JP2012060613A - Self excitation type oscillation circuit, and class d amplifier device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self excitation type oscillation circuit capable of further improving sound quality of a class D amplifier equipped with a self excitation type oscillation circuit.SOLUTION: A self excitation type oscillation circuit SB is connected between switching elements 15A and 15B connected to a signal output terminal OUT and a signal input terminal IN. The circuit includes a current driving type voltage/current conversion part 10 an input end of which is connected to a signal input terminal IN and which contains an amplification element, an integration capacitor 11 whose one end is connected to an output end of the voltage/current conversion part 10 while the other end directly grounded, a feedback resistor 14 connected between an output stage of the switching elements 15A and 15B and one end of the integration capacitor 11, and a hysteresis comparator 12 which is connected between one end of the integration capacitor 11 and a gate driver 13.

Description

  The present invention belongs to the technical field of a self-excited oscillation circuit and a class D amplifier, and more specifically, a self-excited oscillation circuit for driving a class D amplifier circuit by a PWM (Pulse Width Modulation) drive system and the same Belongs to the technical field of class D amplifiers with

  First, the configuration and operation of a class D amplifier that is PWM driven using a conventional self-excited oscillation circuit will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of a conventional class D amplifier.

  As illustrated in FIG. 6 (a), the conventional class D amplifier AA includes, from the signal input terminal IN side, an integration circuit CC including a resistor 30, an operational amplifier 31 and an integration capacitor 11, a comparator 32, and a gate driver. 13, a feedback resistor 14, switching elements 15 </ b> A and 15 </ b> B that are complementarily driven by the gate driver 13, an output filter 16, and DC power sources 17 and 18 whose connection point Cz is grounded are connected. The output is output from the signal output terminal OUT. At this time, in the class D amplification device AA shown in FIG. 6A, the combination of the integration circuit CC and the comparator 32 simultaneously performs an oscillation operation as a self-excited oscillation circuit for PWM driving and a pulse width modulation operation. It is configured. Note that the combination of the integration circuit CC and the comparator 32 may be replaced with a combination of the comparator 32 and the delay circuit. Such a class D amplifying device having an integration circuit equivalent to the conventional class D amplifying device AA is also disclosed in, for example, Patent Document 1 and Patent Document 2 below.

  Here, in the class D amplifier AA illustrated in FIG. 6A, one end of the integrating capacitor 11 (the left terminal in FIG. 6A) is connected via the inverting input terminal and the non-inverting input terminal of the operational amplifier 31. Although it is grounded, this is only a so-called “virtual” ground. On the other hand, when the class D amplifying device AA illustrated in FIG. 6A is used as an audio amplifier, the operational frequency (carrier) is as high as several hundred kilohertz, for example, so that the operational amplifier 31 can operate at high speed or very high speed. It is necessary to use an element.

Japanese Patent Laid-Open No. 2003-204590 (for example, FIG. 4) Japanese Patent Laying-Open No. 2005-269580 (for example, FIG. 1)

  However, according to the configuration of the above-described conventional class D amplifier AA, the frequency band of the operational amplifier 31 is finite, so that a large noise is inevitably included in the triangular wave as the output signal of the integrating circuit CC including the operational amplifier 31. As a result, there is a problem in that the output signal output from the signal output terminal OUT causes distortion and sound quality degradation.

  That is, in the integration circuit CC including the operational amplifier 31 and the virtually grounded integration capacitor 11 illustrated in FIG. 6A, the integration target is between the output filter 16 and the output stages of the switching elements 15A and 15B. The signal is output from the connection point Cy through the feedback resistor 14 (see the upper waveform in FIG. 6B). Therefore, the integration circuit CC is not only operated at a high speed of, for example, several hundred kilohertz, but also receives a signal with a large amplitude waveform having a frequency of, for example, about 20 megahertz from the connection point Cy.

