JP2008125018A - Surround control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain click noise reduction while eliminating the need of a particular capacitor for click noise reduction. <P>SOLUTION: In a surround control circuit comprising a first control circuit which includes a smoothing capacitor C1 for smoothing a voltage resulting from rectifying an audio signal and outputs a voltage Vcont generated in the smoothing capacitor C1 as a surround effect control signal for setting a strength of surround effect and a second control circuit which operates a comparator circuit 4 by changing a comparative potential by controlling ON/OFF of a switch SW and sets a state of surround mode in accordance with an output of the comparator circuit 4, the smoothing capacitor C1 and a current source I2 discharging an electric charge of the smoothing capacitor are connected to a node N where the comparative potential is generated, respectively. While the switch SW is OFF, the output of the comparator circuit 4 is set so as to bring the surround mode into active state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surround control circuit that reduces the audible noise that is an audible band switching sound generated from a speaker.

  FIG. 3 shows the configuration of a conventional surround control circuit designed to reduce the noise. Reference numeral 10 denotes a first control circuit that generates a surround effect control voltage Vcont that determines the strength of the surround effect in the surround circuit (not shown), and reference numeral 20 denotes a second circuit that switches the operation mode / non-operation state of the surround mode in the surround circuit. This is a control circuit.

  In the first control circuit 10, the input audio signal Vin is input to the voltage / current conversion circuit 1 through the resistor R 0, converted into a current signal, rectified by the rectification circuit 2, and smoothed by the smoothing circuit 3. . In the smoothing circuit 3, the operational amplifier OP and the transistor Q1 operate so that the voltage held in the smoothing capacitor C1 becomes the peak value of the voltage generated in the resistor R1, and the surround effect generated in the smoothing capacitor C1. A control voltage Vcont is supplied to the surround circuit. The current source I2 is for discharging the electric charge accumulated in the smoothing capacitor C1. Since the smoothing capacitor C1 requires a relatively large capacitance value, it is externally attached in the semiconductor integrated circuit.

  In the second control circuit 20, the transistors Q2 to Q7, the current source I3, and the voltage source of the reference voltage Vth constitute the comparison circuit 4, and the transistors Q4 and Q5, and Q6 and Q7 each constitute a current mirror circuit. SW is a switch for switching the operation / non-operation state of the surround mode. I1 is a current source, C2 is a noise reduction capacitor, and R2 is a resistor. Since the noise reduction capacitor C2 is required to have a relatively large capacitance value, it is externally attached to the semiconductor integrated circuit, like the smoothing capacitor C1. The current Iout1 of the transistor Q4 and the current Iout2 of the transistor Q7 are supplied to the surround circuit as control signals for switching the operation / non-operation state of the surround mode. The second control circuit 20 has a description similar to Patent Document 1, for example.

  In the first control circuit 10, a voltage indicating the peak value of the input audio signal Vin is generated at the node N1 and supplied to the surround circuit as a surround effect control voltage Vcont that determines the strength of the surround effect. On the other hand, in the second control circuit 20, when the switch SW is OFF, the potential Vn2 of the node N2 is low (approximately ground potential), so that the base potential of the transistor Q2 is lower than the reference voltage Vth, and the transistor Q2 ON and transistor Q3 is OFF. For this reason, the current Iout1 of the transistor Q4 is output, and the current Iout2 of the transistor Q7 is zero. Thereby, the surround mode by the surround circuit is in the operating state.

  Here, when the switch SW is turned on, the current of the current source I1 flows through the resistor R2 and the voltage Vn2 rises. When the voltage Vn2 becomes higher than the reference voltage Vth, the transistor Q2 is turned off and the transistor Q3 is turned on. It becomes. For this reason, the current Iout1 of the transistor Q4 becomes zero, and the current Iout2 of the transistor Q7 is output. As a result, the surround mode by the surround circuit is deactivated.

  FIG. 4 is a diagram showing the characteristics of the operation / non-operation state of the surround mode depending on ON / OFF of the switch SW described above. When the switch SW is OFF, the voltage Vn2 at the node N2 is lower than the reference voltage Vth, the transistor Q2 is turned ON, the current Iout1 is output, and the surround mode by the surround circuit is in the operating state. . The strength of the surround effect at this time is set by the surround effect control voltage Vcont.

  When the switch SW is turned on at time t1, the voltage Vn2 of the node N2 rises with a time constant determined by the current value of the current source I1 and the capacitance value of the noise reduction capacitor C2, and when the reference voltage Vth is exceeded, the surround circuit The surround mode by becomes inactive. As described above, when switching from the operation mode of the surround mode to the non-operation state, the increase in the voltage Vn2 of the node N2 is slow, so that the decrease in the current Iout1 and the increase in the current Iout2 are performed slowly. Occurrence is suppressed.

Further, when the switch SW is turned OFF at time t2, the voltage Vn2 of the node N2 falls with a time constant determined by the resistance value of the resistor R2 and the capacitance value of the noise reduction capacitor C2, and when it falls below the reference voltage Vth, The surround mode by the circuit is activated. As described above, when the surround mode is switched from the non-operating state to the operating state, the decrease in the voltage Vn2 of the node N2 becomes slow, so that the increase in the current Iout1 and the decrease in the current Iout2 are performed slowly. Occurrence of noise is suppressed.
JP 2003-347862 A

  However, in the conventional surround control circuit shown in FIG. 3, the noise generated when the surround circuit switches between the operation mode and the non-operation state of the surround mode is reduced by the noise reduction capacitor C2. Capacitor C2, which has no effect other than sound reduction, is required separately, and when the surround control circuit is composed of a semiconductor integrated circuit, an external terminal for the noise reduction capacitor C2 is specially required and the number of terminals increases. There is a problem of doing.

