JP5414570B2 - AC signal generator - Google Patents

Description

  The present invention relates to an AC signal generator, and particularly to an AC signal generator capable of generating an AC signal such as an attenuated AC signal with a simple configuration.

  Conventionally, in a magnetic proportional type DC current sensor, a magnetic balance type DC current sensor, a CRT, etc., the magnetism of the magnetic material by external magnetism adversely affects the performance and function, so the demagnetizing current is applied to the coil wound around the magnetic material. It is common practice to demagnetize by flowing a current.

  As the demagnetizing current, an attenuated AC signal is used in which the AC signal is gradually reduced from a large current and ends with an amplitude of zero. As a method of generating an attenuated AC signal, there is a method of creating an attenuated signal by applying a Wien bridge oscillation circuit as described in Patent Document 1, for example. In the case of a CRT, there is an example in which a commercial AC power supply is used and a thermistor is used in series with a demagnetizing coil to attenuate the current by increasing the resistance value due to heat generation due to the demagnetizing current.

Japanese Utility Model Publication No. 51-108670

  In the conventional method of generating a damped AC signal as described above, when a Wien bridge oscillation circuit is used, since it is an analog oscillation circuit, there are many components that determine its oscillation conditions and attenuation characteristics, and variations in component characteristics and aging There is a problem that the signal characteristics may be shifted or changed. In addition, when a thermistor is used, an alternating current is required first, and since the current is limited by heat generation, there is a problem that wasteful power is consumed.

  An object of the present invention is to solve the above-described conventional problems and to provide an AC signal generator capable of generating an attenuated AC signal with a simple configuration.

  The AC signal generator of the present invention receives a rectangular wave generating means for generating two rectangular waves having slightly different frequencies and the two rectangular waves, and the voltage of the other rectangular wave is obtained from the voltage value of one rectangular wave. A main feature is that it includes a bipolar differential amplifying means for outputting a difference obtained by subtracting a value, and a low-pass filter means for inputting an output signal of the differential amplifying means and outputting an AC signal. To do.

Further, the AC signal generator described above is characterized in that the rectangular wave generating means is constituted by a microcomputer that outputs two unipolar rectangular wave signals.
In the AC signal generator described above, the microcomputer generates two rectangular waves having an initial phase difference of 180 degrees and slightly different frequencies, and the phase difference between the two rectangular waves. Another feature is that the generation of the rectangular wave is terminated when the value becomes zero.
In the AC signal generator described above, the two rectangular waves are also characterized in that the length of logic 1 is equal.

The present invention has the following effects.
(1) By using a microcomputer for waveform generation, a circuit for attenuation is not particularly required, and a stable attenuation signal can be obtained without being affected by external parts.
(2) Since the attenuation characteristics of the attenuated AC signal can be changed only by software, the quality, expandability, and productivity can be improved.
(3) Regarding the attenuation characteristics of the damped AC signal, the difference between the frequencies of the two signals is important, and a crystal oscillator or the like is not necessarily required as the oscillation source. Is suitable.

FIG. 1 is a block diagram showing a configuration of an AC signal generator of the present invention. FIG. 2 is a circuit diagram showing the configuration of the AC signal generator of the present invention. FIG. 3 is a flowchart showing the processing contents of the microcomputer according to the first embodiment of the present invention. FIG. 4 is a waveform diagram showing waveforms at various parts in the first embodiment of the present invention. FIG. 5 is a flowchart showing the processing contents of the microcomputer according to the second embodiment of the present invention. FIG. 6 is a waveform diagram showing waveforms at various parts in the second embodiment of the present invention.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an AC signal generator of the present invention. The one-chip microcomputer 10 is a known one-chip microcomputer circuit that is commercially available. The microcomputer 10 includes a CPU, a ROM, a RAM, a digital input / output circuit, a hardware timer circuit, and the like. As the microcomputer 10, any commercially available one-chip microcomputer can be adopted as long as it has the functions and processing speed of the present invention.

  The ROM stores a program for executing processing to be described later, and the microcomputer 10 generates rectangular wave generating means for outputting two unipolar rectangular waves of A wave and B wave based on the processing of this program. Function as. The A wave and the B wave are rectangular waves having slightly different frequencies, the initial phase difference between the two rectangular waves is 180 degrees (half cycle), and the rectangular wave when the phase difference between the two rectangular waves becomes zero. End the occurrence of.

  The differential amplifier circuit 11 receives two rectangular waves of A wave and B wave, and outputs a difference (B−A) obtained by subtracting the voltage value of the other rectangular wave from the voltage value of one rectangular wave. The differential amplifier means can be realized by a known operational amplifier. The amplification factor may be 1, for example.