  Here, considering the impedance of the integration circuit CC, as illustrated in FIG. 6A, an input signal as the integration circuit CC is input to the inverting input terminal of the operational amplifier 31 via the resistor 30. The signal is simultaneously input (applied) to the inverting input terminal of the integrating capacitor 11. At this time, in the frequency band where the gain of the operational amplifier 31 is sufficiently high, the inverting input terminal and the non-inverting input terminal are virtually short-circuited, resulting in a low impedance between both terminals. However, in the high frequency band where the gain of the operational amplifier 31 decreases, the impedance between the inverting input terminal and the non-inverting input terminal increases, so that the above-mentioned virtual ground state with respect to the integrating capacitor 11 collapses, so that the integration accuracy is improved. 6 at the apex portion of the triangular wave as an output signal from the output terminal of the integration circuit CC (the connection point Cx in FIG. 6A) (that is, the timing at which the switching element 15A and the switching element 15B are just switched). (B) A large noise N as exemplified in the lower part is generated. The noise N has a high impedance between the inverting input terminal and the non-inverting input terminal of the operational amplifier 31, and a signal having a high-speed large-amplitude waveform from the output stage of the switching elements 15 A and 15 B is connected to the connection point Cx It is also encouraged by being passed through. As a result, distortion and deterioration in sound quality occur in the output signal output from the signal output terminal OUT.

  As described above, in the class D amplifier AA illustrated in FIG. 6A, the signals output from the switching elements 15A and 15B have steep rising and falling waveforms, and in addition to this, a high frequency It has a component and a large amplitude at the same time. For this reason, this signal (signal from the connection point Cy) cannot be integrated with high accuracy by the integrating circuit CC of FIG. Such a decrease in integration accuracy generally results in an increase in distortion in a minute region that is important for the class D amplifier AA, thereby deteriorating the sound quality.

  Therefore, the present invention has been made in view of the above problems, and one example of the problem is a self-excited type that can further improve the sound quality in a class D amplifying device including a self-excited oscillation circuit. An object of the present invention is to provide an oscillation circuit and a class D amplification device including the oscillation circuit.

  In order to solve the above problem, the invention according to claim 1 is a self-excited oscillation connected between a class D amplifier circuit including a switching element connected to a signal output terminal and the signal input terminal. In the circuit, a current-driven voltage / current conversion unit having an input terminal connected to the signal input terminal and including an amplifying element, one end connected to the output terminal of the voltage / current conversion unit, and the other end directly grounded A feedback resistor connected between the integrating capacitor, the output stage of the class D amplifier circuit and the one end, and a comparator connected between the one end and the input terminal of the class D amplifier circuit. And is constituted by.

  According to the first aspect of the present invention, the other end of the integrating capacitor having one end connected between the current-driven voltage / current converting means including the amplifying element and the comparator is directly connected to the amplifying element without passing through the amplifying element or the like. Grounded. A feedback resistor connected to the output stage of the class D amplifier circuit is connected to one end of the integrating capacitor. Therefore, the integration capacitor and the feedback resistor can constitute an integration circuit that does not include an amplification element and the like, and this is driven with high impedance by the voltage / current conversion means, so that the signal input to the comparator Noise can be reduced.

  In order to solve the above-described problem, the invention according to claim 2 is configured such that in the self-excited oscillation circuit according to claim 1, the comparator is a hysteresis comparator.

  According to the invention described in claim 2, in addition to the operation of the invention described in claim 1, the comparator connected to one end of the integrating capacitor and the input terminal of the class D amplifier circuit is a hysteresis comparator. Noise contained in the signal input to the amplifier circuit can be further reduced.

  In order to solve the above problem, the invention according to claim 3 is the self-excited oscillation circuit according to claim 1, the signal input terminal, the class D amplifier circuit, and the signal output terminal. And comprising.

  According to the invention described in claim 3, since the case-type oscillation circuit described in claim 1 or 2 is included, an integration circuit that does not include an amplifying element or the like can be configured by the integration capacitor and the feedback resistor. This is driven by the voltage / current conversion means with high impedance, so that noise in the signal input to the comparator can be reduced.

  According to the present invention, an integration circuit that does not include an amplifying element or the like can be configured, and it is driven with high impedance by the voltage / current conversion means, so that noise in the signal input to the comparator is reduced. Can be reduced.

  Therefore, by further reducing distortion caused by the noise, it is possible to further improve the sound quality of the class D amplification device using the class D amplification circuit.

