JP2005006236A - Audio reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio reproducing device which prevents occurrence of hum noise at the time of standby. <P>SOLUTION: In the audio reproducing device 1 constituted by having a bridge output circuit 13 constituted by serially connecting FETs Q1 to Q4 between a power source and a ground, gate drive circuits 12a, 12b which perform drive control of the FETs, and a power supply circuit 40, in the case of suspending the operation of the bridge output circuit 13, the power supply circuit 40 continues power feeding to power supply lines E1, E2 while stopping power feeding to a power supply line E3, the gate drive circuit 12b makes the FETs Q3, Q4 on the ground side into on states. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an audio reproducing apparatus having a bridge output circuit.
[0002]
[Prior art]
In recent years, digital amplifiers (class D amplifiers, etc.) that are more power efficient than analog amplifiers (class A amplifiers, etc.) have begun to be mounted on audio playback devices against the backdrop of advances in modulation / demodulation technology and improved response of power elements. In particular, the applicant of the present application includes a ΔΣ converter that converts an analog audio signal or a multi-bit digital audio signal into a 1-bit digital audio signal, a switching amplifier that amplifies (amplifies) the 1-bit digital audio signal, and an amplification A 1-bit digital amplifier comprising a digital / analog conversion unit for converting the 1-bit digital audio signal into an analog signal is disclosed and proposed (see, for example, Patent Document 1), and an audio reproduction equipped with the amplifier is provided. The device has been put to practical use.
[0003]
FIG. 2 is a block diagram showing a conventional example of an audio playback apparatus. As shown in this figure, in the 1-bit digital amplifier 110 mounted in the conventional audio reproduction apparatus 100, the switching amplifier 113 is formed by connecting at least a pair of field effect transistors in series between a power supply line and a ground line. A bridge-type push-pull power amplifier circuit is used, and the digital / analog converter 114 is a low-pass filter including a capacitor Ca and a coil La, one end of which is connected to the ground line. When a half-bridge type unbalanced output circuit is used as the switching amplifier 113 in this way, a DC cut capacitor Cb is required between the switching amplifier 113 and the digital / analog converter 114. . The power line of the 1-bit digital amplifier 110 is connected to a power supply circuit 140 that operates by receiving power supply from a device power supply 130 (rechargeable battery or the like), and the ground line is connected to a grounded casing. It was.
[0004]
Further, the conventional audio playback apparatus 100 generally consumes power while temporarily stopping the power supply to the microcomputer 120 other than the main controller 120 and maintaining the power amplification operation of the 1-bit digital amplifier 110 at any time. An operation mode (so-called standby mode) for reducing power was provided.
[0005]
[Patent Document 1]
JP-A-2002-246852 [0006]
[Problems to be solved by the invention]
Certainly, the audio playback device described above can reproduce the original sound more faithfully than an audio playback device equipped with an analog amplifier or multi-bit digital amplifier, while also reducing power consumption and extending battery life. It is also possible to do.
[0007]
However, the conventional audio playback device 100 releases the switch element Qx provided on the power supply path from the device power supply 120 to the power supply circuit 140 in the standby mode to stop the operation of the power supply circuit 140 itself, and to other than the microcomputer 120. In the standby mode, the gates of the field effect transistors Qa and Qb constituting the switching amplifier 113 are in a floating state, and the output terminal of the 1-bit digital amplifier 110 (that is, audio reproduction) The input terminal of the external device 200 connected to the apparatus 100) is to be connected to a grounded casing via the capacitor Ca.
[0008]
Therefore, in the conventional audio playback device 100, when a human touches the case in the standby mode, the electrostatic induction voltage induced in the human body by the commercial AC power source near the device is transferred from the case to the external device 200 via the capacitor Ca. As a result, there is a problem that an unpleasant hum noise is generated in the speaker 300. In the standby mode, since power supply to the gate drive circuit 112 is also stopped, it is impossible to mute the output of the speaker 300.
[0009]
In view of the above problems, an object of the present invention is to provide an audio playback apparatus capable of preventing the occurrence of hum noise during standby.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an audio reproduction device according to the present invention includes a power supply circuit that controls power supply to each part of the device, a bridge output circuit that is formed by connecting at least a pair of switch elements in series between a power source and a ground, And a drive circuit that performs drive control of the switch element based on the input audio signal. When the output operation of the bridge output circuit is temporarily stopped, the power supply circuit While the power supply to the output circuit is stopped, the power supply to the drive circuit is continued, and the drive circuit is configured to turn on the ground side of the switch elements.
