JP4003257B2 - Pulse width modulation audio amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pulse width modulation audio amplifier used in various acoustic devices.
[0002]
[Prior art]
Conventionally, the triangular wave oscillator and the voltage comparison circuit are stable before starting the signal reproduction from the speaker so that no noise such as pop sound is generated when starting or stopping the signal reproduction from the speaker or when the power supply voltage drops. Finally, there is a pulse width modulation audio amplifier in which the power amplifying unit is activated and the power amplifying unit is stopped first when the signal reproduction from the speaker is stopped.
[0003]
A conventional pulse width modulation audio amplifier will be described. FIG. 7 is a circuit diagram of a conventional pulse width modulation audio amplifier. In FIG. 7, 1 is a signal source of an analog input signal wave, 2 is a triangular wave oscillator, 3 is a voltage comparison circuit for comparing the analog input signal wave and the triangular wave, and 5 is a pulse width modulation waveform output from the voltage comparison circuit 3. A power amplifying unit for amplifying the power, 6 is a feedback circuit for feeding back the pulse width modulated wave amplified by the power amplifying unit 5 to the voltage comparison circuit 3, and 9 is an amplifier activation control signal for activating the power amplifying unit 5. Is an amplifier stop control signal for stopping the power amplifying unit 5, 7 is a low-pass filter for demodulating the output of the power amplifying unit 5 into an analog output signal wave, 8 is a speaker, and 11 is a power source for the pulse width modulation audio amplifier. .
[0004]
FIG. 8 is an explanatory diagram of a pulse width modulation wave at the start of signal reproduction in a conventional pulse width modulation audio amplifier. In FIG. 8, 12 is a pulse width modulated wave output from the power amplifier 5, 13 is a triangular wave input to the voltage comparison circuit 3, 14 is an analog input signal wave input to the voltage comparison circuit 3, and T1 is power amplification. This is the time required for starting the unit 5. FIG. 9 is a voltage waveform diagram at the speaker terminal at the start of signal reproduction in the conventional pulse width modulation audio amplifier, and FIG. 10 is a schematic explanation of the pulse width modulation wave at the time of stopping signal reproduction in the conventional pulse width modulation audio amplifier. It is a figure and T4 is the stop required time of the power amplification part 5. FIG. FIG. 11 is a voltage waveform diagram at the speaker terminal when signal reproduction is stopped in a conventional pulse width modulation audio amplifier.
[0005]
[Problems to be solved by the invention]
In the conventional pulse width modulation audio amplifier as described above, the pulse width modulation wave 12 corresponding to the analog input signal wave 14 of the signal source 1 is created from the voltage comparison circuit 3 at the start of signal reproduction from the speaker 8, and finally Since the power amplifying unit 5 is activated by the amplifier activation control signal 9, the pulse width of the pulse width modulation wave 12 becomes wider as the analog input signal wave 14 of the signal source 1 becomes larger, and when the signal reproduction from the speaker 8 is started. In the initial state, as shown in FIG. 9, a pulse 15a having a large amount of energy is suddenly generated in the voltage waveform 15 at the speaker terminal, and the speaker 8 can be heard as noise. Further, when the signal reproduction from the speaker 8 is stopped, the power amplifying unit 5 is first stopped by the amplifier stop control signal 10, so that the pulse of the pulse width modulation waveform 12 becomes larger as the analog input signal wave 14 of the signal source 1 becomes larger. The initial state when the signal reproduction from the speaker 8 is stopped is wide as shown in FIG. 11, and a high-energy pulse 15b is generated in the voltage waveform 15 at the speaker terminal and sounds as noise. Further, when the voltage of the power source 11 of the pulse width modulation audio amplifier is dropped, the power amplifying unit 5 is stopped first, so that there is a problem that noise is similarly heard.
