JPH05235719A - Random pulse position modulation circuit - Google Patents

Abstract

PURPOSE:To attain random pulse position modulation with an excellent modula tion degree in response to white noise without being affected by a temperature change or dispersion in components. CONSTITUTION:An output pulse A of a frequency divider circuit 2 is converted into a triangle pule B at a waveform conversion circuit 3 and the resulting signal is compared with a white noise F resulting from being outputted from a white noise generating means 5 whose frequency band is limited at a band amplifier 7 as a prescribed band by a comparator 4. An output pulse D of the comparator 4 is given to a one-shot multivibrator circuit 6, from which a pulse E of a prescribed width is obtained. On the other hand, the white noise F is subject to peak hold processing by a peak hold circuit 8 and its output level and a reference voltage G are compared by an error amplifier 10. The white noise generating means 5 is controlled by an error voltage H from the error amplifier 10 so that the level of the white noise F is set between a maximum level and a minimum level of the pulse B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a random pulse position modulation circuit suitable for use in a photoelectric switch or the like for determining the presence or absence of an object by projecting light and detecting the presence or absence of reflected light or transmitted light thereof. ..

[0002]

2. Description of the Related Art A photoelectric switch is known as a means for detecting the presence or absence of an object moving on a conveyor line or the like. This is to determine the presence or absence of an object by projecting light onto the path of the object and detecting the presence or absence of reflected light from the moving object. In such a photoelectric switch, in order to eliminate the influence of ambient light, reduce power consumption, prevent mutual interference, etc., the projection light is pulsed and projected intermittently (hereinafter, this projection light is Sensing light).

Usually, a plurality of photoelectric switches are used to detect the presence or absence of an object. For example, in a conveyor line,
A plurality of photoelectric switches are installed at one location, such as a photoelectric switch for projecting light from the lateral direction, a photoelectric switch for projecting light from below, and a photoelectric switch for projecting light from above, so that object detection can be performed more accurately. However, when a plurality of photoelectric switches are installed at one location and each photoelectric switch continuously projects light, each photoelectric switch may receive the sensing light projected by the other photoelectric switches.
This is called mutual interference as described above.In a photoelectric switch, light is emitted intermittently so that the light emission timing does not overlap with other photoelectric switches, and the reflected light from its own light emission and the light emission of other photoelectric switches cause Light received (interference light)
Need to be distinguished.

As a method of preventing such mutual interference, for example, as disclosed in Japanese Patent Publication No. 60-51043, the output of the gate circuit for providing the interference discrimination circuit and extracting the pulse due to the light reception of the light receiving portion is provided. Whether the pulse is due to interference light is discriminated, and when the pulse is due to interference light, the phase of the pulse for determining the light emission timing is advanced or delayed, and JP-A-61-138192.
As disclosed in the publication, a pulse signal generated by receiving the interference light is extracted, a pulse having the same frequency as the pulse signal but a phase different from that of the pulse signal is generated to drive the light projecting unit, and the interference light has the same frequency. In addition, light is emitted with different phases. As disclosed in Japanese Patent Laid-Open No. 63-263917, when a pulse matching the light emitting timing is obtained from the light receiving portion, the light emitting period is changed from the reference period. It is known that the light emitting period is returned to the original reference period when a predetermined number of such pulses are obtained by sequentially shifting.

However, each of the above-mentioned methods has a problem that a means of complicated circuit configuration is required to prevent mutual interference.

On the other hand, the applicant of the present invention has found that white noise (random noise) generated by the white noise generating means.
We proposed a photoelectric switch in which a random pulse position modulation circuit (hereinafter, referred to as an R-PPM circuit) is configured to position-modulate a pulse by using the pulse modulation, and the projection timing is determined by the output pulse of the R-PPM circuit ( Japanese Patent Application No. 3-103542).

The R-PPM circuit will be described with reference to FIG. In the figure, the pulse output from the pulse generation circuit 1 is frequency-divided by the frequency dividing circuit 2, and becomes a pulse A having a square wave shape and a predetermined cycle with a duty ratio of 50%, for example. The square-wave pulse A is subjected to waveform conversion by the waveform conversion circuit 3, becomes a triangular wave (or sawtooth wave) pulse B, and is supplied to the comparator 4. In the comparator 4, the level of the pulse B and the white noise C from the white noise generating means 5 are compared. For example, when the level of the white noise C is equal to or higher than the level of the pulse B, the pulse D output from the comparator 4 is obtained. .. This pulse D is converted by the one-shot circuit 6 into a pulse E having a constant time width. This pulse E determines the projection timing of the photoelectric switch.

