JP4342245B2 - Shock noise suppression circuit - Google Patents

Description

  The present invention relates to a shock noise suppression circuit used in a BTL (Balanced Transformer Less) type audio amplifier, and more particularly to a shock noise suppression circuit for an audio amplifier including two operational amplifiers biased by one reference voltage.

  Some video cameras and digital cameras have an audio output function. A so-called beep sound that informs the user when the power is turned on is also output by the sound output function.

  In a video camera, a digital camera, or the like, the power supply voltage is set to be relatively low (for example, 3V). For this reason, the so-called BTL system is often adopted in which the dynamic range is expanded by applying audio signals having opposite phases to both terminals of the speaker.

  Here, an example of a conventional BTL audio amplifier will be described with reference to FIG. In the audio amplifier 50 of FIG. 3, the audio signal applied to the terminal 28 is input to the terminal 30 via the capacitor C2. The capacitor C2 is a direct current blocking capacitor provided to prevent propagation of unnecessary direct current components in the audio signal and to propagate only alternating current components.

  The audio signal applied to the terminal 30 is amplified by the first operational amplifier 12. The first operational amplifier 12 is an amplifier whose gain is determined according to a feedback rate determined by a resistance ratio between the resistor R9 and the resistor R10. Since the terminal 30 is connected to the negative terminal (−) of the first operational amplifier 12 via the resistor R <b> 9, the first operational amplifier 12 outputs an audio signal (inverted signal) with an inverted phase. This inverted signal is applied to one terminal 24 of the speaker 22.

  The inverted signal is amplified by the second operational amplifier 14. The second operational amplifier 14 is an amplifier whose gain is determined according to a feedback rate determined by a resistance ratio between the resistor R11 and the resistor R12. Since the output terminal of the first operational amplifier 12 is inputted to the negative terminal (−) of the second operational amplifier 14 via the resistor R11, the second operational amplifier outputs an audio signal (normal rotation) whose phase of the inverted signal is inverted. Signal) is output. This normal rotation signal is applied to the other terminal 26 of the speaker 22.

  A reference voltage is applied from the reference voltage source 34 to the positive terminals (+) of the first and second operational amplifiers 12 and 14.

  With such a configuration, an inverted signal is input to one terminal 24 of the speaker 22 and a normal rotation signal is input to the other terminal 26. For this reason, for example, when the gains of the first and second operational amplifiers 12 and 14 are set to be substantially the same, the output level between both terminals of the speaker 22 is approximately 2 as compared with the case where only the normal rotation signal is input. Doubled. This type of audio amplifier is disclosed in, for example, Patent Document 1.

Japanese Patent Laid-Open No. 11-136048

  However, in the conventional audio amplifier, a shock sound (pop sound) may be generated from the speaker due to a change in power supply voltage or the like when the power is turned on or off. In particular, in the BTL system, the dynamic range of the voice amplifier is wide, and even a relatively small potential difference or change thereof may cause a shock sound. The shock sound is not preferable because it gives the user a sense of incongruity and also disturbs the beep sound.

A shock noise suppression circuit according to the present invention is a reference voltage generating unit that generates a reference voltage, the reference voltage generating unit changing with a predetermined time delay according to a change in power supply voltage, and the reference voltage And an audio signal are input, the first operational amplifier whose output terminal is connected to one terminal of the speaker, the reference voltage and the inverted signal of the audio signal are input, and the output terminal is the other terminal of the speaker A comparison between the second operational amplifier connected to the comparator, the comparison point voltage that changes corresponding to the power supply voltage and the reference point voltage that changes corresponding to the reference voltage, and the comparison unit based on the results, when the voltage of the reference point is lower than the voltage of the reference point is applied is the reference voltage to both terminals of the speaker, both ends of the speaker when the voltage of the reference point is higher than the voltage of the reference point So that the reference voltage is not applied, and a switching control unit for switching the predetermined circuit connection.

The shock noise suppression circuit according to the present invention is turned off when the voltage at the reference point is lower than the voltage at the reference point based on the comparison result of the comparison unit, and the voltage at the reference point is the voltage at the reference point. further comprising a switching element to oN when higher, the switching control unit is configured to when the switching element is OFF as a reference voltage is applied to both terminals of the speaker, it is OFF the first and second operational amplifier, said When the switching element is ON, it is preferable that the reference voltage is not applied to both terminals of the speaker and the first and second operational amplifiers are turned ON.