[0006]
The present invention solves the above problems, and even when the analog input signal wave of the signal source is a large input, noise generation at the start, stop, and power supply voltage drop of the signal from the speaker can be reduced as much as possible. An object of the present invention is to provide a pulse width modulation audio amplifier that can be heard and has high quality in terms of hearing.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a pulse width modulation audio amplifier according to the present invention includes a voltage comparison circuit that compares an analog input signal wave from a signal source and a triangular wave from a triangular wave generator, and a pulse width output from the voltage comparison circuit. A power amplifier that amplifies the modulated wave, a low-pass filter that demodulates the pulse width modulated wave amplified by the power amplifier into an analog output signal wave, and the voltage comparison circuit that converts the power amplified pulse width modulated wave And a switching circuit for switching off the analog input signal wave between the feedback circuit and the signal source, and when starting signal reproduction from the speaker, the amplifier activation control signal is connected to the power amplification unit. To the switch circuit, and after starting the power amplification unit in the absence of the analog input signal wave, the analog input signal wave is To enter the circuit, it is obtained so as to operate the switch circuit to preset the long startup required time from the start time required for the power amplifier based on the amplifier activation control signal.
[0008]
As a result, at the start of signal reproduction from the speaker, the power amplification unit is activated first in the absence of the analog input signal wave, so that the initial pulse width of the pulse width modulation waveform is narrow, and the pulse energy is small. There is very little noise audible from the speaker. After that state, the switch circuit is operated to input the analog input signal wave to the voltage comparison circuit. Therefore, even if the initial value of the analog input signal wave when the switch circuit is operated is a large input, the pulse width modulation waveform The peak value does not change, only the amplitude changes, and the analog input signal wave can be smoothly amplified and signal reproduction from the speaker can be started.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the present invention, a voltage comparison circuit for comparing an analog input signal wave from a signal source with a triangular wave from a triangular wave generator, and a power amplification of a pulse width modulated wave output from the voltage comparison circuit A power amplifying unit, a low-pass filter that demodulates the pulse width modulated wave amplified by the power amplifying unit into an analog output signal wave, and a feedback circuit that feeds back the power amplified pulse width modulated wave to the voltage comparison circuit And a switch circuit for connecting an analog input signal wave provided between the feedback circuit and the signal source, and an amplifier activation control signal at the start of signal reproduction from the speaker as the power amplification unit and the switch circuit. And the power amplifier is first activated in the absence of the analog input signal wave, and then the analog input signal wave is input to the voltage comparison circuit. , A pulse width modulation audio amplifier that activates the switch circuit by presetting a required start time longer than the required start time of the power amplifier based on the amplifier start control signal, and starting the reproduction of a signal from a speaker In some cases, the power amplification unit is activated first in the absence of the analog input signal wave, so that the initial pulse width of the pulse width modulation waveform is narrow, the pulse energy is small, and the noise heard from the speaker is extremely small. After that state, the switch circuit is operated to input the analog input signal wave to the voltage comparison circuit. Therefore, even if the initial value of the analog input signal wave when the switch circuit is operated is a large input, the peak value of the pulse width modulation waveform Does not change, only the amplitude changes, and the analog input signal wave can be smoothly amplified and signal reproduction from the speaker can be started.
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, an amplifier stop control signal is supplied to the power amplifier and the switch circuit when the signal reproduction from the speaker is stopped, and the switch circuit is operated. After stopping the input of the analog input signal wave to the voltage comparison circuit first, a stop required time longer than the stop required time of the switch circuit is set in advance based on the amplifier stop control signal to stop the power amplifying unit. When the signal reproduction from the speaker is stopped, the input of the analog input signal wave to the voltage comparison circuit is stopped first when the reproduction of the signal from the speaker is stopped. Even if the final value of the analog input signal wave is large, the peak value of the pulse width modulation waveform does not change, only the amplitude changes. It is possible to stop the signal reproduction from the speakers. Thereafter, since the power amplifying unit is finally stopped in the absence of the analog input signal wave, the final pulse width of the pulse width modulation waveform is narrow, the pulse energy is small, and the noise heard from the speaker is very small.
