JP2005109590A - Switching amplifier circuit and class d amplifier for audio apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching amplifier circuit based on the PWM modulation system for realizing reduction in noise production and in the power consumption at input of a small level signal. <P>SOLUTION: The switching amplifier circuit includes circuits 610, 611 that compare the phase of a reference phase signal 121 with the phase of switching PWM signals 132, 133 shaped by comparing an input signal 101 with a ramp waveform 123 and generate pulse signals 612a, 612b, 613a, 613b in response to a phase difference corresponding to the amplitude of the input signal. The pulse signals in response to the phase difference are supplied to bridge circuits 140, 141 for driving a load such as a speaker in place of an ordinary switching PWM signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching amplifier circuit based on a pulse width modulation system, and more particularly to a class D amplifier used in a device that requires low power consumption characteristics such as a portable audio device.

  Switching amplifier circuits, commonly referred to as class-D amplifiers, use pulse width modulated (PWM) signals that are modulated at a frequency sufficiently higher than the signal frequency. For example, in a class D amplifier, the upper limit frequency of the audio band is generally 20 KHz, but the signal is amplified by performing a switching operation using a modulation signal having a switching frequency of 250 KHz or higher, which is sufficiently higher than that. Is done. In the class D amplifying device, it is possible to achieve higher power efficiency than a linear amplifier used in a general audio amplifier by performing a switching operation at such a high frequency. By adopting such a class D amplification device with high power efficiency in portable equipment such as portable audio equipment, the operating temperature is reduced, the battery life is extended, and the size of the equipment is increased by adopting a small power source. Various practical and application conveniences such as reduction of sheath weight can be obtained. For this reason, various class D amplifiers have been proposed. However, the class D amplifier is disadvantageous in that it generates noise with the switching operation.

  In the class D amplification device having the simplest configuration, the output state is binary. For this reason, the signal-to-noise ratio (SNR) deteriorates particularly when a low-level signal is supplied to the input. In addition, when an input signal having a small amplitude is supplied to the class D amplifier, the class D amplifier has only a binary output state even though large power is not originally required as an output. Another disadvantage is that the same power consumption as when a large amplitude input signal is supplied is required.

  Regarding these drawbacks, it has been proposed to reduce the possibility of crosstalk occurring in the channel by introducing a time delay in the class D amplifier (see, for example, Patent Document 1).

  In addition, in order to reduce the generation of noise associated with the switching operation of the class D amplifier, a method of driving with a pulse density modulation (PDM) signal using a delta-sigma modulation circuit other than PWM modulation as a switching method has been proposed. (For example, refer to Patent Document 2). In this method, the noise accompanying the switching operation is reduced by combining oversampling and driving by the PDM signal.

US Pat. No. 6,262,632 US Pat. No. 5,777,512

  However, the conventional switching amplifier circuit based on the PWM modulation method can reduce noise generation when a small signal is input, but has a problem that power consumption is large. Specifically, the duty ratio of the pulse width of the switching PWM signal (ratio of the pulse width to the pulse repetition period) approaches 50% as the input signal amplitude decreases. That is, by canceling the power in the binary output state, the apparent output amplitude is reduced, and an output operation with a small signal amplitude is performed. As a result, although the input signal amplitude is small, a constant power consumption occurs in the output drive circuit.

  Therefore, in view of the problems of the switching amplifier circuit based on the above-described pulse width modulation method, the present invention is based on a new concept different from the conventionally proposed method and reduces noise generation and power consumption when inputting a small signal. It is a main object to provide a switching amplifier circuit that realizes a reduction in power consumption.

  In particular, the present invention provides a class D amplifying apparatus for portable audio equipment that requires low power consumption characteristics, and that realizes a reduction in noise generation and a reduction in power consumption when a small signal is input. Objective.

  According to a first aspect of the present invention, there is provided a switching amplifying device comprising: a pulse width modulation switching signal generating means for comparing an input signal and a ramp waveform signal to generate a pulse width modulation signal; and a phase of the generated pulse width modulation signal; Pulse signal generation means for comparing the phases of the reference phase signals and generating a pulse width signal corresponding to the phase difference, and a drive circuit for amplifying the power of the generated pulse width signal. The reference phase signal is a phase signal in which the phase difference from the pulse width modulation signal decreases as the amplitude of the input signal decreases. Thereby, when a small signal is input, the pulse width of the pulse width signal is narrowed, the generation of switching noise is reduced, and at the same time, power consumption can be reduced.

  According to the second aspect of the invention, the reference phase signal is adjusted so that the phase difference between the pulse width modulation signal and the reference phase signal is proportional to the amplitude of the input signal. As a result, power corresponding to the amplitude of the input signal can be output.

  According to a third aspect of the present invention, the pulse signal generation means includes a phase comparator having a first input for receiving the pulse width modulation signal and a second input for receiving the reference phase signal. By using the phase comparator, the pulse signal generating means can be easily realized.

  According to a fourth aspect of the present invention, the switching amplifier circuit according to the first aspect further includes a switching oscillator and a ramp waveform generator that receives the output of the switching oscillator and generates the ramp waveform signal. The output of the switching oscillator is supplied to the pulse signal generating means as the reference phase signal. As a result, the switching oscillator used for generating the ramp waveform signal can be shared for generating the reference phase signal, so that the circuit configuration can be simplified.

  According to a fifth aspect of the present invention, the switching amplifier circuit according to the first aspect comprises a first input for receiving the ramp waveform signal and a second input for receiving a reference DC voltage signal, The apparatus further includes a comparator that compares the reference DC voltage signal to generate the reference phase signal. Thereby, the phase of the reference phase signal can be easily and finely adjusted by adjusting the voltage level of the reference DC voltage signal.

