JP2004128750A - Pwm amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive PWM amplifier with a simple circuit constitution. <P>SOLUTION: The PWM amplifier is provided with a PWM modulation circuit to modulate digital audio data to PWM signals and a drive circuit to power-amplify the PWM signals. The PWM modulation circuit is provided with an integral circuit to directly input one-bit digital audio data, and a comparison circuit to output the PWM signals by comparing the output signals of the integral circuit and reference triangular wave signals. As a result, the inexpensive PWM amplifier can be provided by reducing circuits. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a PWM amplifier for power amplifying digital audio data.
[0002]
[Prior art]
Conventionally, in order to obtain a PWM output for driving a speaker from digital audio data composed of multi-bit data, a circuit configuration as shown in FIG. 9 has been adopted. That is, digital audio data that is multi-bit data is converted into 1-bit data in the ΔΣ modulation circuit 1. Then, the converted 1-bit data is further converted from a digital signal to an analog signal in the 1-bit D / A converter 2. The converted analog signal passes through an analog LPF 3 (LPF: Low Pass Filter) and is input to the PWM amplifier 4.
[0003]
As shown in FIG. 10, the PWM amplifier 4 includes an input terminal 5, a triangular wave signal generator 6, a comparator 7, a drive amplifier 8, a pulse amplifier 9, and an LPF 10. The analog signal that has passed through the analog LPF 3 is input from the input terminal 5 to the PWM amplifier 4. The input analog signal is compared with the triangular wave signal output from the triangular wave signal generator 6 by the comparator 7, and the result of the comparison, that is, the difference between the analog signal and the reference triangular wave signal is output as the PWM signal from the comparator 7 Output to the terminal. The PWM signal is amplified by the drive amplifier 8 and further power-amplified by the pulse amplifier 9. Unnecessary components are removed from the power-amplified PWM signal by a low-pass filter (LPF) 10 including a coil and a capacitor, and a speaker serving as a load 11 is driven (see Patent Documents 1 to 3).
[0004]
[Patent Document 1]
JP-A-6-21731 [Patent Document 2]
JP-A-7-15248 [Patent Document 3]
JP-A-7-22861
[Problems to be solved by the invention]
However, the conventional PWM amplifier has many circuits from input of digital audio data to output for driving a load, so that the circuit occupies a large area and is disadvantageous in price.
Accordingly, the present invention has been made in view of the above-described problems, and has as its object to provide a low-cost PWM amplifier with a simple circuit configuration.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention proposes the following means.
The invention according to claim 1 is a PWM amplifier including a PWM modulation circuit that modulates digital audio data into a PWM signal and a drive circuit that power-amplifies the PWM signal, wherein the PWM modulation circuit is a 1-bit digital audio data. , And a comparison circuit that compares the output signal of the integration circuit with a reference triangular wave signal and outputs the PWM signal.
[0007]
According to the present invention, since 1-bit digital data is directly input to the integration circuit forming the PWM amplifier, the conventionally used 1-bit digital data D / A converter and analog LPF circuit can be eliminated, and the circuit configuration can be reduced. A simple and low-cost PWM amplifier can be configured. Further, the 1-bit digital data input to the integration circuit is converted into a substantially triangular waveform, and the comparison circuit compares the reference triangular wave signal with the output of the integration circuit to obtain a PWM output.
[0008]
The invention according to claim 2 proposes a PWM amplifier according to claim 1 having a feedback circuit between an output of the drive circuit and an input of the integration circuit.
[0009]
According to the present invention, since the feedback circuit that feeds back the output of the drive circuit to the input of the integration circuit is provided, the distortion rate of the audio output can be improved.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a PWM amplifier according to an embodiment of the present invention will be described in detail with reference to FIGS.
As shown in FIGS. 1 and 2, the PWM amplifier according to the embodiment of the present invention includes a ΔΣ modulation circuit 1, a multiplexer 21, and a 1-bit input PWM amplifier 22.
