JP5022840B2 - Amplifying device and acoustic apparatus using the same - Google Patents

Description

  The present invention relates to an amplification device of BTL [Balanced Transformer Less] format and an acoustic device using the same, and in particular, removes noise (and hence pop sound of a speaker) generated at the time of starting and stopping the device. It is about technology.

  In recent years, in an audio device such as a CD [Compact Disc] player or a DVD [Digital Versatile Disc] player, a BTL format amplifying apparatus is widely used as an amplifying means for an audio signal.

In addition, as a prior art related to the noise removal of the audio signal amplifier circuit, there can be mentioned Patent Document 1 by the applicant of the present application.
International Publication No. 2006/132202 Pamphlet

  Certainly, if a BTL-type amplifier is used, the voltage level of the input audio signal can be balanced and amplified, so that the power efficiency of the audio equipment can be increased.

  However, the above-described conventional amplifying apparatus has a problem that noise caused by a transient DC offset voltage is unnecessarily balanced and amplified at the time of starting and stopping, and an unpleasant pop sound is generated in the speaker.

  The prior art disclosed in Patent Document 1 can effectively reduce noise generated when the audio signal amplifier circuit is started or stopped, but is premised on application to a single format. The above-mentioned issues specific to the form were not taken into consideration at all.

  In view of the above-mentioned problems, the present invention increases the efficiency by adopting the BTL format, and further effectively removes noise (and hence pop sound of a speaker) generated at the time of starting and stopping. It is an object of the present invention to provide an amplifying device capable of performing the above and an acoustic device using the same.

  In order to achieve the above object, an amplifying apparatus according to the present invention includes an input amplifying circuit that amplifies an analog input signal to generate a first analog output signal, and a second that inverts the phase of the first analog output signal. A BTL type amplification device having a phase inverting circuit for generating an analog output signal, wherein the phase inverting circuit is switched between normal output and inverted output in accordance with a predetermined control signal The output format is such that when the amplifying device is started, the output is gradually inverted from the normal output, and conversely, when the amplifying device is stopped, the output format is such that the inverted output is gradually inverted from the normal output. The configuration is switched (first configuration).

  The amplifying device having the first configuration includes an analog / digital conversion circuit that converts the first and second analog output signals into the first and second digital output signals, respectively, and the first and second digital output signals. A driving circuit that amplifies the power and generates the first and second driving signals; and a smoothing circuit that generates the first and second smoothing signals by respectively smoothing the first and second driving signals. The analog input signal may be configured to amplify class D (second configuration).

  The amplifying apparatus having the second configuration includes a first mute circuit connected to the output terminal of the analog / digital conversion circuit, and a second mute circuit connected to the output terminal of the input amplifier circuit. It is preferable to have a configuration (third configuration).

  The amplifying apparatus having the third configuration is configured to control output switching of the phase inverting circuit and mute the first and second mute circuits according to a shutdown signal for controlling whether or not the amplifying apparatus can be driven. A configuration including a switching circuit that performs control (fourth configuration) is preferable.

  In the amplifying apparatus having the fourth configuration, the switching circuit includes a mute off of the first mute circuit, a normal / inverted switching of the phase inverting circuit, and a second mute circuit when the amplifying apparatus is activated. On the contrary, when the amplifying device is stopped, the second mute circuit is muted on, the phase inversion circuit is inverted / normally switched, and the first mute circuit is muted on (in order) The fifth configuration is preferable.

  Further, in the amplifying device having any one of the first to fifth configurations, the phase inverting circuit outputs a normal output portion without inverting the phase of the first analog output signal, and the phase of the first analog output signal. An inversion output unit that inverts and outputs, and a drive current supply unit that increases and decreases the drive current of the normal output unit and the drive current of the inversion output unit in a complementary manner according to the predetermined control signal, It is preferable to have a configuration (sixth configuration).

  In addition, an acoustic device according to the present invention includes an amplification device having any one of the first to sixth configurations and a speaker driven by an output signal of the amplification device (sixth configuration). It is said that.

  With the amplifying device according to the present invention, it is possible to effectively remove noise (and hence, pop sound of a speaker) generated at the time of starting and stopping after increasing efficiency by adopting the BTL format. It becomes possible.

  In the following, a detailed description will be given by taking as an example a case where the present invention is applied to a BTL class D power amplifier mounted on an acoustic device.

  FIG. 1 is a block diagram showing an embodiment of an audio device according to the present invention.

