JP4465787B2 - Audio signal processing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a camcorder or the like and relates to an audio signal processing circuit having a function of controlling a predetermined IC by communicating a control signal between a plurality of audio signal processing ICs.
[0002]
[Prior art]
Conventionally, in a camcorder or the like, an audio signal processing circuit using a plurality of audio signal processing ICs is used. The audio signal processing circuit controls the operation of a predetermined IC by communicating an external control signal between the audio signal processing ICs. Hereinafter, an audio signal processing IC and a speaker amplifier IC that perform communication control in the camcorder will be described as an example. The camcorder has a function of saving speaker power in order to reduce the power consumption of the camcorder when no speaker is used. As shown in FIG. 2, the audio signal processing IC1 receives an external communication signal S, sends the communication signal S to the speaker amplifier IC2, and controls the power of the speaker amplifier IC2.
[0003]
In the audio signal processing IC and the speaker amplifier IC shown in FIG. 2, when the interface unit for transmitting and receiving the communication signal S is shown in a circuit diagram, the circuit configuration is as shown in FIG. In FIG. 3, when the communication signal S “speaker amplifier operation” is supplied from the outside when the power is on, the audio signal processing IC 1 receives the communication signal S, the current I 1 flows, and the constant current I 2. Are absorbed (condition: current I1> current I2). Therefore, since the constant current I2 does not flow at all in the transistors Q1 and Q2, the base potential is not applied to the transistor Q3. As a result, the collector (standby terminal) potential of the transistor Q3 becomes the power supply voltage Vcc and becomes a High output. When the standby terminal ST becomes High level, the speaker amplifier IC2 operates and sounds are output from the speaker 3. That is, the speaker amplifier IC2 operates when the standby terminal ST is at a high level, and is power-saving when at a low level.
[0004]
On the contrary, when the communication signal S “speaker amplifier power save” is supplied, the audio signal processing IC1 receives the communication signal S and no current I1 flows (condition: current I1 = 0), and the constant current I2 Flows to the collector of transistor Q1 and the base of Q2. As a result, the base potential is applied to the transistor Q3, and the standby terminal ST becomes almost the GND potential (Low) due to the collector current of the transistor Q3 and the voltage drop of the resistor R4. The speaker amplifier IC2 enters a power saving state when the standby terminal is at a low level, and no sound is output from the speaker 3.
[0005]
The above operations are summarized as shown in FIG. That is, when the communication signal S is “speaker amplifier operation”, the audio signal processing IC 1 becomes High output, so that the speaker amplifier IC 2 operates and sound is output from the speaker 3. On the other hand, when the communication signal S is “speaker amplifier power save”, the audio signal processing IC 1 becomes Low output, so that the speaker amplifier IC 2 enters the power save state and no sound is output from the speaker 3.
[0006]
[Problems to be solved by the invention]
By the way, as described above, when communication control is performed between the audio signal processing IC 1 and the speaker amplifier IC 2, a noise due to a malfunction in communication control is generated due to a difference in transient response of each IC. In the case of the circuit configuration shown in FIG. 3, when the camcorder is turned off, a “click” sound is generated from the speaker 3. When the power is turned off, the camcorder saves the power of the speaker amplifier IC2 and turns it off. However, in the conventional interface circuit between the audio signal processing IC1 and the speaker amplifier IC2, the standby terminal ST is maintained at the low level. Must become non-operational.
[0007]
However, as shown in FIG. 5, when the power is turned off, the standby terminal ST is at a high level, so that the speaker amplifier IC2 is in an operating state, which causes a noise. That is, since the output of the audio signal processing IC 2 that controls the standby terminal ST is High / Low controlled by the pull-up resistor R4 as shown in FIG. 3, when the power is off, the standby terminal ST becomes the power supply voltage Vcc. The sound was pulled up to a high level and a noise was generated. As described above, in the conventional audio signal processing circuit, there is a problem that a noise due to noise is generated at the time of a transient response such as power on / off, which is very disturbing.
[0008]
Therefore, an object of the present invention is to provide an audio signal processing circuit that can prevent the generation of a clicking sound when the power is turned off.
