JPS6247366B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an acoustic amplifier.

When the power is turned on, if a transient impact sound (pop sound) is generated from the speaker load connected to the output of the audio amplifier, it is not only unpleasant to the ears, but there is also a risk that the speaker may be destroyed by this impact. .

To prevent popping noises when the power is turned on,
By making the starting transistor conductive at a predetermined time after the power is turned on, and applying the output signal of this starting transistor to the DC-AC negative feedback point of the acoustic amplifier, the output potential of the acoustic amplifier is maintained at the ground level for a while. It has been proposed in Japanese Patent Application Laid-Open No. 49-8153 and Japanese Patent Application Laid-Open No. 50-81246.

However, studies conducted by the present inventors have revealed that in conventionally proposed acoustic amplifiers, when the power is turned on again within a relatively short period of time after the power is turned off, an undesirable popping sound is generated.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an acoustic amplifier in which the generation of pop sounds when the power is turned on and the above-mentioned pop sounds when the power is turned on again is reduced.

The basic structure of the present invention to achieve the above object is as defined in the claims, in particular, by connecting a diode for blocking reverse current passage, the generation of pop noises is reduced when the power is turned on again. It is characterized by the fact that

The present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an acoustic amplifier according to an embodiment of the present invention.

The first stage amplifier circuit 1 consists of transistors Q ₁ to _{Q 5} and resistors.
It is composed of R ₄ to _{R 6} , and the base of the transistor Q ₁ is the non-inverting input terminal (+) of the acoustic amplifier,
An input _signal is applied from the signal source SG via the input coupling capacitor _C1 , and the base of the transistor _Q2 is the inverting input terminal (-), which is _{a DC-} A negative feedback signal from an AC negative feedback circuit 4 is applied.

Resistors R ₁ and R ₂ constitute a DC bias circuit, and a DC bias voltage at a common connection point of both resistors R ₁ and R ₂ is applied to the base of transistor Q ₁ via resistor R ₃ . The ripple removal capacitor _C2 is designed so that the AC ripple component in the power supply voltage +V _CC is connected to the transistor.
Reduces the crosstalk transmitted to the base of _Q1 .

The drive amplifier circuit 2 that responds to the output signal of the first stage amplifier circuit 1 includes transistors Q ₆ , Q ₇ and a diode D _{1 .}
~ _D3 , resistor _R10 ~ _R12 , phase compensation capacitor _C4 ,
Consists of bootstrap capacitor _C5 .

Push-pull output amplifier circuit 3 is drive amplifier circuit 2
In _response to _{the output signal of} are doing. Non-inverting input terminal (+)
When the base potential V ₁ of the transistor Q ₁ increases, the conductivity of the output transistors Q ₁₀ and Q ₁₁ increases, and the conductivity of the output transistors Q ₈ and Q ₉ decreases, so the potential V _q of the output point P becomes Rise.

The resistor _R15 and the Zener diode constitute the reference bias circuit 5, and the power switch SW is connected to the connection point R.
A predetermined reference bias voltage is generated simultaneously with the application of the voltage.

The emitter E of the starting transistor Q ₂ to reduce the generation of pop noise when the power is turned on is connected to the above connection point E, and its base is a connection point having a potential that depends on the potential V _C of the ripple elimination capacitor C ₂ . S, and its collector is connected to the base of transistor _Q2 , which is the inverting input terminal (-). Therefore, after the power switch SW is turned on, the starting transistor is activated for a predetermined period of time until the potential at the connection point S rises to a potential close to the potential at the connection point R.
Since Q ₁₂ is conductive, the output potential V _q is held at a potential close to ground level.

In order to ensure that the output potential V _q is maintained at a potential close to the ground level for the above-mentioned predetermined time, another starting transistor Q ₁₃ is arranged, the collector of which is connected to the base of the drive transistor Q ₆ .

In order to reduce the pop noise generated when the power is turned on again,
A reverse current blocking diode _Q14 is particularly connected according to the invention between the collector of the starting transistor _Q12 and the inverting input terminal (-).

Next, the reason why the present invention not only reduces the generation of pop noise when the power is turned on, but also reduces the generation of pop noise when the power is turned on again will be explained with reference to the circuit operation in each case.