  The switching amplifier circuit according to claim 6 is provided with a pair of paths on the positive side and a pair on the negative side so as to output a pair of drive signals on the positive side and the negative side. Therefore, according to the sixth aspect of the invention, the switching amplifier circuit compares the input signal with the ramp waveform signal, and generates a pair of positive and negative pulse width modulation switching signal generating means for generating a pulse width modulation signal. A pair of positive and negative pulse signal generating means for comparing the phase of the generated pulse width modulation signal with the phase of the reference phase signal and generating a pulse width signal according to the phase difference; A pair of driving circuits on the positive side and the negative side that amplify the power of the pulse width signal, and the phase difference between the reference phase signal and the pulse width modulation signal decreases as the amplitude of the input signal decreases. The phase signal is reduced.

  Thus, by providing a pair of positive and negative paths in the switching amplifier circuit, in particular, as a reference phase signal, in addition to the output of the switching oscillator or the reference DC voltage signal, a complementary pulse width modulation signal Can be used to finely adjust the phase of the reference phase signal. Therefore, according to the invention of claim 11, the switching amplifier circuit receives the switching oscillator and the output of the switching oscillator and generates a pair of positive and negative ramp waveform signals as the ramp waveform signal. And a generator. The positive side pulse width modulation switching means receives one of the positive and negative ramp waveform signals, generates a first pulse width modulation signal, and the negative side pulse width modulation switching means. Receives the other of the positive and negative pair of ramp waveform signals, generates a second pulse width modulation signal complementary to the first pulse width modulation signal, and generates the positive pulse The signal generation means receives the first pulse width modulation signal as the pulse width modulation signal, receives the second pulse width modulation signal as the reference phase signal, and the negative pulse signal generation means receives the pulse The second pulse width modulation signal is received as a width modulation signal, and the first pulse width modulation signal is received as the reference phase signal.

  Furthermore, the idea of reducing switching noise generation and power consumption when a small signal is input by providing a circuit that generates a pulse signal corresponding to the phase difference corresponding to the amplitude of the input signal in the switching amplifier circuit is an audio device. It can be embodied in a class D amplifier. Therefore, the class D amplifier for audio equipment according to claim 12 compares the amplified audio signal and the ramp waveform signal, and generates a pair of positive and negative pulse width modulation switching signals for generating a pulse width modulation signal. Generating means, a pair of positive and negative pulse signal generating means for comparing the phase of the generated pulse width modulation signal and the phase of the reference phase signal and generating a pulse width signal according to the phase difference, and generating A pair of positive and negative driving circuits for amplifying the power of the pulse width signal and a signal supplied to the positive and negative terminals of the speaker. And a pair of filter circuits on the positive side and the negative side that remove high frequency components of the power-amplified signal, respectively, and the reference phase signal has a small amplitude of the input signal The above The phase difference between the width modulation signal is a phase signal becomes smaller.

  Further, by combining two or more class D amplifiers for audio equipment according to claim 12, it is possible to configure a class D amplifier for stereo audio equipment. Accordingly, an invention according to claim 18 is a class D amplifying device for stereo audio equipment including a first class D amplifying device and a second class D amplifying device, wherein the first class D amplifying device and The second class D amplifying device compares the amplified audio signal and the ramp waveform signal, and generates a pair of positive and negative pulse width modulation switching signal generation means for generating a pulse width modulation signal, A pair of positive and negative pulse signal generation means for comparing the phase of the generated pulse width modulation signal with the phase of the reference phase signal and generating a pulse width signal corresponding to the phase difference, and the generated pulse width In order to generate a pair of positive and negative drive circuits for amplifying the signal and a signal supplied to the positive and negative terminals of the speaker, the pair of drive circuits on the positive and negative sides are generated. Each connected and power amplified A pair of filter circuits on the positive side and negative side that remove high-frequency components of the signal, and the reference phase signal has a small phase difference from the pulse width modulation signal when the amplitude of the audio signal is small This is a phase signal.

  According to the present invention, in a switching amplifier circuit based on a PWM modulation method such as a class D amplifier for audio equipment, it is possible to reduce the generation of switching noise when a small signal is input and to reduce power consumption. Can do.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. Throughout the accompanying drawings, the same reference numerals are assigned to the same components or functions.

[Description of Principle of the Present Invention]
First, a conventional typical class D amplifying apparatus for audio equipment, which is a premise for explaining the principle of the present invention in which a pulse corresponding to an input signal amplitude is generated by a phase comparator, will be described.

  FIG. 1 is a block diagram of a conventional class D amplification device 100 for typical audio equipment. In general, the class D amplification device 100 includes a switching oscillator 120 and a ramp waveform generator 122 to which an output 121 of the switching oscillator 120 is supplied. The audio signal 101 input to the complementary push-pull class D amplification device 100 is amplified by one feedback amplification device (integration amplifier) 110 and then supplied to the comparator 130. The comparator 130 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 and generates a PWM switching signal 132. The PWM switching signal 132 is supplied to the half-H bridge circuit 140 for driving the speaker, is power-amplified by the half-H bridge circuit 140, and is supplied to the positive-side speaker output 151. Similarly, the audio signal 101 is amplified by the other feedback amplifier 111 and supplied to the comparator 131. The comparator 131 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 and generates a PWM switching signal 133. The PWM switching signal 133 is a complementary PWM signal to the PWM switching signal 133. The PWM switching signal 133 is supplied to the speaker driving half H bridge circuit 141, amplified in power by the half H bridge circuit 141, and supplied to the negative speaker output 152. A filter for removing high frequency components may be provided between the half H bridge circuits 140 and 141 and the speaker outputs 151 and 152.

