JP2012209770A - Fixed sound generator and switching amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixed sound generator and a switching amplifier capable of reducing power consumption when outputting a fixed sound, such as a beep sound, an alarm and the like, from a loudspeaker immediately after power-on, and of preventing an abnormal noise.SOLUTION: When a command signal S1 for generating a fixed sound, such as a beep sound and the like, for the purpose of notifying an operator of an operation state at an operation of an audio device 11 is inputted to a fixed sound controller 2 from a built-in microcomputer 12 of the audio device 11, the fixed sound controller 2 and a fixed sound generation part 4 generate a fixed sound generation signal S8. A voltage variable power supply part 6 adds a voltage component of the signal S8 to a power supply voltage of a power amplification stage 8. A PWM modulator 3 generates a PWM modulation signal S4 having a pulse width depending on a value of an audio signal in an output time period of the audio signal, and generates the PWM modulation signal having a predetermined pulse width in a fixed sound generation time period. The power amplification stage 8 switches the power supply voltage by the PWM modulation signal to amplify a power of the audio signal and/or the fixed sound.

Description

  The present invention relates to a fixed sound generator and a switching amplifier for generating a fixed sound such as a beep sound or a warning sound by a speaker, and particularly suitable for generating a fixed sound immediately after power-on. The present invention relates to a fixed sound generator and a switching amplifier.

  Conventionally, as this type of fixed sound generator, in order to generate a beep sound in response to an operation or the like in an audio amplifier, the output amplified by switching in the audio amplifier is smoothed and converted to an analog signal on the output side of the filter. In addition to connecting a power element pulled up to a high level voltage and a resistor, a control microcomputer (or DSP: Digital Signal Processor) that is always energized drives this power element to generate a beep sound. There is a technique for generating a beep sound by generating a rectangular wave (or triangular wave) to be generated and applying the rectangular wave to an electromechanical transducer (speaker) that synthesizes an audio signal (see, for example, Patent Document 1 below) ).

Japanese Patent Laying-Open No. 2005-6215 (FIG. 1)

  That is, in this conventional example, when using a common electromechanical conversion element for normal reproduction and beep sound reproduction, a power element is additionally connected to at least one terminal of the electromechanical conversion element, and the power element is connected to the power element. A predetermined voltage such as a power supply is applied, and in response to a rectangular wave that is the source of the beep sound, a power element that turns on and off the supply voltage is driven by a control means such as a microcomputer that is constantly energized in the system. . Therefore, the audio signal source and the buffer amplifier that control the power element that drives the electromechanical transducer during normal playback can generate a beep sound even if it does not start up immediately after the power is turned on. Can also beep.

  However, the conventional method and apparatus for generating a beep sound have the following problems. In other words, the technology described in Patent Document 1 uses a microcomputer or DSP that drives a power element that turns on / off a supply voltage in response to a rectangular wave that is the source of a beep sound, even for confirmation at power-on. Since it is necessary that the system is always energized, there is a problem that power consumption on the system increases.

  Further, in the technique described in Patent Document 1, a signal output from a power element that turns on / off a supply voltage in response to a rectangular wave that is a source of a beep sound is an analog that is directly or smoothed by a low-pass filter. Since it is output to the electromechanical conversion element in a state of being superimposed on the audio signal, there is a problem in that abnormal noise such as a clapping sound is generated. As a technique for preventing this abnormal noise, it is conceivable to add the above power element or the like in front of the smoothing filter. However, the microcomputer and DSP that drive the power element are always energized on the system. Therefore, there is a problem that the power consumption of the entire system increases.

  In view of the problems of the conventional example described above, the present invention can reduce power consumption when a speaker emits a fixed sound such as a beep sound or a warning sound immediately after the power is turned on, and prevents abnormal noise. It is an object of the present invention to provide a fixed sound generator and a switching amplifier that can perform the above-described operation.

In order to achieve the above object, the present invention provides power amplifying means for power amplifying an audio signal;
Fixed sound generating means for generating a fixed sound generating signal for a predetermined period;
Power supply means for adding the voltage component of the fixed sound generation signal generated by the fixed sound generation means to the power supply voltage of the power amplification means;
A drive signal corresponding to the audio signal is applied to the power amplifier during the output period of the audio signal, and a drive signal for generating the fixed sound is applied to the power amplifier during the fixed sound generation period. Driving means for driving the power amplifying means;
It was set as the structure which has.

  With this configuration, voltage components of fixed sound generation signals such as beeps and warning sounds immediately after power-on are applied to the power amplifier, and fixed sound generation is used instead of audio signals during the fixed sound generation period. The drive signal is applied to the power amplifying means to drive the power amplifying means, so that a configuration for generating a fixed sound can be constructed with a logic circuit or an analog element that rises immediately after the power is turned on. Therefore, a fixed sound can be generated immediately after the power is turned on without always energizing. In addition, a smoothing filter that removes unnecessary high-frequency components is usually provided after the power amplification unit, and its output is output to the speaker. Therefore, even if a fixed sound is added by the power amplification unit, abnormal noise is prevented. can do.

