JP2009105664A - D-class amplifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a D-class amplifier circuit, the output signal distortion of which is small. <P>SOLUTION: The D-class amplifier circuit 100 has a BTL structure, and amplifies an input analog signal Vin. Comparing it with a triangular wave signal, the D-class amplifier circuit 100 outputs final antiphase output signals VoutP and VoutN at the same signal level. In addition, the D-class amplifier circuit 100 has a negative feedback circuit which is composed of a differentiator DAMP. The differentiator DAMP calculates the difference between the final output signals VoutP and VoutN of the D-class amplifier circuit 100 to cancel noise components which are included in the signals and have the same phase, and feed backs to an inverting input terminal (-) of an input stage amplifier AMP1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a class D amplifier circuit having a function of reducing distortion of an output signal.

Class D amplifier circuits (digital amplifiers) that amplify power by digitally modulating an input analog audio signal are widely used in fields such as audio (see, for example, Patent Document 1).
Further, a BTL (Bridged Trans Less) type amplifier is known as a technique for increasing output power by bridge-connecting amplifiers in an output stage (see, for example, Patent Document 2). The class D amplifier circuit can also adopt the BTL system in order to increase the output power.
In addition, among class D amplifier circuits and BTL amplifier circuits, a feedback circuit that feeds back an output signal to an input stage may be provided in order to adjust the pulse width and ensure the stability of the output signal ( For example, see Patent Documents 2 and 3.)
JP 2006-101022 A JP 2006-340152 A JP-A-7-38351

The output signal of the class D amplifier circuit may be superposed with relatively long-period component noise due to switching noise or wraparound from the peripheral circuit, which distorts the final output signal.
Further, when an output signal including this noise is fed back, the noise component returns to the input of each amplifier through the feedback circuit, and there is a possibility that a large distortion (distortion) occurs in the final output signal of the class D amplifier circuit. is there.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a class D amplifier circuit with small distortion of the final output signal.
An object of the present invention is to provide a class D amplifier circuit that removes noise input to each amplifier through a feedback circuit.

In order to achieve the above object, the class D amplifier circuit of the present invention includes:
A first amplifier circuit for inverting and amplifying an input signal;
A second amplifier circuit for inverting and amplifying the output signal of the first amplifier circuit;
A triangular wave generation circuit for generating a triangular wave signal;
A first comparison circuit that outputs a rectangular wave signal whose signal level varies based on the signal level of the triangular wave signal generated by the triangular wave generation circuit and the signal level of the output signal of the first amplifier circuit;
A second comparison circuit that outputs a rectangular wave signal whose signal level varies based on the signal level of the triangular wave signal generated by the triangular wave generation circuit and the signal level of the output signal of the second amplifier circuit;
A differential amplification circuit that differentially amplifies the output signal of the first comparison circuit and the output signal of the second comparison circuit and negatively feeds back to the first amplification circuit;
It is characterized by that.

For example, the first comparison circuit compares the signal level of the triangular wave signal generated by the triangular wave generation circuit with the signal level of the output signal of the first amplification circuit, and outputs a rectangular wave signal corresponding to the comparison result. And a circuit for amplifying and outputting the output of the first comparison circuit,
For example, the second comparison circuit compares the signal level of the triangular wave signal generated by the triangular wave generation circuit with the signal level of the output signal of the second amplification circuit, and outputs a rectangular wave signal corresponding to the comparison result. And a circuit for amplifying and outputting the output of the second comparison circuit.

  It is desirable that the first comparison circuit and the second comparison circuit have the same circuit configuration.

  It is desirable that the first comparison circuit and the second comparison circuit are arranged close to each other on a circuit board.

  It is desirable that the first comparison circuit and the second comparison circuit are configured on the circuit board by the same manufacturing process.

  For example, the output signal of the first comparison circuit and the output signal of the second comparison circuit fluctuate with the same bias signal as a reference level, have opposite phases, and constitute a bridged trans less amplifier circuit. .

  The output terminal of the first comparison circuit and the output terminal of the second comparison circuit are preferably connected to an external speaker.