[0009]
[Means for Solving the Problems]
To achieve the above object, an audio signal processing circuit according to claim 1 is an audio signal processing circuit for controlling operation / non-operation of a speaker amplifier circuit that finally outputs an audio signal based on a potential of a standby terminal. A transistor having an emitter grounded and a collector connected to the standby terminal, a first noise removing means connected to the standby terminal, and having the standby terminal as a high impedance when the power is turned off, and connected to the standby terminal And a second noise removing means for forcibly setting the standby terminal having a high impedance by the first noise removing means to a ground potential , wherein the first noise removing means has a transient response when the power is turned off. Sometimes the current source is turned off at the same timing as the other internal elements, The noise removing means includes a first transistor having a collector connected to the standby terminal via a first resistor, an emitter grounded, and a collector pulled up to a power supply voltage by a second resistor. A second transistor having an emitter grounded, and a third resistor, a diode, and a fourth resistor connected in series between a power supply voltage and a ground voltage, and a second resistor between the diode and the fourth resistor. A base of two transistors is connected, and when the power is turned on, the standby transistor becomes high impedance with respect to the standby terminal, and during transient response when the power is turned off, the first transistor is turned on at a timing different from the timing when other internal elements are turned off. It is turned on .
[0014]
In the present invention, the first noise removing means sets the standby terminal to high impedance when the power is turned off, and the second noise removing means forcibly sets the standby terminal set to high impedance by the first noise removing means. To ground potential. Therefore, the standby terminal does not go to a high level when the power is turned off, and it is possible to prevent the occurrence of a clicking sound when the power is turned off.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A. Embodiment FIG. 1 is a circuit diagram showing a schematic configuration of an embodiment of the present invention. It should be noted that parts corresponding to those in FIG. The audio signal processing IC 4 corresponds to the conventional audio signal processing IC 1 shown in FIG. The audio signal processing IC 4 according to the present embodiment is different from the conventional one in that the pull-up resistor R4 in the conventional audio signal processing IC 1 shown in FIG. 2 is replaced with a noise removal circuit 5 composed of a constant current I3, thereby turning off the power. The standby terminal ST is prevented from being pulled up to the power supply voltage Vcc. The constant current I3 is a current source that operates and does not operate at the same timing as the internal circuit during a transient response such as when the power supply voltage Vcc is turned on / off. By providing the constant current I3, the standby terminal ST becomes high impedance, and the potential cannot be determined. However, when only the constant current I3 is present, the transistor Q3 is turned off before the constant current I3 is turned off at the moment when the power is turned off, so that the constant current I3 flows to the base of the transistor Q4 of the speaker amplifier IC2. A voltage Vf is generated in the transistor Q4. As a result, as shown in FIG. 5, the standby terminal ST becomes a high level as in the prior art, and a noise is generated.
[0016]
Therefore, in this embodiment, in addition to the replacement with the constant current I3, a noise removal circuit 6 is provided. The noise removing circuit 6 includes a transistor Q5 whose collector is connected to the standby terminal ST via a resistor R6, an emitter grounded, and a collector pulled up to the power supply voltage Vcc by a resistor R7, and a transistor Q6 whose emitter is grounded. , And a resistor R8, a diode D1, and a resistor R9 connected in series between the power source and the ground. The base of the transistor Q5 is connected to the collector of the transistor Q6. The base of the transistor Q6 is connected between the diode D1 and the resistor R9. In the noise removal circuit 6, the timing at which the transistor Q5 is turned on can be easily changed by changing the resistance value of the resistor R9 shown in FIG. In other words, the resistance value of the resistor R9 in the noise removal circuit 6 is set so that the internal circuit operates at a timing different from the non-operation timing during a transient response such as when the power supply voltage Vcc is turned on / off.
[0017]
Since the voltage Vf is normally generated at the base potential of the transistor Q6 when the power supply is on, the noise elimination circuit 6 has a collector current of the transistor Q6 and a voltage drop of the resistor R7, and the collector potential of the transistor Q6 is The potential almost becomes GND, and the transistor Q5 is not turned on. For this reason, the collector of the transistor Q5 is open and does not affect the exchange of communication control between the audio signal processing IC1 and the speaker amplifier IC2. In contrast, when the power is off, the transistor Q6 is turned off. That is, the current I4 is a value obtained by subtracting 2Vf of the transistor Q6 and the diode D1 from the power supply voltage Vcc and dividing by the resistor R8. Therefore, when the power supply voltage Vcc is turned off, the current I4 decreases and the voltage across the transistor Q6 Vf is not generated. Therefore, the voltage Vf is generated in the transistor Q5, and the transistor Q5 is turned on.