According to such a photoelectric switch, the sensing light is generated completely independently and at random between the photoelectric switches without complicating the circuit structure, and thus the probability of mutual interference becomes negligible.

[0009]

In the R-PPM circuit as described above, the output pulse E of the one-shot circuit 6 is accurately random-position-modulated with respect to the square wave pulse A output from the frequency dividing circuit 2. It is necessary to ensure that the output pulse E of the one-shot circuit 6 is at a position corresponding to the white noise C for this purpose.

However, the white noise generated has a very wide frequency distribution, which is why the R-PPM
The degree of modulation becomes too large for a circuit. Such R-P
In order to process the pulse output from the PM circuit, an expensive circuit having a wide band and a high response speed is required. Also,
The white noise generation means 5 is affected by temperature changes and component variations, and the amplitude of the white noise C fluctuates. When the amplitude of the white noise C fluctuates in this way, the random position modulation is also affected by this. R
-The PPM circuit originally utilizes the randomness of the frequency of the white noise and modulates the position of the pulse according to the random change of the frequency. However, if the amplitude of the white noise C fluctuates, this fluctuation occurs. Not only the position of the pulse modulated in accordance therewith changes, but the level of the white noise C cannot exceed the level of the pulse B, and the pulse D cannot be obtained from the comparator 4, or the white noise C The amplitude becomes too large and exceeds the level of pulse B for a long time.
In some cases, random position modulation cannot be performed.

It is an object of the present invention to provide a random pulse position modulation circuit which solves the above problem and can surely perform pulse random position modulation by white noise.

[0012]

To achieve the above object, the present invention provides first means for limiting the frequency band of white noise output from white noise generating means to a predetermined value, and the first means. The second means for peak-holding the white noise output from the second means and the third means for comparing the output level of the second means with the reference level are provided, and the white noise is output by the output of the third means. Control the generating means.

[0013]

When the output of the second means fluctuates so that the amplitude change of the white noise is out of the predetermined range, the level changes accordingly, but this fluctuation is detected by the third means and the amplitude is changed. The white noise generating means is controlled so that the fluctuation is eliminated to fall within the predetermined range. As a result, the amplitude of the white noise output from the white noise generating means and the frequency band of which is limited by the first means changes within a certain range, and the frequency of the change also falls within a favorable range, The comparator reliably performs level comparison with the triangular wave or sawtooth wave pulse, and the random position modulation is accurately performed with a good degree of modulation.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a random pulse position modulation circuit according to the present invention, in which 7 is a band amplifier,
Reference numeral 8 is a peak hold circuit, 9 is a reference voltage source, and 10 is an error amplifier. Components corresponding to those in FIG.

In this figure, the part surrounded by the alternate long and short dash line is this embodiment. The white noise C output from the white noise generating means 5 is limited to a predetermined frequency band by the band amplifier 7, and then is compared with the output pulse B of the waveform conversion circuit 3 by the comparator 4 as white noise F, and at the same time, The peak level is also supplied to the peak hold circuit 8 to hold the peak level. The output level of the peak hold circuit 8 is level-compared with the reference voltage G from the reference voltage source 9 in the error amplifier 10, and these error voltages H
Is output. The white noise generating means 5 is controlled by the error voltage H so that the difference between the output level of the peak hold circuit 8 and the reference voltage G becomes a predetermined value (for example, zero).

Therefore, the peak hold circuit 8 is used to detect the level fluctuation of the white noise F. Since the peak hold circuit 8 has a high response speed, the white noise F
The white noise generating means 5 is controlled in quick response to the level fluctuation of the above, and therefore, the amplitude change of the white noise F output from the band amplifier 7 is always a triangular or sawtooth waveform conversion circuit. Output pulse B of 3
Is maintained between the minimum level and the maximum level, and the white noise F is limited to a desired frequency band, and does not become random noise in a too wide frequency band. Therefore, the pulse D is always obtained from the comparator 4 for each cycle of the pulse A, and the one-shot circuit 6
A pulse E whose pulse position is accurately modulated depending on the frequency of the white noise C is obtained.

