JP2010263416A - Amplitude modulation circuit and ultrasonic acoustic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic acoustic device that is configured of only general-purpose components so as to attain cost reduction and that is equipped with an amplitude modulation circuit, a preamplifier, a power amplifier and an ultrasonic transmitter. <P>SOLUTION: The amplitude modulation circuit and the ultrasonic acoustic device have a configuration, such that drive-pulse voltage generation is configured, to generate a drive-pulse voltage for transmitting an ultrasonic wave from the ultrasonic transmitter when, for example, a voice signal is inputted to an input; an AC signal based on the voice signal is inputted to the drive-pulse voltage generation; and a voltage for determining ON/OFF of a drive pulse is changed so as to amplitude-modulate the drive-pulse voltage and for transmitting ultrasonic waves from the ultrasonic transmitter by the amplitude-modulated drive-pulse voltage. Each function can be attained readily, by using a general-purpose logic, a general-purpose comparator, a general-purpose transistor and a general-purpose FET (field effect transistor). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an ultrasonic acoustic apparatus that uses an amplitude modulation type ultrasonic transmitter to make an analog signal such as an audio signal an audible sound, and more specifically, transmits an ultrasonic wave including an analog signal such as an audio signal. Thus, the present invention relates to an amplitude modulation type ultrasonic acoustic device that provides information such as sound as audible sound.

Conventional modulation methods of ultrasonic acoustic devices include those using various modulation methods such as a frequency modulation method and a pulse width modulation method in addition to the amplitude modulation method. In addition, signal processing and modulation processing are performed by a digital signal processor (DSP) for signal processing of these modulation methods, and the power is amplified to a predetermined level by a power amplifier, and ultrasonic waves transmitted from an ultrasonic transmitter are transmitted. There is an acoustic device.
Hereinafter, a conventional ultrasonic acoustic apparatus will be described with reference to the drawings.

Special Table 2005-516516 (page 39, FIG. 1, FIG. 2) (page 41, FIG. 13) JP2005-142999 (5th page, FIG. 1 and FIG. 2) JP 2001-346288 (Page 5, FIG. 2, FIG. 3)

"Nonlinear acoustics and its applications" Tomoo Kamakura (h t t p: / / e w 3. e e. U e c. A c. Jp / su b j e c t / n o l l i n e a r _ 1. P d f) “Prototype Envelope Modulator for Driving Parametric Speaker Using D S P”, Kunimoto Yuji et al., IEICE Technical Report E A 2 0 0 2-3 0 (2 0 0 2-6)

  However, in this amplitude modulation type ultrasonic acoustic apparatus, signal correction processing and modulation must be performed on an analog signal such as an audio signal input using a semiconductor integrated circuit (LSI: Large Scale Integration) called DSP. Therefore, there is a problem that the configuration of the entire apparatus is complicated and expensive.

  A manufacturer's amplitude-modulation-type ultrasonic acoustic device uses a DSP, and the audio input unit, DSP, amplitude modulation unit, and pre-amplification unit use hundreds of electronic components, and these components are mounted. The size of the printed circuit board is 150 × 200 [mm], which is physically large, and the cost of the electronic component is expensive. The present invention has been made in view of such a problem, and has a simple configuration and This is an amplitude modulation type ultrasonic acoustic device that can transmit various types of information such as audio information from an ultrasonic transmitter without using a DSP. The number of general-purpose electronic components required to satisfy basic functions is several tens of points. The substrate size is 40 × 50 [mm], and an ultrasonic acoustic device can be provided with a small size and low cost.

  Also, in the amplitude modulation system, the carrier wave is present even when the audio signal, which is a modulated wave, has a low volume below a certain level, and is not efficient with unnecessary power consumption. However, in an amplitude modulation type ultrasonic acoustic device, when a carrier wave is turned on / off by an easy method for power saving or the like, an unpleasant audible noise is generated and cannot be ignored.

  To achieve the above object, the amplitude modulation circuit according to claim 1 is a signal for determining whether or not the signal level is a predetermined input level in the amplitude modulation circuit for controlling the amplitude voltage of the carrier wave according to the signal level of the input signal. A level detection unit, an input signal ON / OFF control unit that allows an input signal to pass when the input level becomes equal to or higher than a predetermined signal level based on a determination result of the signal level detection unit, and the input signal is the input signal A switching type power supply unit that supplies power to the amplitude modulation circuit according to the signal level that has passed through the ON / OFF control unit, a carrier frequency oscillation unit that determines the period of the carrier wave, and a switching type based on the period of the carrier wave And a modulation output control unit that turns ON / OFF the output voltage of the power supply unit.

