JPH06232638A - Muting circuit - Google Patents

Abstract

PURPOSE:To provide a muting circuit for a class D amplifier applying high efficiency power amplification to an audio signal, especially in which production of a shock noise sound at application of power or power interruption is prevented. CONSTITUTION:A switch section 1 outputs a switch control signal of a high or a low level based on a DC voltage obtained by rectifying and smoothing an AC voltage outputted from a secondary winding side of a power transformer. A driver section 8 is operated only when a driver control signal is at a low level and outputs a drive signal to drive a pulse amplifier 12. A driver control section 2 outputs a driver control signal to validate the operation of the driver section 8 after lapse of a time based on a time constant when the switch control signal is at a high level and outputs a driver control signal to invalidate the operation of the driver section 8 momentarily when the switch control signal is at a low level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a class D amplifier for highly efficient power amplification of an acoustic signal, and more particularly to a muting circuit for preventing impact noise when the power is turned on or off.

[0002]

2. Description of the Related Art In recent years, two-state modulation has been used as a signal processing method for high-efficiency power amplifiers for acoustic signals, and has the advantage that particularly high-level power can be processed with high efficiency.

A conventional signal processing method of a two-state modulation amplifier for the purpose of high efficiency power amplification is, for example, a PWM (Pulse Widt).
h Modulation) or PDM (Pulse Density Modula)
is known, and is disclosed as a PWM type power amplifier in Japanese Patent Laid-Open No. 2-177606.

The signal processing method of the conventional two-state modulation power amplifier will be described below. FIG. 4 shows a block diagram of this conventional two-state modulation amplifier. In FIG. 4, 9 is an analog signal input terminal, 10 is a comparator,
11 is a driver unit, 12 is a pulse amplifier, 13 and 14
Is a coil and a capacitor that form a low-pass filter,
Reference numeral 15 is an output terminal, 16 is a load, 17 is a triangular wave signal generator, 18 is an FM modulator, 19 is a basic signal oscillator, and 20 is a random signal oscillator.

The operation of the two-state modulation amplifier configured as above will be described below.

First, the acoustic signal input to the analog signal input terminal 9 is input to the (-) input terminal of the comparator 10, and the triangular wave signal is input from the triangular wave signal generator 17 to the (+) input terminal of the comparator 10. To be done. Amplitudes of these two types of signals are compared by a comparator 10 and converted into a 1-bit digital signal. That is, the output C _{out of the} comparator 10 is C _out = 0 when the acoustic signal> triangular wave signal and C _out = 1 when the acoustic signal <triangular wave signal.

From this, it can be seen that C _out was converted into a two-state modulation signal with the frequency of the triangular wave signal as the carrier.

The output C _{out of the} comparator 10 is amplified by the driver unit 11 and further power-amplified by the pulse amplifier 12. An unnecessary component is removed from the power-amplified two-state modulation signal by a low-pass filter including a coil 13 and a capacitor 14 to become an acoustic signal, and the output terminal 15
Is output from. Further, in order to improve the characteristics of the amplifier, the output of the pulse amplifier 12 is changed to (-) of the comparator 10.
Feedback is applied to the input terminal via a resistor.

Further, the triangular wave signal is generated by FM-modulating the basic signal generated by the basic signal oscillator 19 and the random signal generated by the random signal oscillator 20 by the FM modulator 18, and outputting the output signal of the FM modulator 18 by the triangular wave signal. Generator 1
It is converted into a triangular wave signal by 7. As a result, the carrier signal for converting the acoustic signal input to the analog signal input terminal 9 into the two-state modulation signal is energy-distributed, so that the degree of interference with other electronic and electrical devices can be reduced.

On the other hand, as a power supply method used for the above circuit, for example, a circuit as shown in FIG. 5 can be considered. In FIG. 5, 21 is a power transformer, 24 is a rectifying unit, and 23 is a smoothing unit, and the AC voltage output from the secondary side terminal of the power transformer 21 is rectified by the rectifying unit 24 to the positive (+) pole and the negative (-). The ripple is removed by the smoothing unit 23 after being rectified to the pole. The DC voltage output from the smoothing unit 23 is supplied as + Vcc and −Vcc to each circuit such as the comparator 10 and the driver unit 11.