[0011]
According to a third aspect of the present invention, in the first aspect of the invention, when the signal reproduction from the speaker is stopped due to a power supply voltage drop, the switch circuit operates first regardless of the amplifier stop control signal. After the input of the analog input signal wave to the voltage comparison circuit is stopped and signal reproduction from the speaker is stopped, the voltage amplification unit can be stopped, and then the switch circuit of the power amplification unit can be stopped so that the voltage amplification unit can be stopped. This is a pulse width modulation audio amplifier with a high stop power supply voltage, and when the signal reproduction from the speaker is stopped due to a power supply voltage drop, the stop power supply voltage of the switch circuit is set higher than the stop power supply voltage of the power amplifier. Therefore, after stopping the input of the analog input signal wave to the voltage comparison circuit first, the power amplification unit is stopped last, so the switch Even if the final value of the analog input signal wave during the operation of the road is a large input, the peak value of the pulse width modulation waveform does not change, only the amplitude changes, and the trailing edge of the analog input signal wave is smoothly amplified. There is also very little noise due to the last pulse when the operation of the power amplifier is stopped.
[0012]
(Embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a circuit diagram of a pulse width modulation audio amplifier according to the first embodiment. In the connection of a voltage comparison circuit 3 that compares an analog input signal wave from a signal source 1 and a triangular wave from a triangular wave oscillator 2, the signal source 1 Is connected to the voltage comparison circuit 3 through a switch circuit 4 that cuts off the analog input signal wave. The pulse width modulation wave output from the voltage comparison circuit 3 is amplified by the power amplifier 5 and fed back to the voltage comparison circuit 3 by the feedback circuit 6. On the other hand, the pulse width modulated wave amplified by the power amplifying unit 5 is reproduced by a speaker 8 connected via a low-pass filter 7 that demodulates to an analog output signal wave.
[0014]
FIG. 2 is a conceptual diagram of a pulse width modulation waveform at the start of signal reproduction, and FIG. 3 is a voltage waveform diagram at the speaker terminal at the start of signal reproduction.
[0015]
At the start of signal reproduction from the speaker 8, an amplifier activation control signal 9 is supplied to the power amplifier 5 and the switch circuit 4. Here, the required startup time T1 of the power amplifying unit 5 is set smaller than the required startup time T2 of the switch circuit 4. Therefore, since the power amplifying unit 5 is started first in the absence of the analog input signal wave 14 before the switch circuit 4 is operated, the pulse width modulation waveform 12 output from the power amplifying unit 5 as shown in FIG. The pulse width in the initial state is narrow, the pulse energy is small, and the noise audible from the speaker 8 is extremely small. Even after the initial state, as shown in FIG. 3, only the carrier leakage 15c of the switching waveform when no analog signal is input is generated in the audible frequency band, and the audible noise heard from the speaker 8 is extremely small. After that state, the analog input signal wave 14 of the signal source 1 is input to the voltage comparison circuit 3. For this reason, since the switch circuit 4 having a preset start time T2 longer than the start required time T1 of the power amplifier 5 is operated using the amplifier start control signal 9, even if the initial value of the analog input signal wave 14 is a large input, The peak value of the pulse width modulation waveform 12 does not change, only the amplitude changes, and the rise of the analog input signal wave can be smoothly amplified and signal reproduction from the speaker 8 can be started.
[0016]
4 is a conceptual diagram of a pulse width modulation waveform when signal reproduction is stopped, and FIG. 5 is a voltage waveform diagram at a speaker terminal when signal reproduction is stopped.