  The amplitude modulation circuit according to claim 2 is the amplitude modulation circuit according to claim 1, wherein when the input signal becomes equal to or higher than a predetermined signal level, the ON-resistance control unit immediately decreases the ON resistance. 2. The amplitude modulation circuit according to claim 1, wherein an input signal is allowed to pass, and when the input signal falls below a predetermined signal level, the OFF resistance is gradually increased to control the passage of the input signal.

  The amplitude modulation circuit according to claim 3 is the amplitude modulation circuit according to claim 1, except for a period in which the input signal ON / OFF control unit is completely OFF at an electrical operation timing of the input signal ON / OFF control unit. 2. The amplitude modulation circuit according to claim 1, wherein the operation of the carrier frequency oscillation unit is continued during the period.

  According to a fourth aspect of the present invention, there is provided the ultrasonic acoustic apparatus of the amplitude modulation system, wherein the ultrasonic frequency apparatus uses the frequency of the ultrasonic wave as a carrier wave and performs amplitude modulation with an audio signal and outputs the modulated signal. A characteristic amplitude modulation type ultrasonic acoustic device.

  According to the amplitude modulation circuit of claim 1, for example, when information such as an audio signal is input, amplitude modulation can be performed without using a DSP for signal correction processing and modulation, and the basic function is satisfied. The number of necessary general-purpose electronic components is several tens, and the printed circuit board size is 40 × 50 [mm]. Thus, a small-sized, low-cost, amplitude-modulation type ultrasonic acoustic device can be provided.

  According to the amplitude modulation circuit of the second aspect, the start and stop of the switching power supply unit at the next stage can be controlled by ON / OFF control of the input signal according to the presence or absence of signal input. In addition, by controlling the resistance value of ON / OFF control and the rate of change of the resistance value in this case, the speed of starting and stopping the output voltage of the switching power supply unit is controlled to save power. The carrier wave can be turned ON / OFF by the power supply voltage control of the modulation output control unit, and the power saving operation of stopping the carrier wave without causing any harsh audible sound noise is possible.

  The amplitude modulation circuit according to claim 3 is the amplitude modulation circuit according to claim 1 or 2, wherein the input signal ON / OFF control unit is completely OFF at the electrical operation timing of the input signal ON / OFF control unit. The operation of the carrier frequency oscillating unit is continued during the period except for the above, and in particular, combining the ON / OFF of the carrier for power saving with the operation of controlling the power supply voltage of the modulation output control unit This enables the modulation output control unit to turn on / off the carrier wave with a sufficiently stable carrier frequency oscillation period, and does not cause annoying audible noise generation, power saving operation of carrier wave stop Is possible.

  By using an amplitude-modulation type ultrasonic acoustic device characterized by having the means of claims 1 to 3, it is an inexpensive, ultra-compact, low-power, low-powered operation that is composed of general-purpose components and suppresses heat generation. A sound acoustic device can be provided.

  Hereinafter, an amplitude modulation circuit and an ultrasonic acoustic device according to the best mode for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, the amplitude modulation circuit and the ultrasonic acoustic device include an input signal unit 1, an input signal ON / OFF control unit 2, a signal level detection unit 3, a switching power supply unit 4, and a modulation output control unit 5. A carrier frequency oscillating unit 6, a modulation output circuit unit 7 and an ultrasonic transmission unit 8 are connected so as to modulate the amplitude of the input audio signal and transmit the audio signal as audio in the audible band from the ultrasonic transmitter. Yes.

  Conventionally, this type of modulation and drive circuit is implemented in the form shown in FIG. 2, and is composed of a signal input unit 9, a DSP 10, an amplitude change 11, a preamplifier 12, a power amplifier 13, and an ultrasonic transmitter 14. The connected audio signal is amplitude-modulated and connected to be able to be transmitted as an audible sound from the ultrasonic transmitter.

  FIG. 3A is a basic block diagram of amplitude modulation, and has a configuration of an input signal 15, an amplitude modulation circuit 16, a carrier frequency oscillation unit 17, and a modulation output circuit unit 18. Here, by connecting the ultrasonic transmitter 19 to the modulation output circuit unit, an apparatus having a function as an ultrasonic acoustic apparatus is obtained. Here, the amplitude modulation will be briefly described. A dedicated amplitude modulation circuit uses a low signal as the frequency of the waveform example (b) of the input signal and a high carrier wave as the frequency of the waveform example (c) of the carrier frequency oscillation unit. By performing the processing in (4), a waveform example (d) of the modulation output is obtained.

  An electrical specific embodiment of the present invention has the configuration shown in FIG. 4, and specifically, the amplitude modulation circuit of the present invention is configured by using four comparators.

  In FIG. 4, a window comparator 20 is a signal level detection circuit composed of IC1 and IC2, and when the input signal 201 is no signal, the OR output of IC1 and IC2 is Hi, but the input signal AC component is (+ V When a signal having an amplitude of × R2 / (R1 + R2 + R3) or more is input, the OR outputs of IC1 and IC2 become Low.