  An object of the present invention is to provide a surround control circuit that can reduce the noise while eliminating the need for a special capacitor for reducing noise, and solves the above problems.

According to a first aspect of the present invention, there is provided a surround control circuit comprising a smoothing capacitor for smoothing a voltage obtained by rectifying an audio signal, and outputting a voltage generated in the smoothing capacitor as a surround effect control signal for setting the strength of the surround effect. Surround control comprising: a first control circuit; and a second control circuit that operates a comparison circuit by changing a comparison potential by ON / OFF control of a switch and sets a surround mode state by an output of the comparison circuit In the circuit, the smoothing capacitor and a discharge element for discharging the charge of the smoothing capacitor are respectively connected to a node where the comparison potential is generated.
According to a second aspect of the present invention, in the surround control circuit according to the first aspect, when the switch is OFF, the output of the comparison circuit is set so that the surround mode is in an operating state. .

  According to the present invention, since the smoothing capacitor that generates the surround effect control signal is shared as the noise reduction capacitor, the number of capacitors can be reduced by one, and the number of external terminals for that purpose can be reduced. .

  FIG. 1 is a circuit diagram showing a configuration of a surround control circuit according to one embodiment of the present invention. In the present embodiment, the first control circuit 10 and the second control circuit 20 described with reference to FIG. 3 are integrated, and the smoothing capacitor C1 is shared for the purpose of smoothing the audio signal and reducing the noise. That is, the node N to which the smoothing capacitor C1 of the smoothing circuit 3 is connected is set as a comparison potential generation point (connection point to the base of the transistor Q2) of the comparison circuit 4, and the switch SW and the current source I1 are connected to the node N. A series circuit is connected. The current value of the current source I2 is sufficiently smaller than the current value of the current source I1 (I2 << I1). The current source I2 is not limited to this and may be a discharge element, and may be replaced with the resistor R2. The configuration of each part is the same as that described with reference to FIG.

  FIG. 2 is a diagram showing the characteristics of the operation / non-operation state of the surround mode depending on ON / OFF of the switch SW described above. When the switch SW is OFF, the comparison potential of the node N is determined by the surround effect control voltage Vcont (same as the voltage Vcont shown in FIG. 4) of the smoothing circuit 3, and the value is a voltage lower than the reference voltage Vth. It is. Therefore, the transistor Q2 is turned on, the current Iout1 is output, the current Iout2 becomes zero, and the surround mode by the surround circuit is in the operating state. The strength of the surround effect at this time is set by the voltage Vcont.

  When the switch SW is turned on at time t1, the voltage Vcont at the node N rises with a time constant determined by the current value of the current source I1 and the capacitance value of the smoothing capacitor C1, and when the reference voltage Vth is exceeded, the transistor Q2 is turned off. Then, since the transistor Q3 is turned on, the current Iout1 is zero and the current Iout2 is output, the surround mode by the surround circuit is inactive. Thus, since the surround mode is inactive, no abnormality occurs even when the voltage Vcont becomes a high voltage. At the time of switching from the operation state of the surround mode to the non-operation state, the increase in the voltage Vcont of the node N becomes slow, so that the decrease in the current Iout1 and the increase in the current Iout2 are performed slowly, and a pop noise is generated. Is suppressed.

  Further, when the switch SW is turned off at time t2, the voltage Vcont at the node N decreases with a time constant determined by the capacitance value of the smoothing capacitor C1 and the current value of the current source I2, and when the voltage falls below the reference voltage Vth, the transistor Q2 is turned on. The transistor is turned on, the transistor Q3 is turned off, the current Iout1 is output, and the current Iout2 becomes zero, so that the surround mode is in an operating state. Even when the surround mode is switched from the non-operating state to the operating state, the decrease in the voltage Vcont of the node N becomes slow, so that the current Iout1 increases and the current Iout2 decreases slowly. Sound generation is suppressed.

It is a circuit diagram which shows the structure of the surround control circuit of one Example of this invention. FIG. 2 is a control characteristic diagram of the surround control circuit of FIG. 1. It is a circuit diagram which shows the structure of the conventional surround control circuit. FIG. 4 is a control characteristic diagram of the surround control circuit of FIG. 3.

Explanation of symbols

1: Voltage / current conversion circuit 2: Rectifier circuit 3: Smoothing circuit 4: Comparison circuit

Claims (2)

A first control circuit including a smoothing capacitor for smoothing a voltage obtained by rectifying the audio signal, and outputting a voltage generated in the smoothing capacitor as a surround effect control signal for setting the strength of the surround effect; and ON / OFF control of the switch A surround control circuit comprising: a second control circuit that operates the comparison circuit by changing the comparison potential according to the second control circuit, and sets a surround mode state by an output of the comparison circuit
A surround control circuit, wherein a smoothing capacitor and a discharge element for discharging the charge of the smoothing capacitor are connected to a node where the comparison potential is generated. The surround control circuit according to claim 1,
The surround control circuit, wherein the output of the comparison circuit is set so that the surround mode is in an operating state when the switch is OFF.

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