  In the shock noise suppression circuit according to the present invention, it is preferable that the reference voltage generation unit includes a capacitor, and the time delay corresponding to the capacitance of the capacitor is generated.

  The shock noise suppression circuit according to the present invention further includes a DC blocking capacitor that removes a DC component in the audio signal, and when the reference voltage is applied to both terminals of the speaker, the DC blocking capacitor also includes the reference voltage. It is preferred that a voltage is applied.

In the shock noise suppression circuit according to the present invention, the second comparison for comparing the voltage of the second reference point that changes in response to the power supply voltage and the voltage of the reference point that changes in response to the reference voltage. And when the reference point voltage is lower than the second reference point voltage, and when the reference point voltage is higher than the reference point voltage based on the comparison result of the second comparison unit and the second comparison unit includes a second switching element turns oN, the the, the switching control unit, the switching element or the second switching element is a reference voltage is applied to both terminals of the speaker when OFF, the said switching element and the second When the switching element is ON, it is preferable to switch the predetermined circuit connection so that the reference voltage is not applied to both terminals of the speaker.

  Further, in the shock noise suppression circuit according to the present invention, the switching control unit includes the voltage at the third reference point where the voltage drops when the switching element or the second switching element is turned OFF, and the other fourth reference. Based on the comparison result of the third comparison unit that compares the voltage of the point and the third comparison unit, the reference voltage when the voltage of the third reference point is lower than the voltage of the fourth reference point Is output to both terminals of the speaker, and when the voltage at the third reference point is higher than the voltage at the fourth reference point, the first and second operational amplifiers are turned on. A switching unit that selectively switches a predetermined circuit connection so that the control signal is output, and a mechanism for holding the voltage of the fourth reference point higher than the voltage of the third reference point. Is preferred.

  In the shock noise suppression circuit according to the present invention, it is preferable that the switching element is turned off after the power is opened, and the second switching element is turned off after the power is turned on.

The shock noise suppression circuit according to the present invention receives a reference voltage that changes with a predetermined time delay according to a change in power supply voltage and an audio signal, and a first output terminal connected to one terminal of the speaker. A second operational amplifier whose input terminal is connected to the other terminal of the speaker, a reference point voltage that changes in accordance with the power supply voltage, Based on the comparison result of the comparison point and the comparison point voltage that changes corresponding to the reference voltage, the reference point voltage is OFF when the reference point voltage is lower than the reference point voltage. groups at both terminals of the speaker when the the configured switching element as an open collector voltage of the reference point is sometimes oN higher than the voltage of the reference point, the switching element is OFF Voltage is applied, so that the other the switching element when the ON not applied a reference voltage to both terminals of the speaker, and a switching control unit for switching the predetermined circuit connection.

An audio output device according to the present invention includes a speaker that outputs audio based on an input audio signal, and a reference voltage generator that generates a reference voltage, the reference voltage being predetermined according to a change in power supply voltage. A reference voltage generator that changes with a time delay, a first operational amplifier whose output terminal is connected to one terminal of the speaker, the reference voltage and the audio signal, and the reference voltage and the audio signal. A second operational amplifier whose output terminal is connected to the other terminal of the speaker, a reference point voltage that changes according to the power supply voltage, and a reference that changes according to the reference voltage a comparator for comparing the voltage at the point, based on the comparison result of the comparing unit, the voltage of the reference point sometimes OFF lower than the voltage of the reference point, electrostatic voltage of the reference point of the reference point When configured switching element as an open collector to ON higher Sometimes, the switching element is a reference voltage to both terminals of the speaker is applied when OFF, the other the switching element is a reference voltage to both terminals of the speaker when the ON Includes a switching control unit that switches a predetermined circuit connection so as not to be applied, and a DC blocking capacitor that removes a DC component in the audio signal.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of a sound output device 10 having a shock noise suppression function according to the present embodiment, and FIG. 2 is a diagram illustrating an example of a switching control circuit 40 included in the sound output device 10. Note that the audio output device 10 of FIG. 1 includes the same components as the audio amplifier 50 of FIG. For this reason, in the following, the same constituent elements are denoted by the same reference numerals as those in FIG.

  In the example of FIG. 1, the reference voltage generation unit 11 includes a capacitor C1. A reference voltage defined as a voltage across the capacitor C <b> 1 is applied to the positive terminals (+) of the first operational amplifier 12 and the second operational amplifier 14 via the buffer 16.