  According to the present invention, power consumption can be reduced when a fixed sound such as a beep sound or a warning sound is emitted from a speaker immediately after the power is turned on, and abnormal noise can be prevented.

1 is a block diagram showing a switching amplifier as a first embodiment of a fixed sound generator of the present invention. Circuit diagram for explaining the configuration and operation of a PWM modulation unit according to the first embodiment of the present invention Explanatory drawing which produces | generates a PWM modulation signal from the PWM modulation part in Embodiment 1 of this invention Block diagram for explaining power supply voltage control of a voltage variable power supply unit according to a fixed sound in Embodiment 1 of the present invention Block diagram of a switching amplifier as a second embodiment of the fixed sound generator of the present invention The figure for demonstrating the structure and operation | movement of a PWM modulation part in Embodiment 2 of this invention.

(Embodiment 1)
Hereinafter, a switching amplifier 1 as a first embodiment of the fixed sound generator of the present invention will be described with reference to the block diagram of FIG. In FIG. 1, the input side of the switching amplifier 1 according to the first embodiment is connected to an audio device 11, and the audio device 11 outputs an audio signal S7 of about the line level via an output terminal P1 and operates. A command signal S1 for generating a fixed sound such as a beep sound is sometimes outputted from an internal microcomputer (hereinafter abbreviated as a microcomputer) 12 through an output terminal P2 in order to inform the operator of the operation state. The output terminal P3 of the switching amplifier 1 is connected to an electromechanical transducer 10 such as a speaker.

  The switching amplifier 1 is composed of, for example, a class D amplification audio amplifier, amplifies the power of the audio signal S7 output from the audio device 11, and beeps in response to the command signal S1 output from the built-in microcomputer 12 of the audio device 11. A sine wave (or triangular wave) for generating a fixed sound such as sound is generated, and the power signal and the sine wave after power amplification are superimposed and output to the electromechanical transducer 10 through the output terminal P3. . The electromechanical transducer 10 converts the sound signal after power amplification into sound and emits it, and electroacoustically converts the sine wave into a fixed sound and emits it.

  The switching amplifier 1 and the audio device 11 are connected to a direct current power source (not shown) that supplies electric power necessary to operate them. However, the power source required to operate each of the devices 1 and 11 is not limited to a DC power source, and an AC power source may be used as appropriate according to the characteristics of each device.

  The switching amplifier 1 includes a fixed sound control unit 2, a fixed sound generation unit 4, a voltage variable power supply unit 6, a signal processing unit 5 including a DSP, a PWM (Pulse Width Modulation) modulation unit 3, a gate A power amplifying stage 8 including a driver unit 7 and switching elements (for example, Nch-MosFETs) 8a and 8b that amplify the power of the power supply voltage (and fixed sound) in accordance with the audio signal (and / or fixed sound driving signal). And an LPF (low-pass filter) 9. The PWM modulation unit 3 generates the PWM modulation signal S4 during the output period of the audio signal and / or the generation period of the fixed sound, and outputs the PWM modulation signal S4 via the gate driver unit 7 to the gates of the switching elements 8a and 8b of the power amplification stage 8. Apply to.

  This will be described in detail below. First, from the built-in microcomputer 12 of the audio device 11, a command signal S <b> 1 for generating a fixed sound such as a beep sound is input to the fixed sound control unit 2 in order to inform the operator of the operation state when operating the audio device 11. The fixed sound control unit 2 outputs a fixed sound generation control signal S3 that causes the fixed sound generation unit 4 to generate a fixed sound for a predetermined time, and also causes the PWM modulation unit 3 to be active high (H) during the fixed sound generation period. The PWM modulation period control signal S2 is output. Here, the predetermined time of the control signals S2 and S3 can be realized by controlling with a timer such as a counter.

  When the fixed sound generation control signal S3 for a predetermined time is input from the fixed sound control unit 2, the fixed sound generation unit 4 generates a fixed sound generation signal S8 having a predetermined voltage amplitude and a predetermined frequency for generating the fixed sound. The voltage is sent to the variable voltage power supply unit 6. Here, the fixed sound generation signal S8 may be a sine wave or a triangular wave. The predetermined frequency of the fixed sound generation signal S8 (that is, the sine wave or triangular wave) is determined in consideration of the frequency of the PWM modulation signal S4 output from the PWM modulation unit 3 and the allowable switching frequency of the switching elements 8a and 8b of the power amplification stage 8. It is necessary to set in.

