JP2015185882A - Class d power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate any separate amplifier circuit when a headphone is driven in a single end type, in a constitution where a speaker is differentially driven in a class D.SOLUTION: A left channel is provided with a switch 28L which connects a negative phase terminal mL of an amplifier circuit 23L to one end of an inductor 26L when a plug is not connected to a headphone jack 30, while the switch disconnects the negative phase terminal mL from the one end of the inductor 26L when a plug is connected to the headphone jack 30. A right channel is provided with a switch 28R which connects a negative phase terminal mR of an amplifier circuit 23R to one end of an inductor 26R when a plug is not connected to the headphone jack 30, while the switch disconnects the negative phase terminal mR from the one end of the inductor 26R when a plug is connected to the headphone jack 30.

Description

  The present invention relates to a class D power amplifier with a jack in which components are shared during output to a speaker and output to a headphone or the like.

A class D power amplifier converts an input signal such as an analog audio signal into a pulse modulation signal such as PWM (pulse width modulation) or PDM (pulse density modulation), and switches a transistor based on the pulse modulation signal. After power amplification, the amplified signal is demodulated to analog by an integration circuit and supplied to a speaker.
On the other hand, speaker driving methods include a single-ended type (half-bridge type) that drives only one of the two terminals of the speaker and a full-bridge type that differentially drives both terminals. Each type has advantages and disadvantages, but the full bridge type is often adopted because it is evaluated for its ability to cancel the direct current flowing through the speaker as a load and the point that it can be driven with a large amplitude.
When a speaker is differentially driven by a class D power amplifier, the input signal is converted into a pulse modulation signal, and the pulse modulation signal (positive phase signal) is amplified and integrated by class D, and the speaker terminal. And an inverted signal (reverse phase signal) of the pulse modulation signal is amplified and integrated in class D and supplied to the other speaker terminal (see, for example, Patent Document 1).

By the way, in order to be able to listen to music and the like without disturbing the surroundings even under conditions such as midnight, it is necessary to be able to connect headphones or the like to the amplifier. In general, since one of the left (L) channel and one of the right (R) channel are commonly grounded with each other, the headphones are driven in a single-ended manner (see Patent Document 2).
For this reason, as a configuration for connecting headphones to a class D power amplifier that differentially drives the speakers, the following can be considered in terms of two channels (stereo). That is, as shown in FIG. 4, a configuration in which an amplifier circuit for amplifying an analog audio signal at class AB for headphones is provided for two channels, or as shown in FIG. 5, a pulse width modulated signal is used for headphones. A configuration in which two single-ended amplification circuits for class D output are provided for two channels can be considered.

JP 2002-330035 A (refer to FIG. 4 in particular) Japanese Utility Model Publication No. 62-167432

However, in any configuration, an amplifier circuit dedicated to headphones is required in addition to the amplifier circuit for differentially driving the speaker with a class D power amplifier.
The present invention has been made in view of such circumstances, and one of its purposes is to add a dedicated amplifier circuit even when headphones are connected when the speakers are differentially driven in class D. And to provide a technology capable of driving the headphones and the like in a single-ended manner.

  In order to achieve the above object, the class D power amplifier according to the present invention outputs a positive-phase pulse modulation signal from a positive-phase terminal among pulse-modulated signals obtained by pulse-modulating an input signal. An amplifier circuit that outputs a pulse modulation signal having a phase opposite to that of the pulse modulation signal from a negative phase terminal, one end connected to one of the positive phase terminal and the negative phase terminal, and the other end to one of output terminals to the speaker A first inductor connected to the first inductor, a first capacitor having one end connected to the other end of the first inductor, and at least one end connected to the first capacitor when the plug is not connected to a jack for external output. A second inductor connected to the other end of the speaker and the other of the output terminals to the speaker, and one end connected to the other end of the first inductor, the other end being ungrounded among the jack terminals When the plug is not connected to the second capacitor connected to the child and the jack, the other of the positive phase terminal and the negative phase terminal is connected to one end of the second inductor, and the plug is connected to the jack. A switch that disconnects the other of the positive-phase terminal and the negative-phase terminal from one end of the second inductor. According to this configuration, it is possible to drive a headphone or the like in a single-ended type without providing a separate amplifier circuit, so that parts can be shared.

