JPS60123111A - Amplifiying circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of pop tone at a power-off time by driving an amplifying circuit with a reference voltage whose level falls in accordance with level fall of a power source voltage at the power-off time and reducing the level of an output voltage quickly. CONSTITUTION:When a power switch S1 is turned on to supply a power source voltage +VCC, a base voltage VC is supplied to a transistor TRQ11 to turn on this TR, and a current I1 is flowed to a resistance R14, And a TRQ13 is turned on, and a voltage VA of capacitor C1 rises. When the switch S1 is turned off, the voltage VC falls by the time constant of a filter F1. Since the TRQ13 continues to be in the turn-on state, the electric charge of the capacitor C1 is discharged through a resistance R15, and the voltage VA falls. Then, an output voltage VQ of a differential amplifier to which the voltage VA is supplied as the reference voltage is reduced gradually.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a meeting circuit suitable for use in cassette decks and audio amplifiers.

[Background technology]

It is known that when the power to Audio Amplifier Gin is cut off, a so-called popping sound occurs.

Prior to the invention of the present application, the present inventors investigated the causes of the popping sound in various audio amplifiers. The audio amplifier shown in FIG. 1 is an example of the audio amplifier used in the above study.

Resistance R, , R, is +V. The voltage of the ct source is divided, and the capacitor C1 holds the divided voltage ■□. Resistor R8, Zener diode ZD, ) transistor Q++ resistor RnFi
, constitutes a separate voltage circuit.

The transistors Qt and Q= constitute a differential amplifier, and the divided voltage ■□ is supplied as a reference voltage to the non-inverting input terminal ←). Diode D is a load of the differential amplifier and performs current-voltage conversion operation. Note that the transistor Qa and the resistor 'Rs constitute a constant current circuit, and define the current Iof flowing through the differential amplifier'.

The transistor Q'++ and resistor R6 constitute a constant current circuit, and the diodes Dt and Ds function as a level shifter. The output signal of the differential amplifier obtained from transistor Q6 and diode D1 causes transistors Q7. Q
, drives a push-pull amplifier circuit consisting of .

According to the study conducted by the inventors of the present invention regarding the amplifier circuit having the circuit configuration described above, it has been found that a pop sound is generated when the power is cut off for the following reasons. Below, the process of generating the popping sound will be explained with reference to Figures 2--2.

At time t1, when the power switch S1 fails to turn off, the coil L forming the filter circuit F. , due to the time constant of capacitor C0, the voltage level of the VCC power supply decreases smoothly as shown from t in FIG.

1. After this point, the voltage level of the divided voltage (4) shown in FIG. 2(G) also decreases, but the level of the decrease is smaller than the decrease in +voctm due to the time constant of the capacitor Ct and the resistor Rt.

A decrease in the level of the divided voltage ■□ means a change in the level of the reference voltage of the differential amplifier. Therefore, the voltage level (2) at the inverting input terminal (to) gradually decreases as shown in FIG. 2 with a level change substantially similar to the decrease in the level of the divided voltage VA. Voltage level V at the output terminal.

corresponds to the decrease in the level of the voltage V, 1*VB, as shown in FIG. 20.

As described above, the voltage level of each part of the amplifier circuit decreases, but the Zener voltage Vzti+Vcc" source
2 or more, a constant voltage level is maintained as shown in the m2 diagram (A). Then, as shown after the point 1, +Vc
oii1. When the source voltage drops below the Zener voltage 2, transistor Q is turned off, and at the same time transistors Q4 and Qa are also turned off. As a result, the current 10//im flowing through the differential amplifier is cut off, the transistors Qa, Qt, and Qa are all turned off, and the output voltage (2) also drops rapidly. At this time, the output - pressure ■. On the other hand, the output capacitor Cat speaker Sp operates as a differentiating circuit. At time point 12, speaker 8pVC 2nd
The present inventor's studies have revealed that a current IP having a differentiated waveform as shown in FIG.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a muting circuit that can prevent pop sounds from occurring when power is cut off in various audio devices.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of the invention disclosed in this application is as follows.

That is, when power is supplied, an output voltage at the required voltage level is obtained, and when power is cut off, an output voltage whose level decreases in response to a decrease in the level of the power supply voltage is obtained, and based on this output voltage! To achieve the object of the present invention, which is to prevent pop noises from occurring when the power is cut off by driving the amplifier circuit as an NA voltage and quickly lowering the level of the output voltage of the amplifier circuit when the power is cut off. It is something.