  The voltage variable power supply unit 6 controls the output power supply voltage to the power amplification stage 8 according to the fixed sound generation signal S8 input from the fixed sound generation unit 4, and the power supply voltage on which the voltage component of the fixed sound generation signal S8 is superimposed. (Described in detail later) is sent to the power amplification stage 8. Here, the voltage amplitude of the fixed sound generation signal S8 is such that the power supply voltage on which the voltage component of the fixed sound generation signal S8 is superimposed is always within the allowable voltage range of the switching elements 8a and 8b of the power amplification stage 8. Set.

  On the other hand, the signal processing unit 5 performs acoustic processing (for example, noise reduction by noise shaping processing, etc.) on the input audio signal S7 output from the audio device 11, and sends the analog audio signal S5 to the PWM modulation unit 3 and also analog audio. A PWM modulation period control signal S6 that becomes H active during the output period of the signal S5 is sent to the PWM modulation section 3. Here, the signal processing unit 5 can be realized by a DSP (digital signal processor), a microcontroller, or the like, but does not immediately start up immediately after the power is turned on.

  The PWM modulation unit 3 is set up in a state where PWM modulation can be performed using the PWM modulation period control signal S6 input from the signal processing unit 5 after the system is started and stably operated, and is input from the signal processing unit 5 The analog audio signal S5 thus generated is modulated to generate a PWM modulation signal S4 (details will be described later), and the obtained signal S4 is sent to the gate driver unit 7. The PWM modulation unit 3 also inputs the audio signal S7 and the PWM modulation period control signal S6 from the signal processing unit 5 in a state where the signal processing unit 5 has not yet started up immediately after the switching amplifier 1 (and the audio device 11) is turned on. Therefore, the modulation period control signal S2 of the predetermined time input from the fixed sound control unit 2 is used instead of the signal S6 to generate the PWM modulation signal S4 for the fixed sound drive signal (details will be described later), The obtained signal S4 is sent to the gate driver unit 7.

  The gate driver unit 7 inserts a dead time into the PWM modulation signal S4 input from the PWM modulation unit 3 and supplies high-speed (+ Vdd) and low-side (−Vdd) high-speed switching elements 8a and 8b of the power amplification stage 8. A drive signal in which the potential of the PWM modulation signal S4 is shifted to such an extent that it can be driven is created and sent to the gates of the switching elements 8a and 8b of the power amplification stage 8.

  The power amplifying stage 8 includes a high-side high-speed switching element 8a that is arranged on the high-potential power supply side (+ Vdd) and that is supplied with a positive-side voltage on which a fixed sound component is superimposed from the voltage variable power supply unit 6; A half-bridge circuit including a low-side high-speed switching element 8b to which a negative voltage on which a fixed sound component is superimposed is supplied from the voltage variable power supply unit 6 is provided.

  The power amplification stage 8 performs high-speed switching of the voltage amplitude determined by the positive side voltage (+ Vdd), the negative side voltage (−Vdd), and the voltage component of the fixed sound according to the drive signal input from the gate driver unit 7. As a result, the drive signal input to the power amplification stage 8 is power-amplified to obtain an amplified PWM modulation signal S9 on which a fixed sound component is superimposed, and is sent to the LPF 9. Here, if the drive signal of the power amplification stage 8, that is, the gate input of the switching elements 8a and 8b is 0, the switching elements 8a and 8b are not switched and no fixed sound is generated.

  The LPF 9 is an audio signal on which a fixed sound demodulated by removing an unnecessary high frequency component from the amplified PWM modulation signal S9 output from the power amplification stage 8 is superimposed (when the system is stably operated) or a signal of a fixed sound. This is a filter that outputs (when the system is immediately turned on) to the electromechanical conversion element 10, and is composed of elements such as a coil L and a capacitor C, for example.

<PWM modulation unit 3>
Next, a detailed internal configuration and operation relating to the PWM modulation unit 3 will be described with reference to FIGS. As shown in FIG. 2, the PWM modulation unit 3 includes a PWM modulation period control signal selection unit 31, a PWM modulation control unit 32, a comparator 33, and a triangular wave carrier generation unit.

  The PWM modulation period control signal selection unit 31 ORs the PWM modulation period control signal S2 for a predetermined time input from the fixed sound control unit 2 and the PWM modulation period control signal S6 for the audio output period input from the signal processing unit 5. One of the control signals is selected by performing a logical operation, and is sent to the PWM modulation control unit 32 as the PWM modulation period control signal S10. Here, the selection unit 31 selects the control signal S6 in the audio output period when the control signal S2 and the control signal S6 are “H” control signals at the same time, and when both are “H” control signals. By selecting any one of the “H” control signals, the PWM modulation period control signal S10 is sent to the PWM modulation control unit 32. When the control signal S2 and the control signal S6 are “L” control signals at the same time, a signal having a 0 (V) voltage is sent to the PWM modulation control unit 32 as the signal S10.