  The output terminal of the buffer 16 is connected to both terminals 24 and 26 of the speaker 22 via the buffers 18 and 20. Here, the buffers 18 and 20 are configured to be turned on / off by a control signal supplied from the terminal C of the switching control circuit 40. When the buffers 18 and 20 are turned on, the buffers 18, 20 are turned on. The reference voltage is applied to both terminals 24 and 26 of the speaker 22 via. In this case, since both terminals 24 and 26 of the speaker 22 have the same potential, unnecessary sound output (shock sound or the like) from the speaker 22 is suppressed. Therefore, in this example, the timing at which unnecessary audio output from the speaker 22 is suppressed can be controlled by controlling the timing at which the buffers 18 and 20 are turned on by the control signal. When the buffers 18 and 20 are turned off, the reference voltage is not applied to the terminals 24 and 26. Therefore, it is necessary to turn off the buffers 18 and 20 during normal audio output (a state in which the input audio signal is output from the speaker 22).

  When a reference voltage is applied to both terminals 24 and 26 of the speaker 22, the reference voltage is also applied to the DC blocking capacitor C2 via the resistors R10 and R9. As a result, the voltage at the positive terminal (+) and the voltage at the negative terminal (−) of the first operational amplifier 12 become equal, and the generation of shock noise due to the voltage between these terminals is suppressed. Therefore, in order to exhibit this effect more effectively, the capacity of the capacitor C2 is preferably set as small as possible within a range in which the DC blocking performance is ensured.

  Furthermore, the first and second operational amplifiers 12 and 14 are configured to be turned on / off by a control signal supplied from the D terminal of the switching control circuit 40, and only when turned on are amplifiers of audio signals. When it is turned OFF, the function as an audio signal amplifier is lost. Therefore, in this example, the timing at which the unnecessary audio output of the speaker 22 is suppressed can be controlled by controlling the timing at which the first and second operational amplifiers 12 and 14 are turned OFF by the control signal.

  When a reference voltage is applied to both terminals 24 and 26 of the speaker 22 and the first and second operational amplifiers 12 and 14 are turned off, unnecessary audio output from the speaker 22 can be more effectively suppressed. it can. Therefore, in the example of FIG. 1, the switching control circuit 40 outputs a control signal from only one of the terminal C and the terminal D, and any of the buffers 18 and 20 and the first and second operational amplifiers 12 and 14. Only one of them is controlled to be selectively turned on. That is, when normal audio output is performed based on the input audio signal, the switching control circuit turns off the buffers 18 and 20 and turns on the first and second operational amplifiers 12 and 14 by the control signal, When suppressing unnecessary audio output from the speaker 22, the buffers 18 and 20 are turned on, and the first and second operational amplifiers 12 and 14 are turned off.

  The sound output device 10 in FIG. 1 suppresses shock noise during the period by turning on the buffers 18 and 20 and turning off the first and second operational amplifiers when the power is opened and turned on. Yes. Here, a circuit configuration and control for that purpose will be described.

  The reference voltage V0 of the reference voltage generator 11 varies with a predetermined time delay according to the power supply voltage Vcc. For example, when the power is turned on, the power supply voltage Vcc reaches a desired steady-state voltage (rising and stable voltage; for example, 3 [V]) in a relatively short period from 0 [V], whereas the reference voltage V0 Is delayed by a time constant determined by a circuit constant (capacitance value of the capacitor C1 and resistance values of the resistors R1 and R3) with respect to the change of the power supply voltage Vcc to a desired steady voltage (eg, 1.5 [V]) Will reach. Further, when the power supply is released, the power supply voltage Vcc reaches 0 [V] within a relatively short period from the steady voltage, whereas the reference voltage V0 is a circuit constant (capacitor C1) with respect to changes in the power supply voltage Vcc. And reaches 0 [V] with a delay of a time constant determined by the resistance value of the resistor R2 and the resistance value of the resistor R2. In the present embodiment, the difference in voltage change speed at two points in the circuit, that is, the difference in voltage change speed between the reference voltage V0 and the power supply voltage Vcc is used to turn off the speaker 22 when the power is turned on or off. A period for suppressing unnecessary audio output is set.