  The low-pass filter circuit 12 functions as a low-pass filter unit that receives the output signal of the differential amplifier circuit 11 and outputs an AC signal. The low-pass filter circuit 12 can actually be realized by a known active filter circuit using an operational amplifier.

  FIG. 2 is a circuit diagram showing the configuration of the AC signal generator of the present invention. As described above, the microcomputer 10 is a known one-chip microcomputer incorporating a program related to the present invention. The microcomputer 10 is operated by a unipolar power supply (for example, Vcc = 3 V), and outputs two unipolar rectangular waves of A wave and B wave based on an activation signal from the outside. The resistor 20 and the capacitor 21 are a reset circuit when the power is turned on.

  The differential amplifier circuit 11 is a bipolar differential amplifier circuit realized by a known operational amplifier, and all the resistors 23 to 26 may have the same value and an amplification factor of 1. As the power source, for example, ± 12 V is supplied as a bipolar power source.

  As the low-pass filter circuit 12, a third-order active filter circuit using an operational amplifier is employed. As a power source, for example, ± 12 V is supplied as a bipolar power source. As the frequency characteristics, for example, the cutoff frequency may be about 60 Hz. Note that the type and stage number (order) of the filter circuit may be changed by enemy selection depending on the application of the signal. For degaussing purposes, signal distortion does not matter so much, and the waveform may be a substantially symmetrical waveform.

  FIG. 3 is a flowchart showing the processing contents of the microcomputer according to the first embodiment of the present invention. When the power is turned on, the process waits until an activation signal for generating an attenuated AC signal from an external circuit (not shown) is input in S10, and if it is input, the process proceeds to S11. In S11, the counting time is set in the hardware timer circuit and started. The counting time may be 25 μs, for example. This timer circuit generates a timer interrupt every 25 μs.

  In S12, the A-wave and B-wave soft timers are reset. That is, the time-up value is set and the count value is initialized = 0. The waveform counter is also reset to zero. The soft timer is a program that counts up (+1) the count value stored in the register or RAM by a timer interrupt and determines whether or not a preset time-up value has been reached.

  In the embodiment, 10 ms / 25 μs = 400 is set as the time-up value for counting tA = 1/50 × 1/2 = 1/100 = 10 ms in the A wave timer. In addition, 10.025 ms / 25 μs = 401 is set as a time-up value for counting 1 / 49.875 × 1/2 = 1 / 99.75 = 10.025 ms in the B wave timer. Therefore, the A wave has a frequency of 50 Hz and the B wave has a frequency of 49.875 Hz.

  In S13, the logic 1 (+ Vcc) that is the initial value of the A wave and the logic 0 (0 V) that is the initial value of the B wave are output to the respective digital output terminals. In the initial value, the phase shift between the A wave and the B wave is 180 degrees. In S14, the process waits until there is a hardware timer interrupt. If an interrupt occurs, the process proceeds to S15. In S15, 1 is added to the A and B wave soft timer count values.

  In S16, it is determined whether or not the A-wave timer has expired (whether a predetermined time has elapsed since activation = count value has reached 400). If the determination result is negative, the process proceeds to S20. In this case, the process proceeds to S17. In S17, the output value of the A wave is inverted (0V for + Vcc, + Vcc for 0V), and the A wave timer is set to 400 corresponding to tA, and the A wave timer is started again (count value is set to 0). To do.

  In S18, 1 is added to the value of the waveform counter on the memory or register. In S19, it is determined whether or not the value of the waveform counter has reached a predetermined value. If the determination result is negative, the process proceeds to S14, but if the determination is affirmative, the generation process of the attenuated AC signal is completed. Both the output values of the A wave and the B wave are set to 0, and the process proceeds to S10.

  The predetermined value of the waveform counter is a value corresponding to the time when there is no phase shift between the A wave and the B wave which has been shifted by 180 degrees (half cycle, 10 ms at 50 Hz) at the start-up, and the shift is small by 25 μs every 10 ms. Therefore, when the value of the waveform counter is 400 (10 ms × 10 ms / 25 μs = 10 ms × 400 = 4 seconds), there is no phase shift.

  In S20, it is determined whether or not the B-wave timer has timed up (predetermined time has elapsed since activation = count value has become 401). If the determination result is negative, the process proceeds to S14. To S21. In S21, the output value of the B wave is inverted (+ Vcc if 0V, 0V if + Vcc), and 401 corresponding to tB is set in the B wave timer, the B wave timer is started again, and the process proceeds to S14.

  FIG. 4 is a waveform diagram showing waveforms at various parts in the first embodiment of the present invention. In the present invention, a difference signal between an A wave and a B wave, which are rectangular waves having slightly different frequencies, is used. The A wave and the B wave are generated by the microcomputer 10 as described above. Here, the A wave and the B wave are unipolar (single power supply + Vcc).