  As shown in FIG. 1, the acoustic device of this embodiment includes an input amplifier circuit 10, a phase inversion circuit 20, and an analog / digital conversion circuit 30 (hereinafter referred to as an A / D [Analog / Digital] conversion circuit 30. ), A drive circuit 40, a smoothing circuit 50, a first mute circuit 60, a second mute circuit 70, a power supply circuit 80, a time constant switching circuit 90, and a speaker 100. The circuit group excluding the speaker 100 forms a class D power amplifier of BTL [Balanced Transformer Less] format.

  The input amplifier circuit 10 is an inverting amplifier circuit that inverts and amplifies the analog input signal AIN to generate an analog output signal AOa, and includes resistors 11 and 12 and an operational amplifier 13. The non-inverting input terminal (+) of the operational amplifier 13 is connected to the application terminal for the bias voltage BIAS. The inverting input terminal (−) of the operational amplifier 13 is connected to the application terminal of the analog input signal AIN through the resistor 11 and is also connected to its own output terminal through the resistor 12.

  The phase inversion circuit 20 is means for inverting the phase of the analog output signal AOa and generating an analog output signal AOb having a phase opposite to that of the analog output signal AOa.

  However, the output format of the phase inverting circuit 20 is not fixed to the inverting output, but the normal output / inverted output can be switched according to the control signal T3 generated by the time constant switching circuit 90. Yes, the output format is such that when the class D power amplifier is started, the output is gradually inverted from the normal output, and conversely, when the class D power amplifier is stopped, the output is such that the output is gradually inverted from the inverted output. Can be switched.

  In such a configuration, by adopting the BTL format, the efficiency of the class D power amplifier is increased, and further, noise generated when the class D power amplifier is started and stopped (and, as a result, the pop sound of the speaker 100). ) Can be effectively removed by canceling in-phase.

  The internal configuration of the phase inverting circuit 20 and the forward / inverted output switching control will be described in detail later.

  The A / D conversion circuit 30 is means for converting the analog output signals AOa and AOb into digital output signals DOa and DOb, respectively, integrators 31a and 31b, an oscillator 32, comparators 33a and 33b, and dead time generation. Parts 34a and 34b.

  The integrator 31a is means for performing differential integration between the analog output signal AOa and the drive signal DRVa that is fed back via the first path to generate a first integration result signal. The integrator 31b is means for performing a difference integration between the analog output signal AOb and the drive signal DRVb that is fed back via the second path to generate a second integration result signal.

  The oscillator 32 is means for generating a triangular wave signal or a ramp wave signal having a predetermined frequency.

  The comparator 33a is a means for comparing the first integration result signal and the triangular wave signal to generate a first comparison signal. The comparator 33b is means for comparing the second integration result signal and the triangular wave signal to generate a second comparison signal. The first and second comparison signals are both PWM [Pulse Width Modulation] signals with a fixed pulse frequency and variable pulse width.

  When the dead time generating unit 34a push-pull-drives the upper switch 42a and the lower switch 43a of the drive circuit 40 based on the first comparison signal, the dead time generation unit 34a has a period (dead time) in which both switches are simultaneously turned off. Means for generating a digital output signal DOa. When the dead time generation unit 34b push-pull drives the upper switch 41b and the lower switch 42b of the drive circuit 40 based on the second comparison signal, the dead time generation unit 34b has a period (dead time) in which both switches are simultaneously turned off. Means for generating a digital output signal DOb. As described above, by providing the dead time using the dead time generators 34a and 34b, it is possible to prevent a through current in the drive circuit 40.

  The drive circuit 40 is means for power-amplifying the digital output signals DOa and DOb to generate drive signals DRVa and DRVb. The drivers 41a and 41b, upper switches (P-channel field effect transistors) 42a and 42b, Lower switches (N-channel field effect transistors) 43a and 43b. The output power of the class D power amplifier is determined according to the duty (modulation degree) of the drive signals DRVa and DRVb and the power supply voltage Vcc.

  The smoothing circuit 50 is a low-pass filter that smoothes the drive signals DRVa and DRVb to generate smooth signals BTLa and BTLb, and includes coils 51a and 51b and capacitors 52a and 52b.

  The first mute circuit 60 is connected to the output terminal of the A / D conversion circuit 30, and is a means for muting the digital output signals DOa and DOb in accordance with the control signal T2 generated by the time constant switching circuit 90. A mute unit 61a for muting the output signal DOa and a mute unit 61b for muting the digital output signal DOb are provided. The first mute circuit 60 mainly performs mute control of the digital output signals DOa and DOb when the audio device is activated or stopped.