It is a block diagram which shows the structure of the class D amplifier which concerns on embodiment, etc., (a) is a block diagram which shows the structure of the said class D amplifier, (b) is a circuit diagram which shows an example of a hysteresis comparator (C) is a block diagram which shows the other example of a hysteresis comparator. It is a timing chart which shows operation | movement of the class D amplifier which concerns on embodiment, (a) is a timing chart which shows operation | movement when an input signal is no signal, (b) is a timing chart which shows operation | movement of a positive amplitude period. is there. It is a timing chart which shows operation | movement of the negative amplitude period in the class D amplifier which concerns on embodiment. It is a circuit diagram which shows the structure of the voltage / current conversion part which concerns on embodiment, (a) is a circuit diagram which shows the 1st example of a voltage / current conversion part, (b) is the 2nd of a voltage / current conversion part. It is a circuit diagram which shows an example. It is a circuit diagram which shows the 3rd example of the voltage / current conversion part which concerns on embodiment. It is a block diagram which shows the structure of the conventional class D amplifier, etc., (a) is a block diagram which shows the structure of the said class D amplifier, (b) is a timing chart which shows the operation | movement of the said class D amplifier. is there.

  Next, a mode for carrying out the present invention will be described with reference to FIGS. The embodiment described below is an embodiment when the present invention is applied to a class D amplifier including a self-excited oscillation circuit. FIG. 1 is a block diagram showing the configuration of the class D amplifier according to the embodiment, and FIGS. 2 and 3 are timing charts showing the operation of the class D amplifier. 4 and 5 are circuit diagrams illustrating the configuration of the voltage / current conversion unit according to the embodiment. In FIG. 1, the same components as those of the conventional class D amplifier AA shown in FIG. 6 will be described using the same member numbers.

  As shown in FIG. 1A, the class D amplifier A according to the embodiment includes, from the signal input terminal IN side, a voltage / current converter 10 as an example of a voltage / current converter, an integrating capacitor 11, The hysteresis comparator 12, the gate driver 13, the feedback resistor 14, the switching elements 15A and 15B driven complementarily by the gate driver 13, the output filter 16, and the DC power sources 17 and 18 whose connection point C3 is grounded , Are connected, and the output is output from the signal output terminal OUT.

  The voltage / current converter 10 may be configured as an inverted voltage / current converter in accordance with the polarity of the input signal input from the signal input terminal IN. A specific circuit configuration of the voltage / current conversion unit 10 will be described later with reference to FIGS. 4 and 5. Further, the integrating capacitor 11 may be configured by connecting a plurality of capacitors having different capacities in parallel.

  The hysteresis comparator 12 is a comparator to which positive feedback is applied, and is a comparator having two threshold values as a comparator in order to prevent fluctuations in the input signal from appearing as noise in the output signal. Specifically, as illustrated in FIG. 1B, the hysteresis comparator 12 includes a comparator 23 whose inverting input terminal is grounded, for example, and a non-inverting input terminal of the comparator 23 and an input terminal 20 of the hysteresis comparator 12. And a resistor 22 connected between the output terminal 24 of the comparator 23 (that is, the hysteresis comparator 12) and its non-inverting input terminal to provide positive feedback to the comparator 23. ing. The hysteresis comparator 12 can also be configured by a comparison unit 25 and a delay unit 26 as logic circuits as illustrated in FIG.

  In the configuration shown in FIG. 1A, the voltage / current converter 10 converts a change in voltage applied as an input signal to the signal input terminal IN into a change in current and outputs the change to the hysteresis comparator 12.

  On the other hand, the integrating capacitor 11, the hysteresis comparator 12, and the feedback resistor 14 form a self-excited oscillation circuit SB according to the embodiment. In this self-excited oscillation circuit SB, one end of the integrating capacitor 11 is connected to a connection point C1 between the voltage / current conversion unit 10 and the hysteresis comparator 12. Further, unlike the conventional integrating capacitor 11 illustrated in FIG. 6, the other end is directly grounded without using an active element such as an operational amplifier. The feedback resistor 14 includes a connection point C2 between the output filter 16 and the output stages of the switching elements 15A and 15B, and a connection point between the voltage / current conversion unit 10 and the hysteresis comparator 12 (in other words, one end of the integration capacitor 11). ) It is connected between C1.