[Embodiment 1] Hereinafter, a first embodiment of a muting circuit to which the present invention is applied will be described with reference to FIGS. 3 and 4. Note that the meeting circuit and the amplifier circuit using the same in this example are constructed of a half-bridge integrated circuit (hereinafter referred to as IC), and the numbers in circles indicate external connection terminals. It shows. Furthermore, the muting circuit to which the present invention is applied corresponds to the circuit block A surrounded by a dotted line in FIG. 3, and the circuit configuration of an amplifier circuit using this circuit may be particularly limited. Therefore, for convenience of explanation, the amplifier circuit shown in FIG. 1, which was studied prior to the publication of this application, is used as the amplifier circuit, and circuit elements that perform the same circuit operations are given the same reference numerals.

First, the muting circuit shown as circuit block A will be described.

Transistor Q. IQ+1 is connected to the differential pair, and the base voltage VC of the transistor Qll is connected to the resistor R■.

A divided voltage is supplied by RIt. The transistor Qu operates as a feedback circuit between the transistors Qn* and Q+, and discharges the charge stored in the capacitor C8 when the power is cut off.

The diodes D, , -Dn also supply a full charge current to the capacitor C1 from +VCo power supply, and maintain the voltage VA at a constant level in conjunction with the resistor R18 and the transistor Q+s.

Next, ten ■. The operation of generating voltage VA when C power is supplied will be described.

Base voltage■. is supplied, transistor Qn operates in an on state, and resistor R+s, ) transistor Q, 1 . tRI+ flows through resistor R24. Due to the voltage drop across the resistor RI4, a bias voltage is supplied to the transistor Q+s, turning the transistor on. During this time, diodes D■~D
A charging current flows to the capacitor C1 through , and the voltage ■9
gradually increases.

However, the voltage level of the voltage ■□ is the transistor Ql+
Since it is controlled by transistor Q13 based on the output of transistor Qo+Qtt, each base voltage (%
Pressure ■. and VA) are maintained at approximately the same level. As mentioned in FIG. 1, the voltage ■A is the transistor Q,
, Q, is supplied to the non-inverting input terminal (G) as a reference voltage of the boosting amplifier.

Through the above circuit operation, a predetermined voltage is supplied to each part of the amplifier circuit, and a steady amplification operation can be performed.

By the way, the input signal ■in is connected to the DC blocking capacitor C1.
, is supplied to the base (inverting input terminal 1,000 days) of the transistor Q via the feedback resistor R (2r No. 4 terminal).
The resistor Rft, fz regulates the DC bias voltage VB of the inverting input terminal (to) based on the output voltage obtained from the second terminal.

Next, the pop sound muting operation when the power is cut off will be described.

Assume that the power switch S1 is turned off at time 111 shown in FIG. 4(6) to FIG. 4[F].

Ten ■. . The power source is a coil L, 1 that constitutes a filter F.
Due to the time constant of the capacitor co, it decreases as shown in Fig. 4 after ①tll. Voltage VC is the resistance minus.

Since the voltage is divided by R1, the +vc
Corresponding to the decrease in the level of the c power supply, it decreases as shown in FIG. 40.

What should be noted here is the drop in the level of voltage ■□. That is, 10V even after the +voct source is shut off. C power continues to be supplied while the level decreases, and the voltage ■. Supply is also carried out in the same way. Therefore, transistor Q+s is t1
The on state continues even after 5.1, and the electric charge stored in the capacitor is reduced by the resistance 5. It is discharged through transistor Q+s. For this reason, the voltage level of the voltage ■□ gradually decreases as shown in Figure 4 (Q), but the level of this decrease corresponds to the decrease in the level of the voltage ■, or in other words, the level of the +■cc power supply. This will result in a decline in

While the above circuit operation is being performed, the voltage VA is continuously supplied as a reference voltage to the non-inverting input terminal (G) of the differential amplification Sushi. Therefore, the voltage level of the output voltage V,
It gradually decreases as shown in Figure (G).

Therefore, the voltage obtained by the voltage division of the feedback resistors Rfs and Rfz gradually decreases as shown in FIG.

Next, ten ■. . When the power supply drops to below the Zener voltage 2, as shown at time tltJ, transistor Q is turned off, and transistors Qa and Qs are also turned off.

Therefore, the current ■. M is cut off, the entire amplifier circuit becomes inactive, and the output voltage (2) rapidly decreases as shown at the 1+1 point.