  FIG. 2 is a timing diagram of main signals of a conventional class D amplifier 100 for typical audio equipment. FIG. 2 shows the relationship between the output 121 of the switching oscillator 120, the output signal 123 of the ramp waveform generator 122, and the audio signal 101 having a small amplitude, and the PWM switching signal 132 after being compared by the comparators 130 and 131. And 133 timing relationships are shown. For example, the falling edge of the PWM switching signal 132 coincides with the time when the output signal 123 of the ramp waveform generator 122 crosses the audio signal 101 from the bottom to the top, and the rising edge of the PWM switching signal 132 is the output of the ramp waveform generator 122. It coincides with the time when the signal 123 crosses the audio signal 101 from top to bottom. As can be seen from the figure, although the amplitude of the input audio signal 101 is small, the generated PWM switching signals 132 and 133 are signals having a wide pulse width, and the output drive circuit has a constant power consumption. Arise. When the pulse width of the signal supplied to the output drive circuit becomes wider, power consumption in the output drive circuit increases.

  FIG. 3 shows the relationship between the audio signal 101 and the output signal 123 of the ramp waveform generator 122, the output 121 of the switching generator 120 for generating the ramp, and the PWM when a DC signal of 0V is input as the audio signal 101. It is a figure which shows the timing relationship of the switching signals 132 and 133. FIG. As can be seen from the figure, when a DC signal of 0V is input as the audio signal 101, the output 121 of the oscillator 120 and the PWM switching signal 132 have a phase relationship of 0 degree, and the output 121 of the oscillator 120 and the PWM signal The switching signal 133 has a phase relationship with a phase difference of 180 degrees.

  FIG. 4A shows the relationship between the audio signal 101 and the output signal 123 of the ramp waveform generator 122 and the output 121 of the switching generator 120 for generating the ramp when a DC signal having an amplitude αV is input as the audio signal 101. It is a figure which shows the timing relationship of the PWM switching signals 132 and 133. FIG. FIG. 4B shows the relationship between the audio signal 101 and the output signal 123 of the ramp waveform generator 122 and the output 121 of the switching generator 120 for generating the ramp when a DC signal having an amplitude of −αV is input as the audio signal 101. 4 is a diagram illustrating a timing relationship between the PWM switching signals 132 and 133. FIG.

  FIG. 4A shows how the phase of the PWM switching signal 132 advances by φ in accordance with the amplitude α of the input audio signal 101. The PWM switching signal 132 falls when the output signal 123 of the ramp waveform generator 122 crosses the audio signal 101 (amplitude αV) from below to above, and the output signal 123 of the ramp waveform generator 122 causes the audio signal 101 from above. Get up when you cross down. As a result, the phase of the PWM switching signal 132 is advanced by φ from the output 121 of the switching oscillator 120.

  Similarly, FIG. 4B shows a state in which the phase of the PWM switching signal 132 is delayed by −φ in accordance with the amplitude −α of the input audio signal 101. The PWM switching signal 132 rises when the output signal 123 of the ramp waveform generator 122 crosses the audio signal 101 (amplitude−αV) from top to bottom, and the output signal 123 of the ramp waveform generator 122 pulls the audio signal 101 from below. Fall down when crossing up. As a result, the phase of the PWM switching signal 132 is delayed by −φ from the output 121 of the switching oscillator 120.

  Therefore, the phase of the PWM switching signal 132 shown in FIG. 4A is advanced by φ from the phase of the output of the oscillator 120 according to the amplitude α, and the phase of the PWM switching signal 132 shown in FIG. Accordingly, the phase of the output of the oscillator 120 is delayed by −φ. When the amplitude of the input signal is changed from −α to + α, the phase difference between the phase of the PWM switching signal 132 and the phase of the output of the oscillator 120 may change from −φ to + φ as a linear function of the amplitude. I understand. Thus, the phase relationship between the output 121 of the oscillator 120 and the PWM switching signal 132 is such that the phase difference between the two is expressed as a linear function of the amplitude of the audio signal 101 to which the phase difference is input. It will be apparent that a similar phase relationship exists between the output 121 of the oscillator 120 and the complementary PWM switching signal 133.

  The present invention employs a reference phase signal having a phase relationship such as the output 121 of the oscillator 120 with respect to the PWM switching signal, and compares the phase of this reference phase signal with the PWM switching signal using a phase comparator. Thus, it is based on the principle that a signal having a pulse width corresponding to the amplitude of the input audio signal can be generated.

[Effects of Example 1]
In Embodiment 1 of the present invention, the phase comparator is used to compare the output of the oscillator 120, that is, the phase of the PWM switching signals 132 and 133 with the reference phase signal 121 supplied to the ramp waveform generator 122. By generating a pulse signal having a pulse width corresponding to the amplitude α of the audio signal and driving the output drive circuit, for example, the half H bridge circuits 140 and 141, with the generated pulse signal,
(1) When the amplitude of the input audio signal 101 is small, the pulse width can be controlled to be small, and the power consumption can be reduced according to the amplitude of the signal input in the output drive circuit. ,
(2) Switching noise can be reduced when a small signal is input, and a reduction in the signal-to-noise ratio can be expected.

[Comparison between Example 1 and prior art]
As already described, it is described in US Pat. No. 6,262,632 that switching noise is treated as a problem of crosstalk and switching noise is reduced. Here, the difference between the class D amplifier described in the specification of US Pat. No. 6,262,632 and the switching amplifier circuit according to the first embodiment of the present invention will be described.

  FIG. 5 is a block diagram of a conventional class D amplifier 500 proposed in US Pat. No. 6,262,632. The class D amplifier 500 shown in FIG. 5 is similar to the conventional class D amplifier 100 for typical audio equipment shown in FIG. 1, but the output of the ramp waveform generator 122 is complementary. The difference is that output signals 123 and 124 are obtained and complementary output signals are supplied to the comparator 130 and the comparator 131. US Pat. No. 6,262,632 also introduces a delay in the lamp output to one comparator, or uses offset switching to cause a delay in comparators 40 and 42, Is described. However, the various class D amplifiers described in US Pat. No. 6,262,632 have the configuration of the first embodiment of the present invention described above, that is, the output 121 of the oscillator 120 and the PWM switching signals 132 and 133. There is no configuration in which the phases are compared, a pulse signal having a pulse width corresponding to the amplitude α of the input audio signal is generated, and the half-H bridge circuits 140 and 141 are driven by the generated pulse signal.