  The second mute circuit 70 is connected to the output terminal of the input amplifier circuit 10 and is a means for muting the analog output signal AOa in accordance with the control signal T4 generated by the time constant switching circuit 90. Note that the second mute circuit 70 performs mute control of the analog output signal AOa not only when the audio device is started or stopped but also by a user mute operation.

  The power supply circuit 80 is means for controlling the supply of drive current to each part of the audio equipment in accordance with the control signal T1 generated by the time constant switching circuit 90.

  The time constant switching circuit 90 controls the current supply of the power supply circuit 80 and the mute control of the first mute circuit 60 in response to the shutdown signal SD for controlling whether or not the audio equipment (and hence the class D power amplifier) can be driven. These are means for generating the control signals T1 to T4 described above for performing the output switching control of the phase inversion circuit 20 and the mute control of the second mute circuit 70.

  Note that the output switching control of the phase inversion circuit 20 and the mute control of the second mute circuit 70 are performed gently with a predetermined time constant as will be described later. By appropriately selecting the capacitance value of the capacitor 91 externally connected to the switching circuit 90, it can be arbitrarily adjusted.

  The speaker 100 is a unit that receives the smoothed signals BTLa and BTLb, is driven in the BLT format, and outputs sound. As described above, if the configuration using the BTL class D power amplifier as the driving means of the speaker 100, the voltage level of the input audio signal can be balanced and amplified, so that the power supply efficiency of the audio equipment is improved. Is possible.

  Next, an operation for removing noise (and thus pop sound of the speaker 100) generated when the class D power amplifier having the above configuration is started or stopped will be described in detail with reference to FIG.

  FIG. 2 is a timing chart showing the start / stop sequence of the class D power amplifier, and shows the voltage waveforms of the power supply voltage Vcc, the shutdown signal SD, and the control signals T1 to T4 in order from the top.

  As shown in FIG. 2, after the power supply voltage Vcc is input to the audio equipment, the shutdown signal SD is raised to a high level and the shutdown state of the audio equipment is released. Then, the control signal T1 is raised from the low level to the high level, and the supply of the drive current to each part of the audio equipment is started by the power supply circuit 80 receiving the control signal T1. As a result, the class D power amplifier mounted on the audio device becomes operable.

  Next, in the time constant switching circuit 90, the control signal T2 is raised from the low level to the high level, and the mute of the digital output signals DOa and DOb is canceled by the first mute circuit 60 receiving the control signal T2.

  Next, in the time constant switching circuit 90, the control signal T3 is gradually raised from the low level to the high level, and the output format of the phase inverting circuit 20 that receives this is switched from the normal output to the inverted output gradually. . As described above, when the class D power amplifier is started up, the output format of the phase inverting circuit 20 is set as a normal output, and thereafter, the output is gradually switched to the inverted output. Even when noise caused by a transient DC offset voltage occurs, it can be effectively removed by canceling the common mode.

  When the output format of the phase inverting circuit 20 is switched from the normal output to the inverted output, the time constant switching circuit 90 thereafter raises the control signal T4 gradually from the low level to the high level. The mute of the analog output signal AOa is gradually released by the second mute circuit 70. Thereby, a standby state for the analog input signal AI is established.

  On the other hand, when the shutdown signal SD is lowered to the low level and the shutdown of the audio equipment is instructed, the time constant switching circuit 90 first causes the control signal T4 to gradually fall from the high level to the low level. The analog output signal AOa is gradually muted by the second mute circuit 70 that has received the signal.

  Next, in the time constant switching circuit 90, the control signal T3 is gradually lowered from the high level to the low level, and the output format of the phase inverting circuit 20 receiving this is gradually switched from the inverted output to the normal output. . As described above, when the class D power amplifier is stopped, if the configuration is such that the output form of the phase inverting circuit 20 is gradually switched from the inverted output to the normal output, a transient direct current is generated when the class D power amplifier is stopped. Even when noise due to the offset voltage occurs, it can be effectively removed by canceling the common mode.

  Next, in the time constant switching circuit 90, the control signal T2 falls from the high level to the low level, and the digital output signals DOa and DOb are muted by the first mute circuit 60 receiving the control signal T2.

  Finally, in the time constant switching circuit 90, the control signal T1 falls from the high level to the low level, and the power supply circuit 80 that receives the control signal T1 cuts off the supply of the drive current to each part of the audio equipment.