By the way, when the power supply of the two-state modulation power amplifier having the above-mentioned configuration is turned on or off, a transient DC voltage value is output due to the time constant of the smoothing section 23, so that it is in an unstable state. A circuit operating state may occur, and as a result, an impact sound or noise may be output from the output terminal 15 and the speaker may be damaged. As a so-called muting circuit for avoiding the generation of this impulsive sound, a switch is provided between the driver unit 11 and the pulse amplifier 12 or in the feedback path between the pulse amplifier 12 and the comparator 10 at the time of power-on or power-off. A method of holding the non-connection state for a certain period of time immediately after the time may be considered.

[0012]

However, in the above muting circuit, both the former and the latter cause disconnection or connection of the transmission path of the switching waveform on which the audio signal is superposed, which causes not only a contact failure but also a switch. Therefore, there is a problem in that the performance of the amplifier, especially the distortion rate and the amount of unnecessary radiation noise is increased, because an extension wiring for connecting to is required.

The present invention solves the above-mentioned conventional problems, and provides a muting circuit capable of reliably avoiding the impact noise at the time of power-on and power-off and without affecting the performance of the amplifier. The purpose is to do.

[0014]

In order to achieve this object, the muting circuit of the present invention uses a diode to rectify an AC voltage output from the secondary side of a power transformer according to ON or OFF of a power switch. A switch section for outputting a high or low level switch control signal based on a DC voltage value obtained by smoothing by a capacitor, a driver section for outputting a drive signal for driving a pulse amplifier of a class D amplifier, and a switch Immediately after the power is turned on according to the switch control signal output from the control section, a driver control signal is output to enable the driver section operation after a lapse of time based on a predetermined time constant, and the driver section operation is disabled immediately after the power is turned off. And a driver control unit that instantaneously outputs a driver control signal for performing the operation.

In the muting circuit of the present invention, a DC voltage value obtained by rectifying an AC voltage output from the secondary side of the power transformer with a diode and then smoothing it with a capacitor according to whether the power switch is on or off. A switch unit that outputs a high or low level switch control signal based on the output signal, a driver unit that outputs a drive signal for driving the pulse amplifier of the class D amplifier, and an output signal according to the input high or low level signal A first driver that has an R / S latch that holds or releases the level, and that enables the operation of the driver unit after a lapse of time based on a predetermined first time constant immediately after the power is turned on according to a switch control signal. Outputs the control signal to the R / S latch and immediately after the power is cut off, the first drive for invalidating the operation of the driver The control signal is instantaneously output to the R / S latch, and the second driver control signal for validating the operation of the driver unit during the time based on the second time constant predetermined according to the switch control signal is set to R. It is composed of a driver control section for outputting to the / S latch and an overcurrent detecting section for detecting the current value of the output signal of the class D amplifier and outputting overcurrent information to the R / S latch.

[0016]

According to the present invention, with the above-described structure, the AC voltage output from the secondary side of the power transformer is rectified and smoothed by the diode and the capacitor, and the switch unit makes a high or low level based on the obtained DC voltage value. The switch control signal of is output. Further, immediately after the power is turned on according to the switch control signal, the operation of the driver unit is enabled after a lapse of time based on a predetermined time constant, and immediately after the power is turned off, the driver control signal for invalidating the operation of the driver unit is instantaneously sent. Output from the driver controller. This allows
Since an AC voltage output from the secondary side of the power transformer is detected to enable or disable the operation of the driver unit that drives the power amplification unit, it is possible to avoid the generation of impact noise when the power is turned on or off.