In particular, in order to facilitate understanding of the beneficial effects of the present invention, the circuit operation of the present invention when the power is turned on again is compared with the circuit operation when the reverse current blocking diode _Q14 according to the present invention is not connected. The operation will be explained in detail.

[1 Circuit operation when power is turned on] Immediately after closing the power switch SW at time t ₀ , the terminal voltage of the ripple removal capacitor C ₂ becomes substantially zero volts. Therefore, the starting transistor
The base-emitter junctions of Q ₁₂ and Q ₁₃ are forward biased and both transistors conduct.

The collector current of this conductive starting transistor Q ₁₃ causes the driving transistors Q ₆ and Q ₇ to conduct.

As the drive transistors Q ₆ and Q ₇ become conductive, the output transistors Q ₈ and Q ₉ of the push-pull output stage become conductive, so that the output voltage V of the push-pull output stage
_q maintains a potential close to ground level as shown in Figure 2b.

Ripple removal capacitor _C2 is bias resistor
Since the starting transistors Q 12 and Q 13 are charged via R ₁ , the base potentials of the starting transistors Q ₁₂ and Q ₁₃ continue to rise, and at the subsequent time t ₁ the starting transistors Q ₁₂ and Q ₁₃ become non-conductive. The bias resistor R ₁ has a relatively large resistance value of 20KΩ, and the ripple removal capacitor C ₂
has a relatively large capacitance value of 100μF, the input resistance _R1 is a high resistance of 100KΩ, and the transistor _Q1
Since the input coupling capacitor C ₁ is connected to the base of , the rise time constant of its base potential V ₁ is τ ₁
is a relatively large value.

On the other hand, the resistor R ₁₅ has a relatively small resistance value of 4KΩ.
A negative feedback capacitor C ₃ with a relatively small capacitance value of 10 μF is charged via the emitter-collector current path of the conducting starting transistor Q ₁₂ and a negative feedback resistor R ₁₄ with a relatively small resistance value of 1KΩ. Therefore, the increase constant _{τ 2} of the base potential V 2 of the transistor Q ₂ has a relatively small value.

Therefore, after time t ₀ , the level of the base potential V ₂ of the transistor Q ₂ is higher than the level of the base potential V ₁ of the transistor Q ₁ as shown in FIG. 2a, so the transistor Q ₁ becomes conductive. However, transistor _Q2 becomes non-conductive. Non-conduction of transistor Q ₂ causes load transistors Q ₄ ,
Since Q ₅ becomes non-conductive, the drive transistors Q ₆ ,
Q ₇ remains conductive, and the output potential V _q of the push-pull output stage remains close to ground level, as shown in FIG. 2b.

Since starting transistors Q ₁₂ and Q ₁₃ are non-conductive after time t ₁ , the charging path to negative feedback capacitor C ₃ is cut off, so that the base potential V ₂ of transistor Q ₂ decreases as shown in FIG. 2a. Ascent is stopped. On the other hand, even after time _t1 , the ripple removal capacitor _C2 continues to be charged via the bias resistor _R1 , and the base potential _V1 of the transistor _Q1 continues to rise.

At time t ₂ , the base potential of transistor Q ₁
When the potential difference between V ₁ and the base potential V ₂ of transistor Q ₂ falls within the linear region of the differential input transfer characteristics of transistors Q ₁ and Q ₂ , the conductivity of drive transistors Q ₆ and Q ₇ decreases. The output potential V _q gradually increases as shown in FIG. 2b.

At time t ₂ ′, when the base potentials of differential transistors Q ₁ and Q ₂ become equal to each other, the differential transistor
Since Q ₁ and Q ₂ are balanced, differential transistors Q ₁ and Q ₂
causes the output potential V _q to follow the base potential V ₁ of the transistor Q ₁ by direct current negative feedback via the resistor R ₁₃ .

Since the resistance values of the bias resistors R ₁ and R ₂ are almost equal, the rise in the base potential V ₁ of the transistor Q ₁ stops at 1/2 V _CC (half the potential of the power supply voltage V _CC ) at time _t 3 (the second (see Figure 2b), and the output potential _Vq follows this and is fixed at 1/2V _CC (see Figure 2b).