  By adopting the above sequence, it becomes possible to realize common mode cancellation of noise without hindering the start / stop operation of the class D power amplifier.

  Next, the internal configuration of the phase inverting circuit 20 that can switch the output format will be described in detail.

  FIG. 3 is a circuit diagram showing a configuration example of the phase inverting circuit 20.

  As shown in FIG. 3, the phase inversion circuit 20 includes operational amplifiers 21 and 22, resistors 23 and 24, a constant current source 25, and a selector 26.

  The non-inverting input terminal (+) of the operational amplifier 21 is connected to the output terminal (application terminal for the analog output signal AOa) of the input amplifier circuit 10. The inverting input terminal (−) of the operational amplifier 21 is connected to the output terminal of the operational amplifier 21. The non-inverting input terminal (+) of the operational amplifier 22 is connected to the application terminal of the bias voltage BIAS. The inverting input terminal (−) of the operational amplifier 22 is connected to the output terminal of the input amplifier circuit 10 through the resistor 23, and is also connected to the output terminal of the operational amplifier 22 through the resistor 24. The output terminal of the operational amplifier 21 and the output terminal of the operational amplifier 22 are connected to each other, and the connection node is drawn out as the output terminal of the analog output signal AOb.

  One end of the constant current source 25 is connected to the power supply end. The other end of the constant current source 25 (the output end of the constant current I) is connected to the common end of the selector 26. The first selection terminal (the output terminal of the first drive current I1) of the selector 26 is connected to the drive current input terminal of the operational amplifier 21. The second selection terminal (the output terminal of the second drive current I2) of the selector 26 is connected to the drive current input terminal of the operational amplifier 22. The control end of the selector 26 is connected to the application end of the control signal T3.

  In the phase inverting circuit 20 having the above configuration, the operational amplifier 21 functions as a normal output unit that outputs the analog output signal AOa without inverting the phase, and the operational amplifier 22 and the resistors 23 and 24 include the analog output signal AOa. It functions as an inverting output unit that inverts and outputs the phase.

  The constant current source 25 and the selector 26 function as a drive current supply unit that increases or decreases the drive current I1 of the inverting output unit and the drive current I2 of the normal output unit in a complementary manner according to the control signal T3.

  FIG. 4 is a diagram showing the correlation between the drive currents I1 and I2.

  More specifically, referring to FIG. 4, when the control signal T3 is at a low level, the selector 26 sets the first drive current I1 to a constant current I and the second drive current I2 to a zero value. In addition, the constant current I generated by the constant current source 25 is distributed. At this time, the phase inversion circuit 20 is in a state in which only the normal rotation output unit is driven, that is, a state in which the output format is a normal rotation output.

  As the control signal T3 is gradually changed to the high level from the above state, the selector 26 increases or decreases the first drive current I1 and the second drive current I2 while maintaining the relationship of I1 + I2 = I. . That is, in the phase inverting circuit 20, the driving of the normal output part is gradually weakened, and the driving of the inverting output part is gradually strengthened. As a result, the output format of the phase inverting circuit 20 is gradually switched from the normal output to the inverted output.

  Thereafter, when the control signal T3 reaches a high level, the selector 26 generates a constant current generated by the constant current source 25 so that the first drive current I1 is set to a zero value and the second drive current I2 is set to a constant current I. I is distributed. Therefore, the phase inverting circuit 20 is in a state where only the inverting output unit is driven, that is, in a state where the output format is the inverting output.

  When the control signal T3 is transitioned from the high level to the low level, the selector 26 performs the reverse control.

  In this way, with the phase inverting circuit 20 having the above configuration, the normal output / inverted output can be gently switched with a very simple configuration.

  In the above-described embodiment, the configuration in which the present invention is applied to an acoustic device having a class D power amplifier has been described as an example. However, the application target of the present invention is not limited to this, and the present invention is not limited thereto. Can be widely applied to BTL-type amplifying devices in general.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  For example, in the above-described embodiment, the configuration using the PWM modulation circuit as the A / D conversion circuit 30 has been described as an example. However, the configuration of the present invention is not limited to this, and the ΔΣ modulator Other types of A / D conversion circuits such as a PDM [Pulse Density Modulation] modulation circuit using the above may be adopted.

  The logic of each signal shown in FIG. 2 is merely an example, and the logic may be reversed as long as a similar operation can be realized.