The voltage level V, just before the output voltage V, suddenly drops.

The output voltage V at time 17 shown in FIG. 2a).

The voltage level is lower than the voltage level of . That is, the voltage difference between the output voltage V at the time point 12 and the time point tit is that the former corresponds to a decrease in the level of the voltage VA determined by the time constant of the capacitor CI+resistor R7, while the latter corresponds to +V. , due to a rapid drop in approximately corresponding to the drop in the source level.

In this way, the level of the output voltage ■ is quickly lowered, and as a result, tI! At the time the output condenser C! +
The current IP flowing through the differentiating circuit constituted by the speaker Sp is an extremely small current as shown in FIG. 4 [F]. Therefore, almost no pop sound is generated from the speaker 8p.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to the fifth section. In this embodiment, the meeting circuit has the same structure as the first embodiment, and a non-inverting amplifier circuit is not used as the amplifier circuit.

That is, the voltage ■□ obtained in the same manner as above is the resistance R
It is supplied to the base (non-inverting input terminal) of the transistor Q through X, and the input signal ■in is also supplied through the No. 6 terminal.

The meeting circuit and amplifier circuit configured as described above perform an amplifying operation known to those skilled in the art as a non-inverting amplifier circuit when power is supplied.

Further, even when the power is cut off, the voltage level of each part changes as shown in FIG. 4(g) to FIG. 40.

Therefore, even with the circuit configuration of this embodiment, there is almost no pop noise.

〔effect〕

(1) Since the reference voltage of the differential amplifier is quickly lowered in response to the drop in the level of the power supply voltage after the power is cut off, the output voltage of the differential amplifier is also quickly lowered, and the Zener voltage When the differential amplifier is turned off, the current flowing through the speaker is reduced, and the effect of preventing pop noise from occurring is obtained.

Although the invention made by the present inventor has been specifically explained based on the embodiments above, the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, the power-side output transistor corresponding to transistor Q may be a plurality of Darlington-connected transistor circuits, and the ground-side output transistor corresponding to transistor Q8 may be a plurality of inverted Darlington (complementary connection) transistor circuits. You can replace it with

[Application field]

In the above description, the invention made by the present inventor was mainly applied to an amplifier circuit, which is the background field, but the invention is not limited thereto, and can be applied to, for example, a radio receiver.

It can be used in audio circuits for television receivers, radio cassettes, tape recorders, etc.

The present invention can be used at least as a reference power source for differential amplifiers and the like.

[Brief explanation of drawings]

FIG. 1 shows a circuit diagram of an amplifier circuit studied by the inventor prior to the present invention, FIG. 2 shows a waveform diagram explaining the circuit operation of the amplifier circuit, and FIG. The figure shows W,1 of a muting circuit to which the present invention is applied.
FIG. 4 shows a circuit diagram of an amplifier circuit showing an embodiment of
Barrel point [F] shows a waveform diagram explaining the circuit operation of the first embodiment, and FIG. 5 shows a circuit diagram of an amplifier circuit showing the second embodiment of the present invention. A...Circuit block showing the meeting circuit, Q+
r Qt r Qs + Q4 r Qa t Qa
+ Q, + Qa +Q++ + Q10 + Qr
s...transistor, D I+ D t r Ds
+DII T Dn...Diode, ZD...Zener diode, CI * CI # CS... Capacitor, ■2... Zener voltage, ■. +VB+V(・
...Voltage, ■9...Output voltage, Vin...Input signal, ■,...Current, t, l tll...When the power is cut off, t2+ tll...The power supply voltage drops below the Zener voltage At the time.

Claims (1)

[Claims] 1. Supply a reference voltage whose level changes in response to the level change of the power supply voltage to the first transistor control terminal connected to the differential pair, and connect it to the differential pair. The capacitor's front box voltage is supplied to the control terminal of the second transistor, and the voltage level of the control terminal of the second transistor is controlled by a third transistor that operates based on the output signal of the first transistor. In a steady state, the voltage at the control terminal of the second transistor is used as a reference voltage to drive the amplifier circuit, and when the power is cut off, the voltage at the control terminal of the first transistor is increased in response to a decrease in the level at the reference terminal of the first transistor. 1. An amplifier circuit characterized in that the voltage level of a control terminal of a transistor is lowered, and the output voltage of the amplifier circuit is quickly lowered by kneading, thereby preventing the generation of pop sounds.