[0017]
When signal reproduction from the speaker 8 is stopped, an amplifier stop control signal 10 is supplied to the power amplifier 5 and the switch circuit 4. Here, the required stop time T3 of the switch circuit 4 is set smaller than the required stop time T4 of the power amplifier 5. Therefore, since the input of the analog input signal wave 14 to the voltage comparison circuit 3 is first stopped by the operation of the switch circuit 4, as shown in FIG. 4, even if the final value of the analog input signal wave 14 is a large input, the pulse width modulation waveform The peak value of 12 does not change, only the amplitude changes, and the signal reproduction from the speaker 8 can be smoothly stopped. As for the output of the speaker 8 thereafter, as shown in FIG. 5, only the carrier leakage 15c of the switching waveform when no analog signal is input occurs in the audible frequency band, and the noise on hearing is very small. Finally, using the amplifier stop control signal 10, the power amplifying unit 5, which has previously set a stop required time T 4 longer than the stop required time T 3 of the switch circuit 4, is stopped without the analog input signal wave 14. The final pulse width of the pulse width modulation waveform is narrow, the pulse energy is small, and the noise audible from the speaker 8 is very small.
[0018]
FIG. 6 is an explanatory diagram showing the relationship between the voltage waveform at the speaker terminal and the power supply voltage waveform when signal reproduction is stopped when the power supply voltage drops.
[0019]
When the signal reproduction from the speaker 8 is stopped due to the voltage drop of the power supply 11, the stop power supply voltage V1 of the switch circuit 4 is compared with the stop power supply voltage V2 of the power amplifier 5 regardless of the amplifier stop control signal 10. Is set high. Accordingly, since the switch circuit 4 is stopped when a drop in the amplifier power supply voltage 16 is detected, the input of the analog input signal wave 14 to the voltage comparison circuit 3 is stopped first. Thereafter, since the power amplifying unit 5 is finally stopped, the signal reproduction from the speaker 8 can be smoothly stopped, and the final pulse noise heard from the speaker 8 is extremely small. In the case of audio equipment used for car audio, the battery voltage as a power source may drop when the engine is started, and the circuit of the present invention can extremely reduce unpleasant pulse noise.
[0020]
In the present embodiment, a switch using a field effect transistor is used as the switch circuit 4, but a transistor switch or a relay circuit may be used. In this embodiment, the switch circuit 4 that cuts off the analog input signal wave is out of the loop of the feedback circuit 6. However, the same effect can be obtained as a non-feedback pulse width modulation audio amplifier by removing the feedback circuit. .
[0021]
【The invention's effect】
As described above, the pulse width modulation audio amplifier of the present invention is provided with the switch circuit that cuts off the previous analog input signal wave of the voltage comparison circuit, and the amplifier activation control signal is transmitted to the power amplification unit at the start of signal reproduction from the speaker. And the switch activation circuit, the power amplifier is first activated in the absence of the analog input signal wave, and then the amplifier activation control signal is input so that the analog input signal wave is input to the voltage comparison circuit. Since the switch circuit that has been set in advance with a start time longer than the start time required for the power amplifier is used, the noise due to the initial pulse at the start of the operation of the power amplifier is very small, and the switch Even if the initial value of the analog input signal wave during circuit operation is large, the peak value of the pulse width modulation waveform does not change, only the amplitude changes. Ri can be started smoothly by amplifying the rising edge of the analog input signal wave without noise due to pulse signals reproduced from the speaker.
[0022]
When stopping signal reproduction from the speaker, the amplifier stop control signal is supplied to the power amplifier and the switch circuit, and the switch circuit is activated to stop the analog input signal wave input to the voltage comparison circuit first. After that, the amplifier amplifying control signal is used to stop the power amplifying unit that has been set in advance to the stop required time longer than the required stop time of the switch circuit. Even if the final value of the signal wave is a large input, the peak value of the pulse width modulation waveform does not change, only the amplitude changes, and the falling edge of the analog input signal wave is smoothly amplified, There is also very little noise from the last pulse.
[0023]
Further, even when the signal reproduction from the speaker is stopped due to a power supply voltage drop, the stop power supply voltage of the switch circuit is set higher than the stop power supply voltage of the power amplifier regardless of the amplifier stop control signal. Therefore, after stopping the input of the analog input signal wave to the voltage comparison circuit first, the power amplifying unit is stopped last, so even if the final value of the analog input signal wave during the operation of the switch circuit is a large input, the pulse width The peak value of the modulation waveform does not change, only the amplitude changes, the fall of the analog input signal wave is smoothly amplified, and the noise due to the last pulse when the operation of the last power amplifier is stopped is extremely small.