  INDUSTRIAL APPLICABILITY The present invention is a technique that can be used to remove noise generated at the time of starting and stopping of a BTL-type amplifying device used in general audio equipment such as TV equipment, desktop PCs, AV receivers, and car audio. .

These are block diagrams which show one Embodiment of the audio equipment which concerns on this invention. These are timing charts showing the start / stop sequence of the amplification device. FIG. 2 is a circuit diagram showing a configuration example of a phase inverting circuit 20. These are figures which show the correlation of the drive currents I1 and I2.

Explanation of symbols

10 Input amplifier circuit (inverting amplifier circuit)
DESCRIPTION OF SYMBOLS 11, 12 Resistance 13 Operational amplifier 20 Phase inversion circuit 21, 22 Operational amplifier 23, 24 Resistance 25 Constant current source 26 Selector 30 Analog / digital conversion circuit (PWM modulation circuit)
31a, 31b Integrator 32 Oscillator 33a, 33b Comparator 34a, 34b Dead time generator 40 Drive circuit 41a, 41b Driver 42a, 42b Upper switch (P-channel field effect transistor)
43a, 43b Lower switch (N-channel field effect transistor)
50 Smoothing circuit 51a, 51b Coil 52a, 52b Capacitor 60 First mute circuit 61a, 61b Mute unit 70 Second mute circuit 80 Power supply circuit 90 Time constant switching circuit 91 Capacitor 100 Speaker

Claims (6)

A BTL comprising: an input amplifier circuit that amplifies an analog input signal to generate a first analog output signal; and a phase inverter circuit that inverts the phase of the first analog output signal to generate a second analog output signal. An amplification device of the form,
The phase inversion circuit is configured to switch its normal output / inverted output in accordance with a predetermined control signal. On the contrary, when starting up the amplifying device, the phase inversion circuit is reversed so that the normal output is gradually inverted. When the amplifying device is stopped, the output format is switched so that the normal output is gradually reversed from the inverted output ,
The amplifier further includes an analog / digital conversion circuit that converts the first and second analog output signals into first and second digital output signals, respectively, and power-amplifies the first and second digital output signals, respectively. 1. A driving circuit that generates a second driving signal, and a smoothing circuit that generates first and second smoothing signals by smoothing the first and second driving signals, respectively, Class D amplification,
The amplifying device further includes a first mute circuit connected to the output terminal of the analog / digital conversion circuit, and a second mute circuit connected to the output terminal of the input amplifier circuit,
The amplifying device further includes a switching circuit that performs output switching control of the phase inverting circuit and mute control of the first and second mute circuits in response to a shutdown signal for controlling whether or not the amplifying device can be driven. Comprising
The switching circuit sequentially performs mute off of the first mute circuit, forward / reverse switching of the phase inversion circuit, and mute off of the second mute circuit when the amplification device is activated, and conversely, the amplification device When the second mute circuit is stopped, the mute on of the second mute circuit, the inversion / forward rotation switching of the phase inversion circuit, and the mute on of the first mute circuit are sequentially performed.
The amplifying apparatus , wherein the switching circuit gently switches mute on / mute off of the second mute circuit .   The phase inversion circuit includes a normal output unit that outputs the first analog output signal without inverting the phase, an inverting output unit that inverts and outputs the phase of the first analog output signal, and the predetermined control signal. The amplifying apparatus according to claim 1, further comprising: a drive current supply unit that complementally increases or decreases the drive current of the normal output unit and the drive current of the inverted output unit. .   The analog / digital conversion circuit performs an analog / digital conversion operation based on a difference between the first and second drive signals fed back from the drive circuit and the first and second analog output signals. The amplification device according to claim 1 or 2.   The analog / digital conversion circuit includes:
  An integrator for performing differential integration between the first and second drive signals and the first and second analog output signals to generate first and second integration result signals;
  An oscillator that generates a triangular wave signal or a ramp wave signal of a predetermined frequency;
  A comparator that compares the first and second integration result signals with the triangular wave signal or the ramp wave signal to generate first and second comparison signals;
  The amplifying apparatus according to claim 3, comprising:   The analog / digital conversion circuit has a first based on the first and second comparison signals so as to have a period in which both switches are simultaneously turned off during push-pull driving of the upper switch and the lower switch included in the drive circuit. The amplification device according to claim 4, further comprising a dead time generation unit that generates the second digital output signal.   6. An audio device comprising: the amplifying device according to claim 1; and a speaker driven by an output signal of the amplifying device.

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