  The self-excited oscillation circuit SB according to the embodiment generates a current having a magnitude proportional to the voltage of the input signal input to the signal input terminal IN and outputs the current to the gate driver 13. Based on the current from the self-excited oscillation circuit SB, the gate driver 13 complementarily drives the switching elements 15A and 15B using the DC power sources 17 and 18 as voltage sources. The output filter 16 removes unnecessary high frequency components from the output signals from the switching elements 15A and 15B, and outputs them to the signal output terminal OUT. With the above operation, an output signal as the class D amplifier A is output from the signal output terminal OUT. The operations of the gate driver 13, the switching elements 15A and 15B, the output filter 16, and the DC power supplies 17 and 18 using the current from the self-excited oscillation circuit SB are described with reference to FIG. The operations of the gate driver 13, the switching elements 15A and 15B, the output filter 16, and the DC power supplies 17 and 18 in the conventional class D amplifier AA are the same.

  In the above operation, the self-excited oscillation circuit SB functions as a so-called inverting amplifier by itself. This self-excited oscillation circuit SB has a sufficiently large amplification in the low frequency band. By using such a self-excited oscillation circuit SB and using a highly accurate circuit configuration as the voltage / current converter 10, the average value of the voltage generated at both ends of the feedback resistor 14 (low frequency voltage) is It is proportional to the voltage of the input signal input to the signal input terminal IN with high accuracy. As a result, the entire class D amplification device A according to the embodiment can achieve a low distortion rate and high stability.

  Next, the operation of the self-excited oscillation circuit SB according to the embodiment will be described in more detail with reference to FIGS. The scales of the time axis (horizontal axis) in the timing charts illustrated in FIGS. 2 and 3 are all the same.

  First, the operation of the self-excited oscillation circuit SB when the input signal from the signal input terminal IN is a so-called no signal will be described with reference to FIG. The “no signal” refers to a period in which the input signal from the signal input terminal IN has neither a positive amplitude nor a negative amplitude. FIG. 2A is a timing chart showing the operation of the class D amplifying apparatus A centering on the self-excited oscillation circuit SB when there is no signal.

As shown in FIG. 2 (a), the gate GA of the switching element 15A is turned on at the timing _{T 01} with a no-signal state, when the gate GB of the switching element 15B is turned off, the current _{I 14} in the feedback resistor 14 As a result, the terminal voltage of the integrating capacitor 11 (in other words, the voltage at the connection point C1) increases. Next, when the terminal voltage of the integrating capacitor 11 reaches the upper threshold value of the two threshold values in the hysteresis comparator 12, the output signal C12 of the hysteresis comparator 12 is inverted. Thus the gate driver 13 turns off the gate GA of the switching element 15A at the timing _{T 02,} to turn off the gate GB of the switching element 15B. Then, a current _{I 14} of the feedback resistor 14 is inverted, the terminal voltage of the timing _{T 02} after integrating capacitor 11 is reduced. Thereafter, when the terminal voltage of the integrating capacitor 11 reaches the lower threshold value of the two threshold _values in the hysteresis comparator 12 at timing _T03 , the output signal C12 of the hysteresis comparator 12 is inverted again. Thus the gate driver 13 turns off the gate GB of the switching element 15B at the timing _{T 03,} to turn on the gate GA of the switching element 15A. When the input signal from the signal input terminal IN is no signal, the above series of operations are alternately repeated to realize the self-excited oscillation operation as the self-excited oscillation circuit SB. The duty ratio of the voltage at the connection point C2 during this period is exactly 50%. Therefore, the voltage V _OUT of the output signal from the signal output terminal OUT via the output filter 16 is maintained at 0 volt as shown in FIG.

  Next, the operation of the self-excited oscillation circuit SB during a period in which the input signal from the signal input terminal IN has a positive amplitude will be described with reference to FIG. In the following description, a period in which an input signal from the signal input terminal IN has a positive amplitude is referred to as a “positive amplitude period”. FIG. 2B is a timing chart showing the operation of the class D amplification device A centering on the self-excited oscillation circuit SB in the positive amplitude period.