[Configuration of Example 1]
FIG. 6 is a block diagram of the switching amplifier circuit 600 according to the first embodiment of the present invention. As described above, the switching amplifier circuit 600 according to the first embodiment of the present invention pays attention to the phase relationship between the output of the oscillator and the PWM switching signal, and uses the phase comparator to change the phase of the output of the oscillator and the PWM switching signal. The comparison is based on the idea that a signal having a pulse width corresponding to the amplitude of the input signal can be generated. The switching amplifier circuit 600 includes a switching oscillator 120 and a ramp waveform generator 122 to which an output 121 of the switching oscillator 120 is supplied. A signal having a wide dynamic range, for example, an audio signal 101 that is a low-frequency signal, input to the switching amplifier 600 is amplified by one feedback amplifier (integral amplifier) 110 and then supplied to the non-inverting input of the comparator 130. The The comparator 130 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 supplied to the inverting input, and generates a PWM switching signal 132. Similarly, the audio signal 101 is amplified by the other feedback amplifier 111 and supplied to the inverting input of the comparator 131. The comparator 131 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 supplied to the non-inverting input, and generates a PWM switching signal 133. The PWM switching signal 133 is a PWM signal complementary to the PWM switching signal 132.

  The switching amplifier circuit 600 includes phase comparators 610 and 611 that generate a signal having a pulse width corresponding to the amplitude of the input signal by comparing the output of the oscillator 120 and the phase of the PWM switching signals 132 and 133. The phase comparator 610 compares the phase of the PWM switching signal 132 and the output 121 of the switching oscillator 120, and generates signals 612a and 612b having a pulse width proportional to the phase difference. As described above, it should be noted that the pulse width proportional to the phase difference is proportional to the signal amplitude of the input of the switching amplifier circuit 600. The signals 612a and 612b are supplied to, for example, a speaker driving half-H bridge circuit 140, power amplified by the half-H bridge circuit 140, and supplied to the output 151. Similarly, the phase comparator 611 compares the phase of the PWM switching signal 133 with the phase of the output 121 of the switching oscillator 120, and a signal 613 a having a pulse width proportional to the phase difference, that is, the signal amplitude of the input of the switching amplifier circuit 600. 613b is generated. The signals 613 a and 613 b are supplied to, for example, a half H bridge circuit 141 for driving a speaker, power amplified by the half H bridge circuit 141, and supplied to the output 152.

FIG. 7 is a circuit diagram of an example of a phase comparator used in Embodiment 1 of the present invention. In the figure, both phase comparators 610 and 611 in FIG. 6 are shown as a phase comparator 700. The first signal Φ _x 710 and the second signal Φ _y 711 whose phases are compared by the phase comparator 700 are respectively supplied to clock terminals of D-type flip-flops 720 and 721 with reset whose inputs are connected to a power source. Supplied. The outputs Q740 and 741 of the D type flip-flops 720 and 721 are supplied to the NAND logic operation unit 730, and the result of the NAND logic operation is supplied to the reset terminal R of the D type flip-flops 720 and 721. In the first embodiment of the present invention, the first signal Φ _x of the phase comparator 700 is a switching signal from the comparator. In addition, the second signal Φ _y 711 that is a reference phase signal to the phase comparator 700 is an output 121 from the switching oscillator 120 in this example. The two outputs OUTa and OUTb of the phase comparator 700 corresponding to the phase comparator 610 in FIG. 6 are supplied as signals 612a and 612b to the half-H bridge circuit 140 in the subsequent stage in the switching amplifier 600 in FIG. Similarly, two outputs OUTa and OUTb of the phase comparator 700 corresponding to the phase comparator 611 in FIG. 6 are supplied as signals 613a and 613b to the half-H bridge circuit 141 in the subsequent stage in the switching amplifier 600 in FIG. The The phase comparator 700 is only an example of a phase comparator that can be used in various embodiments of the present invention, and does not limit the present invention.

  8A and 8B are timing charts showing the relationship among the phase comparator outputs 612a and 612b, the input signal 101, the PWM switching signals 132 and 133, and the reference phase signal 121 in the first embodiment of the present invention. FIG. 8A shows the relationship between these signals when the magnitude of the input signal is 0V, and FIG. 8B shows the relationship between these signals when the magnitude of the input signal is + αV.

  As can be seen from FIG. 8A, when the amplitude of the signal input to the switching amplifier circuit 600 is small (when it is 0V), there is no phase difference between the reference phase signal 121 and the PWM switching signal 132. It can be seen that the levels of the outputs 612a and 612b of the device 610 are reduced, the generation of switching noise is avoided, and the power consumption at the load is also reduced (becomes 0).

  On the other hand, as shown in FIG. 8B, when the amplitude of the signal input to the switching amplifier circuit 600 is large (when + αV), the PWM switching signal 132 is advanced in phase by φ with respect to the reference phase signal 121. Therefore, an output corresponding to the phase difference is generated at the output 612a of the phase comparator 610. By supplying this output to the half H bridge circuit 140, a large output can be obtained at the load.