Further, according to the present invention, with the above configuration, the AC voltage output from the secondary side of the power transformer is rectified and smoothed by the diode and the capacitor, and based on the obtained DC voltage value, the switching section is turned to high or low. Outputs a low level switch control signal. Further, the driver control unit outputs the first driver control signal for validating the operation of the driver unit to the R / S latch immediately after the power is turned on according to the switch control signal and after the lapse of the time based on the predetermined first time constant. To the R / S latch immediately after the power is turned off and for invalidating the operation of the driver unit immediately after the power is cut off, and immediately after the power is turned on according to the switch control signal, a predetermined second control signal is output. The second driver control signal for validating the operation of the driver unit during the time based on the time constant of is output to the R / S latch. As a result, the operation of the driver unit is enabled or disabled by the combination of the first driver control signal and the second driver control signal, so that it is possible to avoid the generation of impact noise when the power is turned on or off, and further the overcurrent is generated. The operation of the driver unit can be forcibly stopped by detecting the current value of the output signal of the class D amplifier by the detection unit and outputting the overcurrent information as the third driver control signal to the R / S latch.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a muting circuit according to the first embodiment of the present invention. In FIG. 1, reference numeral 1 is a switch unit, 2 is a driver control unit, 8 is a driver unit, and the others are the same as the conventional configuration. FIG. 3 is a block diagram of the power supply circuit.
2 is a rectification part, and others are the same as that of the conventional structure.

The operation of the muting circuit of this embodiment having the above structure will be described below.

First, when the switch of the power supply transformer 21 is turned on and the power is turned on, an AC voltage is output to the rectification unit 22, and further rectified by the rectification unit 22 and then the smoothing unit 23.
And the resulting DC voltage smoothed by
Vcc and -Vcc are output to the class D amplifier, respectively.

At this time, output from the secondary side of the power transformer 21.
AC voltage applied, that is, branched from the input terminal of the rectification unit 22
AC voltage (A) and the reverse of the AC voltage (A)
Phases (B) are capacitors C₁And C_FourIs input to
It The intersection of (A) or (B) that occurs when the power is turned on.
Current voltage is diode D₁And D₂Rectified by
And capacitor C₂And C₃DC after being smoothed by
The voltage is transistor Q ₁And Q₂Input to the base terminal of
Be done.

The resistors R ₂ and R ₆ are for overcurrent protection of the transistor, and the resistors R ₃ and R ₅ determine the bias voltage required for the operation of Q ₁ and Q ₂ . Since Q ₁ and Q ₂ are connected to obtain a differential output, Q ₁ and Q ₂
It is possible to detect that the power is turned on in synchronization with any of the above operations.

As described above, when the power is turned on, either Q ₁ or Q ₂ is on, that is, the collector terminal and the emitter terminal have the same potential, and therefore the switch section 1 is a low level switch. Output a control signal.

Next, since the switch control signal input to the base terminal of the transistor Q ₃ is at low level, Q
Collector output of ₃ charging is initiated by the capacitor C ₅ becomes a high level which is connected to the collector terminal of Q _3,
Charging is performed until the time constant of the resistor R ₈ and the capacitor C _{5, that} is, the time obtained by multiplying the resistance value of R ₈ and the capacitance of C ₅ . Since the base terminal of the transistor Q ₄ is at low level during the charging time, the collector output of Q ₄ , that is, the driver control signal output from the driver control unit 2 is at high level. After that, the base terminal of Q ₄ and the collector terminal of Q ₃ are at the same potential, that is, high level, so that the collector output of Q ₄ is switched to low level.

The driver unit 8 is shut down (Sh
utdown, hereinafter referred to as SD), which enables operation at low level. Therefore, since the SD terminal is at the high level immediately after the power is turned on, the driver section 8 does not operate, and the SD terminal becomes the low level after a lapse of a time predetermined by the time constant of R ₈ and C _5, and the driver section 8 becomes low. 8 starts operation. This time constant needs to be set to a voltage output from the smoothing unit 23, that is, a time at which + Vcc and −Vcc are in a steady state or more. In this case, R ₈ is 10 [KHZ] and C ₅ is 330 [μF]. Is.