  According to the present invention, the common-mode noise included in the output signal can be canceled and negative feedback can be performed, and distortion of the final output signal can be reduced.

  A class D amplifier circuit (class D amplifier) 100 according to an embodiment of the present invention will be described below with reference to the drawings.

  The class D amplifier circuit 100 is a circuit that performs pulse width conversion on the analog input voltage signal Vin and outputs it as a rectangular wave signal. The class D amplifier circuit 100 has a BTL (Bridged Trans Less) system configuration, and has two positive and negative polarity configurations. The output terminal is directly connected to the speaker SP.

  As shown in FIG. 1, the class D amplifier circuit 100 includes an input terminal Tin, output terminals ToutN and ToutP, an amplifier AMP1, an amplifier AMP2 and an amplifier AMP3, a triangular wave generator TRI, a comparator CMP1 and a comparator CMP2. , Level shifter LS1 and level shifter LS2, a differential part DAMP, an inverting amplifier INV, and the like. The amplifiers AMP1 and AMP2, the comparators CMP1 and CMP2, and the like are supplied with appropriate power from a power supply device (not shown).

  The input terminal Tin is connected to the inverting input terminal (−) of the amplifier AMP1. The negative input (negative feedback) of the output signal Vamp from the amplifier AMP1 is applied to the inverting input terminal (−) of the amplifier AMP1 via the resistor R12. A reference voltage such as a ground voltage is applied to the non-inverting input terminal (+) of the amplifier AMP1. With this configuration, the amplifier AMP1 outputs an amplified signal Vamp obtained by amplifying the analog input signal Vin.

  The amplifier AMP2 constitutes an inverting amplifier having a gain of 1 with the resistors R21 and R22. The amplified signal Vamp output from the amplifier AMP1 is applied to the inverting input terminal (−) of the amplifier AMP2 via the resistor R21. Further, a negative feedback of the output signal −Vamp of the amplifier AMP2 is applied to the inverting input terminal (−) of the amplifier AMP2 via the resistor R22. A reference voltage such as a ground voltage is applied to the non-inverting input terminal (+) of the amplifier AMP2.

  The output terminal of the amplifier AMP1 is connected to the non-inverting input terminal (+) of the comparator CMP1. The output terminal of the amplifier AMP2 is connected to the non-inverting input terminal (+) of the comparator CMP2.

  The triangular wave generator TRI generates a triangular wave signal Vtri and supplies it to the inverting input terminal (−) of the comparator CMP1 and the input terminal of the inverting amplifier INV.

  The comparator CMP1 compares the voltage of the triangular wave signal Vtri supplied from the triangular wave generator TRI and the voltage of the amplified signal Vamp. When the voltage of the amplified signal Vamp is higher than the voltage of the triangular wave signal Vtri, the comparator CMP1 becomes high level. When the voltage of Vamp is lower than the voltage of the triangular wave signal Vtri, a rectangular wave signal Vcmp that is low level is output.

  The inverting amplifier INV has the same configuration as that of the inverting amplifier having the amplification factor of 1 and composed of the amplifier AMP2 and the resistors R21 and R22, and inverts the polarity of the triangular wave signal Vtri supplied from the triangular wave generator TRI − Vtri is generated and supplied to the inverting input terminal (−) of the comparator CMP2.

  The comparator CMP2 compares the voltage of the inverted triangular wave signal −Vtri supplied from the inverting amplifier INV with the voltage of the amplified signal −Vamp, and when the voltage of the amplified signal −Vamp is higher than the voltage of the inverted triangular wave signal −Vtri. When the voltage is high and the voltage of the amplified signal −Vamp is lower than the voltage of the inverted triangular wave signal −Vtri, the rectangular wave signal −Vcmp that is low is output.

  Since the amplified signals Vamp and −Vamp are the same level and opposite phase signals, the rectangular wave signals Vcmp and −Vcmp are also opposite phase signals.