  The PWM modulation control unit 32 inputs the start-up voltage S11 of the comparator 33 and the positive phase input terminal (+) of the comparator 33 during the period indicated by the PWM modulation period control signal S10 input from the PWM modulation period control signal selection unit 31. The voltage signal S12 is set. Here, the PWM modulation control unit 32 includes a MOS transistor 32a, a resistor R3, and a resistor R4. The transistor 32a has a negligible on-resistance compared to the resistors R3 and R4. The resistor R3 has the same value as the resistor R4. The PWM modulation period control signal S10 is applied to the gate of the transistor 32a, the power supply of the voltage + Vcc (V) is applied to one end thereof, and the other end is connected to one end of the resistor R3 and the power input terminal of the comparator 33. ing. The other end of the resistor R3 is connected to one end of the resistor R4 and the positive phase input terminal (+) of the comparator 33. The other end of the resistor R4 is connected to GND (ground).

  In the PWM modulation control unit 32, when the PWM modulation period control signal S10 is input from the PWM modulation period control signal selection unit 31, the transistor 32a is turned on, and the starting voltage S11 of voltage + Vcc (V) is sent to the comparator 33. Then, the comparator 33 is activated. At this time, the input voltage signal S12 of the voltage + Vcc / 2 (V) divided by the resistors R3 and R4 is applied to the positive phase input terminal (+) of the comparator 33. If the analog audio signal S5 is also input from the signal processing unit 5 after the system is stabilized, the input voltage signal S12 (= + Vcc / 2 + S5) in which the analog audio signal S5 is superimposed on the voltage + Vcc / 2 is the positive phase of the comparator 33. It is sent to the input terminal. When the PWM modulation period control signal S10 of 0V voltage is input from the PWM modulation period control signal selection unit 31, the transistor 32a is turned off, and the starting voltage S11 and the positive phase input terminal (+) of the comparator 33 are connected to the ground GND. Thus, the operation of the comparator 33 is stopped.

  The triangular wave carrier generation unit 34 generates a triangular wave carrier S13 having a predetermined frequency within a voltage amplitude range of 0 (V) to + Vcc (V), and outputs the triangular wave carrier S13 to the negative phase input terminal (−) of the comparator 33. When the start-up voltage S11 of the voltage + Vcc (V) is input from the PWM modulation control unit 32, the comparator 33 is input to the signal S12 input to the positive phase input terminal (+) and to the negative phase input terminal (−). The carrier waves S13 to be compared are compared, and a PWM modulation signal S4 that becomes high in a period of S12> S13 is sent to the gate driver unit 7.

Here, operations related to the PWM modulation unit 3 in the following cases (1), (2), and (3) will be described with reference to FIGS. .
<Case 1: Immediately after turning on the power>
Case 1 is a case immediately after power-on of the audio device 11 and the switching amplifier 1, and the switching amplifier 1 (and the audio device 11) except for the signal processing unit 5 is operating stably, and the audio device 11 is an audio signal. This is a case where S7 is not output to the switching amplifier 1 and a command signal S1 for generating a fixed sound is output from the microcomputer 12 of the audio apparatus 11 to the switching amplifier 1 by the operation of the audio apparatus 11.

  When the command signal S <b> 1 is input to the fixed sound control unit 2, a PWM modulation period control signal S <b> 2 that becomes H active during the fixed sound generation time is input from the fixed sound control unit 2 to the PWM modulation unit 3. At the same time, since the signal processing unit 5 has not yet started up or the audio signal S7 has not been input since the power has just been turned on, the PWM modulation period control signal S6 from the signal processing unit 5 becomes “L”, and The analog audio signal S5 becomes “0”, and the signals S6 and S5 are sent to the PWM modulation period control signal selection unit 31 and the PWM modulation control unit 32, respectively. The PWM modulation period control signal selection unit 31 performs an OR logic operation on the control signal S2 that is set to “H” and the control signal S6 that is set to “L”, and selects the control signal S2 that is set to “H”. The PWM modulation period control signal S10 is sent to the PWM modulation control unit 32.

