals is supplied as in a photoelectric switch device as shown in FIG. The present invention can be similarly applied to a case where a detection signal obtained by an object detection device other than the photoelectric switch device, for example, an object detection device using an ultrasonic sensing signal is supplied.

FIG. 3 is a signal waveform diagram showing signal waveforms and supply timings of various parts in the synchronous amplifying device of the present embodiment when a detection signal including the many interference signals is supplied.

In FIG. 3, (a) shows a detection signal waveform (point E in FIG. 1) input to the direct-coupled inverting amplifier circuit 1, and (b)
Represents the output detection signal waveform of the direct connection type inverting amplifier circuit 1 (F in FIG. 1).
(C), the output hold signal waveform of the second sample hold circuit 11 (point G in FIG. 1), and (d) the comparison circuit 12
3 (a point H in FIG. 1), and the detection signal input to the direct-coupled inverting amplifier circuit 1 is shown in FIG.
As shown in (1), it is composed of a detection signal supplied periodically and many interference signals supplied during the supply of the detection signal.

The operation of the synchronous amplifying apparatus according to the present embodiment when a detection signal including many interference signals as shown in FIG. 3 is supplied operates according to the synchronous amplifying apparatus according to the present embodiment already described in detail. Since the operation is almost the same, the detailed description is omitted.

Even when the synchronous amplifying device of the present embodiment amplifies the detection signal including the many interference signals, the interference signals n _C1 , n _C existing at portions deviating from the supply timing of the detection signal are also used. _Since the AC signal gain of the direct connection type inverting amplifier circuit 1 for _C2 is smaller than the AC signal gain for the detection signal, the interference signal n _C1 ,
The amplification degree of n _C2 is limited, and as shown in FIG. 3B, the levels of the interference signals n _C1 and n _C2 are reduced to a level that is inconspicuous in the output detection signal. Even when the levels of n _C1 and n _C2 are considerably large, the amplification degree is limited, so that the waveforms of the interference signals n _C1 and n _C2 are not clipped in the direct connection type inverting amplifier circuit 1. The functions achieved in the operation of the synchronous amplifying apparatus of the present embodiment, which have already been described in detail, include many functions, such that the DC operating point of the direct-coupled inverting amplifier circuit 1 does not fluctuate due to the clipping of the waveform. This is also achieved in the operation of the synchronous amplifying device of the present embodiment when the detection signal including the interference signal is supplied.

As described above, the functions and effects achieved by the synchronous amplifying apparatus according to the present embodiment are as follows.

First, the AC feedback circuit 2 reduces the amount of negative feedback only at the timing of supply of the detection signal, and the direct connection type inverting amplifier 1 increases the AC signal gain only at the timing. The amplification of noise signals n ₁ , n ₂ and interference signals n _C1 , n _C2, etc. (hereinafter referred to as noise signals, etc.) present in portions deviating from the supply timing is limited, and the noise signals are included in the output detection signal. Etc. drop to inconspicuous levels. Even if the level of the noise signal or the like is considerably large, the waveform of the noise signal or the like is not clipped in the direct-coupled inverting amplifier circuit 1, and the DC operating point of the direct-coupled inverting amplifier circuit 1 based on the waveform clip Does not occur. When a large-level detection signal is input, the direct-coupled inverting amplifier circuit 1 is once in a saturated state. However, a large amount of the negative feedback that is performed at the end of the supply timing of the detection signal causes the saturated state in a short time. Is eliminated, and an operation delay with respect to the detection signal can be prevented. Since the signal band characteristic of the direct-coupled inverting amplifier circuit 1 is a filter characteristic having the same discrete spectrum as the detection signal, the signal band can be narrowed without dulling the pulse signal waveform, and the S / N ratio can be reduced. An excellent synchronous amplifier can be obtained.

When the synchronous amplifying device is applied to a photoelectric switch device, the synchronous amplifying device only needs to have a small dynamic range. Amplifying circuit 8A,
12A also requires a low voltage operation.

Second, the direct-coupled inverting amplifier circuit 1 has its DC operating point constantly maintained at a constant value by the DC negative feedback action of the DC negative feedback circuit 3, so that the stability of the DC operating point is remarkably improved. The reference level of the output detection signal can be maintained at a constant value. In this case, since the DC operating point exhibits high stability, even if the duty cycle of the input detection signal is small, the fluctuation of the DC operating point is extremely small, and the ringing component is added to the detection signal. Is included, the DC operating point does not fluctuate.