  First, a specific configuration example and its operation for suppressing unnecessary audio output when power is turned on will be described. When the power is turned on, the voltage change rate difference between the voltage at the reference point P0 and the voltage at the second reference point P2 is used. Here, in this example, the voltage at the reference point P0 is the reference voltage V0 itself. However, the voltage is not limited to this as long as it is a voltage at a point that changes (follows relatively quickly) in response to a change in the reference voltage V0 and changes with a predetermined time delay with respect to the power supply voltage Vcc. On the other hand, in this example, the voltage V2 at the second reference point P2 is a divided voltage of the power supply voltage Vcc determined by the resistance values of the resistors R6, R7, and R8, and corresponds to the power supply voltage Vcc (relatively quickly). Change).

  As described above, when the power is turned on, the power supply voltage Vcc immediately rises, whereas the reference voltage V0 rises with a predetermined time delay. Therefore, when the power is turned on, the voltage V2 at the second reference point P2 rises first, and the voltage V0 at the reference point P0 rises with a delay. For this reason, if the resistors R6, R7, and R8 are set so that the voltage V2 at the second reference point P2 is lower than the reference voltage V0 in the steady state (the normal state in which the voltage has risen and is stable). A period from when the voltage V0 at the reference point P0 rises until it reaches the voltage V2 at the second reference point P2 after the power supply is started can be set as a period during which unnecessary audio output from the speaker 22 is suppressed.

  Therefore, in the example of FIG. 1, the second comparison unit 35 is formed by the resistor R4, the transistor Q4 (PNP) based on the reference point P0, and the transistor Q5 (PNP) based on the second reference point. ing. In this case, when the voltage V0 at the reference point P0 is lower than the voltage V2 at the second reference point P2, the transistor Q4 is turned on and the transistor Q5 is turned off, and the voltage V0 at the reference point P0 is the voltage at the second reference point P2. When it is higher than V2, the transistor Q4 is turned off and the transistor Q5 is turned on.

  Further, in this example, a transistor Q7 (NPN) that is linked to the transistor Q5 is provided. In this example, the base of the transistor Q7 is connected to the collector of the transistor Q5. Therefore, the transistor Q7 is ON when the transistor Q5 is ON, that is, when the voltage V2 at the second reference point P2 is lower than the voltage V0 at the reference point P0 (V2 <V0), and when the transistor Q5 is OFF, That is, when the voltage V2 at the second reference point P2 is higher than the voltage V0 at the reference point P0 (V2> V0), it is turned OFF.

  The transistor Q7 is configured as an open collector in this example. That is, the collector is connected to the switching control circuit 40 as an output terminal, and when the transistor Q7 is OFF, that is, when the voltage V0 at the reference point P0 is lower than the voltage V2 at the second reference point P2, the switching control circuit 40. The terminal A becomes H (high) level. Here, when the terminal A is at the H level, the switching control circuit 40 turns on the buffers 18 and 20 and turns off the first and second operational amplifiers 12 and 14 to suppress unnecessary audio output from the speaker 22. . With this configuration, it is possible to suppress unnecessary audio output from the speaker 22 during the period from when the power supply is started until the voltage V0 at the reference point P0 rises and reaches the voltage V2 at the second reference point P2. A detailed configuration example of the switching control circuit 40 will be described later.

  On the other hand, when the transistor Q7 is ON, the terminal A becomes L (low) level. At that time, the switching control circuit 40 turns off the buffers 18 and 20, and turns on the first and second operational amplifiers 12 and 14. That is, after the voltage V0 at the reference point P0 rises and exceeds the voltage V2 at the second reference point P2, the audio signal input from the terminal 28 is output from the speaker 22 during the steady state. The Instead of the configuration described here, a transistor linked to the transistor Q4 may be provided, and the comparison result of the second comparison unit 35 may be input to the switching control circuit 40 as ON or OFF of the transistor. .

  In this example, a transistor Q6 (NPN) is provided for the operation of the second comparison unit 35 when the power is turned on. The base of transistor Q6 is connected to the collector of transistor Q5, and the collector is connected to second reference point P2 (ie, the base of transistor Q5). Therefore, when the transistor Q5 is turned on, the transistor Q6 is turned on, and the voltage V2 at the second reference point P2 is thereby lowered. That is, by providing the transistor Q6, the transition from the state in which the transistor Q4 is ON to the state in which the transistor Q5 is ON, that is, the switching operation of the second comparison unit 35 is performed more quickly and reliably. It becomes like this.