  The output terminal of the comparator CMP1 is connected to the input terminal of the level shifter LS1. The level shifter LS1 shifts the output signal Vcmp of the comparator CMP1 from the voltage level of the signal system to the voltage level of the driving system, and outputs an output signal VoutN in which the signal obtained by amplifying the rectangular wave signal Vcmp and the bias voltage Vbis are superimposed. . The output terminal of the comparator CMP2 is connected to the input terminal of the level shifter LS2. The level shifter LS2 shifts the output signal −Vcmp of the comparator CMP2 from the voltage level of the signal system to the voltage level of the drive system, and outputs an output signal VoutP in which the rectangular wave signal −Vcmp is amplified and the bias voltage Vbis is superimposed. Output.

  The output terminal of the level shifter LS1 is connected to the output terminal ToutN, and is connected to the inverting input terminal (−) of the amplifier AMP3 via the resistor R31. The output terminal of the level shifter LS2 is connected to the output terminal ToutP, and is connected to the non-inverting input terminal (+) of the amplifier AMP3 via the resistor R33.

  The output terminals ToutN and ToutP are directly connected to the input terminal of the speaker SP. The bias voltage components Vbis included in the output signals VoutN and VoutP of the level shifters LS1 and LS2 are equal, and no DC voltage component is applied to the speaker SP. Therefore, it is not necessary to provide a coupling capacitor for cutting the DC component.

  The differential unit DAMP includes an amplifier AMP3, a resistor R31, a resistor R32, a resistor R33, and a resistor R34. Negative feedback (negative feedback) due to the output of the amplifier AMP3 is applied to the inverting input terminal (−) of the amplifier AMP3 via the resistor R32. The non-inverting input terminal (+) of the amplifier AMP3 is connected to a reference voltage such as a ground voltage via a resistor R34. The output terminal of the amplifier AMP3 is connected to the inverting input side (−) of the amplifying unit AMP1 via the resistor R4, and the output signals VoutN and VoutP of the level shifter LS1 and the level shifter LS2 are fed back to the amplifier AMP1.

The differential unit DAMP outputs a voltage obtained by amplifying the potential difference between the two input voltages. The relational expression between the input voltage Vfin1 and input voltage Vfin2 of the differential part DAMP and the output voltage Vfout is expressed by the following expression (1).
Vfout = (Vfin1-Vfin2) (R32 / R31) (1)
However, R32 / R31 = R34 / R33

  From equation (1), Vfout = 0 when Vfin1 = Vfin2. That is, when the same voltage of the same phase is input, it does not appear in the output, so that the differential unit DAMP can remove in-phase signal noise (common mode noise) included in the output signals VoutN and VoutP.

Next, a general amplification operation of the class D amplifier circuit 100 having the above configuration will be described.
First, the analog input signal (sound signal) Vin supplied to the input terminal Tin is inverted and amplified by the amplifier AMP1 at the amplification factor α and output as the amplified signal Vamp.

  This amplified signal Vamp is inverted and amplified by the amplifier AMP2 at an amplification factor of 1, and becomes an amplified signal -Vamp having the same voltage as the opposite phase to the amplified signal Vamp.

  The triangular wave generator TRI generates a triangular wave signal Vtri and supplies it to the inverting input terminal (−) of the comparator CMP1 and the inverting amplifier INV. The inverting amplifier INV inverts the polarity of the triangular wave signal Vtri and supplies it to the inverting input terminal (−) of the comparator CMP2.

  As shown in FIGS. 2A and 2B, the comparator CMP1 becomes a high level when the voltage of the amplified signal Vamp is higher than the voltage of the triangular wave signal Vtri, and the voltage of the amplified signal Vamp is equal to that of the triangular wave signal Vtri. When the voltage is lower than the voltage, a rectangular wave signal Vcmp that is low level is output. Here, the waveforms of the amplified signal Vamp and the amplified signal −Vamp shown in FIG. 2 are actually sine waves, but the frequency is smaller than that of the triangular wave signal Vtri, and the level change is not so much in a period such as one cycle of the triangular wave signal Vtri. Because there is no line, it is shown as a straight line for convenience.