  In the PWM modulation control unit 32, the transistor 32a is turned on by the modulation period control signal S10 having a predetermined level voltage inputted thereto, whereby the start-up voltage S11 (= + Vcc) is supplied to the comparator 33 and the comparator 33 is started up. Since the analog audio signal S5 is input as “0”, a predetermined voltage + Vcc / 2 (V) divided by the resistor R3 and the resistor R4 is obtained as the input voltage signal S12 as shown in FIG. It is applied to the positive phase input terminal (+) of the comparator 33. The comparator 33 has an input voltage signal S12 (= + Vcc / 2) input to the positive phase input terminal (+) and a voltage amplitude of 0 (V) to + Vcc (V) input to the negative phase input terminal (−). Compared with the triangular wave carrier S13 in the range, as shown in FIG. 3 (a-2), the PWM modulation signal S4 having a fixed duty ratio (for example, 50%) that is high in the section where + Vcc / 2> S13 is output. And output to the gate driver unit 7. For this reason, the PWM signal S4 can be output even if the signal processor 5 does not output the audio signal S5 and the modulation period control signal S6 immediately after the power is turned on.

<Case 2: After system stabilization>
Case 2 is a case where all the circuits (and the audio device 11) in the switching amplifier 1 operate stably and the audio signal S7 is output from the audio device 11 to the switching amplifier 1 regardless of whether or not the audio device 11 is operated. It is. When the audio signal S7 is input from the audio apparatus 11 to the signal processing unit 5, the signal processing unit 5 outputs the analog audio signal S5 to the PWM modulation control unit 32 and sets the control signal S6 to be “H” to the PWM modulation period. As described above, the PWM modulation period control is performed regardless of whether the control signal S2 for a predetermined time input from the fixed sound control unit 2 to the PWM modulation unit 3 is “H” or “L”. The signal selection unit 31 selects the control signal S6 to be “H” and sends it to the PWM modulation control unit 32 as a control signal S10 having a predetermined level voltage.

  In the PWM modulation control unit 32, the transistor 32a is turned on by the input control signal S10 having a predetermined level voltage, whereby the power supply voltage + Vcc (V) is supplied to the comparator 33 and the comparator 33 is activated. -1), the voltage + Vcc / 2 (V) divided by the resistors R3 and R4 and the input voltage signal S12 (= + Vcc / 2 + S5) on which the analog audio signal S5 is superimposed are input in the positive phase of the comparator 33. Applied to terminal (+). The comparator 33 has an input voltage signal S12 (= + Vcc / 2 + S5) input to the positive phase input terminal (+) and a voltage amplitude of 0 (V) to + Vcc (V) input to the negative phase input terminal (−). Comparing the triangular wave carrier S13 in the range, as shown in FIG. 3 (b-2), the duty ratio that becomes high in the section where (+ Vcc / 2 + S5)> S13 is variable, that is, the component of the analog audio signal S5 is included. A PWM modulation signal S4 is generated and sent to the gate driver unit 7.

<Case 3: No sound and no fixed sound>
Case 3 is a case where the audio device 11 and all the circuits in the switching amplifier 1 operate stably, but there is no operation of the audio device 11 and no audio signal S7 is output from the audio device 11 to the switching amplifier 1. . In this case, both the control signal S2 for a predetermined time input from the fixed sound control unit 2 and the analog audio signal S5 input from the signal processing unit 5 become “L” and are input to the PWM modulation period control signal selection unit 31. The As a result, the PWM modulation period control signal selection unit 31 sends a signal S10 of 0V voltage to the PWM modulation control unit 32.

  In the PWM modulation control unit 32, the transistor 32a is turned off by the signal S10 of 0V voltage, whereby 0 (V) is supplied to the comparator 33 as the power supply voltage. As a result, the comparator 33 does not operate and does not send out the PWM modulation signal S4 to the gate driver unit 7. Therefore, in the power amplification stage 8, even when the power supply voltage is supplied from the voltage variable power supply unit 6, no current flows because the switching elements 8a and 8b are off. Thereby, power consumption can also be reduced.

<Voltage variable power supply unit 6>
Next, the internal configuration and operation of the voltage variable power supply unit 6 will be described with reference to the block diagram of FIG. The voltage variable power supply unit 6 may be a power supply provided with a control function for performing normal output voltage stabilization. Here, FIG. 4 shows, as an example, a circuit of a control loop portion that provides a control function for stabilizing the output voltage of the voltage variable power supply unit 6. Below, the operation | movement which controls the output power supply voltage of the voltage variable power supply part 6 according to the fixed sound generation signal S8 input from the fixed sound generation part 4 is demonstrated.

