JP4295604B2 - Audio signal playback device - Google Patents

Description

  The present invention relates to an audio signal reproducing apparatus that amplifies a 1-bit digital signal such as a pulse density modulation (PDM) signal or a pulse width modulation (PWM) signal by a switching operation of a switching circuit, and in particular, makes an output impedance of the switching circuit variable. The present invention relates to an audio signal reproduction apparatus that performs volume adjustment.

  A 1-bit digital signal obtained by subjecting an analog audio signal to delta-sigma modulation has a very high sampling frequency and a short data length, and widens the transmittable frequency band by appropriately setting the coefficients of an integrator and an adder. can do. In addition, a high dynamic range can be secured for an audio band that is a low frequency with respect to the sampling frequency. For this reason, it is possible to set the frequency according to the sound source, which is adopted for new standards such as CD (compact disc) and DVD (digital video disc).

  As shown in FIG. 5, a conventional audio signal reproducing apparatus that reproduces a 1-bit digital signal inputs a 1-bit digital signal generated from PCM data by a 1-bit generating circuit 20 to a driver circuit 1 and outputs a 1-bit digital signal. The driver circuit 1 to which a signal is input is configured to switch two field effect transistors 3 and 4 (hereinafter referred to as FETs 3 and 4) of the switching circuit 2 based on a 1-bit digital signal. 2 is connected to a constant voltage power source + Vcc and a speaker 6 through a low-pass filter 5.

  The 1-bit digital signal is output as an output signal that is switched and power amplified based on the level of the constant voltage power source + Vcc supplied to the switching circuit 2, and is input to the low-pass filter 5 including a coil, a capacitor, and the like. By integrating, the output signal from the switching circuit 2 which is a pulse wave signal is converted into an analog signal and input to the speaker 6. The volume adjustment is performed by the digital ATT 21 provided in the preceding stage of the 1-bit generation circuit 20, and the digital ATT 21 adjusts the volume of the PCM data input based on the volume setting value set by the volume setting unit 7. And output to the 1-bit generation circuit 20.

  In addition, the present applicant generates a volume control signal by changing the pulse width of the clock signal when obtaining a 1-bit digital signal by ΔΣ modulation according to the setting in the volume setting unit 7, and generates a pulse of the 1-bit digital signal. An audio signal reproducing apparatus for adjusting volume by providing a PDC circuit for generating a switching control signal by changing the width to a pulse width of a volume control signal and switching the switching circuit 2 by the switching control signal from the PDC circuit. It has been proposed (see, for example, Patent Document 1).

However, in any of the conventional techniques, the switching operation of the switching circuit 2 is performed based on a 1-bit digital signal that has been subjected to volume adjustment. However, there is a problem that the power supply noise of the supplied constant voltage power supply + Vcc rides a certain amount, and if the volume setting value becomes small, the influence of the power supply noise cannot be ignored.
JP-A-6-335082

  The present invention has been made in view of such a problem, and an object of the present invention is to reduce power source noise of a constant voltage power source when the volume setting value becomes small, and to reduce the volume setting value. Therefore, it is an object to provide an audio signal reproducing apparatus capable of reducing the influence of power supply noise.

In order to solve the above problems, the present invention has the following configurations.
The audio signal reproduction apparatus of the present invention reproduces an audio signal by amplifying the input 1-bit digital signal by the switching means by causing the driver circuit to perform switching operation based on the input 1-bit digital signal by the driver circuit. wherein a device, and volume setting means for setting the volume setting value, by including an impedance changing means for changing the output impedance of the switching means in response to the volume setting value set by the volume setting means And

Furthermore, in the audio signal reproduction device of the present invention, the impedance changing means compares the volume setting value set by the volume setting means with the output level of the output signal from the switching means, When the output level of the output signal from the switching means is large, the output level of the output signal from the switching means is lowered by changing the output impedance to be higher, and the output from the switching means is lower than the volume setting value. When the output level of the signal is small, feedback control is performed to increase the output level of the output signal from the switching means by changing the output impedance low .

Further the audio signal reproducing apparatus of the present invention, the impedance changing means, by changing the gate voltage for driving the switching elements of the switching means by said driver circuit, to change the on resistance of the switching element, the switching means The output impedance is changed.