[Circuit operation when power is turned on again after power-off without diode _Q14 ] If the power switch SW is closed until time _t4 , the base potentials of transistors _Q1 and _Q2 , _V1 , _V2 ,
The output potentials V _q are each maintained at a value of 1/2 V _CC (see Figures 2c and d).

When the power switch SW is opened at time _t4 , the power supply voltage V _CC becomes zero. Ripple removal capacitor
C ₂ is left alone via a relatively large resistor R ₂ , and the drop in the potential V _C of capacitor C ₂ due to this discharge is delayed by resistor R ₃ and capacitor C ₁ and is transmitted to the base of transistor Q ₁ . The base potential V ₁ decreases with a relatively large time constant τ ₁ '. The base B and collector C of the transistor _Q12 start up due to the drop in the potential V _C of the ripple elimination capacitor _C2 .
The PN junction between is forward biased. Therefore, the negative feedback capacitor C ₃ is discharged to the potential V _C in the direction of the current i _R in FIG. 1 through the negative feedback resistor R ₁₄ and the above-mentioned forward PN junction.
The base potential V ₂ of Q ₂ decreases with a relatively small time constant τ ₂ ′. Due to the difference between these two base potentials V ₁ and V ₂ , transistor Q ₁ is turned off and transistor Q ₂ is turned off.
is on, drive transistors Q ₆ and Q ₇ are off, output transistors Q ₈ and Q ₉ are off, output transistor
Since Q ₁₀ and Q ₁₁ are turned on, the output potential V _q has a relatively small time constant τ that is almost equal to the above time constant τ ₂ ′.
It decreases from the value of 1/2V _CC at _q ' (see Figure 2 c, d).

When the power switch SW is turned on again at time _t5 ,
The base potentials V ₁ and V ₂ of the transistors Q ₁ and Q ₂ rise with the previously explained time constants τ ₁ and τ ₂ , respectively. At time t ₆ , the base potential of transistors Q ₁ and Q ₂
Although V ₁ and V ₂ become equal, the base potential V ₂ of the transistor Q ₂ becomes lower than the base potential _{V 1} of the transistor Q 1 from time t ₅ to _{t 6} (see FIG. 2c).

Therefore, between this time _t5 and _t6 , the transistor
Q ₁ is off, transistor Q ₂ is on, drive transistors Q ₆ , Q ₇ are off, output transistors Q ₈ , Q ₉
is off and the output transistors Q ₁₀ and Q ₁₁ are on, so the output potential V _q is the same as that of the output transistors Q ₁₀ and
When _Q11 is turned on and the power supply voltage V _CC is applied, the voltage suddenly rises to the power supply voltage V _CC (FIG. 2d). This rapid rise in the output potential _Vq causes a loud popping sound.

[Circuit operation when power is turned on again after power is cut off when diode _Q15 is connected] If the power switch SW is closed until time _t4 , the base potentials of transistors _Q1 and _Q2 , _V1 , _V2 ,
The output potentials V _q are each maintained at a value of 1/2 V _CC (see Figure 2 e, f).

When the power switch SW is opened at time _t4 , the base potential _V1 of the transistor _Q1 decreases with the above-mentioned time constant _τ1 '. On the other hand, according to the invention, a diode Q ₁₄ is connected especially for blocking the passage of reverse current, so that
The current value of the current flowing in the direction of symbol i _R in FIG. 1 becomes substantially negligible. Therefore, the time constant τ ₂ ″ when the base potential V ₂ of the transistor Q ₂ decreases has a larger value than the time constant τ ₁ ′ when the base potential V ₁ of the transistor Q ₁ decreases (Fig. 2). e
reference).

The output potential V _q decreases due to the decrease in the base potential V 1 of the transistor Q ₁ , but at time t ₄ ' _the potential difference between the base potentials V ₁ and V ₂ of the transistors Q ₁ and Q ₂ changes the differential input transfer characteristic. When outside the linear region, transistor Q ₁ is completely on, transistor Q ₂ is completely off, drive transistors Q ₆ and Q ₆ are completely on, output transistors Q ₈ and Q ₉ are completely on, and output transistor Q ₁₀ is completely on. ，Q ₁₁ is completely turned off,
The output potential V _q is maintained at ground level (second
Figure f).