  As shown in FIGS. 2D and 2E, the comparator CMP2 becomes high level when the voltage of the amplified signal −Vamp is higher than the voltage of the inverted triangular wave signal −Vtri, and the voltage of the amplified signal −Vamp is When the voltage is lower than the voltage of the inverted triangular wave signal -Vtri, a rectangular wave signal -Vcmp that is low is output.

  The level shifter LS1 converts the signal voltage system rectangular wave signal Vcmp shown in FIG. 2B into the drive voltage system output signal VoutN shown in FIG. 2C, and outputs it to the output terminal ToutN. Further, the level shifter LS2 converts the signal voltage system rectangular wave signal -Vcmp shown in FIG. 2E into the drive voltage system output signal VoutP shown in FIG. 2F, and outputs it to the output terminal ToutP. The output signals VoutN and VoutP are rectangular wave signals that vary around the same bias voltage Vbis.

  The speaker SP is driven by the output voltage VoutN-VoutP.

  The differential unit DAMP amplifies the difference (VoutP−VoutN) of the output voltage (usually amplification factor <1) and negatively feeds back to the inverting input terminal (−) of the amplifier AMP1, thereby obtaining the output voltage (pulse width). Adjust and stabilize circuit operation.

Next, a method for removing noise from the negative feedback signal will be described with reference to FIG.
Usually, noise is superimposed on the output signals of the comparators CMP1 and CMP2 and the output signals of the level shifters LS1 and LS2.

Since the configurations of the comparators CMP1 and CMP2 and the configurations of the level shifters LS1 and LS2 are the same as each other, the output signals Vcmp and -Vcmp of the comparators CMP1 and CMP2 and the output signals VoutN and VoutP of the level shifters LS1 and LS2 As shown schematically in FIGS. 3A and 3C, and FIG. 3B and FIG. 3D, in-phase noise is often superimposed.
When this common-mode noise is negatively fed back to the amplifier AMP1, the noise is amplified and the distortion of the output signals VoutN and VoutP increases.

  However, in the class D amplifier circuit 100 of FIG. 1, the differential unit DAMP takes the difference between the output signals VoutP and VoutN. For this reason, as shown in FIG. 3 (e), the anti-phase signal components included in the output signals VoutP and VoutN are almost doubled and then amplified with a constant amplification factor. Ingredients are reduced to near zero level.

  For this reason, the feedback signal negatively fed back to the amplifier AMP1 is substantially only the signal component included in the output signals VoutP and VoutN. For this reason, it is possible to prevent the negative feedback noise from being amplified by the amplifier AMP1 and affect the output signals VoutN and VoutP, and to suppress the distortion of the final output signals VoutN and VoutP.

  In the above configuration, in order to reduce the negative feedback of the common mode noise, it is desirable that the noises included in the output signals VoutN and VoutP of the level shifters LS1 and LS2 are completely in phase and have the same voltage level.

For this purpose, it is desirable that the comparators CMP1 and CMP2 have the same configuration. Here, the same configuration means that the circuit configuration of the comparator (element connection relationship) and the characteristics and sizes of the elements (transistor, resistor) constituting the circuit are equal to each other.
Further, it is desirable that the comparators CMP1 and CMP2 and the level shifters LS1 and LS2 are arranged close to each other.

Further, it is desirable that the comparators CMP1 and CMP2 and the level shifters LS1 and LS2 are configured on the same substrate and are applied with the same power supply voltage and ground voltage.
More preferably, the comparators CMP1 and CMP2 and the level shifters LS1 and LS2 are preferably formed and incorporated in the same semiconductor substrate through the same manufacturing process. With such a configuration, various variations in the manufacturing process such as the influence of mask displacement, pressure fluctuation, gas concentration, and diffusion impurity concentration variation in the manufacturing process are caused by comparators CMP1 and CMP2, level shifters. This affects both LS1 and LS2. For this reason, the characteristics of the comparators CMP1 and CMP2 and the characteristics of the level shifters LS1 and LS2 are equal.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation and application are possible.