  In the present invention, a control circuit may be provided that changes the signal amplitude output from the other end of the first inductor when the plug is connected to the headphone jack from when the plug is not connected. According to this configuration, it is possible to prevent the sound volume from changing greatly when the speaker is switched to headphones or the like.

It is a figure which shows the structure of the system containing the class D power amplifier which concerns on embodiment. It is operation | movement explanatory drawing at the time of the speaker output in the same power amplifier. It is operation | movement explanatory drawing at the time of the headphone output in the power amplifier. It is a figure which shows the structure of the conventional power amplifier. It is a figure which shows another structure of the conventional power amplifier.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration example of a system 1 including a class D power amplifier 10 according to the embodiment. As shown in this figure, the system 1 is a class D power amplifier 10 that amplifies and outputs a two-channel audio signal, a speaker 2L that acoustically converts a signal for the left channel, and a signal for the right channel. The configuration includes a speaker 2R for conversion.
For example, a digital audio signal Sdata conforming to the Inter-IC Sound (I2S) standard is serially supplied to the class D power amplifier 10 with the channel being distinguished by the clock signal LRclk in synchronization with the bit clock Bclk.
The D / A converter (DAC) 12 first separates the audio signal Sdata for each channel, and secondly converts the left channel audio signal into an analog signal and outputs the analog signal to the supply line L1. Are converted into analog signals and output to the supply line R1.
When the D-class power amplifier 10 inputs an analog audio signal instead of digital, the analog signal may be directly supplied to the supply line L1 for the left channel and to the supply line R1 for the right channel. good.

  The processing system after the D / A converter 12 in the class D power amplifier 10 is divided into a left channel and a right channel. Here, the left channel will be described first. First, the switch 21L has one end connected to the supply line L1 and the other end grounded, and is turned on or off in accordance with an instruction from the control circuit 42 described later.

The class D power amplifier 10 is provided with a volume not shown, and a coefficient α corresponding to the rotation angle is supplied. The multiplier 43 outputs a coefficient γ obtained by multiplying the coefficient α by the coefficient β supplied from the control circuit 42. The arithmetic circuit 22L multiplies the voltage amplitude of the audio signal output to the supply line L1 by a coefficient γ and outputs the result as an audio signal Lin. This audio signal Lin is an input signal to be amplified.
The amplifying circuit 23L converts the audio signal Lin into a pulse modulation signal, and then amplifies the positive phase signal of the pulse modulation signal using a DC power source and performs class D amplification to output from the positive phase terminal pL. A negative phase signal in which the logic is inverted with respect to the positive phase signal is amplified by class D and output from the negative phase terminal mL.
Note that the ground potential is approximately between the low-order side and the high-order side of the DC power supplies of the amplifier circuits 23L and 23R.

In the inductor 24L, one end is connected to the positive phase terminal pL, and the other end is connected to the positive terminal PL for the left channel among the output terminals in the class D power amplifier 10. One end of the capacitor 25L is connected to the other end of the inductor 24L. In the inductor 26L, one end is connected to the negative phase terminal mL via the switch 28L, the other end is the other end of the capacitor 25L, and the negative electrode for the left channel among the output terminals in the class D power amplifier 10. Connected to terminal ML.
When the switch 28L is on, the inductor 24L, the capacitor 25L, and the inductor 26L constitute a low-pass filter. The inductor 24L, the capacitor 25L, and the inductor 26L constituting the low-pass filter demodulate the pulse modulation signal output from the positive phase terminal pL into an analog signal, and demodulate the pulse modulation signal output from the negative phase terminal mL into an analog signal. .

The switch 28L is turned on or off in accordance with an instruction from the control circuit 42.
The speaker 2L has one of the two terminals connected to the positive terminal PL and the other terminal connected to the negative terminal ML.
One end of the DC cut capacitor 29L is connected to a connection point between the other end of the inductor 24L and the capacitor 25L via a resistor 27L. The resistor 27L disperses the energy stored in the inductor 24L when the switch 28L is switched on / off. The attenuation of the signal by the resistor 27L may be corrected by adjusting each coefficient in the class D power amplifier 10. The other end of the capacitor 29L is connected to the output terminal 31 for the left channel, which is the non-ground side in the headphone jack 30.

