JP5492488B2 - Class D amplifier - Google Patents

Description

  The present invention relates to a class D amplifier, and more particularly to a non-feedback class D amplifier.

  Although the class D amplifier is also called a digital amplifier, unlike an analog amplifier, no loss occurs in the power amplifying element, so that effective amplification can be performed. There is also an advantage of small size and light weight. However, noise due to distortion, switching noise, wraparound from peripheral circuits, etc. is likely to occur. In general, class D amplifiers are classified into a feedback type and a non-feedback type. The feedback type has advantages that it is easy to reduce distortion and stabilizes the system, but it is difficult to set a feedback coefficient, and the circuit Has the disadvantage of becoming larger. On the other hand, the non-feedback type is the opposite of the feedback type and has the inconvenience that switching noise is likely to be mixed in and the system tends to become unstable. However, the circuit can be made smaller and the number of pins required for the feedback element is unnecessary. There is an advantage that it is.

  The non-feedback type is suitable for the recent demand for circuit miniaturization. However, the non-feedback type has a disadvantage that noise is likely to be generated, so that the feedback type tends to be used because it is difficult to use. As an example of the feedback type D amplifier, a means for converting an input signal into a pulse width modulation signal, for example, a comparator, an amplifying means for amplifying the output of the converting means, for example, a buffer amplifier, and an output of the amplifying means In a configuration including feedback means for feedback to the input side of the conversion means, a class D in which a delay means is inserted between the conversion means and the amplification means in order to prevent noise generated with the switching operation. An amplifier is known (Patent Document 1).

JP 2006-128787 A

  However, in the feedback class D amplifier, as described above, the generation of noise can be reduced, but the inconvenience that it is difficult to downsize the circuit cannot be solved. As in the above-described conventional example, when a delay unit is provided as a further noise generation preventing unit, it is more difficult to reduce the size of the circuit.

  By the way, in a non-feedback class D amplifier capable of downsizing the circuit, if oscillation noise from an oscillator that generates a comparison wave or switching noise passes through a comparator, unnecessary oscillation components are generated in the generated PWM wave. Power consumption loss and output waveform THD (Total Harmonic Distortion) increase. In addition, since the class D amplifier is connected to a speaker, headphones, or the like having a low load resistance, it has a large output buffer having a low on-resistance output transistor in order to increase its power efficiency. Thus, even a slight unnecessary oscillation component in the PWM wave tends to cause a through current, and latch-up is likely to occur.

  FIG. 5 is a waveform diagram showing a relationship between a comparator input wave and a comparator output wave of a conventional non-feedback class D amplifier, and FIG. 6 is an enlarged view of a portion shown in FIG. 5B. As is apparent from these figures, in the conventional example, a large distortion occurs due to the influence of noise when the output waveform is inverted. In FIG. 6, the output wave is inverted from the position where the triangular wave and the sine wave intersect, but this is because there is a delay in the response of the comparator.

  The present invention has been made in view of such circumstances, and in a non-feedback type class D amplifier capable of reducing the size of a circuit, it is possible to reduce the influence of noise and switching noise derived from an oscillator. An object is to provide a class amplifier.

In order to achieve the above object, a class D amplifier according to the present invention is generated using an input buffer amplifier that amplifies an input signal composed of sine waves such as an audio signal, an amplified input signal, and an oscillator. A class D comprising a comparator that compares a comparison wave composed of a triangular wave signal to generate a pulse width modulation signal corresponding to the input signal, and an output buffer that amplifies the pulse width modulation signal output from the comparator In the amplifier, the amplified input signal is input to an inverting input terminal, the comparison wave is input to the non-inverting input terminal via an input resistor, and the comparator has an output terminal and an input terminal of the comparison wave. obtained by a positive feedback circuit hysteresis comparator formed by providing a having a feedback resistor between it preferably adjusting the resistance value of the feedback resistor and the input resistor It is obtained by allowing a more adjustment of the hysteresis. In addition, when a fully differential buffer amplifier is used as the input buffer amplifier, common-mode noise can be easily canceled and the circuit can be made more compact.

  According to the class D amplifier of the present invention, by reducing the influence of noise, distortion of the output waveform can be eliminated, latch-up of the output buffer can be prevented, and power consumption can be reduced. There is an effect that it can be suppressed.