[0011]
The ΔΣ modulation circuit 1 is a circuit that converts, for example, digital audio data (PCM audio data, PCM: Pulse Code Modulation) composed of 16 bits into a 1-bit data stream that expresses a level with coarse and fine pulses. The multiplexer 21 is an element having a function of selecting and outputting only one of a plurality of signals. In the embodiment of the present invention, the multiplexer 21 receives 1-bit data directly input from the outside, for example, DSD It has a role of switching between data (DSD: Direct Stream Digital) and the 1-bit data stream output from the ΔΣ modulation circuit 1 with respect to the input of the 1-bit input PWM amplifier 22 at the next stage.
[0012]
The 1-bit input PWM amplifier 22 is an amplifier that inputs 1-bit data and supplies a PWM output to a load. As shown in FIG. 2, the integration circuit 23, the triangular wave signal generator 6, the comparison circuit 7, the output driver 24, the LPF 10, and the load 11. The integration circuit 23 is a circuit composed of an operational amplifier, a resistor, and a capacitor, and integrates the input 1-bit data to output a substantially triangular waveform. The integration circuit 23 also has a role of removing unnecessary high-frequency components outside the audio band by a combination of a resistor and a capacitor. The triangular wave signal generator 6 generates a triangular wave signal serving as a reference for comparison with an output waveform output from the integrating circuit 23, and has a configuration including a reference signal generator and a modulation circuit (not shown). .
[0013]
The comparison circuit 7 compares the output from the integration circuit 23 with the triangular wave signal from the triangular wave signal generator 6, and outputs the result as a PWM signal subjected to pulse width modulation. The output driver 24 is a circuit that amplifies the power of the input PWM signal. The LPF 10 has a role of removing unnecessary high-frequency components outside the audio band. The load 11 is a speaker driven by the output of the output driver 24.
[0014]
Next, a first embodiment of the present invention will be described using a specific circuit (FIG. 3).
FIG. 3 shows a so-called separately excited PWM amplifier circuit. The PWM amplifier according to the present embodiment includes a ΔΣ modulation circuit 1, a multiplexer 21, a DSD I / F circuit 25 (I / F: Interface), and resistors R1, R2, R3 (reference numerals 101, 102, and 103). , Capacitors C1, C2, C3 (reference numerals 111, 112, 113), inductor L1 (reference numeral 131), driver 141, CMOS inverter 142, operational amplifier 121, triangular wave signal generator 6, comparator 122, speaker 11 is comprised.
[0015]
The PCM audio data (LRCK: L channel, R channel clock, BCK: bit clock, DATA: multi-bit data) is connected to the ΔΣ modulation circuit 1 as an input, and the output converted to a 1-bit data stream is It is connected to one of the switching terminals. On the other hand, to the other switching terminal of the multiplexer 21, DSD data configured in the format of a 1-bit data stream is connected via a DSD I / F circuit 25.
[0016]
The output terminal of the multiplexer 21 is connected to one end of a resistor R1 (reference numeral 101), and the other end of the resistor R1 is connected to a capacitor C1 (reference numeral 111).
The other end of the capacitor C1 is connected to the reference voltage of the circuit, and forms a low-pass filter in combination with the resistor R1. Here, the reference voltage is a voltage value that is １ ／ of the power supply voltage supplied to the circuit. This low-pass filter has a role of attenuating high-frequency noise outside the audio band included in the output of the multiplexer 21, that is, 1-bit data.
[0017]
A resistor R2 (reference numeral 102), which is an input resistance of the operational amplifier 121, is connected to the capacitor C1 and the resistor R1, and one end thereof is connected to an inverting input terminal of the operational amplifier 121. A capacitor C2 (reference numeral 112) is connected between the inverting input terminal and the output terminal of the operational amplifier 121, and the non-inverting input terminal of the operational amplifier 121 is connected to the reference voltage of the circuit. As a result, an integrating circuit is formed by the resistor R2, the capacitor C2, and the operational amplifier 121.