  In this example, the positive side of the capacitor C1 is connected between resistors R1 and R2 provided in series between the power supply line (Vcc) and the ground. For this reason, the charge speed to the capacitor C1 is determined by the capacitance of the capacitor C1 and the circuit constant of the resistor R1 (and R2). In addition, this example includes a circuit configuration that allows the charge rate to be adjusted. That is, a transistor Q1 (PNP) is provided in parallel with the resistor R1, and the transistor Q1 and the transistor Q2 form a current mirror circuit. Further, a transistor Q3 (PNP) linked to the resistor R3 and the transistor Q4 is arranged on the transistor Q2 side line. ) In series. With this configuration, the current flowing from the power supply line to the capacitor C1 via the transistor Q1 can be adjusted also by the size of the resistor R3. This current mirror circuit is effective when the transistor Q3 is ON only when the transistor Q4 is ON, that is, when the reference voltage V0 rises from 0 [V] when the power is turned on. It functions. Further, what is shown in FIG. 1 is merely an example, and a similar function can be realized by another equivalent circuit configuration.

  Now, a specific configuration example and its operation for suppressing unnecessary audio output when the power is opened will be described. When the power is opened, the difference in voltage change rate between the voltage at the reference point P0 and the voltage at the first reference point P1 is used. Here, in this example, the voltage at the reference point P0 is the reference voltage V0 itself. However, the voltage is not limited to this as long as it is a voltage at a point that changes (follows relatively quickly) in response to a change in the reference voltage V0 and changes with a predetermined time delay with respect to the power supply voltage Vcc. On the other hand, the voltage V1 at the first reference point P1 is a divided voltage of the power supply voltage Vcc determined by the resistance values of the resistors R6, R7, and R8 in this example, and corresponds to the power supply voltage Vcc (relatively quickly). Change).

  As described above, when the power supply is opened, the power supply voltage Vcc immediately decreases, while the reference voltage V0 decreases with a predetermined time delay. Therefore, when the power supply is released, the voltage V1 at the first reference point P1 decreases first, and the voltage V0 at the reference point P0 decreases with a delay. Therefore, the resistors R6, R7, and R8 should be set so that the voltage V1 at the first reference point P1 in the steady state (normal state in which the voltage has risen and is stable) is higher than the reference voltage V0 in the steady state. (However, it is necessary to consider the circuit including the transistor Q6) After the power supply is opened, the voltage V1 at the first reference point P1 drops and becomes lower than the voltage V0 at the reference point P0. Voice output can be suppressed.

  Therefore, in the example of FIG. 1, the first comparison unit 33 is formed by the resistor R5, the transistor Q9 (PNP) based on the reference point P0, and the transistor Q10 (PNP) based on the first reference point P1. is doing. In this case, when the voltage V0 at the reference point P0 is lower than the voltage V1 at the first reference point P1, the transistor Q9 is turned on and the transistor Q10 is turned off, and the voltage V0 at the reference point P0 is the voltage at the first reference point P1. When it is higher than V1, the transistor Q9 is OFF and the transistor Q10 is ON.

  In this example, a transistor Q8 (NPN) linked to the transistor Q9 is provided. In this example, the base of the transistor Q8 is connected to the collector of the transistor Q9. Therefore, the transistor Q8 is ON when the transistor Q9 is ON, that is, when the voltage V1 at the first reference point P1 is lower than the voltage V0 at the reference point P0 (V1 <V0), and when the transistor Q9 is OFF, That is, when the voltage V1 at the first reference point P1 is higher than the voltage V0 at the reference point P0 (V1> V0), the voltage is turned OFF.

  The transistor Q8 is configured as an open collector in this example. That is, the collector is connected to the switching control circuit 40 as an output terminal, and when the transistor Q8 is OFF, that is, when the voltage V0 at the reference point P0 is lower than the voltage V1 at the first reference point P1, the switching control circuit 40. The terminal B is at the H level. Here, when the terminal B is at the H level, the switching control circuit 40 turns on the buffers 18 and 20 and turns off the first and second operational amplifiers 12 and 14 to suppress unnecessary audio output from the speaker 22. . With this configuration, after the power supply is opened, the unnecessary sound output from the speaker 22 can be suppressed after the voltage V1 at the first reference point P1 drops and becomes lower than the voltage V0 at the reference point P0.

  On the other hand, when the transistor Q8 is ON, the terminal B becomes L level. At that time, the switching control circuit 40 turns OFF the buffers 18 and 20, and turns ON the first and second operational amplifiers 12 and 14. That is, during the steady state and until the voltage V1 at the first reference point P1 drops after the power supply is released and becomes lower than the voltage V0 at the reference point P0, the audio signal input from the terminal 28 is the speaker 22. Is output from.