The frequency band of the white noise F output from the band amplifier 7 is preferably in the frequency range of about 1/10 to 1 times the repetition frequency of the output pulse B of the waveform conversion circuit 3 (eg, the frequency range). When the repetition frequency of the pulse B is 900 kHz, the frequency band of the white noise F is 90 to 900 kHz), whereby one pulse E can be obtained from the one-shot circuit 6 for each cycle of the pulse B, which is preferable. Random pulse position modulation of modulation degree is used.

FIG. 2 is a circuit diagram showing a specific example of each part in FIG. 1, in which 11 and 12 are transistors, 13 is a Zener diode, 14 is a transistor, 15 is a resistor,
Reference numeral 16 is a differential amplifier, and parts corresponding to those in FIG.

In the figure, white noise generating means 5
Generates white noise C by utilizing the noise characteristic of the Zener diode 13. The collector current of one of the transistors 11 forming the current mirror circuit is supplied to the Zener diode 13, and the noise characteristic of the Zener diode 13 is determined according to the collector current. The white noise C generated in the Zener diode 13 is output from the white noise generating means 5 via the emitter follower and supplied to the band amplifier 7.

On the other hand, the collector of the other transistor 12 forming the above-mentioned current mirror circuit in the white noise generating means 5 is grounded via the transistor 14 and the resistor 15 in the error amplifier 10, and is connected to the base of this transistor 15. The error voltage H output from the dynamic amplifier 16 is applied.

Therefore, the level of the white noise F output from the band amplifier 7 is the output pulse B of the waveform conversion circuit 3.
The current flowing through the Zener diode 13 is set so as to be between the maximum level and the minimum level of
Assuming that the changing amplitude of the white noise F deviates from the specified range, an error voltage H between the output level of the peak hold circuit 8 and the reference voltage G is output from the differential amplifier 16, which controls the transistor 14. It Therefore, in the white noise generating means 5, the collector current of the transistor 12 changes, but the transistors 11 and 12 forming the current mirror circuit operate so that the collector currents of the transistors 11 and 12 are always equal to each other. The current also changes like the collector current of the transistor 12, and therefore the Zener diode 1
The current flowing in 3 also changes, and its noise characteristics change.

In this way, the white noise generation means 5 is controlled so that the error voltage H output from the differential amplifier 16 becomes a predetermined value such as zero, and the level of the white noise F output from the band amplifier 7. Always changes within the above-mentioned fixed range.

In the band amplifier 7, here, bandpass filters 17 and 18 of two stages are connected in cascade, and the band-limited white noise F is amplified by the comparator 4 to a voltage level required for comparison. There is. Circuits other than those described above have a circuit configuration that is normally used, and therefore description thereof is omitted.

Next, an example of the photoelectric switch using the above embodiment will be described with reference to FIG. In the figure, 19 is the R-PPM circuit of the above-mentioned embodiment, and the parts corresponding to those of FIG.

As described with reference to FIG. 1, the output pulse A of the frequency dividing circuit 2 is supplied to the R-PPM circuit 19 and the pulse E subjected to random pulse position modulation is obtained. This pulse E
Is a transistor 21 for switching via a resistor 20.
And is turned on for that pulse period. Therefore, when the transistor 21 is turned on, a drive current flows through the LED 22,
Sensing light is randomly projected from the LED 20 in synchronization with the pulse E.

On the other hand, when the photodiode 23 receives light, it generates a pulse having a pulse width close to the light receiving period. This pulse is amplified by the amplifier 24 and supplied to the comparator 25 as a pulse I. This comparator 2
5 compares the level of this pulse I with the reference level, and outputs "L".
The (low level) binarized pulse J is output. If there is an object (not shown) in the vicinity, the sensing light from the LED 22 is reflected by this object and is received by the photodiode 23, so that the pulse I whose timing coincides with the output pulse E of the R-PPM circuit 19 is obtained. However, when other photoelectric switches are installed close to each other, the sensing light may be received by the photodiode 23 as interference light, and as a result, the pulse I due to the interference light is also obtained. Each of these pulses I is binarized by the comparator 26, and the pulse J of "L" is obtained. This pulse J is supplied to the D-FF circuit 26 as a gate circuit together with the output pulse E of the R-PPM circuit 19.

The D-FF circuit 26 uses the data input D as the output pulse J of the comparator 25 and the clock CK as the output pulse E of the R-PPM circuit 19. The D-FF circuit 26 has a rising edge (front edge) of the “H” pulse E.
The pulse J level is sampled and held. As a result, the pulse E of the output pulse J of the comparator 25 is
Only the pulse that coincides with the timing of D-FF circuit 26
It is extracted and held by. Therefore, the pulse J whose timing does not match the pulse E is removed by the D-FF circuit 26. When N pulses J whose timing coincides with the pulse E are sequentially supplied, the D-FF circuit 26 outputs the N pulses.
A pulse K of "H" that rises at the timing of the first pulse of the individual pulses and falls at the timing of the first pulse E after the Nth pulse is output.