[0018]
The output terminal of the operational amplifier 121 is connected to the non-inverting input terminal of the comparator 122. The triangular wave signal generator 6 is connected to the inverting input terminal of the comparator 122, and the result of comparison is output as a PWM signal. The output PWM signal is amplified by a driver 141 which is a driving circuit. The amplified signal performs switching driving of the CMOS inverter 142, and the output of the CMOS inverter 142 is supplied to the speaker 11 as a load via a low-pass filter including an inductance L1 (reference number 131) and a capacitor C3 (reference numeral 113). .
[0019]
As shown in FIG. 4, the CMOS inverter 142 connects the drain of the PMOS transistor 152 and the drain of the NMOS transistor 153 to form an output terminal 154, and connects the gate of the PMOS transistor 152 and the gate of the NMOS transistor 153 to each other. Are connected to form an input terminal 151. The source of the PMOS transistor 152 is connected to the power supply of the power supply voltage + Vcc, and the source of the NMOS transistor 153 is connected to GND.
[0020]
The output terminal 154 of the CMOS inverter 142 is connected to the inverting input terminal of the operational amplifier 121 via the resistor 3 (reference numeral 103). As a result, the output of the CMOS inverter 142 is fed back, so that the distortion rate of the audio output is improved. Since the above-described circuit is a PWM amplifier corresponding to one audio channel, if the number of audio channels is large, similar circuits are required for the number of channels.
[0021]
Next, the operation of the PWM amplifier according to the embodiment of the present invention will be described with reference to the waveform diagrams of the respective parts of the circuit in FIG.
FIG. 6A shows a 1-bit data stream input to the PWM amplifier (IN signal in FIG. 3). In the present embodiment, 16-bit PCM audio data having a sampling frequency of 44.1 kHz is modulated into a 1-bit data stream. The 1-bit data stream has a Hi level of “1” and a Low level of “0”. Is equivalent to
[0022]
The input IN signal passes through a primary low-pass filter composed of a resistor R1 and a capacitor C1, undergoes band limitation, and is input to an inverting input terminal of an operational amplifier 121 via a resistor R2. On the other hand, the output voltage of the CMOS inverter 142 is also input to the inverting input terminal of the operational amplifier 121 via the resistor R3. As a result, the IN signal and the output voltage of the CMOS inverter 142 are added by the resistor and input to the integration circuit.
[0023]
These signals input to the inverting input terminal of the operational amplifier 121 are integrated by an integrating circuit composed of the resistor 2, the capacitor C2 and the operational amplifier 121, and converted into a waveform as shown in FIG. INT signal in). The INT signal output from the integration circuit is input to the non-inverting input terminal of the comparator 122, and the reference triangular signal (see FIG. 6C) input from the triangular signal generator 6 to the inverting terminal of the comparator 122. (TRI signal inside).
[0024]
The comparator 122 outputs a Hi-level signal to a portion where the voltage value of the INT signal output from the integration circuit is larger than the reference triangular wave signal (TRI signal). In a portion where the voltage value of the INT signal output from the integration circuit is small, a Low level signal is output, and the INT signal output from the integration circuit is converted into a pulse width modulated PWM signal (FIG. 6 ( d)).
[0025]
When there is no input signal in the operational amplifier 121 which is an integrating circuit, the output voltage of the CMOS inverter 142 is output with a duty of 50% between a Hi level and a Low level. On the other hand, when the operational amplifier 121 serving as an integrating circuit has a Hi-level input signal, the input signal is connected to the inverting input terminal of the operational amplifier 121, so that the output of the operational amplifier 121 is inverted and increases in the negative direction.
[0026]
The output of the comparator 122 that compares this output with the reference triangular wave signal (TRI signal) becomes Low level (or Hi level) at a point where the output waveform of the operational amplifier and the reference triangular wave signal (TRI signal) intersect. This signal is inverted by the driver 141 and supplied to the input terminal 151 of the CMOS inverter 142. The supplied signal turns on the NMOS transistor 153 to output a low level signal.