On the other hand, when the switch of the power transformer 21 is turned off and the power is cut off, the voltages input to (A) and (B) of the switch section 1 are both zero, so that the transistors Q ₁ and Q are turned on. ₂ does not operate, so the switch unit 1 outputs a high level switch control signal. Similar to the operation described above, the base terminal of the transistor Q ₃ is at the high level and the collector terminal of the Q ₃ is at the low level. Therefore, the charge charged by the C ₅ is discharged through the Q ₃ and the base terminal of the Q ₄ is discharged. Becomes low level. Since this discharging time is instantaneously performed, the driver control unit 2 outputs a high-level driver control signal to the SD terminal immediately after the power supply is cut off, and the driver unit 8 is deactivated.

The capacitors C ₂ and C ₃ for smoothing in order to operate the transistors Q ₁ and Q ₂ normally have to be made as small as possible in order to improve the response when the power is cut off. It is preferably about 0.1 [μF].

In the present embodiment, the reference potential of the switch section 1 and the driver control section 2 is set to -Vcc, but it may be 0 [V], in which case C ₁ and C ₄ and R ₁ and R _{7 are used.} Is unnecessary. Further, in the present embodiment, the voltage of the two poles of the AC waveform branched and extracted from the input terminal of the rectification unit 22 is used as the input to the switch unit 1. However, only one of them may be input, and in that case, the differential voltage is applied. A circuit having (A) or (B) as an input, which includes either the output transistor Q ₁ or Q ₂ , becomes unnecessary.

As described above, according to the first embodiment of the present invention, the diodes D ₁ and D ₂ for rectifying the AC voltage branched from the input terminal of the rectifying unit 22 and the rectified waveform are smoothed. Capacitors C ₂ and C that output a DC waveform by
₃ and a switch unit 1 that outputs a high or low level switch control signal based on the obtained DC waveform voltage value.
And a driver control section 2 for outputting a high or low level driver control signal for starting or stopping the operation of the driver section 8 after a lapse of time based on a time constant predetermined according to the switch control signal. ,
The operation of the driver unit 8 is stopped when the power is turned on and when the power is turned off.

Next, FIG. 2 is a block diagram of a muting circuit according to the second embodiment of the present invention.
In FIG. 2, 3 is a driver control unit, 4 is an overcurrent detection unit, 7 is a coil, 8 is a driver unit, 25 is an R / S latch composed of a flip-flop, and others are the same as the conventional configuration. .

The operation of the muting circuit of this embodiment having the above configuration will be described below.

First, when the switch of the power transformer 21 is turned on and the power is turned on, an AC voltage is output to the rectifying unit 22 and further rectified by the rectifying unit 22 and then the smoothing unit 23.
And the resulting DC voltage smoothed by
Vcc and -Vcc are output to the class D amplifier, respectively.

At this time, the AC voltage (A) branched from the input terminal of the rectifying unit 22 and the opposite phase (B) of the AC voltage (A) are input to the capacitors C ₁ and C ₄ , respectively. The (A) or (B) AC voltage generated by turning on the power is rectified by the diodes D ₁ and D ₂ , and the DC voltage value after being smoothed by the capacitors C ₂ and C ₃ is the transistors Q ₁ and Q _2. Input to the base terminal of. Resistors R ₂ and R ₆ are for transistor overcurrent protection, and resistors R ₃ and R ₅ determine the bias voltage required to operate Q ₁ and Q ₂ . Since the transistors Q ₁ and Q ₂ are connected so as to obtain a differential output, it can be detected that the power is turned on in synchronization with the operation of either Q ₁ or Q ₂ .

As described above, when the power is turned on, either Q ₁ or Q ₂ is on, that is, the collector terminal and the emitter terminal have the same potential, and therefore the switch section 1 is a low level switch. Output a control signal.