Third, since the direct-coupled inverting amplifier circuit 1 does not have a DC bias supply circuit or a differential circuit therein, the direct-coupled inverting amplifier circuit 1 can be operated at high speed. It can be operated in a wide dynamic range even with low voltage driving. In addition, since the direct-coupled inverting amplifier circuit 1 does not have a loop feedback circuit inside, a high signal AC gain can be obtained.

Fourth, since the AC feedback circuit 2 and the DC feedback circuit 3 are respectively connected between the input and output of the direct connection type inverting amplifier circuit 1, the signal AC gain and the signal gain in the direct connection type inverting amplifier circuit 1 are provided. The setting of the frequency characteristics and the setting of the stabilization of the DC operating point can be independently performed.

Fifth, since the differential amplifier 8A in the DC feedback circuit 3 only processes the DC component,
A low speed differential amplifier circuit can be used.

Sixth, all of the synchronous amplifying devices according to the present embodiment use ordinary structures, so that the synchronous amplifying device can be obtained without increasing the overall cost.

In the above-described embodiment, the direct connection type inverting amplifier circuit 1 has a configuration including three transistor amplifier stages. However, the direct connection type inverting amplifier circuit 1 has the above configuration. The present invention is not limited to this, and a one-stage transistor amplifier stage may be used as the direct-coupled inverting amplifier circuit 1.
A MOS inverter gate or a bipolar inverter gate may be used.

In the above embodiment, the AC feedback circuit 2 includes two feedback resistors 22 and 23, one of which is inserted into and removed from the AC feedback circuit 2 by the switch 20. Although the description has been given of the configuration used, the AC feedback circuit 2 is not limited to the configuration described above, and any configuration may be used in which the amount of negative feedback is made variable by supplying a timing signal or a signal similar thereto. Any circuit can be used.

Further, in the above-described embodiment, as the bias voltage generating circuit 8, a feedback capacitance is provided between the inverting input and the output of the differential amplifier circuit 8A, and a feedback resistor is connected in series with the output of the differential amplifier circuit 8A. Are described, but the bias voltage generating circuit 8 is not limited to the above-described configuration, but any circuit may be used as long as the DC voltage gain is larger than the AC voltage gain. A simple circuit can be used.

In addition, the first and second sample-hold circuits are not limited to the circuits described in the above-mentioned embodiments, but may be any circuit as long as the sample-hold circuit function can be achieved. May be used.

[0064]

As described above, according to the present invention,
The AC feedback circuit 2 reduces the amount of negative feedback only at the timing of supply of the detection signal, and the direct-coupled inverting amplifier circuit 1 increases the gain of the AC signal only at the timing. Noise signal n present in
₁ , n ₂ and the interference signals n _C1 , n _C2, etc. (noise signals, etc.) are limited in amplification degree, so that noise signals, etc. in the output detection signal can be reduced to a level that is not noticeable. Further, even if the level of the noise signal or the like is considerably large, the waveform of the noise signal or the like is not clipped in the direct-coupled inverting amplifier circuit 1, and the DC operating point of the direct-coupled inverting amplifier circuit 1 based on the waveform clip is determined. Fluctuation can be prevented. Further, when a large-level detection signal is input, the direct-coupled inverting amplifier circuit 1 is once in a saturated state, but a large amount of the negative feedback is performed at the end of the supply timing of the detection signal. The saturation state is eliminated, and an operation delay with respect to the detection signal can be prevented. Further, the signal band characteristic of the direct-coupled inverting amplifier circuit 1 is a filter characteristic having the same discrete spectrum as the detection signal, so that the signal band can be narrowed without dulling the pulse signal waveform, and S / There are various effects that a synchronous amplifier having excellent N can be obtained.

Further, according to the present invention, the direct-coupled inverting amplifier circuit 1 has its DC operating point set by the DC negative feedback voltage supplied from the DC negative feedback circuit 3, so that the DC operating point is always constant. , And the stability can be significantly increased, and at the same time, the reference level of the output detection signal can be maintained at a constant value. In this case, the direct-coupled inverting amplifier circuit 1 has a very small fluctuation in the DC operating point even when the duty cycle of the input detection signal is small because the DC operating point exhibits high stability. In addition, even if a ringing component is included in the detection signal, there is an effect that the DC operating point does not fluctuate.