  Next, a B wave and an A wave are respectively added to the + input and the − input of the differential amplifier circuit 11. The differential amplifier circuit 11 uses a bipolar circuit (both power supplies (±)). When the amplification factor is 1, the difference that is the output of the differential amplifier circuit 11 when the A wave applied to the − input is + Vcc (logic 1) and the B wave applied to the + input is 0 V (logic 0). The signal is -Vcc.

  On the other hand, when the A wave applied to the-input is 0 V and the B wave applied to the + input is + Vcc, the difference signal that is the output of the differential amplifier circuit 11 is + Vcc. When both the A wave and the B wave are 0V or + Vcc, the difference signal that is the output of the differential amplifier circuit 11 is 0V.

  As a result, the difference signal that is the output of the differential amplifier circuit 11 becomes a bipolar pulse as shown in the figure, and the pulse width becomes narrower as time passes. This signal is passed through a low-pass filter (LPF) circuit 12 to form an attenuated alternating current waveform close to a sine wave.

  The frequency of the A wave is a desired signal frequency (for example, Fa = 50 Hz). The signal length (T) is an integral multiple of the period of the A wave (for example, 4 seconds). The B wave is a signal whose frequency is lower than that of the A wave, whose phase is shifted by 1/2 period in T seconds. That is, Fb = ((the number of A wave cycles for T seconds−½ cycle) ÷ T) = ((T * Fa−0.5) / T). Therefore, for example, when T is 4 seconds and the frequency of the A wave is 50 Hz, Fb = 49.875 Hz.

  In the first embodiment, the generation of an attenuated AC signal whose amplitude is Vcc to 0 at a frequency of 50 Hz and a signal time of 4 seconds has been disclosed. The amplitude at the start and end of AC signal generation can be controlled by a program.

  In the first embodiment, since the width of the rectangular wave becomes shorter every half cycle of the AC signal, strictly speaking, the + side waveform and the − side waveform are not equal. The second embodiment generates an AC signal having a more equal positive and negative waveform than the first embodiment. The second embodiment is different from the first embodiment only in the program of the microcomputer 10, and the circuit is the same as the first embodiment. In the second embodiment, a waveform having the same length is balanced and output on the plus side and the minus side of the difference signal every cycle.

  In the second embodiment, the A wave is the same as the first embodiment. For the B wave, the period is the same as in the first embodiment, but the time when the output is logic 1 (Vcc) is the same as the time “tA” when the output of the A wave is logic 1 (Vcc). Therefore, the duty ratio is smaller than 50%.

  The logical 0 (0 V) time tB of the B wave is obtained by the following formula. The frequency Fa of the A wave is a desired signal frequency (for example, Fa = 50 Hz, tA = 10 ms). The signal length (T) is an integral multiple of the period of the A wave (for example, 4 seconds). Since tB is a time that is longer than tA by tA in total for T seconds, tB = tA + tA / (Fa * T), and the frequency is Fb = 1 / (tA + tB).

  Therefore, for example, when T is 4 seconds and the frequency of the A wave is 50 Hz, tA = 10 ms, tB = 10 ms + (10 ms / (50 × 4)) = 10.05 ms, and Fb = 1 / 20.05 ms≈49.875 Hz. It becomes.

  FIG. 5 is a flowchart showing the processing contents of the microcomputer according to the second embodiment of the present invention. When the power is turned on, the process waits until an activation signal for generating an attenuated AC signal from an external circuit (not shown) is input in S30, and if it is input, the process proceeds to S31. In S31, the counting time is set in the hardware timer circuit and started. The counting time may be 25 μs, for example. This timer circuit generates a timer interrupt every 25 μs.

  In S32, the A-wave soft timer is reset. That is, the time-up value is set and the count value is initialized = 0. The soft timer is a program that counts up (+1) the count value stored in the register or RAM by a timer interrupt and determines whether or not a preset time-up value has been reached. In the embodiment, 10 ms / 25 μs = 400 is set as the time-up value for counting tA = 1/50 × 1/2 = 1/100 = 10 ms in the A wave timer.

  In S33, logic 1 (+ Vcc) which is the initial value of the A wave and logic 0 (0 V) which is the initial value of the B wave are output to the respective digital output terminals. In the initial value, the phase shift between the A wave and the B wave is 180 degrees. In S34, the process waits until there is a hardware timer interrupt. If an interrupt occurs, the process proceeds to S35. In S35, 1 is added to the A-wave soft timer count value.