  Here, it is meaningful to make the transistor Q8 an open collector linked to the transistor Q9. Now, suppose that a transistor (an NPN whose base is connected to the collector of the transistor Q10 and whose collector is connected to the terminal B) is provided instead of the transistor Q8 in conjunction with the operation of the transistor Q10. In order to turn on, at least a voltage corresponding to the sum of the base-emitter voltage of the transistor, the saturation voltage of the transistor Q10, and the drop voltage of the current flowing through the resistor R5 is required. However, since the voltage at the first reference point P1 decreases following the power supply voltage Vcc, the base voltage of the transistor (that is, the collector voltage of the transistor Q10) also decreases at a relatively early stage, and the transistor is turned on. Therefore, there is a possibility that it is not possible to secure a sufficient voltage, and the output of unnecessary sound from the speaker 22 cannot be suppressed. Therefore, in the present embodiment, the transistor Q8 is configured as an open collector that is linked to the transistor Q9 side where a relatively high voltage is secured when the power supply is opened, and the voltage V1 of the first reference point P1 is the reference point when the power supply is opened. This is to stabilize the output of the comparison result after the voltage becomes lower than the voltage of P0.

  In the example of FIG. 1, it is preferable that the constituent elements within the dashed-dotted line frame are configured as one integrated circuit (for example, IC), and the capacitors C1 and C2 are both external capacitors. Accordingly, the capacities of the capacitors C1 and C2 can be easily adjusted, for example, by replacing the capacitors C1 and C2.

  Next, a configuration example of the switching control circuit 40 will be described with reference to FIG. As described above, an H level signal for suppressing unnecessary audio output from the speaker 22 when the power is turned on is input to the terminal A. The terminal B receives an H level signal for suppressing unnecessary audio output from the speaker 22 when the power is opened. Therefore, the switching control circuit 40 in FIG. 2 turns on the buffers 18 and 20 and turns off the first and second operational amplifiers 12 and 14 when either the terminal A or the terminal B becomes H level. It is comprised so that. In addition, although the switching control circuit corresponding to the input to each terminal may be provided separately, in that case, the circuit scale becomes larger.

  In the switching control circuit 40 of FIG. 2, the terminal A is connected to the power supply line (Vcc) via the resistor Rs1, and the terminal B is connected to the power supply line via the resistor Rs2. Transistors Qs1 and Qs2 (both NPN) are provided in parallel with each other. The base of the transistor Qs1 is connected to the terminal A, and the base of the transistor Qs2 is connected to the terminal B. Their emitters are grounded and their collectors are connected to the power supply line via two resistors Rs3 and Rs4 in series with each other.

  In such a configuration, when either one of the terminal A and the terminal B is at the H level, the transistor Qs1 or Qs2 is turned on, and the voltage V3 at the point between the resistors Rs3 and Rs4 (third reference point P3) decreases. . By using this, in the example of FIG. 2, a third comparison unit 37 that compares the voltage V3 of the third reference point P3 with the voltage V4 of the fourth reference point P4 is provided, and the third reference point is provided. When the voltage V3 of P3 is lower than the voltage V4 of the fourth reference point P4, the terminal C that turns on the buffers 18 and 20 is set to H level, and the voltage V3 of the third reference point P3 is the voltage of the fourth reference point P4. When it is higher than V4, the terminal D for turning on the first and second operational amplifiers 12 and 14 is set to the H level. At this time, only one of the terminal C and the terminal D is at the H level.

  Specifically, the resistor Rs5, the transistor Qs4 (PNP) whose base is connected to the third reference point P3, and the transistor Qs7 (PNP) whose base is connected to the fourth reference point P4, The comparison part 37 is formed. The fourth reference point P4 is a point between two resistors Rs6 and Rs7 provided in series between the power supply line and the ground. The resistance values of the resistors Rs3, Rs4, Rs6, and Rs7 are such that when the transistor Qs1 or Qs2 is OFF, the voltage V3 at the third reference point P3 is higher than the voltage V4 at the fourth reference point P4, and the transistor Qs1 or Qs2 Is set so that the voltage V3 at the third reference point P3 is lower than the voltage V4 at the fourth reference point P4. Thereby, when either one of the terminal A and the terminal B is at the H level, the transistor Qs4 is turned on, and when both the terminal A and the terminal B are at the L level, the transistor Qs7 is turned on.