  FIG. 9 is a circuit diagram of an example of a ramp waveform generator used in the first embodiment of the present invention. In this figure, the ramp waveform generator 122 of FIG. 6 is shown as a ramp waveform generator 900 as a whole. The ramp waveform generator 900 connects the charge-side current source 901 or the discharge-side current source 902 and the charge / discharge capacitor 904 according to the clock signal CLK to generate a ramp waveform. Here, switching to the charging-side current source 901 or the discharging-side current reduction 902 is performed by the switch 903. The output of the ramp waveform is performed by an output amplifier 905 connected in a voltage follower. The ramp waveform generator 900 is only an example of a ramp waveform generator that can be used in various embodiments of the present invention, and the present invention is not limited thereto.

  In addition, Example 1 demonstrated above is only one of the best forms for implementing this invention, and this invention can be implemented in various deformation | transformation, unless it deviates from the meaning.

  Next, a switching amplifier circuit according to Embodiment 2 of the present invention will be described. FIG. 10 is a configuration diagram of the switching amplifier circuit 1000 according to the second embodiment of the present invention. As described above, the switching amplifier circuit 1000 according to the second embodiment of the present invention pays attention to the phase relationship between the reference phase signal and the PWM switching signal, and uses the phase comparator to change the phases of the reference phase signal and the PWM switching signal. By comparison, a signal having a pulse width corresponding to the amplitude of the input signal is generated. However, according to the second embodiment, the reference phase signal 1012 obtained by comparing the output signal 123 of the ramp waveform generator 122 and the output potential Vx from the reference DC voltage source 711 in the comparator 1010 as the reference phase signal. Is different from the above-described first embodiment.

  Similar to the switching amplifier circuit 600 according to the first embodiment, the switching amplifier circuit 1000 according to the second embodiment includes a switching oscillator 120 and a ramp waveform generator 122 to which an output 121 of the switching oscillator 120 is supplied. A signal having a wide dynamic range, for example, an audio signal 101 that is a low-frequency signal, input to the switching amplifier circuit 1000 is amplified by one feedback amplifier (integral amplifier) 110 and then supplied to the non-inverting input of the comparator 130. Is done. The comparator 130 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 supplied to the inverting input, and generates a PWM switching signal 132. Similarly, the audio signal 101 is amplified by the other feedback amplifier 111 and supplied to the inverting input of the comparator 131. The comparator 131 compares the amplified audio signal with the output signal 123 of the ramp waveform generator 122 supplied to the non-inverting input, and generates a PWM switching signal 133. The PWM switching signal 133 is a PWM signal complementary to the PWM switching signal 132.

  The switching amplifier circuit 1000 according to the second embodiment of the present invention further includes a comparator 1010 that compares the output signal 123 of the ramp waveform generator 122 and the output potential Vx from the reference DC voltage source 1011 to generate the reference phase signal 1012. That is, the reference phase signal is a voltage whose ramp waveform crosses the output potential Vx of the reference DC voltage source 1011 and is recreated as a rectangular wave reference phase signal 1012. The phase comparator 610 compares the phases of the PWM switching signal 132 and the reference phase signal 1012, and generates signals 612a and 612b having a pulse width proportional to the phase difference. As described above, the reference phase signal 1012 is set so that the pulse width proportional to the phase difference is proportional to the signal amplitude of the input of the switching amplifier circuit 1000. The signals 612a and 612b are supplied to, for example, a speaker driving half-H bridge circuit 140, power amplified by the half-H bridge circuit 140, and supplied to the output 151. Similarly, the phase comparator 611 compares the phases of the PWM switching signal 133 and the reference phase signal 1012, and generates signals 613a and 613b having a pulse width proportional to the phase difference, that is, the signal amplitude of the input of the switching amplifier circuit 1000. . The signals 613 a and 613 b are supplied to, for example, a half H bridge circuit 141 for driving a speaker, power amplified by the half H bridge circuit 141, and supplied to the output 152.

  In the second embodiment of the present invention, the phase of the reference phase signal 1012 obtained by comparing the output potential Vx of the reference DC voltage source 1011 with the ramp signal 123 is easily changed by changing the output potential Vx of the reference DC voltage source 1011. Can be changed. As a result, the amplitude of the signals 612 and 613 having a pulse width proportional to the input signal amplitude can be finely adjusted in an analog manner. Therefore, according to the second embodiment of the present invention, it is required for audio or the like. You can adjust the delicate tone.

  The phase comparators 610 and 611 used in the switching amplifier circuit 1000 according to the second embodiment of the present invention are realized by the phase comparator used in the switching amplifier circuit according to the first embodiment of the present invention described with reference to FIG. Yes, but not limited to that example. The ramp waveform generator 122 used in the switching amplifier circuit 1000 can be realized by the ramp waveform generator used in the switching amplifier circuit according to the first embodiment of the present invention described with reference to FIG. It is not limited to.

  In addition, Example 2 demonstrated above is only one of the best forms for implementing this invention, and this invention can be implemented in various deformation | transformation, unless it deviates from the meaning.

  Next, a switching amplifier circuit according to Embodiment 3 of the present invention will be described. FIG. 11 is a configuration diagram of the switching amplifier circuit 1100 according to the third embodiment of the present invention. As described above, the switching amplifier circuit 1100 according to the third embodiment of the present invention pays attention to the phase relationship between the reference phase signal and the PWM switching signal, and uses the phase comparator to change the phases of the reference phase signal and the PWM switching signal. By comparison, a signal having a pulse width corresponding to the amplitude of the input signal is generated. However, according to the third embodiment, the ramp waveform signal supplied to the comparator 130 and the ramp waveform signal supplied to the comparator 131 are in an inverted relationship with each other, and the comparator is used as the reference phase signal of the phase comparator 610. The PWM switching signal 1133 output from 131 is supplied, and the PWM switching signal 1132 output from the comparator 130 is supplied as the reference phase signal of the phase comparator 611, which is different from the first embodiment.