[0011]
More specifically, the audio reproduction apparatus according to the present invention includes a grounded casing, a power supply circuit that controls power supply to each part of the apparatus, an analog audio signal and a multi-bit digital audio signal, and a 1-bit digital audio signal. Obtained by the 1-bit conversion section, the bridge type switching amplifier circuit in which at least a pair of field effect transistors are connected in series between the power supply circuit and the housing, and the 1-bit conversion section Obtained by the switching amplifier circuit by a gate drive circuit that controls the driving of the field effect transistor based on a bit digital audio signal, and a coil and a capacitor connected in series between the output terminal of the switching amplifier circuit and the housing. Digit to convert the amplified 1-bit digital audio signal In the audio reproducing apparatus comprising the analog / digital converter, when the amplifying operation of the switching amplifier circuit is temporarily stopped, the power supply circuit stops power supply to the switching amplifier circuit while the gate drive Power supply to the circuit is continued, and the gate drive circuit is configured to turn on the ground side of the field effect transistor.
[0012]
With this configuration, when the switching amplifier circuit is temporarily stopped, its output terminal is connected to a grounded casing through a parallel circuit composed of a coil and a capacitor. Even when the body is touched, the anti-resonance action of the parallel circuit can prevent the generation of hum noise.
[0013]
In the audio reproducing apparatus having the above-described configuration, the gate drive circuit performs drive control of the field effect transistor based on a mute signal for muting when the amplification operation of the switching amplifier circuit is temporarily stopped. Good. By adopting such a configuration, it is not necessary to prepare a separate control signal, so that control complexity can be avoided.
[0014]
In the audio reproducing apparatus having the above-described configuration, the switching amplifier circuit may be a full bridge type balanced output circuit having four field effect transistors. With such a configuration, distortion and noise cancel each other, so that the fidelity to the original sound can be improved.
[0015]
In the audio reproducing apparatus having the above configuration, the power supply circuit may be configured to variably control the voltage applied to the gate drive circuit in accordance with the voltage applied to the switching amplifier circuit. By adopting such a configuration, the drive voltage can be suppressed to the minimum necessary without affecting the operation of the switching amplifier circuit, so that it is possible to reduce the power consumption when the output amplitude is small. .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram (partially including a circuit diagram) showing an embodiment of an audio reproducing apparatus according to the present invention, and particularly shows an analog signal output unit thereof.
[0017]
As shown in this figure, the audio reproduction apparatus 1 of this embodiment includes a 1-bit digital amplifier 10 that digitally amplifies an input signal, a microcomputer 20 that performs overall control of apparatus operation, and a rechargeable battery 30 that is a DC power supply of the apparatus. And a power supply circuit 40 that controls power supply to each part of the apparatus, and has a function of outputting an analog audio signal to the external device 2 connected in the subsequent stage. The external device 2 is a device that drives the L and R channel output speakers 3L and 3R based on an analog audio signal from the audio playback device 1, and a commercial AC power source is generally used as the drive power source. It is done.
[0018]
As shown in the figure, the 1-bit digital amplifier 10 includes a ΔΣ converter 11, upper and lower gate drive circuits 12a and 12b, a switching amplifier circuit 13, and digital / analog converter circuits 14a and 14b (hereinafter referred to as D). / A [Digital / Analog] conversion circuits 14a and 14b).
[0019]
The ΔΣ converter 11 converts an analog audio signal or a multi-bit digital audio signal into a PDM [Pulse Density Modulation] signal or a PWM [Pulse Width Modulation] signal, which is a 1-bit digital audio signal, using a ΔΣ modulation method. The data is sent to the upper and lower gate drive circuits 12a and 12b in the subsequent stage.
[0020]
The structure of the switching amplifier circuit 13 is a full bridge type (H type) composed of four N channel MOS type field effect transistors Q1 to Q4. The drains of the transistors Q1 and Q2 are connected to each other, and the connection node is connected to the power supply voltage line. The sources of the transistors Q1 and Q2 are connected to the drains of the transistors Q3 and Q4, respectively. The sources of the transistors Q3 and Q4 are each grounded. By using such a balanced output circuit, distortion and noise cancel each other, so that the fidelity to the original sound can be improved.