The shift register 27 as an integrating circuit is R
-The falling edge of the output pulse E of the PPM circuit 19 is used as the clock CK, and the D-FF circuit 26 is provided for each clock CK.
The output K of is taken in and sequentially shifted. So now,
When pulses K from D-FF circuit 26 "H" is output, each Q _A output becomes "H" of the shift register 27 by the pulse K is captured by the clock CK, which is subsequently clock CK supplied to Q _B, Q _C, Q _D
It becomes "H" in the order of output. Therefore, when the timing pulse E is incorporated into the D-FF circuit 26 a pulse J is continuously four or more that match, the shift register 27 Q _A to Q _D
The outputs become "H" at the same time.

The determination circuit 28 is the Q _{A of the} shift register 27.
AND gate 29 which receives the to Q _D output, as well as a set timing a rising edge of the output of the NOR circuit 30 and an AND gate 29 which receives these Q _A to Q _D output, the rising edge of the output of the NOR circuit 30 It is composed of an RS-FF circuit 31 for reset timing. When the AND gate 29 to all Q _A to Q _D output of the shift register 27 becomes "H" rise, these even one "L"
Then, the set pulse L of "H" that falls is generated,
At the rising edge of the set pulse L, the RSFF circuit 31 is set. The NOR circuit 30 is the shift register 2
When any one of the Q _{A to} Q _D outputs of 7 falls to "H", a reset pulse M of "L" which rises when all of them become "L" is generated, and R is generated at the rising edge of the reset pulse M. -The S-FF circuit 31 is reset. As a result, the output of the R / S-FF circuit 31, that is, the determination circuit 28
Becomes Q _A to Q _D output of all shift registers 27 all from a "H" to "L" and becomes up to a period of "H" of the output N.

When the pulse J whose timing coincides with the output pulse E of the R-PPM circuit 19 is sequentially obtained from the comparator 25 by the operation of each of the above parts, the judging circuit 28
Output N becomes "H", which means that the sensing light from the LED 22 is reflected by the object and the photodiode 23
Is received, that is, the object is present. When the output N of the judgment circuit 28 becomes "H",
The transistor 32 turns on and the level at the output terminal 33 decreases, which indicates the presence of an object.

As described above, in this photoelectric switch, the sensing light is randomly generated for each pulse A at the position corresponding to the white noise, and the generation start timing of this sensing light is also random. When each photoelectric switch generates sensing light in this way, the probability of mutual interference between photoelectric switches becomes extremely small.

In the above, the R-PPM circuit according to the present invention is used for the photoelectric switch, but it goes without saying that the R-PPM circuit can be applied to any device using random pulses.

[0033]

As described above, according to the present invention,
The input pulse is subjected to pulse position modulation with a favorable degree of modulation according to white noise without being affected by temperature changes, component variations, and the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a random pulse position modulation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of each part in FIG.

FIG. 3 is a block diagram showing an application example of a random pulse position modulation circuit according to the present invention.

FIG. 4 is a block diagram showing a random pulse position modulation circuit which is the basis of the present invention.

[Explanation of symbols]

 3 Waveform conversion circuit 4 Comparator 5 White noise generating means 6 One-shot circuit 7 Band amplifier 8 Peak hold circuit 9 Reference voltage source 10 Error amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisashi Murata 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd.

Claims (1)

[Claims] 1. A waveform converting means for converting an input pulse into a square wave or sawtooth wave pulse, white noise generating means, white noise output from the white noise generating means and an output pulse of the waveform converting means. In a random pulse position modulation circuit including a comparator for level comparison and a waveform shaping means for making an output pulse of the comparator a pulse having a constant time width, a frequency band of white noise output from the white noise generating means is set to a predetermined value. First means for limiting, second means for peak-holding white noise output from the first means, and third means for detecting an error between an output level of the second means and a reference level And the white noise output from the first means is output by the comparator to the output pulse of the waveform converting means. By using the white noise for level comparison and controlling the white noise generating means by the output of the third means, the change of the level of the white noise output from the first means is limited within a certain range. A random pulse position modulation circuit characterized by the above.