  A transistor Qs5 (NPN) is provided in series with the transistor Qs4 and on the ground side thereof, and its base is connected to the terminal C and the base and collector are connected. Thereby, when the transistor Qs4 is ON, the transistor Qs5 is turned ON, a current flows toward the terminal C, and the terminal C becomes H level. This is a control signal for turning on the buffers 18 and 20.

  On the other hand, a transistor Qs8 (NPN) is provided in series with the transistor Qs7 and on the ground side thereof, and its base is connected to the terminal D and the base and collector are connected. Thereby, when the transistor Qs4 is ON, the transistor Qs8 is ON, a current flows toward the terminal D, and the terminal D becomes H level. This is a control signal for turning on the first and second operational amplifiers 12 and 14.

  Here, in the above circuit configuration, it is necessary that the voltage V3 at the third reference point P3 is lower than the voltage V4 at the fourth reference point P4 when the terminal B is at the H level when the power is opened. However, since the power supply voltage Vcc itself decreases when the power supply is opened, the balance is lost for some reason, and the voltage V3 at the third reference point P3 does not become higher than the voltage V4 at the fourth reference point P4. Not necessarily. Therefore, in this example, the diode D1 is provided to maintain the voltage V4 at the fourth reference point P4 higher than the voltage V3 at the third reference point P3. The diode D1 allows only a current from the fourth reference point P4 to the ground side, and relatively increases the potential on the fourth reference point P4 side.

  In this example, the current flowing as the control signal is determined by the constant current source 42. That is, when the transistor Qs4 and the transistor Qs7 are turned on, the current mirror circuit is configured so that the current flowing through the lines provided with the transistors Qs4 and Qs7 is the same as the current flowing through the line provided with the constant current source 42. Is formed. Specifically, a transistor Qs3 (PNP) is provided on the power supply side of the transistor Qs4, a transistor Qs6 (PNP) is provided on the power supply side of the transistor Qs7, and a transistor Qs9 (PNP) is provided on the power supply side of the constant current source 42. These bases are shared, and the base and collector of the transistor Qs9 are connected. However, what is shown in FIG. 2 is merely an example, and a similar function can be realized by another equivalent circuit configuration.

  The preferred embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and the shock noise suppression circuit and the sound output device according to the present invention are realized by other equivalent circuit configurations. It will be easy to understand that this is possible.

It is a figure which shows an example of the audio | voice output apparatus which has the shock sound suppression function concerning embodiment of this invention. It is a figure which shows an example of the switching control circuit contained in the audio | voice output apparatus which has the shock sound suppression function concerning embodiment of this invention. FIG. 3 is a circuit diagram of a BTL audio amplifier.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Audio | voice output apparatus, 11 Reference voltage generation part, 12, 14 Operational amplifier, 16, 18, 20 Buffer, 22 Speaker, 24, 26, 28, 30 terminal, 33 1st comparison part, 34 Reference voltage source, 35 2nd Comparison unit, 37 third comparison unit, 40 switching control circuit, 42 constant current source, 50 audio amplifier, C1 capacitor, C2 (DC blocking) capacitor, D1 diode, P0 reference point, P1 first reference point, P2 Second reference point, P3 Third reference point, P4 Fourth reference point, Q1-Q10, Qs1-Qs9 transistors (switching elements), R1-R12, Rs1-Rs7 resistors, V0 reference voltage, V1-V4 each Reference point voltage, Vcc supply voltage.

Claims (9)