Furthermore, in the audio signal reproducing device of the present invention, the switching means includes a plurality of switching elements connected in parallel and having the same on-resistance, and the impedance changing means is driven by the driver circuit. The output impedance of the switching means is changed by changing the ON resistance of the switching means by changing the number.

Furthermore, in the audio signal reproducing device of the present invention, the switching means includes a plurality of switching elements connected in parallel and having different on-resistances, and the impedance changing means includes the switching element driven by the driver circuit. 3. The audio signal reproducing apparatus according to claim 1, wherein the output impedance of the switching means is changed by changing the combination to change the on-resistance of the switching means.

  The audio signal reproducing device of the present invention is configured to change the on-resistance of the switching circuit by changing the gate voltage for driving the switching element based on the volume setting value, thereby changing the output impedance and load (speaker) of the switching circuit. ) The volume can be adjusted according to the impedance of the constant voltage power supply when the volume setting value is reduced, and the power supply noise of the constant voltage power supply can be reduced by the voltage dividing resistor. There is an effect that the influence of noise can be reduced.

  Furthermore, the audio signal reproduction device of the present invention is configured to feedback control the on-resistance of the switching circuit based on the output level of the output signal of the switching circuit, so that the on-resistance of the switching circuit with respect to the change amount of the gate voltage Even if the change amount varies, there is an effect that the volume can be accurately adjusted to the volume setting value.

  Furthermore, the audio signal reproduction device of the present invention uses a switching circuit composed of a plurality of switching elements connected in parallel and having the same on-resistance, and changes the number of switching elements to be driven based on the volume setting value. By configuring the on-resistance of the switching circuit to change, the volume can be adjusted according to the output impedance of the switching circuit and the impedance of the load (speaker), and the constant voltage when the volume setting value decreases The power source noise of the power source can be reduced by the voltage dividing resistor, and the effect of the power source noise can be reduced even if the volume setting value is reduced.

  Furthermore, the audio signal reproducing device of the present invention uses a switching circuit composed of a plurality of switching elements connected in parallel and having different on-resistances, and switching the combination of the switching elements driven based on the volume setting value. By configuring the circuit to change the on-resistance, the volume can be adjusted according to the output impedance of the switching circuit and the impedance of the load (speaker), and the constant-voltage power supply when the volume setting value becomes small The power source noise can be reduced by the voltage dividing resistor, and the influence of the power source noise can be reduced even when the volume setting value is reduced.

  Furthermore, the audio signal reproduction device of the present invention is configured to feedback control the on-resistance of the switching circuit based on the output level of the output signal of the switching circuit, so that even if the on-resistance of each switching element varies. The effect is that the volume can be accurately adjusted to the volume setting value.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a first embodiment of an audio signal reproduction device according to the present invention, and FIG. 2 is an explanation for explaining a comparison operation in an output level comparison unit shown in FIG. FIG.

  In the first embodiment, referring to FIG. 1, a 1-bit digital signal such as a pulse density modulation (PDM) signal or a pulse width modulation (PWM) signal is input to the driver circuit 1 and a 1-bit digital signal is input. The driver circuit 1 is configured to switch the switching circuit 2 based on a 1-bit digital signal. The switching circuit 2 includes a FET 3 that is a high-side switching element and an FET 4 that is a low-side switching element. A speaker 6 is connected to + Vcc through a low-pass filter 5.

  The 1-bit digital signal is output as an output signal that is switched and power amplified based on the level of the constant voltage power source + Vcc supplied to the switching circuit 2, and is input to the low-pass filter 5 including a coil, a capacitor, and the like. By integrating, the output signal from the switching circuit 2 which is a pulse wave signal is converted into an analog signal and input to the speaker 6.

  The output signal from the switching circuit 2 is input to the A / D conversion unit 8, and the A / D conversion unit 8 converts the input output signal from the switching circuit 2 into a digital signal and outputs an output level comparison unit. Output to 9.

  The output level comparison unit 9 is preset with a value of the constant voltage power supply + Vcc, and the output level comparison unit 9 refers to the switching circuit 2 converted into a digital signal by the A / D conversion unit 8 with reference to FIG. The H level of the output signal from is compared with the constant voltage power supply + Vcc, and the difference is output to the gate voltage control unit 10 as a volume comparison value.