Next, since the switch control signal input to the base terminal of the transistor Q ₃ is at low level, Q
Collector output of ₃ charging is initiated by the capacitor C ₅ becomes a high level which is connected to the collector terminal of Q _3,
Charging is performed until the time constant of the resistor R ₈ and the capacitor C _{5, that} is, the time obtained by multiplying the resistance value of R ₈ and the capacitance of C ₅ . Since the enable terminal of the R / S latch 25 is at the low level during the charging time, the output signal Q1 of the R / S latch 25 is open, but is output to the driver unit 8 because it is pulled up by the resistor R ₁₃ . The driven driver control signal becomes high level, and the driver unit 8 becomes inactive. Immediately after the power is turned on, the set terminal S1 of the R / S latch 25 is at a low level, the reset terminal R1 of the R / S latch 25 receives the differential waveform of R ₁₂ and C _6, and the decay time is R.
It is predetermined by the time constant of ₁₂ and C ₆ . The reset terminal R1 once becomes a high level by the input differential waveform and then attenuates to a low level, so that the R / S
The internal operation of the latch 25 shifts from the low level to the holding state, but at this point the influence on the output terminal Q1 does not appear because the enable terminal is at the low level.

Next, when the charge of C ₅ is completed,
When the collector output of Q ₃ becomes high level, the enable terminal also becomes high level, and since the reset terminal R1 already set low level is held, the output terminal Q1 becomes low level and the driver section 8 becomes in the operating state.

On the other hand, if the power source is cut off here, the rectifying unit 2
Since the AC voltage branched from the input terminal of 2 becomes zero, that is, low level, the switch section 1 immediately outputs high level, the base terminal of the transistor Q ₃ becomes high level, and the capacitor C ₅ is charged. The generated electric charge is instantly discharged through the transistor Q ₃ . Therefore, the enable terminal instantly becomes low level, and the driver unit 8
The SD terminal becomes high level, and the driver unit 8 becomes inactive.

Further, the coil 7 is provided with a coil which operates as a band limiting filter for the output signal of the pulse amplifier 12 and detects a current by mutual induction, and is in operation of the class D amplifier, that is, the R / S latch 25. Reset terminal R
When 1 is at the low level and the enable terminal is at the high level, the overcurrent detection unit 4 causes the R / S latch 25 to operate when an abnormal current occurs due to a short circuit of the output terminal of the class D amplifier or damage of the pulse amplifier 12. Of the set unit S1 and the output terminal Q1 is forcibly set to the high level, the driver unit 8 is in the non-operating state, and this state is maintained until the abnormal state is avoided and the power is turned on again. .

The capacitors C ₂ and C ₃ for smoothing the transistors Q ₁ and Q ₂ to operate normally must be made as small as possible in order to improve the response when the power is cut off. It is preferably about 0.1 [μF].

In the present embodiment, the reference potential of the switch section 1 and the driver control section 2 is set to -Vcc, but it may be 0 [V], in which case C ₁ and C ₄ and R ₁ and R _{7 are used.} Is unnecessary. Further, in the present embodiment, the voltage of both poles of the AC waveform output from the secondary side of the power transformer 21 is input to the switch unit 1, but only one of them may be input, in which case a differential output is provided. The circuit connected to the base terminal including either the transistor Q ₁ or Q ₂ that operates is unnecessary.

As described above, according to the second embodiment of the present invention, the diodes D ₁ and D ₂ for rectifying the AC voltage branched from the input terminal of the rectifying unit 22 and the rectified waveform are smoothed. Capacitors C ₂ and C that output a DC waveform by
₃ and a switch unit 1 that outputs a high or low level switch control signal based on the obtained DC waveform voltage value.
And a first driver control which has an R / S latch 25 composed of a flip-flop and makes the operation of the driver unit 8 effective after a lapse of a time based on a predetermined time constant immediately after power-on according to a switch control signal. A signal is output to the R / S latch 25, and immediately after the power is cut off, a first driver control signal for invalidating the operation of the driver unit 8 is instantaneously output to the R / S latch 25, and according to the switch control signal. A driver control unit 3 that outputs a second driver control signal to the R / S latch for validating the operation of the driver unit during the time based on a second predetermined time constant, and an overcurrent detection of the pulse amplifier. By providing the overcurrent detection unit 4 that performs
And the muting operation for avoiding the impulsive sound at power-on and power-off by operating the set terminal of the R / S latch 25 according to the overcurrent information detected by the overcurrent detection unit 4. It controls the protective operation at the time of abnormal operation of the class D amplifier.