1 is a circuit diagram showing a first embodiment of the present invention. The wave form diagram which shows the relationship between the comparator input wave and comparator output wave of this embodiment. The enlarged view of the FIG. 2A section. The circuit diagram which shows 2nd Embodiment of this invention. The wave form diagram which shows the relationship between the comparator input wave and comparator output wave of the conventional non-feedback class D amplifier. The enlarged view of the FIG. 5B section.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. First, the first embodiment will be described with reference to FIGS.

  As shown in FIG. 1, the non-feedback class D amplifier circuit according to this embodiment includes input buffer amplifiers 1 and 2, a triangular wave generator 3, hysteresis comparators 4 and 5, and output buffers 6 and 7. Become. The input buffer amplifiers 1 and 2 have the same configuration, and the hysteresis comparators 4 and 5 and the output buffers 6 and 7 have the same configuration.

  An input signal such as an audio signal is input from the input terminal 100 to the inverting input terminal of the operational amplifier 11 of the input buffer amplifier 1 through the input resistor 12. On the other hand, the non-inverting input terminal of the operational amplifier 11 is connected to the reference potential 101. The output terminal of the operational amplifier 11 is connected to its inverting input terminal via a feedback resistor 13, is connected to the inverting input terminal of the operational amplifier 21 of the input buffer amplifier 2 via an input resistor 22, and the hysteresis comparator 4 The operational amplifier 41 is also connected to the inverting input terminal.

  A non-inverting input terminal of the operational amplifier 21 of the input buffer amplifier 2 is connected to the reference potential 101. The output terminal of the operational amplifier 21 is connected to the inverting input terminal via the feedback resistor 23 and to the inverting input terminal of the operational amplifier 51 of the hysteresis comparator 5.

  Triangular waves, which are comparison waves generated by an oscillator, are input from the triangular wave generator 3 to the non-inverting input terminals of the respective operational amplifiers 41 and 51 of the hysteresis comparators 4 and 5 through the input resistors 42 and 52. The output terminals of the operational amplifiers 41 and 51 are connected to the non-inverting input terminals via feedback resistors 43 and 53, respectively, to form a positive feedback circuit. Further, the output terminal of the operational amplifier 41 is connected to the input terminal of the output buffer 6, while the output terminal of the operational amplifier 51 is connected to the input terminal of the output buffer 7. The output terminals of the output buffers 6 and 7 are connected to output terminals 102 and 103 connected to a load such as a speaker.

  Since this embodiment is configured as described above, an input signal (sin wave) such as an audio signal input from the input terminal 100 is inverted in phase and amplified by the input buffer amplifier 1, and the operational amplifier of the hysteresis comparator 4. The signal is input to the inverting input terminal of 41 and input to the inverting input terminal of the operational amplifier 21 of the input buffer amplifier 2, whereby the phase is inverted again and input to the inverting input terminal of the operational amplifier 51 of the hysteresis comparator 5. Since the triangular wave as a comparison wave is input from the triangular wave generator 3 to the non-inverting input terminals of the respective operational amplifiers 41 and 51 of the hysteresis comparators 4 and 5 via the input resistors 42 and 52, respectively. 5, the inputted triangular wave and sine wave are compared with each other to generate a PWM signal, which is output to the output buffers 6 and 7, amplified, and then output to the output terminals 102 and 103, and a load such as a speaker. To be supplied.

  FIG. 2 and FIG. 3 show the relationship between the sin wave and the triangular wave, which are input waves in the hysteresis comparators 4 and 5, and the output wave, which are affected by noise as compared with FIG. 5 and FIG. 6 of the conventional example. It can be understood that no distortion occurs in the output wave. In FIG. 3, the interval between Vuth and Vdth indicates the width of the hysteresis, and in the illustrated state, the sin wave is at a critical point exceeding the upper limit Vuth of the hysteresis width. As shown in the figure, even if the sine wave exceeds the triangular wave, the output wave is not inverted, and when the sine wave exceeds the upper limit Vuth of the hysteresis width, the output wave is inverted. Even if it is, it is not affected by noise and the output wave is not distorted.

  In the class D amplifier, the load power efficiency is generally 80% or more, and the on-resistance of the transistors constituting the output buffer is kept low in order to achieve this. Therefore, if an unnecessary oscillation component is included in the PWM signal, a through current is likely to occur in the output buffer. As a result, latch-up is likely to occur due to the influence of the parasitic transistor. In the present invention, since the hysteresis comparators 4 and 5 are provided, unnecessary oscillation components in the PWM signal can be removed, so that latch-up can be prevented.