  In FIG. 4, an input signal ON / OFF control unit 21 performs ON / OFF control of an input signal by a comparator IC3 and a PNP transistor Q1. In this case, ON / OFF of Q1 is controlled not only by using ON / OFF of the saturation region of the transistor but also by using the ON resistance of the linear region, and the ON resistance of Q1 and the resistor R11 connected to the collector of Q1 The voltage divided by ((input signal) × R11 / (Q1 ON resistance + R11)) is supplied as a reference voltage to the comparator IC4 in the next stage.

This will be described in detail below.
In a state where the input signal is supplied to the comparator IC4 at the next stage when the mute is OFF, it is desirable that Q1 is ON, the operation is in the saturation region, and the ON resistance is low. Therefore, a resistance value satisfying the above condition is selected for the bias current limiting resistor R10 of Q1. Here, when the DC bias voltage of the input signal is set to ½ of the power supply voltage + V of the entire circuit, the voltage of the input signal is an input signal on which an AC signal such as voice is superimposed with (+ V / 2) as a zero cross. As a result, the above-mentioned input signal is always continuously supplied to the emitter of the normal Q1. Therefore, the base voltage of Q1 when mute is OFF is about ((+ V / 2) −0.6) V, and the OUT of IC3 is about 0V.

Next, a transition from mute OFF to mute ON will be described.
If the audio signal of the input signal is determined to be no signal by the above-described window comparator, electric charge is stored in C1 up to + V via R6 and R7. At this time, for the purpose of avoiding pop noise and delay of mute ON time, the charging time constant to C1 is set later than that at the time of discharging. When the voltage is stored in C1, when the voltage reaches (+ V × R5 / R4), the output of IC3 changes from Low to Hi, and the operation of Q1 is controlled from ON to OFF. However, if the voltage at the output point of IC3 is expanded in time axis, after passing through the voltage of (+ V / 2) from Low, it gradually rises to + V by the feedback resistance of R9. At this time, since the ON resistance of Q1 is controlled in a linear region, the ON resistance gradually increases, and the voltage corresponding to the voltage of ((input signal) × R11 / (Q1 ON resistance + R11)) is applied to the collector of Q1. Can be observed. Therefore, both the voltage at the collector of Q1 and the voltage at the (−) terminal of the next stage IC 4 gradually drop to the GND level.

  The switching power supply unit 22 supplies power to the power amplification unit 25 using an audio signal or the like of the input signal as a reference voltage. In such a switching power supply, it is necessary to switch the switching frequency at a frequency sufficiently higher than the frequency of the input signal and the carrier wave frequency of the amplitude modulation. Is similar to the reference voltage and supplies the power necessary for driving the power amplification unit in the next stage.

  The power amplifying unit 25 turns on / off the full-bridge FET based on a clock pulse generated by the carrier frequency oscillating unit 23 and having a driving capability of the power amplifying unit 25 by the gate driving circuit 24. Here, the power amplifying unit 25 is supplied with the output 22a of the switching power supply unit described above, so that the Hi voltage of each output of the power amplifying units 25a and 25b is the voltage following the input signal. Is output.

  FIG. 5 shows an example of waveform observation during operation of the circuit of the embodiment of FIG.

  (A) is an example in which an announcement is used as a sound source of an input signal, and an amplitude-modulated waveform 26a, which is an output appearing at both ends of the ultrasonic transmitter 26, can be observed following an intermittent announcement sound. The waveform of the output unit 21a of the IC3 of the input signal ON / OFF control unit 21 transitions from 0 of the GND level to + V / 2 and + V. Here, it can be observed that the mute release operation from ON to OFF quickly shifts from + V to 0, and the mute operation from OFF to ON, + V / 2 and + V, gradually shifts, and thus soft mute is applied.

  (B) is an example in which a 1 [KHz] sine wave is used as the sound source of the input signal and the mute is switched from ON to OFF. An input signal 201 represents a 1 [KHz] sine wave of the window comparator input unit, and represents a waveform of the output 21a of the input signal ON / OFF control unit IC3. In addition, a waveform of the 1 [KHz] sine wave of the input unit 201 amplified by the output 22a of the switching power supply unit and supplied to the power supply of the power amplification unit 25 can be observed. The voltage applied to both ends of the ultrasonic wave transmitter 26 is indicated by 26a. The voltage of the switching power supply unit 22a is switched at the frequency generated by the carrier frequency oscillating unit 23, and the resonance inductor L1 As a result of the combined capacitance component of the sonic wave transmitter 26 being in a series resonance state, the amplitude modulation voltage 26a is applied to the ultrasonic wave transmitter 26, and ultrasonic waves are transmitted to the air as a medium, and in the air. It is possible to obtain an audible sound in the process of transmitting ultrasonic waves.