  In S36, it is determined whether or not the A-wave timer has expired (whether a predetermined time has elapsed since activation = count value has become 400). If the determination result is negative, the process proceeds to S34, but affirmative In this case, the process proceeds to S37. In S37, the output values of A wave and B wave are inverted (+ Vcc is set to 0V, and 0V is set to + Vcc), and A wave timer is set by setting 400 corresponding to tA to both A wave timer and B wave timer. And both B wave timers are activated (count value is set to 0). In addition, the waveform counter is reset to zero.

  In S38, the process waits until there is a hardware timer interrupt. If an interrupt occurs, the process proceeds to S39. In S39, 1 is added to the soft timer count values of the A and B waves. In S40, it is determined whether or not the A-wave timer has expired (whether a predetermined time has elapsed since activation = a count value has reached 400). If the determination result is negative, the process proceeds to S44. If yes, the process proceeds to S41.

  In S41, the A-wave output value is inverted (+ Vcc is set to 0V, and 0V is set to + Vcc), and the A-wave timer is set to 400 corresponding to tA to start the A-wave timer (count value is set to 0). . In S42, 1 is added to the value of the waveform counter. In S43, it is determined whether or not the value of the waveform counter has reached a predetermined value. If the determination result is negative, the process proceeds to S44, but if the determination is affirmative, the generation process of the attenuated AC signal is completed. Both the output values of the A wave and the B wave are set to 0, and the process proceeds to S30.

  The predetermined value of the waveform counter is a value corresponding to the time when there is no phase shift between the A wave and the B wave, which is shifted by 180 degrees (half cycle, 10 ms at 50 Hz) at the start-up, and the shift is small by 50 μs every 20 ms. Therefore, when the value of the waveform counter is 400 (10 ms × 20 ms / 50 μs = 10 ms × 400 = 4 seconds), there is no phase shift.

  In S44, it is determined whether or not the B-wave timer has expired (predetermined time has elapsed since startup = count value has reached 400 (when output is 0) or 402 (when output is 1 (Vcc))). If the determination result is negative, the process proceeds to S38, but if the determination result is affirmative, the process proceeds to S45.

  In S45, the output value of the B wave is inverted. (If 0V, set to + Vcc, + Vcc, set to 0V) In S46, it is determined whether or not the output value of the B wave is 0. If the determination result is negative (output value is 1), the process proceeds to S47. In this case, the process proceeds to S48. In S47, 400 corresponding to tA is set in the B wave timer, the B wave timer is started again, and the process proceeds to S38. In S48, 402 (= 10.05 ms / 25 μs) corresponding to tB is set in the B wave timer, the B wave timer is started again, and the process proceeds to S38.

  FIG. 6 is a waveform diagram showing waveforms at various parts in the second embodiment of the present invention. In the second embodiment, a difference signal between the A wave and the B wave, which is a rectangular wave having a single polarity (single power supply + Vcc) slightly different in two frequencies, is used. However, the time when the output of the A wave and the B wave is logic 1 (Vcc) is the same (= tA), and only the time when the output is logic 0 (0 V) is different.

  Next, a B wave and an A wave are respectively added to the + input and the − input of the differential amplifier circuit 11. The subsequent operation is the same as that of the first embodiment. In the difference signal, except for the first half cycle, the length of the + side rectangular wave is equal to the length of the − side rectangular wave for each cycle, and the length is gradually shortened.

  Although the embodiments have been described above, the following modifications are also conceivable. In the embodiment, the example of generating the A wave and the B wave using a microcomputer is disclosed, but the A wave and the B wave may be generated by a logic circuit, for example. In addition to the active filter, a filter circuit including an inductor and a capacitor may be used as the filter circuit.

  The present invention is applicable to any device that requires an AC attenuation signal, such as a demagnetization circuit of a magnetic material.

10 ... One-chip microcomputer 11 ... Differential amplifier circuit 12 ... Low-pass filter circuit

Claims (4)

Rectangular wave generating means for generating two rectangular waves having slightly different frequencies;
Bipolar differential amplification means for inputting the two rectangular waves and outputting a difference obtained by subtracting the voltage value of the other rectangular wave from the voltage value of the one rectangular wave;
The differential output signal of the amplifying means to enter, bipolar alternating signal generating apparatus characterized by comprising a low-pass filter means bipolar that outputs an AC signal. 2. The AC signal generating apparatus according to claim 1, wherein the rectangular wave generating means is constituted by a microcomputer that outputs two unipolar rectangular wave signals based on processing of a program .   The microcomputer generates two rectangular waves having an initial phase difference of 180 degrees and slightly different frequencies, and generates a rectangular wave when the phase difference between the two rectangular waves becomes zero. The AC signal generator according to claim 2, wherein the AC signal generator is terminated.   The AC signal generator according to claim 3, wherein the two rectangular waves have the same logical 1 length.

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