  The volume setting value set by the volume setting unit 7 is input to the gate voltage control unit 10, and the gate voltage control unit 10 sets the volume comparison value from the output level comparison unit 9 and the volume setting unit 7. Compared with the set volume value, the gate voltage control signal based on the comparison result is output to the D / A converter 11. The volume setting value set by the volume setting unit 7 is a numerical value representing the volume set by the user. In this embodiment, the volume set by the user is “0” when the volume is MAX, and the user sets the volume setting value. It is assumed that the smaller the set volume, the larger the value.

  The gate voltage control signal is a signal for instructing the direction and amount of change for changing the gate voltage, and the gate voltage control unit 10 determines that the volume setting value is larger than the volume comparison value, that is, from the switching circuit 2 than the volume setting value. When the output level of the output signal is high, the gate voltage control signal in the direction of decreasing the gate voltage is output from the switching circuit 2 when the volume setting value is smaller than the volume comparison value, that is, from the volume setting value. When the level is small, a gate voltage control signal in the direction of increasing the gate voltage is output. Further, the gate voltage control unit 10 outputs a gate voltage control signal for changing the gate voltage to a greater extent as the difference between the volume comparison value and the volume setting value is larger.

  The D / A converter 11 converts the gate voltage control signal from the gate voltage controller 10 into an analog signal and outputs the analog signal to the transformer 12. The transformer 12 is converted into an analog signal by the D / A converter 11. The gate voltage input to the driver circuit 1 is transformed based on the gate voltage control signal.

  The driver circuit 1 switches the switching circuit 2 with the gate voltage transformed by the transformer 12, and uses the fact that the on-resistance varies depending on the gate voltage in the non-saturated region in the drain current-drain voltage characteristic curves of the FETs 3 and 4. Then, the on-resistances of the FETs 3 and 4 are changed according to the gate voltage. That is, by decreasing the gate voltage for driving the FETs 3 and 4, the on-resistance between the drains and sources of the FETs 3 and 4 is increased, and by increasing the gate voltage for driving the FETs 3 and 4, the drains and sources of the FETs 3 and 4 Reduce the on-resistance between.

  With the above operation, when the output level of the output signal from the switching circuit 2 is higher than the volume set by the user, the gate voltage for driving the FETs 3 and 4 is lowered to turn on the drain-source between the FETs 3 and 4. Feedback control is performed to increase the output impedance of the switching circuit 2 and reduce the output level of the output signal from the switching circuit 2 by increasing the resistance, and the output signal from the switching circuit 2 is higher than the volume set by the user. When the output level of the switching circuit 2 is small, the gate voltage for driving the FETs 3 and 4 is increased to reduce the on-resistance between the drain and source of the FETs 3 and 4, thereby reducing the output impedance of the switching circuit 2. Feedback control to increase output level of output signal from circuit 2 It takes place.

  As described above, according to the first embodiment, by changing the on-resistance of the switching circuit 2 by changing the gate voltage for driving the FETs 3 and 4 based on the volume setting value, The volume can be adjusted according to the output impedance of the switching circuit 2 and the impedance of the load (speaker 6), and the power source noise of the constant voltage power source when the volume setting value becomes small can be reduced by the voltage dividing resistor. Thus, even if the volume setting value is reduced, the effect of power supply noise can be reduced.

  Further, according to the first embodiment, the on-resistance of the switching circuit 2 is feedback-controlled based on the output level of the output signal of the switching circuit 2, so that the switching circuit 2 with respect to the amount of change in the gate voltage. Even if there is a variation in the amount of change in the on-resistance, there is an effect that the volume can be accurately adjusted to the volume setting value.

(Second Embodiment)
FIG. 3 is a block diagram showing the configuration of the second embodiment of the audio signal reproducing apparatus according to the present invention, and FIG. 4 is a block diagram showing the configuration of the switching circuit shown in FIG.

  In the second embodiment, referring to FIG. 3, the driver circuit 16 selects a plurality of switching elements using a switching circuit 13 having a plurality of switching elements connected in parallel on each of the high side and the low side. Thus, the on-resistance of the switching circuit 13 is made variable so that the volume is adjusted.