  A low-frequency signal having a wide dynamic range, for example, the audio signal 101 is amplified by the feedback amplifier 110 and then supplied to the non-inverting input of the comparator 130, and after being amplified by the feedback amplifier 111, the inverting input of the comparator 131. Supplied to. The ramp waveform generator 1122 generates a complementary ramp waveform signal 1123 and a ramp waveform signal 1124 based on the output 121 from the switching oscillator 120. The comparator 130 compares the amplified audio signal with the ramp waveform signal 1123 and generates a PWM switching signal 1132. The comparator 131 compares the amplified audio signal and the ramp waveform signal 1124 to generate a PWM switching signal 1133.

  The phase comparator 610 compares the phases of the complementary PWM switching signals 1132 and 1133, and generates signals 612a and 612b having a pulse width proportional to the signal amplitude of the input audio signal 101. Similarly, the phase comparator 611 compares the phases of the complementary PWM switching signals 1133 and 1132, and generates signals 613a and 613b having a pulse width proportional to the signal amplitude of the input audio signal 101. The complementary ramp waveform signals 1123 and 1124 are adjusted so that the pulse widths of the output signals of the phase comparators 610 and 611 are proportional to the signal amplitude of the audio signal 101.

  The signals 612a and 612b are supplied to, for example, a speaker driving half-H bridge circuit 140, power amplified by the half-H bridge circuit 140, and supplied to the output 151. Similarly, the signals 613 a and 613 b are supplied to, for example, a speaker driving half H bridge circuit 141, power amplified by the half H bridge circuit 141, and supplied to the output 152.

  In this third embodiment, the PWM switching signals 1132 and 1133 are generated by comparing the amplified audio signal with the complementary output signals 1123 and 1124 of the ramp waveform generator 1122. Therefore, by independently controlling the amplitude and phase of the complementary output signals 1123 and 1124 of the ramp waveform generator 1122, the amplitude of the signals 612a and 612b and 613a and 613b having a pulse width proportional to the input signal amplitude is independently controlled. This makes it possible to adjust the subtle timbres required for audio.

  12A and 12b are diagrams for explaining the operation of the third embodiment of the present invention. FIG. 12A shows the phase difference of the complementary PWM switching signal according to the input amplitude α when the input signal is αV. FIG. 12B shows a state in which the phase difference of the complementary PWM switching signal becomes zero according to the input 0V amplitude when the input signal is 0V.

  In FIG. 12A, when the input signal 101 having the amplitude αV is compared with the ramp waveform signals 1123 and 1124, the period during which the input signal 101 is larger than the ramp waveform signal 1123 corresponds to the pulse width of the PWM switching signal 1132. The period in which 101 is smaller than the ramp waveform signal 1124 corresponds to the pulse width of the PWM switching signal 1133. As can be seen from the figure, the phase of the PWM switching signal 1132 is advanced by φ from the phase of the PWM switching signal 1133.

  Similarly, in FIG. 12B, when the input signal 101 having an amplitude of 0 V is compared with the ramp waveform signals 1123 and 1124, the period during which the input signal 101 is larger than the ramp waveform signal 1123 corresponds to the pulse width of the PWM switching signal 1132. The period during which the input signal 101 is smaller than the ramp waveform signal 1124 corresponds to the pulse width of the PWM switching signal 1133. As can be seen from the figure, the phase difference φ between the phase of the PWM switching signal 1132 and the phase of the PWM switching signal 1133 is zero.

  When the amplitude of the input signal 101 is changed from −αV to + αV via 0V, the phase relationship between the PWM switching signal 1132 and the PWM switching signal 1133 is such that the phase difference changes from −φ to + φ as a linear function of the amplitude. It can be seen that there is a relationship. Therefore, according to the switching amplifier circuit 1100 of the third embodiment of the present invention, the phase comparators 610 and 611 are used to compare the phases of the complementary PWM switching signals 1132 and 1133 with each other in accordance with the amplitude of the input signal. A pulse width signal can be generated.

  The phase comparators 610 and 611 used in the switching amplifier circuit 1100 according to the third embodiment of the present invention are realized by the phase comparator used in the switching amplifier circuit according to the first embodiment of the present invention described with reference to FIG. Yes, but not limited to that example. The ramp waveform generator 1122 used in the switching amplifier circuit 1100 can be realized by the ramp waveform generator used in the switching amplifier circuit according to the first embodiment of the present invention described with reference to FIG. It is not limited to.

  The third embodiment described above is only one of the best modes for carrying out the present invention, and the present invention can be implemented with various modifications without departing from the gist thereof.

  In the first to third embodiments, the switching amplifier circuit for a low frequency signal having a wide dynamic range has been described. In the following, an embodiment of a class D amplifier device for audio equipment in which the switching amplifier circuit is applied to an audio equipment will be described. explain.

  FIG. 13A is a diagram showing basic components of a conventional typical class D amplifying device for audio equipment, and FIG. 13B shows basic components of a class D amplifying device for audio equipment according to Embodiment 4 of the present invention. FIG.

  As shown in FIG. 13A, the class D amplifying device for audio equipment combines the input audio signal and the ramp signal by the combiner 1301 and then acquires the PWM signal by the comparator 1302, and the acquired PWM An output drive circuit 1303 that amplifies signal power and a filter 1304 that removes high-frequency components are included. The output of the filter 1304 is supplied to the speaker 1305. According to such a conventional configuration, switching noise is generated even when a small signal is input, and power consumption is large.

  In contrast, the class D amplifying device for audio equipment according to the fourth embodiment of the present invention synthesizes the input audio signal and the ramp signal by the synthesizer 1301, and then obtains the PWM signal by the comparator 1302. A generator, a phase comparison circuit 1306 that compares the PWM signal and the reference clock signal, generates a signal having a pulse width corresponding to the amplitude of the input audio signal, and amplifies the power of the signal generated from the phase comparison circuit 1306 An output drive circuit 1303 for performing high frequency components, and a filter 1304 for removing high frequency components.