  For example, if the common-mode noise included in the two output signals VoutN and VoutP can be canceled, the circuit configuration of the differential unit DAMP can be arbitrarily changed.

  Further, the circuit configuration of the circuit portion that amplifies the input signal, the circuit portion that generates the rectangular wave, and the portion that converts the signal level can be changed as appropriate.

  For example, in the configuration of FIG. 1, as a comparison circuit for generating a differential signal to be output, a circuit composed of a comparator CMP1 and a level shifter LS1, and a circuit composed of a comparator CMP2 and a level shifter LS2 However, other circuit configurations can be used. For example, if the output voltage levels of the comparators CMP1 and CMP2 have a voltage level sufficient for driving the speaker SP, the comparators CMP1 and CMP2 may be constituted by only the comparator. Further, a high power amplifier or the like may be used instead of the level shifter.

  Further, in order to improve the circuit characteristics, other arbitrary circuit functions may be added. For example, a low frequency component of an electric signal may be extracted by providing an LPF (Low Pass Filter) after an output terminal of each amplifier or each comparator.

It is a block diagram which shows the structure of the class D amplifier circuit which concerns on embodiment of this invention. (A)-(f) is a timing chart for demonstrating normal operation | movement of the class D amplifier circuit shown in FIG. (A)-(e) is a timing chart for demonstrating the noise reduction operation | movement of the class D amplifier circuit shown in FIG.

Explanation of symbols

100 Class D amplifier circuit AMP1, AMP2, AMP3 Amplifier CMP1, CMP2 Comparators R11, R12, R21, R22, R31, R32, R33, R34, R4 Resistor TRI Triangular wave generator LS1, LS2 Level shifter DAMP Differential section SP Speaker

Claims (7)

A first amplifier circuit for inverting and amplifying an input signal;
A second amplifier circuit for inverting and amplifying the output signal of the first amplifier circuit;
A triangular wave generating circuit for generating a triangular wave signal;
A first comparison circuit that outputs a rectangular wave signal whose signal level varies based on the signal level of the triangular wave signal generated by the triangular wave generation circuit and the signal level of the output signal of the first amplifier circuit;
A second comparison circuit that outputs a rectangular wave signal whose signal level varies based on the signal level of the triangular wave signal generated by the triangular wave generation circuit and the signal level of the output signal of the second amplification circuit;
A differential amplification circuit that differentially amplifies the output signal of the first comparison circuit and the output signal of the second comparison circuit and negatively feeds back to the first amplification circuit;
A class D amplifier circuit. The first comparison circuit compares the signal level of the triangular wave signal generated by the triangular wave generation circuit with the signal level of the output signal of the first amplification circuit, and outputs a rectangular wave signal corresponding to the comparison result And a circuit for amplifying and outputting the output of the first comparison circuit,
The second comparison circuit compares the signal level of the triangular wave signal generated by the triangular wave generation circuit with the signal level of the output signal of the second amplification circuit, and outputs a rectangular wave signal corresponding to the comparison result A second comparison circuit that amplifies and outputs the output of the second comparison circuit,
The class D amplifier circuit according to claim 1. The first comparison circuit and the second comparison circuit have the same circuit configuration.
The class D amplifier circuit according to claim 1, wherein the class D amplifier circuit is provided. The first comparison circuit and the second comparison circuit are arranged close to each other on a circuit board.
The class D amplifier circuit according to claim 1, 2, or 3. The first comparison circuit and the second comparison circuit are configured by the same manufacturing process on the circuit board.
The class D amplifier circuit according to any one of claims 1 to 4, wherein The output signal of the first comparison circuit and the output signal of the second comparison circuit fluctuate with the same bias signal as a reference level, and have opposite phases,
Configure a Bridged Trans Less type amplifier circuit,
The class D amplifier circuit according to any one of claims 1 to 5, wherein The output terminal of the first comparison circuit and the output terminal of the second comparison circuit are connected to an external speaker.
The class D amplifier circuit according to claim 1, wherein:

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