  Referring to FIG. 4, the switching circuit 13 includes a plurality of FETs 14-1 to 14-n connected in parallel as a plurality of high-side switching elements, and a plurality of FETs 15-1 to 15-n as a plurality of low-side switching elements. Connected in parallel. The FETs 14-1 to 15-n and the FETs 15-1 to 15-n have equivalent on-resistance, and the number of the FETs 14-1 to 14-n and 15-1 to 15-n is determined according to the number of volume setting steps. The FETs 14-1 to n and FETs 15-1 to 15-n having the number of setting steps or more are connected in parallel.

  The output signal from the switching circuit 13 is input to the A / D conversion unit 8, and the A / D conversion unit 8 converts the input output signal from the switching circuit 13 into a digital signal and outputs it to the output level comparison unit 9. Output.

  The output level comparison unit 9 is preset with a value of the constant voltage power supply + Vcc. The output level comparison unit 9 outputs the H of the output signal from the switching circuit 13 converted into a digital signal by the A / D conversion unit 8. The level is compared with the constant voltage power source + Vcc, and the difference is output to the on-resistance control unit 17 as a volume comparison value.

  The volume setting value set by the volume setting unit 7 is input to the on-resistance control unit 17, and the on-resistance control unit 17 is set by the volume comparison value from the output level comparison unit 9 and the volume setting unit 7. The volume setting value that has been set is compared, and an on-resistance control signal based on the comparison result is output to the selector 18. The volume setting value set by the volume setting unit 7 is “0” when the volume set by the user is MAX, and becomes a larger value as the volume set by the user becomes smaller.

  The on-resistance control signal is a signal for instructing the direction and change amount for changing the on-resistance of the switching circuit 13, and the on-resistance control unit 17 has a volume setting value larger than the volume comparison value, that is, the volume setting value. When the output level of the output signal from the switching circuit 13 is large, an on-resistance control signal in the direction of increasing the on-resistance is sent from the switching circuit 13 when the volume set value is smaller than the volume comparison value, that is, from the volume set value. When the output level of the output signal is small, an on-resistance control signal in a direction to reduce the on-resistance is output. Further, the on-resistance control unit 17 outputs an on-resistance control signal for changing the on-resistance to the selector 18 as the difference between the volume comparison value and the volume setting value increases.

  The selector 18 is a means for outputting to the driver circuit 16 a drive element number instruction signal for instructing the number of switching elements used for the switching operation in the switching circuit 13, and according to the on-resistance control signal input from the on-resistance control unit 17. The drive element number instruction signal in which the number of switching elements is increased or decreased is output to the driver circuit 16, and the driver circuit 16 uses the number of switching elements designated by the drive element number instruction signal from the selector 18 to switch the switching circuit 13. Is switched to change the on-resistance of the switching circuit 13. That is, the on-resistance of the switching circuit 13 is increased by increasing the number of switching elements used for the switching operation, and the on-resistance of the switching circuit 13 is decreased by decreasing the number of switching elements used for the switching operation.

  By the above operation, when the output level of the output signal from the switching circuit 13 is larger than the volume set by the user, the on-resistance of the switching circuit 13 is increased by increasing the number of switching elements used for the switching operation. When feedback control is performed to increase the output impedance of the switching circuit 13 and lower the output level of the output signal from the switching circuit 13, and the output level of the output signal from the switching circuit 13 is lower than the volume set by the user In this case, the number of switching elements used for the switching operation is reduced to reduce the on-resistance of the switching circuit 13, thereby lowering the output impedance of the switching circuit 13 and increasing the output level of the output signal from the switching circuit 13. Back control is performed.

  In the second embodiment, the switching circuit 13 is configured to connect switching elements having the same on-resistance in parallel. However, the switching circuit 13 is configured to connect switching elements having different on-resistances in parallel. May be. That is, when the ratio of the on-resistances of the FETs 14-1 to n and 15-1 to n is set to 1: 2: 4:...: 2n-1, for example, n = 7 (7 FETs in parallel Connection), the on-resistance can be varied in 128 ways, and the on-resistance can be varied in multiple stages with a small number of FETs.