As shown in FIG. 2B, in the positive amplitude period, the input signal from the signal input terminal IN is converted into a negative current by the voltage / current conversion unit 10. The gate GA of the switching element 15A is turned on at the timing T ₁₁ with a positive amplitude period, the gate GB of the switching element 15B is turned off, current I ₁₄ flows through the feedback resistor 14, similarly to the thereby no signal Then, the terminal voltage of the integrating capacitor 11 rises. At this time, the negative current from the current / voltage converter 10 flows in the opposite direction to the current flowing through the integrating capacitor 11. For this reason, the charging current of the integrating capacitor 11 is reduced, and thereby the rate of voltage increase between the terminals of the integrating capacitor 11 is reduced as compared with the case of no signal illustrated in FIG. C1 "). Therefore, the time until the terminal voltage of the integrating capacitor 11 reaches the upper threshold value of the timing T ₁₁ after the hysteresis comparator 12 is longer than the time of no signal illustrated in FIG. 2 (a) (FIG. 2 (b) code (See “C1”). Next, at a timing T ₁₂ the terminal voltage of the integration capacitor 11 to the upper threshold value is reached, the output signal C12 of the hysteresis comparator 12 is inverted, thereby the gate driver 13, on the gate GB of the switching element 15B And the gate GA of the switching element 15A is turned off. Then, a current I ₁₄ of the feedback resistor 14 is inverted, the terminal voltage of the integration capacitor 11 is reduced. At this time, the output current of the voltage / current converter 10 the discharge direction with respect to the integrating capacitor 11, the voltage drop rate of the integrating capacitor 11 of the timing T ₁₂ is greater than the no-signal illustrated in FIGS. 2 (a) (See FIG. 2B, reference numeral “C1”). As a result, the time until the terminal voltage of the integrating capacitor 11 reaches the lower threshold value of the hysteresis comparator ₁₂ after the timing T12 is shorter than when there is no signal illustrated in FIG. 2A (FIG. 2B). ) Reference sign “C1”). Then, at timing T ₁₃ where the terminal voltage of the integration capacitor 11 to the threshold of the lower reaches, and the output signal C12 of the hysteresis comparator 12 is reversed again, thereby the gate driver 13, a gate GB of the switching element 15B The switching element 15A is turned on and the gate GA of the switching element 15A is turned on. In the positive amplitude period, the above series of operations are alternately repeated, so that the voltage V _OUT of the output signal from the signal output terminal OUT via the output filter 16 is positive as shown in FIG. Will have the value of

  Finally, the operation of the self-excited oscillation circuit SB during a period in which the input signal from the signal input terminal IN has a negative amplitude will be described with reference to FIG. In the following description, a period in which an input signal from the signal input terminal IN has a negative amplitude is referred to as a “negative amplitude period”. FIG. 3 is a timing chart showing the operation of the class D amplifier A centering on the self-excited oscillation circuit SB in the negative amplitude period.

As shown in FIG. 3, in the negative amplitude period, the input signal from the signal input terminal IN is converted into a positive current by the voltage / current conversion unit 10. The gate GA of the switching element 15A is turned on at the timing T ₂₁ with a negative amplitude period, the gate GB of the switching element 15B is turned off, current I ₁₄ flows through the feedback resistor 14, similarly to the thereby no signal Then, the terminal voltage of the integrating capacitor 11 rises. At this time, the positive current from the current / voltage conversion unit 10 flows in the same direction as the current flowing through the integrating capacitor 11. As a result, the charging current of the integrating capacitor 11 increases, whereby the rate of voltage increase between the terminals of the integrating capacitor 11 increases compared to the case of no signal illustrated in FIG. 2A (see “C1” in FIG. 3). ). Therefore, the terminal voltage of the integration capacitor 11 is the time to reach the upper threshold value of the timing T ₂₁ after the hysteresis comparator 12 is shorter than the no-signal illustrated in FIG. 2 (a) (Fig. 3 reference numeral "C1" reference). Next, at a timing T ₂₂ where the terminal voltage of the integration capacitor 11 to the upper threshold value is reached, the output signal C12 of the hysteresis comparator 12 is inverted, thereby the gate driver 13, on the gate GB of the switching element 15B And the gate GA of the switching element 15A is turned off. Then, a current I ₁₄ of the feedback resistor 14 is inverted, the terminal voltage of the integration capacitor 11 is reduced. At this time, since the output current of the voltage / current converter 10 charging direction to integrating capacitor 11, the voltage drop rate of the timing T ₂₂ after the integration capacitor 11 is less than the no-signal illustrated in FIGS. 2 (a) (See reference numeral “C1” in FIG. 3). Accordingly, the time until the terminal voltage of the integrating capacitor 11 reaches the lower threshold value of the timing T ₂₂ after the hysteresis comparator 12 is longer than the time of no signal illustrated in FIG. 2 (a) (Fig. 3 reference numeral " C1 "). Then, at timing T ₂₃ where the terminal voltage of the integration capacitor 11 to the threshold of the lower reaches, and the output signal C12 of the hysteresis comparator 12 is reversed again, thereby the gate driver 13, a gate GB of the switching element 15B The switching element 15A is turned on and the gate GA of the switching element 15A is turned on. In the negative amplitude period, the above series of operations are alternately repeated, so that the voltage V _OUT of the output signal from the signal output terminal OUT via the output filter 16 has a negative value as shown in FIG. Will have.