The circuit of the control loop portion shown in FIG. 4 includes a reference voltage unit 61, a detection unit 62 that detects an output power supply voltage (Vdd) to the power amplification stage 8, and a voltage control amplifier 63. The reference voltage unit 61 is constructed by a power source having a reference voltage of + Vref (V). In the case 1 and case 2 described above, the fixed sound generation signal S8 input from the fixed sound generation unit 4 to the reference voltage + Vref (V). Can be superimposed. As a result, the reference voltage Vref becomes the new reference voltage V′ref (V) shown in Equation 1, and the new reference voltage V′ref (V) is applied to the + input terminal of the voltage control amplifier 63.
V′ref = Vref + (voltage component of fixed sound generation signal S8) (Expression 1)

The detection unit 62 includes a resistor R1 and a resistor R2 connected in series. The output power supply voltage + Vdd (V) of the voltage variable power supply unit 6 is applied to one end of the resistor R1, and one end of the resistor R2 is connected to the other end. The other end of the resistor R2 is connected to GND (ground). The contact voltage VFB (V) between the resistors R1 and R2 is a voltage obtained by dividing + Vdd (V) by the resistors R1 and R2 as shown in Equation 2, and is applied to the negative input terminal of the voltage control amplifier 63. .
VFB = + Vdd × R2 / (R1 + R2) (Formula 2)

The voltage control amplifier 63 is composed of a normal operational amplifier, calculates a differential voltage Verr (V) between the contact voltage VFB and the new reference voltage V′ref as shown in Equation 3, and outputs the output voltage ( Vdd) is sent to a control circuit (not shown) for stabilization.
Verr = V'ref-VFB
= V′ref−Vdd × R2 / (R1 + R2) (Formula 3)

As the normal operation control of the voltage variable power supply unit 6, the control circuit for stabilizing the output voltage adjusts the output power supply voltage + Vdd so that the differential voltage Verr becomes zero. That is, the output power supply voltage + Vdd is adjusted so that Formula 4 is obtained, and the contact voltage VFB is made to follow the reference voltage Vref.
Vref = VFB
= Vdd × R2 / (R1 + R2) (Formula 4)

In the case 1 and case 2 described above, when the fixed sound generation signal S8 is input from the fixed sound generation unit 4 to the voltage variable power supply unit 6, the reference voltage Vref becomes the new reference voltage V′ref according to Equation 1. Substituting Equation 4 into Equation 1 leads to Equation 5.
V'ref = Vref + (voltage component of fixed sound generation signal S8)
= Vdd × R2 / (R1 + R2) + (voltage component of fixed sound generation signal S8)
= {Vdd + [(Voltage component of fixed sound generation signal S8) × (R1 + R2) / R2]}
× R2 / (R1 + R2) (Formula 5)

  In order to make the output power supply voltage of the voltage variable power supply unit 6 follow the new reference voltage V′ref by the normal operation control of the voltage variable power supply unit 6 described above, the output power supply voltage is based on Vdd [(fixed sound generation It is necessary to adjust the voltage component of the signal S8) × (R1 + R2) / R2]. In other words, the component of the fixed sound generation signal S8 whose voltage amplitude is [(R1 + R2) / R2] times is superimposed on the output power supply voltage of the voltage variable power supply unit 6.

  The voltage variable power supply unit 6 outputs the superimposed voltage component of the fixed sound generation signal S8 with a voltage amplitude of [(R1 + R2) / R2] times by the fixed sound generation signal S8 input from the fixed sound generation unit 4. The power supply voltage is sent to the power amplification stage 8. In the case 1 and the case 2 described above, the power amplification stage 8 outputs the drive signal input from the gate driver unit 7 to the output power supply voltage on which the component of the fixed sound generation signal S8 input from the voltage variable power supply unit 6 is superimposed. The amplified PWM signal S9 in which the voltage component of the fixed sound generation signal S8 is superimposed on the voltage amplitude is obtained and sent to the LPF 9. The LPF 9 removes unnecessary high-frequency components from the amplified PWM signal S9 output from the power amplification stage 8, and outputs only the fixed sound of the fixed sound generation signal S8 in case 1 or the voltage of the fixed sound generation signal S8 in case 2. The normal reproduction audio signal on which the component is superimposed is sent to the electromechanical conversion element 10, and the electromechanical conversion element 10 converts the audio signal into sound and emits the sound.

  As described above, according to the first embodiment of the present invention, the voltage variable power supply unit 6 that varies the power supply voltage of the power amplification stage 8 is used, and the output voltage of the voltage variable power supply unit 6 includes a beep sound and a warning sound. By superimposing the voltage component of the fixed sound generation signal S8, the power amplification stage 8 can superimpose components such as a beep sound and a warning sound on the voltage amplitude of the amplified PWM modulation signal S9. Further, the amplified PWM modulation signal S9 on which the voltage component of the fixed sound generation signal S8 such as a beep sound and a warning sound is superimposed is reproduced by the electromechanical transducer 10 via the LPF 9 that smoothes the normal reproduction signal. That is, since the fixed sound generation signal S8 is added at the front stage of the LPF 9, it is possible to solve the problem of generating a clicking sound as in the prior art.