Next, the right channel will be described in the same manner as the left channel. The switch 21R is connected to the supply line R1 at one end and grounded at the other end, and follows the instructions of the control circuit 42 in the same manner as the switch 21L. Turn on and off. The arithmetic circuit 22R multiplies the voltage amplitude of the audio signal output to the supply line R1 by a coefficient γ and outputs the result as an audio signal Rin. The amplifier circuit 23R, which is an input signal to be amplified by the audio signal Rin, converts the audio signal Rin into a pulse modulation signal, and then positively classifies the positive phase signal of the pulse-varying signal by class D amplification using a DC power source. While outputting from the phase terminal pR, the negative phase signal of the pulse modulation signal is amplified by class D and output from the negative phase terminal mR.
In the inductor 24R, one end is connected to the positive phase terminal pR, and the other end is connected to the positive terminal PR for the right channel among the output terminals in the class D power amplifier 10. One end of the capacitor 25R is connected to the other end of the inductor 24R. The inductor 26R has one end connected to the reverse phase terminal mR via the switch 28R, the other end connected to the other end of the capacitor 25R, and the negative terminal for the right channel among the output terminals of the class D power amplifier 10. Connected to terminal MR.
When the switch 28R is on, the inductor 24R, the capacitor 25R, and the inductor 26R constitute a low-pass filter. The inductor 24R, capacitor 25R, and inductor 26R constituting the low-pass filter demodulate the pulse modulation signal output from the positive phase terminal pR into an analog signal, and demodulate the pulse modulation signal output from the negative phase terminal mR into an analog signal. .

The switch 28R is turned on and off in accordance with an instruction from the control circuit 42, similarly to the switch 28L.
The speaker 2R has one of the two terminals connected to the positive terminal PR and the other terminal connected to the negative terminal MR.
One end of the DC cut capacitor 29R is connected to a connection point between the other end of the inductor 24R and one end of the capacitor 25R via a resistor 27R. The resistor 27R is provided to disperse the energy stored in the inductor 24R when the switch 28R is switched on / off. The attenuation of the signal by the resistor 27R may be corrected by adjusting each coefficient in the class D power amplifier 10. The other end of the capacitor 29R is connected to the output terminal 32 for the right channel which is the non-ground side in the headphone jack 30.
The terminal 33 in the headphone jack 30 is grounded in order to be shared by one of the left channel and one of the right channel in the output to the headphones.

The sensor 41 detects the connection state or the like of the headphone plug in the headphone jack 30 and supplies a detection signal corresponding to the state or the like to the control circuit 42. More specifically, the sensor 41 detects whether the headphone jack 30 is unplugged or plugged in, and can also be unplugged. For example, it is detected whether the plug is in the process of being inserted from the state or, on the contrary, if the plug is in the state of being inserted, whether the plug is being removed from the state.
If the plug is removed, the control circuit 42 controls the switches 28L and 28R to ON and outputs “1” as the coefficient β. On the other hand, if the plug is in the inserted state, the control circuit 42 controls the switches 28L and 28R to OFF and changes the coefficient β to a preset value that satisfies 0 <β <1. Furthermore, the control circuit 42 controls the switches 21L and 21R to be turned on when the plug is being inserted or removed, and otherwise the switches 21L and 21R are turned off. Control.

  As a mode of detection by the sensor 41, a contact whose potential changes when the plug is inserted may be provided in the headphone jack 30 to detect a change in the potential of the contact, or an optical sensor or the like may be provided. The connection state of the plug and the moving direction of the plug tip may be detected. Further, whether the signals from the amplifier circuits 23L and 23R are output to the speaker or the headphones may be defined by an external control signal such as the I2S standard. When the output is switched from the speaker to the headphones by the external control signal, it may be considered that the plug is inserted until a predetermined time elapses from the switching instruction. Similarly, when the output is switched from the headphone to the speaker by the external control signal, it may be considered that the plug is being removed until a predetermined time elapses from the switching instruction.