[0024]
Therefore, even when the analog input signal wave of the signal source is a large input, noise generation at the start, stop and power supply voltage drop of the signal from the speaker can be reduced as much as possible, and audio equipment used for car audio In this case, it is possible to provide a superior pulse width modulation audio amplifier that can cope with a drop in battery voltage, which is a problem in the case of engine startup, without generating noise, and has high quality in terms of hearing.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a pulse width modulation audio amplifier according to Embodiment 1 of the present invention. FIG. 2 is a conceptual diagram of a pulse width modulation waveform at the start of signal reproduction of the amplifier. Fig. 4 is a conceptual diagram of the pulse width modulation waveform when the signal reproduction of the amplifier is stopped. Fig. 5 is a voltage waveform diagram of the speaker terminal when the signal reproduction of the amplifier is stopped. FIG. 7 is a circuit diagram of a conventional pulse width modulation audio amplifier. FIG. 8 is a circuit diagram of a conventional pulse width modulation audio amplifier. FIG. 9 is a conceptual diagram of a pulse width modulation waveform at the start of reproduction. FIG. 9 is a voltage waveform diagram at the speaker terminal when signal reproduction is started by the amplifier. FIG. 10 is a pulse width modulation waveform when signal reproduction is stopped by the amplifier. Conceptual diagram 11 voltage waveform diagram of the speaker terminal at the time of signal reproduction stop by the amplifier [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Signal source 2 Triangular wave oscillator 3 Voltage comparison circuit 4 Switch circuit 5 Power amplification part 6 Feedback circuit 7 Low pass filter 8 Speaker 9 Amplifier starting control signal 10 Amplifier stop control signal 11 Power supply 12 Pulse width modulation waveform 13 output from the power amplification part Triangular wave 14 Analog input signal wave 15 Speaker terminal voltage waveform T1 Power amplifier start time T2 Switch circuit start time T3 Switch circuit stop time T4 Power amplifier stop time V1 Switch circuit stop power supply voltage V2 Stop power supply voltage of power amplifier

Claims (3)

A voltage comparison circuit that compares the analog input signal wave from the signal source with the triangular wave from the triangular wave generator, a power amplification unit that amplifies the pulse width modulated wave output from the voltage comparison circuit, and the power amplification unit A low-pass filter that demodulates the amplified pulse width modulated wave into an analog output signal wave, a feedback circuit that feeds back the power amplified pulse width modulated wave to the voltage comparison circuit, and a circuit between the feedback circuit and the signal source And a switch circuit that cuts off the analog input signal wave, and supplies an amplifier activation control signal to the power amplifier and the switch circuit at the start of signal reproduction from the speaker, and the power amplifier is connected to the analog input. The amplifier start-up control signal is input so that the analog input signal wave is input to the voltage comparison circuit after starting in the absence of a signal wave first. Pulse width modulation audio amplifier with preset long startup required time from the start time required for the power amplifier and configured to actuate the switch circuit based on.   When the signal reproduction from the speaker is stopped, an amplifier stop control signal is supplied to the power amplifier and the switch circuit, and the switch circuit is activated to stop the input of the analog input signal wave to the voltage comparison circuit first. 2. The pulse width modulation audio amplifier according to claim 1, wherein the power amplifying unit is stopped by presetting a stop required time longer than the stop required time of the switch circuit based on the amplifier stop control signal.   When the signal reproduction from the speaker is stopped due to a power supply voltage drop, regardless of the amplifier stop control signal, the switch circuit operates first to stop the input of the analog input signal wave to the voltage comparison circuit, 3. The pulse width modulation audio amplifier according to claim 2, wherein the stop power supply voltage of the switch circuit is set higher than the stop power supply voltage of the power amplifier so that the voltage amplifier can be stopped after the signal reproduction from the speaker is stopped. .

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