[0018]
As described above, when only the constant current I3 is used, the standby terminal ST becomes High level immediately after the power is turned off. By providing the noise removal circuit 6, the standby terminal ST is forcibly lowered to Low level. It becomes possible. Therefore, when the power is turned off, the standby terminal ST will not be in the high state, and the speaker amplifier IC2 is maintained in the power saving state and does not generate a clicking sound.
[0019]
B. Application Example When the power supply voltage Vcc is turned off, the internal circuit also follows the power supply voltage Vcc and is turned off. Therefore, at the time of the BUF output PIN, noise is output and the power supply voltage Vcc is turned off. When the noise at the time of power-off is anxious, if the current source of the output BUF is turned off by using the noise removal circuit 6 described above, the output BUF is turned off at the moment when the power-supply voltage Vcc is turned off. So no noise is generated.
[0020]
As described above, according to the above-described embodiment, the standby terminal ST is forcibly set to the low level when the power is turned off, and the open collector (high impedance) is set during the normal operation, so that other circuits are not affected. With a simple circuit configuration, it is possible to prevent the occurrence of a clicking sound when the power is turned off.
[0021]
【The invention's effect】
According to the first aspect of the present invention, when the power is turned off, the first noise removing unit sets the standby terminal to high impedance, and the second noise removing unit sets the high impedance to the first noise removing unit. Since the standby terminal is forcibly set to the ground potential, there is an advantage that the standby terminal does not become a high level when the power is turned off, and it is possible to prevent the occurrence of a clicking sound when the power is turned off.
[0022]
Also, the pre-Symbol first noise removing means, emitter grounded, since the potential of the collector and a current source which is inserted on the collector side of the transistor to a potential of the standby terminal, a simple circuit configuration, power supply There is an advantage that the standby terminal does not go to a high level when the power is off, and it is possible to prevent the generation of a clicking sound when the power is off.
[0023]
Also, the previous SL second noise removing means, at the time of power-on, since such a high impedance to the standby terminal, during normal operation, without affecting the other circuits, power off It is possible to obtain an advantage that the generation of a squeal noise can be prevented.
[0024]
Also, the pre-Symbol first noise removing means, at the time of a transient response when the power-off, since the current source turned off at the same timing as the other internal elements, a simple circuit configuration, standby terminal when the power is off Is not high, and there is an advantage that it is possible to prevent the generation of a clicking sound when the power is turned off.
[0025]
Also, the pre-Symbol second noise removing means, when the transient response of the power off, the other internal elements is such that the first transistor to the ON state at different timings with the timing at which the OFF state, a simple With the circuit configuration, there is an advantage that the standby terminal does not become high level when the power is turned off, and it is possible to prevent the generation of a clicking sound when the power is turned off.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a schematic configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing a schematic configuration of an audio processing circuit in the camcorder.
FIG. 3 is a circuit diagram illustrating a schematic configuration of an interface unit that transmits and receives a communication signal S in a conventional audio signal processing IC and a speaker amplifier IC.
FIG. 4 is a diagram for explaining the operation of an audio processing circuit.
FIG. 5 is a conceptual diagram for explaining the cause of noise generation in a conventional audio processing circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Audio signal processing IC, 2 ... Speaker amplifier IC (speaker amplifier circuit), 3 ... Speaker, 4 ... Audio signal processing IC, 5 ... Noise removal circuit (1st noise removal means, current source) , 6 ... Noise removal circuit (second noise removal means)

Claims (1)

In the audio signal processing circuit for controlling the operation / non-operation of the speaker amplifier circuit that finally outputs the audio signal based on the potential of the standby terminal,
A transistor having an emitter grounded and a collector connected to the standby terminal;
A first noise removing unit connected to the standby terminal and having a high impedance when the power is off;
A second noise removing means connected to the standby terminal and forcing the standby terminal to have a high impedance by the first noise removing means to forcibly set the ground potential ;
The first noise removing means is a current source that is turned off at the same timing as other internal elements during a transient response when the power is turned off.
The second noise removing means includes a first transistor having a collector connected to the standby terminal via a first resistor, an emitter grounded, and a collector pulled up to a power supply voltage by a second resistor. A second transistor connected to the base of the transistor and having an emitter grounded; a third resistor connected in series between a power supply voltage and a ground voltage; the diode and the fourth resistor; The base of the second transistor is connected between them, and when the power is turned on, the standby terminal has a high impedance, and during the transient response when the power is turned off, the other internal elements are turned off at a timing different from the timing at which the other internal elements are turned off. An audio signal processing circuit for turning on one transistor .

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