  As described above, according to the second embodiment, the switching circuit 13 including a plurality of FETs 14-1 to 14-n and 15-1 to 15 n connected in parallel and having the same on-resistance is used. By changing the number of FETs 14-1 to n and 15-1 to n driven based on the set values to change the on-resistance of the switching circuit 13, the output impedance and load (speaker) of the switching circuit 13 are changed. 6) The volume can be adjusted according to the impedance, and the power supply noise of the constant voltage power supply when the volume setting value becomes small can be reduced by the voltage dividing resistor, and even if the volume setting value becomes small There is an effect that the influence of power supply noise can be reduced.

  Furthermore, according to the second embodiment, the switching circuit 13 including a plurality of FETs 14-1 to 14-n and 15-1 to 15-n connected in parallel and having different on-resistances is used, and based on the volume setting value. By changing the combination of the driving FETs 14-1 to n and 15-1 to n to change the on-resistance of the switching circuit 13, the output impedance of the switching circuit 13 and the impedance of the load (speaker 6) The volume adjustment according to the volume can be adjusted, and the power supply noise of the constant voltage power supply when the volume setting value becomes small can be reduced by the voltage dividing resistor. There is an effect that it can be reduced.

  Furthermore, according to the second embodiment, each FET 14-1 to n, 15- is configured to feedback control the on-resistance of the switching circuit 13 based on the output level of the output signal of the switching circuit 13. Even if the ON resistances 1 to n vary, there is an effect that the volume can be accurately adjusted to the volume setting value.

  It should be noted that the present invention is not limited to the above-described embodiments, and it is obvious that each embodiment can be appropriately changed within the scope of the technical idea of the present invention. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a suitable number, position, shape, and the like in practicing the present invention. In each figure, the same numerals are given to the same component.

1 is a block diagram showing a configuration of a first embodiment of an audio signal reproduction device according to the present invention. It is explanatory drawing for demonstrating the comparison operation | movement in the output level comparison part shown in FIG. It is a block diagram which shows the structure of 2nd Embodiment of the audio signal reproducing | regenerating apparatus based on this invention. It is a block diagram which shows the structure of the switching circuit shown in FIG. It is a block diagram which shows the structure of the conventional audio signal reproducing | regenerating apparatus.

Explanation of symbols

1 Driver circuit (first embodiment)
2 Switching circuit (first embodiment)
3, 4 FET (first embodiment)
5 Low-pass filter 6 Speaker 7 Volume setting unit 8 A / D conversion unit 9 Output level comparison unit 10 Gate voltage control unit (impedance changing means)
11 D / A converter 12 Transformer 13 Switching circuit (second embodiment)
14-1 to n, 15-1 to n FET (second embodiment)
16 Driver circuit (second embodiment)
17 On-resistance control unit (impedance changing means)
18 Selector

Claims (5)

An audio signal reproducing apparatus for amplifying the input 1-bit digital signal by the switching means by switching the switching means based on the input 1-bit digital signal by a driver circuit,
A volume setting means for setting a volume setting value;
Characterized by comprising an impedance changing means for adjusting the output level of the output signal from said switching means to change the output impedance of the switching means in response to the volume setting value set by the volume setting means Audio signal playback device. The impedance changing means compares the volume setting value set by the volume setting means with the output level of the output signal from the switching means, and the output level of the output signal from the switching means is higher than the volume setting value. Is large, by changing the output impedance high, the output level of the output signal from the switching means is lowered, and when the output level of the output signal from the switching means is smaller than the volume setting value, 2. The audio signal reproducing apparatus according to claim 1 , wherein feedback control is performed to increase an output level of an output signal from the switching means by changing an output impedance to be low .   The impedance changing means changes the on-resistance of the switching element and changes the output impedance of the switching means by changing a gate voltage for driving the switching element of the switching means by the driver circuit. The audio signal reproducing device according to claim 1 or 2. The switching means includes a plurality of switching elements connected in parallel and having similar on-resistance,
The impedance changing means changes the output impedance of the switching means by changing the number of the switching elements driven by the driver circuit to change the on-resistance of the switching means. Or the audio signal reproducing device of 2. The switching means includes a plurality of switching elements connected in parallel and having different on-resistances,
2. The impedance changing unit changes an output impedance of the switching unit by changing a combination of the switching elements driven by the driver circuit to change an ON resistance of the switching unit. Or the audio signal reproducing apparatus according to 2;

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