[0043]

As described above, according to the present invention, the power is turned on or off based on the DC voltage value obtained by rectifying and smoothing the AC voltage output from the secondary side of the power transformer. A switch control signal is output, and when the power is turned on according to the switch control signal, the driver section is operated after a lapse of time based on a predetermined time constant, that is, after the power supply voltage supplied to the class D amplifier reaches a steady state. Output the driver control signal to enable it to the driver control unit,
When the power is cut off, the driver control signal for invalidating the operation of the driver is output instantaneously to the driver control section, so there is no impact on the audio signal transmission path when the power is turned on and power is cut off. The sound can be avoided.

Further, according to the present invention, the switch control signal according to the state of power-on or power-off is provided based on the DC voltage value obtained by rectifying and smoothing the AC voltage output from the secondary side of the power transformer. Further, when the power is turned on according to the switch control signal, the operation of the driver unit is started after the time based on the predetermined first time constant elapses, that is, after the power supply voltage supplied to the class D amplifier reaches the steady state. A first driver control signal for enabling is output to the R / S latch, and a second time constant corresponding to a time shorter than the first time constant causes a standby inside the R / S latch for enabling driver operation. When the power is cut off, the driver control signal for invalidating the operation of the driver is output instantaneously. Further, since the overcurrent detection unit detects the abnormality of the output current of the class D amplifier and outputs the overcurrent information to the R / S latch, the muting operation for avoiding the impulsive sound at power-on and power-off, and Since the protection operation at the time of abnormal operation of the class D amplifier is controlled, it is possible to avoid the impulsive sound at power-on and power-off without affecting the transmission path of the audio signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a muting circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a muting circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a power supply circuit in the first and second embodiments of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional class D amplifier and a muting circuit.

FIG. 5 is a block diagram showing a configuration of a power supply circuit in a conventional class D amplifier.

[Explanation of symbols]

 1 Switch Section 2, 3 Driver Control Section 4 Overcurrent Detection Section 7, 13 Coil 8 Driver Section 9 Analog Signal Input Terminal 10 Comparator (1 Bit Quantizer) 11 Drive Amplifier 12 Pulse Amplifier 14 Capacitor 15 Output Terminal 16 Load 17 Triangular Wave Signal generator 18 FM modulator 19 Basic signal oscillator 20 Random signal oscillator 21 Power transformer 22, 24 Rectifying unit 23 Smoothing unit

Claims (2)

[Claims] 1. A high or low level based on a DC voltage value obtained by rectifying an AC voltage output from the secondary side of the power transformer with a diode according to ON or OFF of a power switch and then smoothing it with a capacitor. A switch unit for outputting a switch control signal, a driver unit for outputting a drive signal for driving the pulse amplifier of the class D amplifier, and a predetermined unit immediately after power-on according to the switch control signal output from the switch unit. A driver control unit that outputs a driver control signal that validates the operation of the driver unit after a lapse of time based on a time constant, and immediately outputs a driver control signal that invalidates the operation of the driver unit immediately after power-off. Muting circuit with and. 2. A high or low level based on a DC voltage value obtained by rectifying an AC voltage output from the secondary side of the power transformer with a diode according to ON or OFF of a power switch and then smoothing it with a capacitor. Switch unit that outputs the switch control signal, a driver unit that outputs the drive signal for driving the pulse amplifier of the class D amplifier, and holds or releases the output signal level according to the input high or low level signal Immediately after the power is turned on according to the switch control signal and having an R / S latch, the first driver control signal for validating the operation of the driver unit after the lapse of a time based on a predetermined first time constant is set to the first driver control signal. A first driver control signal for outputting to the R / S latch and invalidating the operation of the driver unit immediately after the power is cut off. A second driver for instantaneously outputting to the R / S latch and validating the operation of the driver unit during a time based on a second predetermined time constant immediately after power-on according to the switch control signal. A driver control unit that outputs a control signal to the R / S latch, and an overcurrent detection unit that detects the current value of the output signal of the class D amplifier and outputs overcurrent information to the R / S latch. Ting circuit.