  The output drive circuit 1303 includes normal half H bridge circuits 140 and 141 used in the first to third embodiments of the present invention. FIG. 14 is a configuration diagram of an example of a speaker driving bridge circuit in which the half H bridge circuit 140 and the half H bridge circuit 141 are combined. The positive-side half H bridge circuit 140 is supplied with signals 612a and 612b having a pulse width proportional to the phase difference from the phase comparison circuit, and generates a positive-side speaker output 151. The negative-side half H bridge circuit 141 is supplied with signals 613a and 613b having a pulse width proportional to the phase difference from the phase comparison circuit, and a negative-side speaker output 152 is generated.

  In the above description, the same reference numerals are given to the same components as those in any of the first to third embodiments, and the description thereof is omitted. The fourth embodiment described above is only one of the best modes for carrying out the present invention, and the present invention can be implemented with various modifications without departing from the spirit of the present invention.

  In the above description of the first to fourth embodiments, a switching amplifier circuit or a class D amplifier that can be used to drive a single speaker has been described. However, the switching amplifier circuit described in the first to fourth embodiments. Alternatively, the present invention can be applied to a stereo audio device by providing a class D amplifier for each of the left and right channels of the stereo audio signal. FIG. 15 is a configuration diagram of a class D amplification device for stereo audio equipment according to embodiment 5 of the present invention in which the switching amplifier circuit 600 according to embodiment 1 of the present invention is applied to stereo audio equipment. As shown in the figure, by providing separate switching amplifier circuits for the left and right channels of the stereo, the left and right speakers of the stereo audio device can be easily driven. In the figure, for the sake of simplicity, a configuration in which the left channel and the right channel are completely separated is shown. However, the switching oscillator 120 of the switching amplifier circuit 600 and the lamp to which the output 121 of the switching oscillator 120 is supplied. The waveform generator 122 can be configured to be shared by the left and right channels.

  The fifth embodiment described above is only one of the best modes for carrying out the present invention, and the present invention can be implemented with various modifications without departing from the gist thereof.

It is a block diagram of the conventional class D amplifier for typical audio equipment. It is a timing diagram of the main signals of the conventional class D amplifier for typical audio equipment. FIG. 5 is a diagram showing the relationship between the audio signal and the output signal of the ramp waveform generator and the timing relationship between the output of the ramp generating switching oscillator and the PWM switching signal when a DC signal having an amplitude of 0 V is input as the audio signal. is there. FIG. 6 is a diagram showing the relationship between the audio signal and the output signal of the ramp waveform generator and the timing relationship between the output of the switching oscillator for ramp generation and the PWM switching signal when a DC signal having an amplitude αV is input as the audio signal. is there. The figure which shows the timing relationship of the output of a switching oscillator for a ramp generation, and the timing of a PWM switching signal when the direct current signal of amplitude-(alpha) V is input as an audio signal, and the output signal of a ramp waveform generator. It is. It is a block diagram of the conventional class D amplifier. It is a block diagram of the switching amplifier circuit by Example 1 of this invention. It is a circuit diagram of the phase comparator used with the switching amplifier circuit by Example 1 of this invention. 6 is a timing chart showing a relationship among an output of a phase comparator, an input signal, a PWM switching signal, and a reference phase signal when the input signal is 0V. 6 is a timing chart showing a relationship among an output of a phase comparator, an input signal, a PWM switching signal, and a reference phase signal when the input signal is αV. It is a circuit diagram of a ramp waveform generator used in the switching amplifier circuit according to the first embodiment of the present invention. It is a block diagram of the switching amplifier circuit by Example 2 of this invention. It is a block diagram of the switching amplifier circuit by Example 3 of this invention. In Example 3 of this invention, when an input signal is (alpha) V, it is a figure explaining a mode that the phase difference (phi) arises according to the input amplitude (alpha). In Example 3 of this invention, when an input signal is 0V, it is a figure explaining a mode that a phase difference becomes 0 according to the input 0V amplitude. It is a figure which shows the basic component of the conventional typical D class amplification apparatus for audio equipment. It is a figure which shows the basic component of the class D amplifier for audio equipment by Example 4 of this invention. It is a block diagram of an example of the bridge circuit for a speaker drive in Example 4 of this invention. It is a block diagram of the class D amplifier for stereo audio equipment by Example 5 of this invention.

Explanation of symbols

110, 111: feedback amplifier 120 ... switching oscillator 122 ... ramp waveform generator 130, 131 ... comparator 140, 141 ... half H bridge circuit 600 ... switching amplifier circuit 610 611 ... Phase comparator

Claims (18)