Next, the operation of the class D power amplifier 10 according to the embodiment will be described.
When it is detected that the headphones are unplugged, that is, when the audio signal is output from the speakers 2L and 2R, the control circuit 42 outputs “1” as the coefficient β. Is supplied to the arithmetic circuits 22L and 22R as a coefficient γ. In this case, since the control circuit 42 controls the switches 21L and 21R to be off, it does not affect the output signal of the D / A conversion unit 12. Therefore, the voltage amplitudes of the audio signals Lin and Rin are obtained by adjusting the voltage amplitude of the signal converted from the audio signal Sdata to analog according to the rotation angle of the volume, that is, the designated volume.

  In addition, in a state where the plug is removed, the control circuit 42 controls the switches 28L and 28R to be on, so that eventually, of the class D power amplifier 10 shown in FIG. The circuit is as shown in FIG. For this reason, in the class D power amplifier 10 according to the embodiment, the difference between the speaker 2L by the integration signal of the positive phase signal output from the positive phase terminal pL and the integration signal of the negative phase signal output from the negative phase terminal mL. It is driven dynamically. Similarly, the speaker 2R is differentially driven by the integration signal of the positive phase signal output from the positive phase terminal pR and the integration signal of the negative phase signal output from the negative phase terminal mR. As a result, a sound according to the audio signal Sdata is generated from the speakers 2L and 2R at a volume corresponding to the rotation angle of the volume.

  On the other hand, when it is detected that the headphones are plugged in, the control circuit 42 outputs a preset value satisfying 0 <β <1, for example, “0.7” as the coefficient β. Accordingly, the voltage amplitudes of the audio signals Lin and Rin are obtained by changing the voltage amplitude of the signal converted from the audio signal Sdata to analog to a value smaller than the volume specified by the volume at the time of speaker output.

In a state where the plug is inserted, the control circuit 42 controls the switches 28L and 28R to be turned off. As a result, the signal path from the negative phase terminal mL to the speaker 2L is blocked, and the path from the negative phase terminal mR to the speaker 2R is blocked.
In the left channel, the switch 28L is turned off and the signal path from the positive phase terminal pL to the speaker 2L is blocked, so that no voltage is applied across the speaker 2L.
The same applies to the right channel. Since the switch 28R is turned off and the signal path from the positive phase terminal pR to the speaker 2R is blocked, no voltage is applied across the speaker 2R.
Therefore, if the plug is in the inserted state, among the class D power amplifier 10 shown in FIG. 1, the circuits after the amplifier circuits 23L and 23R are actually connected to the speakers 2L and 2R as shown in FIG. Each of the D-class power amplifiers 10 is electrically disconnected. For this reason, no sound is generated from the speakers 2L and 2R.

The signal output from the positive phase terminal pL is supplied to the capacitor 29L via the resistor 27L, and after the direct current component is cut by the capacitor 29L, the signal is supplied to the driver unit 101L for the left ear in the headphones 100. The As a result, the driver unit 101L is driven in a single-ended manner by the amplifier circuit 23L, and as a result, generates a sound according to the audio signal Lin.
Similarly, the signal output from the positive phase terminal pR is supplied to the capacitor 29R via the resistor 27R, the direct current component is cut by the capacitor 29R, and supplied to the driver unit 101R for the right ear. As a result, the driver unit 101R is driven as a single end type by the amplifier circuit 23R, and as a result, generates a sound according to the audio signal Rin.

In general, when comparing the load between a speaker and headphones, the load on the headphones is smaller. In addition, in the embodiment, the speakers are driven differentially, while the headphones are driven by a single-ended type, that is, only one pole. For this reason, when the volume is fixed and the speaker and the headphones are switched alternately, unless there is any ingenuity, there is a tendency for a large difference in the volume felt when listening. Alternatively, when switching between a speaker and headphones, it is necessary to rotate the volume in order to try to listen at the same volume, which tends to give a listener a complicated feeling. On the other hand, in the class D power amplifier 10 according to the embodiment, the control circuit 42 changes the coefficient β to be small when the headphone plug is inserted, so that the coefficient γ is unplugged as a result. Smaller than when For this reason, it is possible to reduce the difference in volume that is felt when switching from a speaker to headphones.
Note that the value of the coefficient β output with the plug inserted may be selected in consideration of the characteristics of the headphones used. Further, if there are special circumstances such as a heavy load on the headphones, the coefficient β may be set larger than “1”.