A reference voltage generating unit for generating a reference voltage, wherein the reference voltage changes with a predetermined time delay according to a change in the power supply voltage;
The reference voltage and the audio signal are input, a first operational amplifier whose output terminal is connected to one terminal of the speaker;
The reference voltage and the inverted signal of the audio signal are input, a second operational amplifier whose output terminal is connected to the other terminal of the speaker;
A comparison unit that compares a reference point voltage that changes in response to a power supply voltage and a reference point voltage that changes in response to the reference voltage;
Based on the comparison result of the comparison unit, when the reference point voltage is lower than the reference point voltage , a reference voltage is applied to both terminals of the speaker, and when the reference point voltage is higher than the reference point voltage. and is such that the reference voltage to both terminals of the speaker is not applied, the switching control unit for switching the predetermined circuit connection,
A shock noise suppression circuit comprising: A switching element that is turned off when the voltage at the reference point is lower than the voltage at the reference point based on the comparison result of the comparison unit, and that is turned on when the voltage at the reference point is higher than the voltage at the reference point;
The switching control unit
When the switching element is OFF, a reference voltage is applied to both terminals of the speaker, the first and second operational amplifiers are turned OFF,
2. The shock noise suppression circuit according to claim 1, wherein when the switching element is ON , a reference voltage is not applied to both terminals of the speaker, and the first and second operational amplifiers are turned ON.   3. The shock noise suppression circuit according to claim 1, wherein the reference voltage generation unit includes a capacitor, and the time delay corresponding to the capacitance of the capacitor is generated. Furthermore, it has a DC blocking capacitor that removes the DC component in the audio signal,
The shock noise suppression circuit according to any one of claims 1 to 3, wherein when the reference voltage is applied to both terminals of the speaker, the reference voltage is also applied to the DC blocking capacitor. A second comparison unit that compares a voltage at a second reference point that changes in response to a power supply voltage and a voltage at a reference point that changes in response to the reference voltage;
Based on the comparison result of the second comparison unit, it is turned off when the voltage at the reference point is lower than the voltage at the second reference point, and turned on when the voltage at the reference point is higher than the voltage at the reference point. Two switching elements;
With
The switching control unit, the switching element or the second switching element is a reference voltage is applied to both terminals of the speaker when OFF, the said switching element and the second reference is to both terminals of the speaker when the switching element is ON The shock noise suppression circuit according to any one of claims 2 to 4, wherein a predetermined circuit connection is switched so that a voltage is not applied. The switching control unit
A third comparison unit that compares the voltage of the third reference point that drops when the switching element or the second switching element is turned off, and the voltage of the other fourth reference point;
Based on the comparison result of the third comparison unit, when the voltage at the third reference point is lower than the voltage at the fourth reference point, a control signal for applying a reference voltage to both terminals of the speaker is output. On the other hand, if the voltage at the third reference point is higher than the voltage at the fourth reference point, a predetermined circuit connection is made so that a control signal for turning on the first and second operational amplifiers is output. A switching unit for selectively switching;
A mechanism for holding the voltage of the fourth reference point higher than the voltage of the third reference point;
The shock noise suppression circuit according to claim 5 , comprising: 7. The shock noise suppression circuit according to claim 5 , wherein the switching element is configured to be turned off after power is released, and the second switching element is configured to be turned off after power is turned on. A first operational amplifier in which a reference voltage and an audio signal that change with a predetermined time delay according to a change in the power supply voltage are input, and an output terminal of which is connected to one terminal of the speaker;
The reference voltage and the inverted signal of the audio signal are input, a second operational amplifier whose output terminal is connected to the other terminal of the speaker;
A comparison unit that compares a reference point voltage that changes in response to a power supply voltage and a reference point voltage that changes in response to the reference voltage;
Based on the comparison result of the comparison unit, the voltage of the reference point is sometimes OFF lower than the voltage of the reference point, the switching configured as an open collector voltage of the reference point is sometimes ON higher than the voltage of the reference point Elements,
A switching control unit that switches a predetermined circuit connection so that a reference voltage is applied to both terminals of the speaker when the switching element is OFF, and a reference voltage is not applied to both terminals of the speaker when the switching element is ON;
A shock noise suppression circuit comprising: A speaker for outputting sound based on the input sound signal;
A reference voltage generating unit for generating a reference voltage, wherein the reference voltage changes with a predetermined time delay according to a change in the power supply voltage;
A first operational amplifier, to which the reference voltage and the audio signal are input, and an output terminal of which is connected to one terminal of the speaker;
The reference voltage and the inverted signal of the audio signal are input, a second operational amplifier whose output terminal is connected to the other terminal of the speaker;
A comparison unit that compares a reference point voltage that changes in response to a power supply voltage and a reference point voltage that changes in response to the reference voltage;
Based on the comparison result of the comparison unit, the voltage of the reference point is sometimes OFF lower than the voltage of the reference point, the switching configured as an open collector voltage of the reference point is sometimes ON higher than the voltage of the reference point Elements,
A switching control unit that switches a predetermined circuit connection so that a reference voltage is applied to both terminals of the speaker when the switching element is OFF, and a reference voltage is not applied to both terminals of the speaker when the switching element is ON; ,
A DC blocking capacitor that removes the DC component in the audio signal;
An audio output device.

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