  Here, the oscillation frequency of the carrier frequency oscillating unit 23 is in the vicinity of the center frequency of the ultrasonic wave transmitter 26, and it is possible to efficiently transmit ultrasonic waves. Further, although the voltage 26a applied to both ends of the ultrasonic wave transmitter 26 is delayed by 2.5 [msec] with respect to the rising edge of the input signal 201, there is no problem with hearing. However, when it becomes necessary to eliminate this delay, it can be achieved by combining a microcomputer, a RAM (Random Access Memory) and the like.

  (C) is an example in which a sine wave of 1 [KHz] is used as the sound source of the input signal and the mute is switched from OFF to ON. After the input signal 201 is stopped, the output 21a of the input signal ON / OFF control unit IC3 immediately rises to the emitter potential of Q1, that is, the direct current potential + V / 2 of the input signal 201, and thereafter (C1 · (R8 + R9)). The time constant rises to + V. During this time, by gradually increasing the ON resistance of Q1 in the vicinity of + V / 2, a voltage of ((input signal) × R11 / (ON resistance of Q1 + R11)) is output to the collector of Q1. Therefore, a voltage that gently falls from + V / 2 to 0 [V] of the GND level can be obtained in the switching power supply unit 22a. As a result, the voltage applied to both ends of the ultrasonic transmitter 26 also gradually decreases 26a, and it is possible to suppress the generation of an unpleasant audible sound with mute ON.

  Here, even after the input signal 201 is stopped, it is possible to suppress the generation of an unpleasant audible sound with mute ON by gradually lowering the transmitted sound pressure while continuing to transmit the carrier wave.

  Note that this amplitude modulation circuit can transmit radio waves by connecting a capacitive load, for example, an antenna or the like, instead of the ultrasonic wave transmitter 26.

It is a block diagram which shows the structure of the amplitude modulation and ultrasonic acoustic apparatus which concern on the best form for implementing this invention. It is a block diagram which shows the structure of the ultrasonic acoustic apparatus which concerns on the conventional form. It is the figure which showed the basic example of amplitude modulation. It is the figure which showed a part of Example of the circuit structure of the ultrasonic acoustic apparatus of this invention. The actual signal timing in the Example of the circuit structure of the ultrasonic acoustic apparatus of this invention.

DESCRIPTION OF SYMBOLS 1 Input signal part 2 Input signal ON / OFF control part 3 Signal level detection part 4 Switching type electric power supply part 5 Modulation output control part 6 Carrier frequency oscillation part 7 Modulation output circuit part 8 Ultrasonic transmission part 9 Signal input part 10 DSP
DESCRIPTION OF SYMBOLS 11 Amplitude modulation 12 Preamplifier 13 Power amplifier 14 Ultrasonic transmitter 15 Input signal 16 Amplitude modulation circuit part 17 Carrier frequency transmission part 18 Modulation output circuit part 19 Ultrasonic transmitter 20 Window comparator 21 Input signal ON / OFF control part 22 Switching power supply unit 23 Carrier frequency transmission unit 24 Gate drive circuit 25 Power amplification unit 26 Ultrasonic transmitter

Claims (4)

  In an amplitude modulation circuit that controls an amplitude voltage of a carrier wave according to a signal level of an input signal, a signal level detection unit that determines whether or not the input signal is a predetermined signal level, and a determination result of the signal level detection unit An input signal ON / OFF control unit that allows an input signal to pass when the signal level becomes equal to or higher than a predetermined signal level, and the amplitude modulation circuit according to a signal level that the input signal has passed through the input signal ON / OFF control unit A switching power supply for supplying power to the carrier, a carrier frequency oscillating unit for determining the period of the carrier wave, a modulation output control unit for turning on / off the output voltage of the switching power supply unit based on the period of the carrier wave, An amplitude modulation circuit comprising:   The input signal ON / OFF control unit quickly decreases the ON resistance when the input signal becomes equal to or higher than a predetermined signal level and allows the input signal to pass, and the input signal becomes equal to or lower than the predetermined signal level. 2. The amplitude modulation circuit according to claim 1, wherein the OFF resistance is gradually increased to prevent passage of an input signal.   In the operation of the carrier frequency oscillating unit for determining the cycle of the carrier wave and the electrical operation timing of the input signal ON / OFF control unit, the carrier wave is in a period other than the period in which the input signal ON / OFF control unit is completely OFF. 2. The amplitude modulation circuit according to claim 1, wherein the operation of the frequency oscillation unit is continued.   4. An ultrasonic acoustic apparatus of amplitude modulation type, characterized in that the ultrasonic acoustic apparatus outputs the frequency of ultrasonic waves as a carrier wave, amplitude-modulated with an audio signal, and having the means of claims 1 to 3.

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