  When the headphones are in the process of being plugged in or unplugged, the control circuit 42 controls the switches 21L and 21R to be on. As a result of this control, the supply lines L1 and R1 of the D / A converter 12 are both forcibly grounded, so that the voltage amplitude of the audio signals Lin and Rin is zero regardless of the audio signal Sdata and the rotation angle of the volume. become. Therefore, according to the present embodiment, no unpleasant sound is generated from the speakers 2L, 2R or the headphones when the plug is attached or detached.

As described above, according to the class D power amplifier 10 according to the present embodiment, the left and right channels of the headphones are used by using the amplifier circuit 23L for driving the speaker 2L and the amplifier circuit 23R for driving the speaker 2R. Since each is driven by a single end type, there is no need to provide a separate amplifier circuit for headphones. Therefore, according to the present embodiment, compared with the amplifiers shown in FIGS. 4 and 5, the circuit space can be reduced or simplified by sharing the amplifier circuit.
The class D power amplifier 10 can be applied not only to two stereo channels but also to a mono amplifier having only one channel such as an earphone.

In addition to the above, the present invention can be variously applied and modified as follows.
In the class D power amplifier 10 according to the embodiment, the volume adjustment is achieved by changing the voltage amplitude of the audio signals Lin and Rin by the arithmetic circuits 22L and 22R. This may be achieved by changing the amplitude of the reference wave (triangular wave or sawtooth wave) used for the conversion, changing the amplitude of the pulse modulation signal in the amplifier circuits 23L and 23R, or appropriately combining them. In such a configuration, the control circuit 42 changes the amplitude of the reference wave for the amplifier circuits 23L and 23R or changes the power supply voltage for the amplifier circuits 23L and 23R according to the connection state of the plug. The amplitude of the pulse modulation signal is changed.
In the embodiment, the switches 28L and 28R are provided for the negative phase signal (negative electrode side), but may be provided for the positive phase signal (positive electrode side). If the switches 28L and 28R are provided for the positive phase signal (positive side), the headphone is driven in the reverse phase as it is, and therefore a circuit for returning it to the positive phase may be added.

  In addition, the system 1 may include a configuration for adjusting the output volume according to the impedance of the headphones connected to the headphone jack 30. Specifically, an impedance detection circuit that detects the impedance of the headphones connected to the headphone jack 30 is provided, and the impedance detected by the impedance detection circuit is input to the control circuit 42. Then, the control circuit 42 performs control to make the output volume from the headphones constant by adjusting (optimizing) the coefficient β based on the impedance detected by the impedance detection circuit. Thereby, the variation in the output volume caused by the headphones connected to the headphone jack 30 is suppressed.

DESCRIPTION OF SYMBOLS 1 ... System, 2L (2R) ... Speaker, 10 ... Class D power amplifier, 23L (23R) ... Amplifier circuit, 24L (24R) ... Inductor (first inductor), 25L (25R) ... Capacitor (first capacitor), 26L (26R) ... inductor (second inductor), 27L (27R) ... resistance, 28L (28R) ... switch, 29L (29R) ... capacitor (second capacitor), 30 ... headphone jack, 41 ... sensor, 42 ... control circuit

Claims (2)

Amplification that outputs a positive-phase pulse modulation signal from the positive-phase terminal among the pulse-modulated signals obtained by pulse-modulating the input signal, and outputs a reverse-phase pulse modulation signal from the negative-phase terminal to the positive-phase pulse modulation signal Circuit,
A first inductor having one end connected to one of the positive phase terminal and the negative phase terminal and the other end connected to one of the output terminals to the speaker;
A first capacitor having one end connected to the other end of the first inductor;
A second inductor whose other end is connected to the other end of the first capacitor and the other output terminal to the speaker when a plug is not connected to at least a jack for external output;
One end is connected to the other end of the first inductor, and the other end is connected to a non-grounded terminal among the terminals of the jack;
When the plug is not connected to the jack, the other of the positive phase terminal and the negative phase terminal is connected to one end of the second inductor, and when the plug is connected to the jack, the positive phase terminal and the jack A switch for disconnecting the other end of the negative phase terminal from one end of the second inductor;
A D-class power amplifier comprising: 2. The control circuit according to claim 1, further comprising: a control circuit that changes a signal amplitude output from the other end of the first inductor when the plug is connected to the jack from when the plug is not connected. 3. Class D power amplifier.

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