  Here, except for the signal processing unit 5, the fixed sound control unit 2, the fixed sound generation unit 4, the voltage variable power supply unit 6, and the PWM modulation unit 3 can be constructed with a logic circuit or an analog element, so the system power is turned on. Since the circuit immediately rises immediately after the signal is generated, a fixed sound generation signal (S8) such as a beep sound or a warning sound can be generated even when the signal processing unit 5 is not activated. Also, a fixed sound generation signal (S8) such as a beep sound or a warning sound can be generated. Therefore, there is no need for a control microcomputer that is always energized as in the prior art, and the problem of increased power consumption on the system can be solved.

(Embodiment 2)
Hereinafter, the switching amplifier 1a according to the second embodiment of the present invention will be described with reference to the block diagram of FIG. However, in the following description, only differences from the switching amplifier 1 of FIG. 1 shown in Embodiment 1 of the present invention will be described, and the same components will be denoted by the same reference numerals and the description thereof will be given. Omitted. In FIG. 5, the switching amplifier 1a according to the second embodiment is different from the configuration of the switching amplifier 1 according to the first embodiment in that it includes a signal processing unit 5a and a PWM modulation unit 3a.

  The signal processing unit 5a performs acoustic processing (for example, noise reduction by noise shaping processing) on the audio signal output from the audio device 11 as the input audio signal S7 of the switching amplifier 1a, and the digital audio signal S5a to the PWM modulation unit 3a. In addition, the PWM modulation period control signal S6 is sent to the PWM modulation unit 3a. Here, the digital audio signal S5a indicates a pulse modulation signal such as PCM (Pulse Code Modulation). The PWM modulation unit 3a is set up in a state in which PWM modulation can be performed using the PWM modulation period control signal S6 input from the signal processing unit 5a after the system is started and stably operated, and input from the signal processing unit 5a. The modulated digital audio signal S5a is modulated to generate a PWM modulated signal S4, and the obtained signal S4 is sent to the gate driver section 7.

  The PWM modulation unit 3a also uses the control signal S2 for a predetermined time input from the fixed sound control unit 2 because the signal processing unit 5a has not yet started up immediately after the audio device 11 and the switching amplifier 1a are turned on. A PWM modulation signal S4 having a fixed duty ratio (for example, 50%) is generated, and the obtained signal S4 is sent to the gate driver unit 7.

<PWM modulation unit 3a>
A detailed internal configuration and operation regarding the PWM modulation unit 3a will be described with reference to the block diagram of FIG. The PWM modulation unit 3a includes a PWM modulation period control signal selection unit 3a1 and a PWM modulator 3a2 as shown in FIG. PWM modulation period control signal selection unit 3a1 operates in the same manner as PWM modulation period control signal selection unit 31 in the first embodiment of the present invention. That is, which control signal is selected by OR logic operation of the PWM modulation period control signal S2 of a predetermined time input from the fixed sound control unit 2 and the PWM modulation period control signal S6 input from the signal processing unit 5a, The control signal S31 is sent to the PWM modulator 3a2.

  Here, the PWM modulation period control signal selection unit 3a1 selects the control signal S6 when the control signal S2 and the control signal S6 simultaneously become the “H” control signal, and either of them becomes the “H” control signal. In this case, by selecting one of the “H” control signals, the “H” control signal is sent to the PWM modulator 3a2 as the control signal S31. When the control signal S2 and the control signal S6 become the “L” control signal at the same time, the selection unit 3a1 sends the “L” signal to the PWM modulation 3a2 as the control signal S31.

  Similarly to the first embodiment, the PWM modulator 3a2 is also constructed by a logic circuit or an analog element that rises immediately after the power is turned on. The PWM modulator 3 a 2 generates a PWM modulation signal S 4 using the signal S 31 that is an “H” control signal input from the PWM modulation period control signal selection unit 3 a 1, and sends it to the gate driver unit 7. The PWM modulator 3a2 also stops the PWM modulation using the selection signal S31 that becomes the “L” control signal input from the PWM modulation period control signal selection unit 3a1.

  Here, in the case where the control signal S31 becomes “H” by the control signal S2 that becomes the “H” control signal in the fixed sound generation period, that is, in the same manner as in <Case 1> in Embodiment 1 of the present invention, the audio signal When the device 11 and the switching amplifier 1a are just turned on, or even when the audio device 11 and the switching amplifier 1a are operating stably, the audio signal S7 from the audio device 11 is not input to the switching amplifier 1a. When a command signal S1 for generating a fixed sound is input to the switching amplifier 1a from the microcomputer 12 of the audio device 11 by operation, the PWM modulator 3a2 generates a PWM modulation signal S4 having a fixed duty ratio (for example, 50%). Then, the data is sent to the gate driver unit 7.

  Further, when the control signal S31 becomes “H” by the control signal S6 that becomes the “H” control signal in the audio output period, that is, as in <Case 2> in the first embodiment of the present invention, the audio device 11 When the switching amplifier 1a operates stably and the audio signal S7 is input from the audio device 11 to the switching amplifier 1a, the PWM modulator 3a2 modulates the digital audio signal S5a input from the signal processing unit 5a. A PWM modulation signal S4 is generated and sent to the gate driver unit 7.