  According to the configuration and operation of the self-excited oscillation circuit SB according to the embodiment described above with reference to FIGS. 2 and 3, the integrating capacitor 11 is directly grounded without passing through the amplifying element or the like, and the feedback resistor 14 is integrated. The capacitor 11 is connected to a connection point C1 at one end. Therefore, an integrating circuit that does not include an amplifying element or the like can be configured by the integrating capacitor 11 and the feedback resistor 14, and this is driven by the voltage / current converting unit 10 with high impedance. It is possible to reduce noise at the apex portion of the triangular wave in the signal (see reference numeral N in FIG. 6B).

  Next, a specific circuit configuration of the voltage / current conversion unit 10 will be described with reference to FIGS. 4 and 5.

  As described above, the requirement for the voltage / current conversion unit 10 constituting the class D amplification device A according to the embodiment is that the voltage of the input signal input to the signal input terminal IN is converted into a current with high accuracy. In addition to being able to output, the impedance is high when viewed from the connection point C1 to which the integration capacitor 11 is connected. Examples of specific circuit configurations of the voltage / current conversion unit 10 that satisfy these requirements include, for example, three circuit configurations shown in FIGS. 4 and 5. Each of the circuit configurations shown in FIG. 4 and FIG. 5 has been conventionally known as a circuit configuration constituting the voltage / current conversion unit, but both of these are the voltage / current converters according to the above-described embodiments. All the requirements for the current converter 10 are provided.

  First, a first example of the circuit configuration of the voltage / current conversion unit 10 according to the embodiment will be described with reference to FIG.

  As the first example, as illustrated in FIG. 4A, active elements 35 to 39 such as transistors, resistors 40 to 47, current sources 50 and 51, diodes 55 and 56, a capacitor 57, The voltage / current conversion unit 10 configured by In this configuration, input signals as the class D amplifier A are applied to the signal input terminals IN, respectively, and are converted into currents and output to the connection point C1. The voltage / current conversion unit 10 having the circuit configuration illustrated in FIG. 4A has high voltage / current conversion accuracy, a wide bandwidth, a small number of components, and the voltage / current viewed from the connection point C1. The converter 10 has a feature that the impedance is high over a wide frequency band. On the other hand, there is a weak point that the amount of change in the current output to the connection point C1 flows to the power supply unit including the current sources 50 and 51.

  Next, a second example of the circuit configuration of the voltage / current conversion unit 10 according to the embodiment will be described with reference to FIG.

  As the second example, as illustrated in FIG. 4B, a voltage constituted by active elements 60 to 67 such as transistors, resistors 70 to 81, current sources 85 to 88, and a capacitor 89. / Current conversion unit 10 may be mentioned. In this configuration, input signals as the class D amplifier A are applied to the signal input terminals IN, respectively, and are converted into currents and output to the connection point C1. The voltage / current conversion unit 10 having the circuit configuration illustrated in FIG. 4B has high voltage / current conversion accuracy similar to the voltage / current conversion unit 10 having the circuit configuration illustrated in FIG. In addition to the feature that the impedance as the voltage / current converter 10 seen from the connection point C1 is high over a wide frequency band, the change in the current output to the connection point C1 is the current source 87 and It has the feature that it is a fully differential type that does not flow through the power supply unit including 88. On the other hand, as is apparent from FIG. 4B, there is a weak point that the number of parts is larger than that of the voltage / current conversion unit 10 of another example.