  Next, a second embodiment of the present invention will be described. As shown in FIG. 4, the non-feedback class D amplifier circuit according to this embodiment includes a fully differential buffer amplifier 8, a triangular wave generator 3, hysteresis comparators 4 and 5, and output buffers 6 and 7. Thus, the only difference from the configuration of the first embodiment described above is that a fully differential buffer amplifier 8 is used instead of the input buffer amplifiers 1 and 2, and the other configurations are the same as those of the first embodiment. is there. Therefore, only the fully-differential buffer amplifier 8 will be described, and the other components will be designated by the same reference numerals and will not be described.

  An input signal such as an audio signal is input from the input terminal 100 to the inverting input terminal of the operational amplifier 81 in the fully differential buffer amplifier 8 via the input resistor 82. On the other hand, the non-inverting input terminal of the operational amplifier 81 is connected to the reference potential 101 via the input resistor 83. The operational amplifier 81 has two output terminals that output signals having different polarities, and a non-inverting output terminal that outputs a non-inverting signal is connected to an inverting input terminal of the operational amplifier 81 via a feedback resistor 84, and The hysteresis comparator 4 is connected to the inverting input terminal of the operational amplifier 41. An inverting output terminal for outputting an inverting signal of the operational amplifier 81 is connected to a non-inverting input terminal of the operational amplifier 81 via a feedback resistor 85 and to an inverting input terminal of the operational amplifier 51 of the hysteresis comparator 5. Yes.

  Since this embodiment is configured as described above, an input signal (sin wave) such as an audio signal input from the input terminal 100 is amplified by the fully-differential buffer amplifier 8 and is output from the non-inverting output terminal of the operational amplifier 81. The input signal (sin wave) whose phase is inverted while being input to the inverting input terminal of the operational amplifier 41 of the hysteresis comparator 4 is input from the inverting output terminal of the operational amplifier 81 to the inverting input terminal of the operational amplifier 51 of the hysteresis comparator 5. As in the first embodiment, the non-inverting input terminals of the respective operational amplifiers 41 and 51 of the hysteresis comparators 4 and 5 receive a comparative wave from the triangular wave generator 3 via the input resistors 42 and 52, respectively. Since a triangular wave is input, the hysteresis comparators 4 and 5 respectively compare the input triangular wave and the sine wave to generate a PWM signal, which is output to the output buffers 6 and 7, respectively, amplified, and output terminals. 102 and 103 and supplied to a load such as a speaker.

  Also in the present embodiment, as in the first embodiment, the relationship between the sin wave, the triangular wave, and the output wave that are input waves in the hysteresis comparators 4 and 5 is as shown in FIGS. Compared to FIGS. 5 and 6, even if some noise is placed on the sine wave or the triangular wave, there is no influence of the noise and the output wave is not distorted. In the present embodiment, since the fully-differential buffer amplifier 8 is used, there is an advantage that a common class noise can be easily canceled and a class D amplifier that can be further reduced in size can be provided.

  The class D amplifier according to the present invention is not limited to the above-described embodiments. For example, variable resistors are used for the feedback resistors 43 and 53 and the input resistors 42 and 52 of the hysteresis comparators 4 and 5, or By connecting a plurality of resistors in series so that they can be disconnected and connected, it is possible to change the resistance value of the feedback resistor and adjust the hysteresis.

1, 2 Input buffer amplifier 3 Triangular wave generator 4, 5 Hysteresis comparator 6, 7 Output buffer 8 Fully differential buffer amplifier 42, 52 Input resistance 43, 53 Feedback resistance

Claims (3)

A pulse width corresponding to the input signal by comparing an input buffer amplifier for amplifying an input signal composed of a sine wave and a comparison wave composed of a triangular wave signal generated using an oscillator with an amplified input signal In a class D amplifier including a comparator that generates a modulation signal and an output buffer that amplifies the pulse width modulation signal output from the comparator, the comparator receives the amplified input signal at its inverting input terminal and is non-inverted The comparison wave is input to the input terminal via an input resistor, and a hysteresis comparator is provided in which a positive feedback circuit having a feedback resistor is provided between the output terminal and the input terminal of the comparison wave. Class D amplifier.   2. The class D amplifier according to claim 1, wherein the resistance values of the feedback resistor and the input resistor are adjustable.   3. The class D amplifier according to claim 1, wherein the input buffer amplifier is a fully differential buffer amplifier.

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