[0021]
The upper and lower gate drive circuits 12a and 12b are configured using CMOS gates, and generate control signals for the transistors Q1 to Q4 based on the 1-bit digital audio signal generated by the ΔΣ converter 11. The control signal generated by the upper gate drive circuit 12a is input to the gates of the transistors Q1 and Q2, and the control signal generated by the lower gate drive circuit 12b is input to the gates of the transistors Q3 and Q4. ing. By these control signals, the transistors Q1 and Q4 at the diagonal positions and the transistors Q2 and Q3 are driven in the same phase, and the upper transistors Q1 and Q2 and the lower transistors Q3 and Q4 are driven in the opposite phases. Is done. As a result, the push-pull operation of the switching amplifier circuit 13 is realized, and the 1-bit digital audio signal is amplified to a necessary output level.
[0022]
The D / A conversion circuits 14a and 14b are low-pass filters that convert the amplified 1-bit digital audio signal obtained by the switching amplifier circuit 13 into an analog signal and send it to the external device 2 at the subsequent stage. The coils L1 and L2 and the capacitor C1 , C2. One ends of the coils L1 and L2 are connected to the positive phase output terminal (a connection node between the source of the transistor Q1 and the drain of the transistor Q3) and the negative phase output terminal (the source of the transistor Q2 and the drain of the transistor Q4). Connection node). The other ends of the coils L1 and L2 are connected to external output terminals, respectively, and are also connected to ground lines via capacitors C1 and C2.
[0023]
The power line of the 1-bit digital amplifier 10 described above is connected to a power circuit 40 that operates by receiving power from the rechargeable battery 30, and the ground line is connected to a grounded casing. A first variable voltage (for example, 2.5 to 4.5 [V]) is applied to the first power supply line E1 from the power supply circuit 40 to the upper gate drive circuit 12a, and the first variable voltage to the lower gate drive circuit 12b is applied. A fixed voltage (for example, 2.5 [V]) is applied to the two power supply lines E2. A second variable voltage (for example, 0 to 2 [V]) is applied to the third power supply line E3 from the power supply circuit 40 to the switching amplifier circuit 13.
[0024]
Therefore, the output amplitude of the amplified 1-bit digital audio signal obtained by the switching amplifier circuit 13 can be appropriately controlled according to the second variable voltage. Further, the power supply circuit 40 of the present embodiment is configured to variably control the first variable voltage applied to the upper gate drive circuit 12a in addition to the variable control of the second variable voltage. For example, as in the present embodiment, when the switching element constituting the switching amplifier circuit 13 is an N-channel MOS field effect transistor, the gate voltage when turned on is always higher than the source voltage by a predetermined value. The first variable voltage is controlled. By performing such power supply control, the driving voltage can be suppressed to the minimum necessary without affecting the amplification operation of the switching amplifier circuit 13, so that the consumption of the 1-bit digital amplifier 10 at a small output amplitude is achieved. Electric power can be reduced.
[0025]
The audio playback apparatus 1 having the above-described configuration is provided with an operation mode (so-called standby mode) for reducing the power consumption of the apparatus while maintaining the power amplification operation of the 1-bit digital amplifier 10 at any time. The present invention is characterized by drive control of the switching amplifier circuit 13 in the standby mode.
[0026]
More specifically, the audio playback device 1 according to the present embodiment stops power supply to the third power supply line E3 instead of stopping the operation of the power supply circuit 40 itself when shifting to the standby mode. Thus, the power supply to the first power supply line E1 is continued, and the transistors Q3 and Q4 on the ground side among the transistors Q1 to Q4 are turned on.
[0027]
With this configuration, in the standby mode, the output terminal of the 1-bit digital amplifier 10 (that is, the input terminal of the external device 2 connected to the audio playback device 1) is connected to the coils L1, L2 and the capacitor C1, It will be connected to a grounded enclosure via a parallel circuit consisting of C2. Therefore, even when a person touches the case in the standby mode, the electrostatic induction voltage induced in the human body by the commercial AC power source in the vicinity of the device is caused from the case to the external device by the anti-resonance action of the parallel circuit. Therefore, it is possible to prevent an unpleasant hum noise from occurring in the speaker 3.
[0028]
In the audio playback device 1 of the present embodiment, it is necessary to continue power supply to the upper and lower gate drive circuits 12a and 12b after the transition to the standby mode, but the push-pull drive of the switching amplifier circuit 13 is performed. Since it is completely stopped, no through current flows through the transistors Q1 to Q4 and no switching loss occurs. Accordingly, it is possible to realize power saving substantially equivalent to the conventional configuration in which the power supply circuit 40 itself is not operated.