  Finally, a third example of the circuit configuration of the voltage / current conversion unit 10 according to the embodiment will be described with reference to FIG.

  As the third example, as illustrated in FIG. 5, a voltage / voltage composed of an operational amplifier 91 and active elements 91 and 92 such as a transistor, resistors 93 to 101, diodes 102 and 103, and a capacitor 104. An example of the current converter 10 is given. In this configuration, input signals as the class D amplifier A are applied to the signal input terminals IN, respectively, and are converted into currents and output to the connection point C1. The voltage / current conversion unit 10 having the circuit configuration illustrated in FIG. 5 has a high voltage / current conversion accuracy, a small number of parts, and a wide frequency band as the voltage / current conversion unit 10 viewed from the connection point C1. It has the feature that it is high over the range. On the other hand, the change in the current output to the connection point C1 flows to the power supply unit including the current sources 50 and 51, similar to the voltage / current conversion unit 10 having the circuit configuration illustrated in FIG. It has a weak point.

  The three circuit configurations exemplified above should be appropriately selected and adopted in consideration of the above-described features and weak points when actually designing a class D amplifier A having the voltage / current converter 10. It is.

  As described above, according to the configuration and operation of the class D amplifier A according to the embodiment, the integrating capacitor 11 and the feedback resistor 14 form an integrating circuit that does not include an amplifying element, and this is the voltage / current converting unit 10. Therefore, noise in the input signal of the hysteresis comparator / comparator 12 can be reduced.

  Therefore, the sound quality of the class D amplifying apparatus A can be further improved by further reducing distortion caused by the noise.

  Further, since the comparator connected between the connection point C1 to which one end of the integrating capacitor 11 is connected and the gate driver 13 is the hysteresis comparator 12, noise included in the signal input to the gate driver 13 is further reduced. be able to.

  Although three examples of the circuit configuration of the voltage / current conversion unit 10 according to the embodiment are shown in FIGS. 4 and 5, a circuit including all the requirements for the voltage / current conversion unit 10 described above is also provided. As long as the configuration is employed, the effect of improving the sound quality as the class D amplification device A according to the embodiment can be obtained regardless of the circuit configuration of the voltage / current conversion unit 10.

  As described above, the present invention can be used in the field of class D amplifiers, and particularly when applied to the field of class D amplifiers where higher sound quality is desired, a particularly remarkable effect can be obtained.

DESCRIPTION OF SYMBOLS 10 Voltage / current conversion part 11 Integration capacitor 12 Hysteresis comparator 13 Gate driver 14 Feedback resistance 15A, 15B Switching element 16 Output filter 17, 18 DC power supply 20 Input terminal 21, 22, 30, 40, 41, 42, 43, 44, 45, 46, 47, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 93, 94, 95, 96, 97, 98, 99, 100, 101 Resistance 23, 32 Comparator 24 Output terminal 25 Comparison unit 26 Delay unit 31, 90 Operational amplifier 35, 36, 37, 38, 39, 60, 61, 62, 63, 64, 65, 66, 67, 91, 92 Active element 50, 51, 85, 86, 87, 88 Current source 55, 56, 102, 103 Diode 57, 89, 104 Condensate A, AA Class D amplifier GA, GB Gate IN Signal input terminal OUT Signal output terminal SB Self-excited oscillation circuit I ₁₄ Current C1, C2, C3, Cx, Cy, Cz Connection point C12 Output signal CC Integration circuit N Noise

Claims (3)

In a self-excited oscillation circuit connected between a class D amplifier circuit including a switching element connected to a signal output terminal and a signal input terminal,
Current-driven voltage / current conversion means having an input terminal connected to the signal input terminal and including an amplifying element;
An integrating capacitor having one end connected to the output end of the voltage / current converting means and the other end directly grounded;
A feedback resistor connected between the output stage of the class D amplifier circuit and the one end;
A comparator connected between the one end and the input end of the class D amplifier circuit;
A self-excited oscillation circuit comprising: The self-excited oscillation circuit according to claim 1,
The self-excited oscillation circuit, wherein the comparator is a hysteresis comparator. The self-excited oscillation circuit according to claim 1 or 2,
The signal input terminal;
The class D amplifier circuit;
The signal output terminal;
A class-D amplifying apparatus comprising:

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