The state in which the output potential V _q is maintained at the ground level is such that after the power switch SW is turned on again at time t ₅ , the base potentials V ₁ and V ₂ of transistors Q ₁ and Q ₂ are approximately equal to each other at time t ₆ '. held until they are equal. Therefore, at time t ₆ ', transistors Q ₁ and Q ₂
When the base potentials V ₁ and V ₂ of the transistor Q 1 become approximately equal, the output potential V _q follows the base potential V ₁ of the transistor Q ₁ and stabilizes at a value of 1/2 V _CC (Fig. 2 e, f).

Therefore, by connecting the diode _Q14 for blocking reverse current passage, the output potential V _q can be reduced after the power is turned on again.
It is possible to prevent the voltage from suddenly rising to the power supply voltage V _CC and causing a loud popping sound.

The present invention is not limited to the above embodiments, and various modified embodiments can be adopted.

For example, in order to more reliably prevent pop noises from occurring when the power is turned on, it is desirable to connect the collector of the startup transistor _Q13 to the base of the other drive transistor _Q7 rather than to the base of the drive transistor _Q6 .

FIG. 3 shows a circuit diagram of an acoustic amplifier according to a modified embodiment of the invention, in which circuit elements having the same functions as in FIG. 1 are given the same reference symbols.

Unlike the embodiment shown in FIG. 1, the first stage amplifier circuit 1 is
Consists of NPN differential transistors Q ₁ , Q ₂ , buffer transistors Q ₁₃ , constant current transistors Q ₁₂ , Q ₁₄ , load resistors R ₁₈ , R ₁₉ , and diode D ₅ , and direct current is applied to the base of transistor Q ₁ . The DC bias circuit for supplying bias voltage is a resistor.
It is composed of R ₁ ′, R ₁ ″, R ₁ , R ₂ , and diode D ₄ , and the reference bias circuit 5 is composed of resistors R ₁₅ and R ₁₆ , but when the power is turned on, a pop sound is generated. The same circuit operation as in the embodiment shown in FIG. 1 is performed with regard to the reduction of noise and the generation of pop noise when the power is turned on again.

[Brief explanation of the drawing]

FIG. 1 shows a circuit diagram of an acoustic amplifier according to an embodiment of the present invention, and FIGS. 2a and 2b are waveform diagrams showing potential changes at main connection points in the embodiment circuit of FIG. 1 after power is turned on. , Fig. 2c and d are diodes for blocking reverse current passage in the embodiment circuit of Fig. 1, respectively.
Waveform diagrams showing the potential changes at the main connection points when the power is turned on again in the circuit where Q ₄ is omitted; Figure 2e and f are waveform diagrams showing the potential changes at the main connection points when the power is turned on again in the example circuit shown in Figure 1. FIG. 3 shows a waveform diagram showing potential changes and a circuit diagram of an acoustic amplifier according to a modified embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... First stage amplifier circuit, 2... Drive amplifier circuit, 3... Push-pull output amplifier circuit, 4... Negative feedback circuit, 5...
Reference bias circuit, C ₂ ... Ripple removal capacitor, Q ₁₂ , Q ₁₃ ... Start-up transistor, Q ₁₄ ... Reverse current blocking diode, C ₆ ... Output capacitor, SP ... Speaker load.

Claims (1)

[Claims] 1 Non-inverting input terminal (+) and inverting input terminal (-)
a first-stage amplifier circuit 1 having a first-stage amplifier circuit, a push-pull output amplifier circuit 3 responsive to the output signal of the first-stage amplifier circuit, and a push-pull output amplifier circuit 3 arranged between the output P of the push-pull output amplifier circuit and the inverting input terminal (-) and at least negative feedback. a negative feedback circuit 4 having a capacitor C ₃ ; another capacitor C ₂ that is charged when the power supply voltage V _CC is applied; a bias voltage circuit 5 that generates a predetermined bias voltage almost simultaneously with the application of the power supply voltage V _CC ; A starting transistor whose emitter is connected to the bias voltage circuit 5 and whose base is connected to the connection point S that depends on the potential of the other capacitor.
Q ₁₂ , an acoustic amplifier comprising reverse current passage blocking means Q ₁₄ connected between the collector of the starting transistor and the inverting input terminal.