In addition, in connection with the above point, the direct connection type inverting amplifier circuit 1 does not have a separate DC bias supply circuit and a differential circuit inside. There is also an effect that the amplifier circuit 1 can be operated at a high speed and can be operated with a wide dynamic range even under a low voltage.

According to the present invention, the AC feedback circuit 2 and the DC feedback circuit 3 are connected between the input and output of the direct-coupled inverting amplifier circuit 1.
Are coupled to each other, there is an effect that the setting of the signal AC gain and the signal gain frequency characteristic and the setting of the stabilization of the DC operating point in the direct connection type inverting amplifier circuit 1 can be independently performed.

Further, according to the present invention, when a synchronous amplifying device is configured, only ordinary components are used, so that there is an effect that a low-cost synchronous amplifying device can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a synchronous amplifying device according to the present invention.

FIG. 2 is a signal waveform diagram showing signal waveforms and supply timings of respective units in the synchronous amplifying device of the embodiment of FIG.

FIG. 3 is a signal waveform diagram showing signal waveforms and supply timings of respective units when a detection signal obtained by the photoelectric switch device of FIG. 4 is supplied to the synchronous amplifying device of the embodiment of FIG. 1;

FIG. 4 is a block diagram showing an example of a photoelectric switch device to which the synchronous amplifying device according to the present invention is applied.

FIG. 5 is a block diagram showing an example of an object detecting means in a conventional photoelectric switch device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 direct-coupled inverting amplifier circuit 1 A, 1 B, 1 C amplifying transistor 2 AC feedback circuit 3 DC feedback circuit 4 input coupling capacitance 5 signal input terminal 6 signal output terminal 7 first sample and hold circuit 8 bias voltage generation circuit 8 A, 12 A differential Amplification circuit 10 Reference voltage source 11 Second sample-hold circuit 12 Comparison circuit 13 Output terminal of comparison circuit 15 Timing generation circuit 16 Preamplifier 17 Photodiode (optical sensor) 18 Light-emitting diode (LED) 19 LED drive circuit 20 Switch 21, 24 Sampling Switch 22, 23 Feedback resistor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/34 H03F 3/08 H03G 3/20-3/34

Claims (8)

(57) [Claims] An AC feedback circuit including a direct connection type inverting amplifier circuit to which a periodic detection signal is supplied, a switch connected between input and output of the direct connection type inverting amplifier circuit, and a switch for varying a signal feedback amount; A direct current feedback circuit including a first sample and hold circuit; and a second sample and hold circuit connected to the output side of the direct-coupled inverting amplifier circuit. All sampling of the hold circuit is performed in synchronization with the periodic detection signal, and the DC feedback circuit is configured to set the DC operation bias voltage of the direct-coupled inverting amplifier circuit by the feedback output. A synchronous amplifying device. 2. A switch in the AC feedback circuit is switched to reduce a signal negative feedback amount during a supply period of the detection signal and increase a signal negative feedback amount during a non-supply period of the detection signal. The synchronous amplifying device according to claim 1, wherein 3. The synchronous amplifying device according to claim 1, wherein said first sample and hold circuit performs sampling during a period in which said detection signal is not supplied. 4. The synchronous amplifying device according to claim 1, wherein said second sample and hold circuit performs sampling during a supply period of said detection signal. 5. The DC feedback circuit further includes at least an operating point extracting circuit for extracting a DC component and a bias voltage generating circuit, and a DC operating bias voltage of the direct connection type inverting amplifier circuit based on an output of the bias voltage generating circuit. 2. The synchronous amplifying device according to claim 1, wherein the setting is performed. 6. The apparatus according to claim 2, wherein the bias voltage generating circuit in the DC feedback circuit includes a differential amplifier circuit configured so that a DC signal gain is larger than an AC signal gain. The synchronous amplifying device according to the above. 7. The direct-coupled inverting amplifying circuit includes a circuit having no individual DC bias supply means in each amplifying stage and having no differential circuit portion. The synchronous amplifying device according to the above. 8. A comparison circuit according to claim 1, wherein a comparison circuit is connected to an output side of said second sample and hold circuit.
The synchronous amplifying device according to the above.