  As described above, as in the first embodiment of the present invention, according to the second embodiment of the present invention, the voltage variable power supply unit 6 that varies the power supply voltage to the power amplifying stage 8 is used to change the voltage. By superimposing a fixed sound generation signal S8 such as a beep sound or a warning sound on the output voltage of the power supply unit 6, the power amplification stage 8 superimposes a component such as a beep sound or a warning sound on the voltage amplitude of the amplified PWM modulation signal. Can do. Further, the amplified PWM modulation signal S9 on which the voltage component of the fixed sound generation signal S8 such as a beep sound and a warning sound is superimposed is reproduced by the electromechanical transducer 10 via the LPF 9 that smoothes the normal reproduction signal. That is, since the fixed sound generation signal S8 is added at the front stage of the LPF 9, it is possible to solve the problem of generating a noise as in the prior art.

  Similarly, in the second embodiment, the fixed sound control unit 2, the fixed sound generation unit 4, the voltage variable power supply unit 6, and the PWM modulation unit 3 are constructed by a logic circuit or an analog element, except for the signal processing unit 5. Therefore, immediately after the system power is turned on, the circuit immediately rises, so that a fixed sound generation signal (S8) such as a beep sound and a warning sound can be generated. A fixed sound generation signal (S8) such as a sound or a warning sound can be generated. Therefore, there is no need for a control microcomputer that is always energized as in the prior art, and the problem of increased power consumption on the system can be solved.

  The present invention has an effect that power consumption can be reduced when a fixed sound such as a beep sound or a warning sound is emitted from a speaker immediately after power is turned on, and abnormal noise can be prevented. It can be used in the field of designing and manufacturing switching amplifiers.

DESCRIPTION OF SYMBOLS 1 Switching amplifier 2 Fixed sound control part 3 PWM modulation part 3a in Embodiment 1 PWM modulation part in Embodiment 2 4 Fixed sound generation part 5 Signal processing part in Embodiment 1 5a Signal processing part in Embodiment 2 6 Voltage variable power supply unit 7 Gate driver unit 8 Power amplification stage 9 LPF (low pass filter)
DESCRIPTION OF SYMBOLS 10 Electric conversion mechanical element 11 Audio apparatus S1 Command signal which generates fixed sounds, such as a beep sound S2 PWM modulation period control signal of predetermined time S3 Control signal which generates fixed sound of predetermined time S31 PWM modulation period control signal S4 PWM Modulation signal S5 Analog audio signal S5a Digital audio signal S6 PWM modulation period control signal S7 Audio signal S8 Fixed sound generation signal with predetermined voltage amplitude and predetermined frequency S9 Amplified PWM modulation signal with fixed sound component superimposed S10 PWM modulation period control signal S11 Start-up voltage of comparator 33 S12 Input voltage signal of positive phase input terminal of comparator 33 S13 Triangular wave carrier wave of predetermined frequency 31 PWM modulation period control signal selection unit in Embodiment 1 3a1 PWM modulation period control signal selection unit in Embodiment 2 32 PWM modulation Control unit 3a2 PWM modulator 33 comparator 34 the triangular wave carrier generating unit 61 reference voltage unit 62 outputs the power supply voltage of the detector unit 63 the voltage controlled amplifier R1, R2, R3, R4 resistor

Claims (4)

Power amplifying means for power amplifying the audio signal;
Fixed sound generating means for generating a fixed sound generating signal for a predetermined period;
Power supply means for adding the voltage component of the fixed sound generation signal generated by the fixed sound generation means to the power supply voltage of the power amplification means;
A drive signal corresponding to the audio signal is applied to the power amplifier during the output period of the audio signal, and a drive signal for generating the fixed sound is applied to the power amplifier during the fixed sound generation period. Driving means for driving the power amplifying means;
A fixed sound generator. The power amplification means has switching means for power amplification of the audio signal by switching the power supply voltage with a pulse width corresponding to the audio signal,
The fixed unit according to claim 1, wherein the driving unit applies a driving signal having a predetermined pulse width to the switching unit instead of a pulse width corresponding to the audio signal during the generation period of the fixed sound. Sound generator.   The fixed sound generating means controls the fixed sound generating signal to output the fixed sound generating signal for a predetermined period based on the fixed sound generating command signal when the power is turned on, and the driving means is in the fixed sound generating period. The fixed sound generator according to claim 2, further comprising fixed sound control means for controlling to generate a drive signal having a predetermined pulse width instead of a pulse width corresponding to the audio signal.   A switching amplifier comprising the fixed sound generator according to claim 2.