[0029]
Further, in the audio reproduction device 1 of the present embodiment, the lower gate drive circuit 12b turns on the mute signal for mute input from the microcomputer 20 during the transition to the standby mode (the transistors Q3 and Q4 are turned on when enabled). Based on the switching control signal), the drive control of the transistors Q3 and Q4 described above is performed. In this way, by diverting the conventional mute signal, it becomes unnecessary to prepare a separate control signal, so that it is possible to avoid complication of microcomputer control.
[0030]
Furthermore, in the audio reproducing apparatus 1 of the present embodiment, since it is not necessary to provide a switch element for cutting off the power supply to the power supply circuit 40, the number of parts is reduced as compared with the conventional configuration, the associated cost is reduced, and the process is simplified. It is possible to reduce the size of the apparatus and the like.
[0031]
In the above embodiment, the audio reproducing apparatus including the ΔΣ conversion unit and the D / A conversion circuit has been described as an example. However, the configuration of the present invention is not limited to this, A 1-bit digital audio signal may be directly input from the outside, or a D / A conversion circuit may be provided outside the apparatus.
[0032]
In the above embodiment, the switching amplifier circuit 13 is described as an example of a full bridge type (H type) composed of four N channel MOS type field effect transistors Q1 to Q4. The configuration is not limited to this, and may be a half-bridge type including two transistors, or a configuration using a P-channel MOS field effect transistor.
[0033]
In the above embodiment, the switching amplifier circuit 13 has been described by taking as an example a positive power supply configuration in which the upper transistors Q1 and Q2 are connected to the power supply line and the lower transistors Q3 and Q4 are grounded. The configuration of the invention is not limited to this, and a negative power supply configuration in which the upper transistors Q1 and Q2 are grounded and the lower transistors Q3 and Q4 are connected to the power supply line may be employed.
[0034]
【The invention's effect】
As described above, the audio playback device according to the present invention can prevent hum noise from being superimposed on the playback sound during standby.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an audio playback apparatus according to the present invention.
FIG. 2 is a block diagram showing a conventional example of an audio playback device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Audio reproduction apparatus 2 External apparatus 3L, 3R Speaker 10 1-bit digital amplifier 11 ΔΣ conversion units 12a, 12b Upper and lower gate drive circuits 13 Switching amplifier circuits 14a, 14b Positive phase side, negative phase side low-pass filter (LPF)
20 microcomputer 30 rechargeable battery 40 power supply circuit Q1, Q2, Q3, Q4 N-channel MOS field effect transistor L1, L2 coil C1, C2 capacitors E1, E2 first and second power supply lines (first and second variable power supply voltages )
E3 Third power line (fixed power supply voltage)

Claims (5)

A power supply circuit that controls power supply to each part of the device, a bridge output circuit in which at least a pair of switch elements are connected in series between the power supply and the ground, and a drive that controls drive of the switch elements based on an input audio signal And an audio playback device comprising: a circuit;
When temporarily suspending the output operation of the bridge output circuit, the power supply circuit stops supplying power to the bridge output circuit while continuing to supply power to the drive circuit. An audio reproducing apparatus characterized in that a grounding side is turned on. A grounded case, a power supply circuit for controlling power supply to each part of the apparatus, a 1-bit conversion unit for converting an analog audio signal or a multi-bit digital audio signal into a 1-bit digital audio signal, the power supply circuit, and the case And driving control of the field effect transistor based on a 1-bit digital audio signal obtained by the 1-bit converter and a bridge-type switching amplifier circuit in which at least a pair of field-effect transistors are connected in series with each other Digital / analog conversion for analog conversion of an amplified 1-bit digital audio signal obtained by the switching amplifier circuit by a gate drive circuit, a coil and a capacitor connected in series between the output terminal of the switching amplifier circuit and the housing And an audio playback device comprising Stomach,
When temporarily suspending the amplification operation of the switching amplifier circuit, the power supply circuit stops supplying power to the switching amplifier circuit while continuing to supply power to the gate drive circuit, and the gate drive circuit includes the field effect An audio reproducing apparatus characterized in that a ground side of a transistor is turned on. 3. The audio reproduction according to claim 2, wherein when the amplification operation of the switching amplifier circuit is temporarily stopped, the gate drive circuit performs drive control of the field effect transistor based on a mute signal for muting. apparatus. 4. The audio reproducing apparatus according to claim 2, wherein the switching amplifier circuit is a full-bridge type balanced output circuit including four field effect transistors. 5. The audio reproduction device according to claim 2, wherein the power supply circuit variably controls the voltage applied to the gate drive circuit in accordance with the voltage applied to the switching amplifier circuit. 6. .

Images