A pulse width modulation switching signal generating means for comparing the input signal and the ramp waveform signal and generating a pulse width modulation signal;
Pulse signal generation means for comparing the phase of the generated pulse width modulation signal with the phase of the reference phase signal and generating a pulse width signal according to the phase difference;
A driving circuit for amplifying power of the generated pulse width signal;
Have
The reference phase signal is a phase signal in which the phase difference with the pulse width modulation signal decreases as the amplitude of the input signal decreases.
Switching amplifier circuit.   The switching amplifier circuit according to claim 1, wherein the reference phase signal is a phase signal in which a phase difference between the pulse width modulation signal and the reference phase signal is proportional to an amplitude of the input signal.   2. The switching amplifier circuit according to claim 1, wherein said pulse signal generating means includes a phase comparator having a first input for receiving said pulse width modulation signal and a second input for receiving said reference phase signal. A switching oscillator;
A ramp waveform generator that receives the output of the switching oscillator and generates the ramp waveform signal;
Further comprising
The output of the switching oscillator is supplied to the pulse signal generation means as the reference phase signal.
The switching amplifier circuit according to claim 1. A comparator having a first input for receiving the ramp waveform signal and a second input for receiving a reference DC voltage signal, and comparing the ramp waveform signal with the reference DC voltage signal to generate the reference phase signal; ,
The switching amplifier circuit according to claim 1. A pair of positive and negative pulse width modulation switching signal generation means for comparing the input signal and the ramp waveform signal and generating a pulse width modulation signal;
A pair of positive and negative pulse signal generating means for comparing the phase of the generated pulse width modulation signal and the phase of the reference phase signal and generating a pulse width signal according to the phase difference;
A pair of driving circuits on the positive side and the negative side that amplify the power of the generated pulse width signal; and
Have
The reference phase signal is a phase signal in which the phase difference with the pulse width modulation signal decreases as the amplitude of the input signal decreases.
Switching amplifier circuit.   The switching amplifier circuit according to claim 6, wherein the reference phase signal is a phase signal in which a phase difference between the pulse width modulation signal and the reference phase signal is proportional to an amplitude of the input signal.   7. The switching amplifier circuit according to claim 6, wherein each of the pulse signal generating means includes a phase comparator having a first input for receiving the pulse width modulation signal and a second input for receiving the reference phase signal. A switching oscillator;
A ramp waveform generator that receives the output of the switching oscillator and generates the ramp waveform signal;
Further comprising
The output of the switching oscillator is supplied as the reference phase signal to the pair of positive and negative pulse signal generators,
The switching amplifier circuit according to claim 6. A comparator having a first input for receiving the ramp waveform signal and a second input for receiving a reference DC voltage signal, and comparing the ramp waveform signal with the reference DC voltage signal to generate the reference phase signal; ,
The switching amplifier circuit according to claim 6. A switching oscillator;
A ramp waveform generator that receives the output of the switching oscillator and generates a pair of positive and negative ramp waveform signals as the ramp waveform signal;
Further comprising
The positive pulse width modulation switching means receives one of the positive and negative ramp waveform signals and generates a first pulse width modulation signal;
The negative side pulse width modulation switching means receives the other one of the positive and negative ramp waveform signals and is complementary to the first pulse width modulation signal. Produces
The positive-side pulse signal generation means receives the first pulse width modulation signal as the pulse width modulation signal, receives the second pulse width modulation signal as the reference phase signal,
The negative pulse signal generation means receives the second pulse width modulation signal as the pulse width modulation signal, and receives the first pulse width modulation signal as the reference phase signal.
The switching amplifier circuit according to claim 6. A pair of positive side and negative side pulse width modulation switching signal generating means for comparing the amplified audio signal and the ramp waveform signal and generating a pulse width modulation signal;
A pair of positive and negative pulse signal generating means for comparing the phase of the generated pulse width modulation signal and the phase of the reference phase signal and generating a pulse width signal according to the phase difference;
A pair of driving circuits on the positive side and the negative side that amplify the power of the generated pulse width signal; and
A positive side connected to the pair of driving circuits on the positive side and the negative side, respectively, for removing the high frequency components of the power amplified signal, in order to generate a signal supplied to the positive side terminal and the negative side terminal of the speaker; A pair of negative side filter circuits;
Have
The reference phase signal is a phase signal in which the phase difference with the pulse width modulation signal decreases as the amplitude of the audio signal decreases.
Class D amplifier for audio equipment.   The class D amplification device according to claim 12, wherein the reference phase signal is a phase signal in which a phase difference between the pulse width modulation signal and the reference phase signal is proportional to an amplitude of the input signal.   13. The class D amplifier according to claim 12, wherein each of the pulse signal generating means includes a phase comparator having a first input for receiving the pulse width modulation signal and a second input for receiving the reference phase signal. A switching oscillator;
A ramp waveform generator that receives the output of the switching oscillator and generates the ramp waveform signal;
Further comprising
The output of the switching oscillator is supplied as the reference phase signal to the pair of positive and negative pulse signal generators,
The class D amplification device according to claim 12. A comparator having a first input for receiving the ramp waveform signal and a second input for receiving a reference DC voltage signal, and comparing the ramp waveform signal with the reference DC voltage signal to generate the reference phase signal; ,
The class D amplification device according to claim 12. A switching oscillator;
A ramp waveform generator that receives the output of the switching oscillator and generates a pair of positive and negative ramp waveform signals as the ramp waveform signal;
Further comprising
The positive pulse width modulation switching means receives one of the positive and negative ramp waveform signals and generates a first pulse width modulation signal;
The negative side pulse width modulation switching means receives the other one of the positive and negative ramp waveform signals and is complementary to the first pulse width modulation signal. Produces
The positive-side pulse signal generation means receives the first pulse width modulation signal as the pulse width modulation signal, receives the second pulse width modulation signal as the reference phase signal,
The negative pulse signal generation means receives the second pulse width modulation signal as the pulse width modulation signal, and receives the first pulse width modulation signal as the reference phase signal.
The class D amplification device according to claim 12. A class D amplifying device for stereo audio equipment including a first class D amplifying device and a second class D amplifying device,
The first class D amplifier and the second class D amplifier are respectively
A pair of positive side and negative side pulse width modulation switching signal generating means for comparing the amplified audio signal and the ramp waveform signal and generating a pulse width modulation signal;
A pair of positive and negative pulse signal generating means for comparing the phase of the generated pulse width modulation signal and the phase of the reference phase signal and generating a pulse width signal according to the phase difference;
A pair of driving circuits on the positive side and the negative side that amplify the power of the generated pulse width signal; and
A positive side connected to the pair of driving circuits on the positive side and the negative side, respectively, for removing the high frequency components of the power amplified signal, in order to generate a signal supplied to the positive side terminal and the negative side terminal of the speaker; A pair of negative side filter circuits;
Have
The reference phase signal is a phase signal in which the phase difference with the pulse width modulation signal decreases as the amplitude of the audio signal decreases.
Class D amplifier.

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