[0027]
The output signal passes through a low-pass filter including an inductor L1 (reference numeral 131) and a capacitor C3 (reference numeral 113) to remove unnecessary high-frequency components, and is then supplied to a speaker as a load 11. The output signal is fed back to the inverting input terminal of the operational amplifier 121 via the resistor R3 (reference numeral 103) in order to improve the distortion factor.
[0028]
Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 5 shows a so-called self-excited PWM modulation circuit. The PWM amplifier according to this embodiment includes a ΔΣ modulation circuit 1, a multiplexer 21, a DSD I / F circuit 25 (I / F: Interface), and resistors R1, R2, R3, R4, and R5 (reference numerals 101 and 102). , 103, 104, 105), capacitors C1, C2, C3 (reference numerals 111, 112, 113), inductor L1 (reference numeral 131), operational amplifier 121, comparator 122, driver 141, CMOS inverter 142, and speaker 11 It is composed of Note that the same reference numerals as in the first embodiment denote the same elements, and a detailed description thereof will be omitted.
[0029]
The PWM amplifier according to the second embodiment of the present invention operates as an inverting amplifier having a gain of R3 / R2 which is a ratio of the resistors R2 and R3. That is, a PWM amplifier which integrates a difference between an input signal and an output signal of a PWM amplifier by an integration circuit, converts the difference into a binary PWM signal by a comparator 122, and feeds back the output signal to the integration circuit to self-excit the PWM amplifier. It is.
[0030]
Next, self-excited modulation will be described. When there is no input from the ΔΣ modulation circuit 1 to the operational amplifier 121 constituting the integration circuit, the CMOS inverter 142 outputs a Hi level (+ Vcc) and a Low level (0 V) at a duty of 50%. This waveform is shown by the dashed line in FIG.
[0031]
At this time, the output voltage V1 of the operational amplifier 121 is obtained by integrating the output voltage V3 of the CMOS inverter 142 because the non-inverting input terminal is fixed to the reference voltage (= VCC / 2). That is, when the output voltage V3 is at the Hi level, it is inverted and increases in the negative direction over time, and increases in the positive direction when the output voltage V3 reaches the Low level. As a result, a voltage waveform having a triangular waveform as shown by a broken line in FIG.
[0032]
As the output voltage V1 of the integrating circuit increases in the negative direction, the input voltage V2 at the non-inverting input terminal of the comparator 122 also increases in the negative direction. When the input voltage V2 of the comparator 122 reaches the reference voltage, the output voltage V3 of the CMOS inverter 142, which has changed to the low level, is positively fed back via the resistor R5. The input voltage V2 of the comparator 122 is abruptly pulled in the negative direction up to the voltage level determined by the output voltage V3 of the CMOS inverter 142 and the ratio of the resistors 4 and 5.
[0033]
On the other hand, the input voltage V2 of the comparator 122 increases as the output voltage V1 of the integration circuit increases in the positive direction. When the input voltage V2 reaches the reference voltage, the output voltage V3 of the CMOS inverter 142, which has changed to the Hi level when the input voltage V2 reaches the reference voltage, becomes higher. Since the positive feedback is performed via the resistor R5, the output voltage V1 of the integrating circuit, the output voltage V3 of the CMOS inverter 142, and the voltage level determined by the ratio of the resistor 4 and the resistor 5 at this time are adjusted by the comparator 122. The input voltage V2 sharply increases in the positive direction. Thus, the input voltage V2 of the comparator 122 changes as shown by the solid line in FIG.
[0034]
Next, the state of each unit when a signal is input from the ΔΣ modulation circuit 1 to the integration circuit will be described. When a signal (IN signal) as shown in FIG. 7A is input from the ΔΣ modulation circuit 1 to the integration circuit, the input IN signal and the output voltage of the CMOS inverter 142 are connected to the resistor R2, R3 adds and integrates. The waveform at this time is shown in FIG. 7B (INT2 signal).
[0035]
The INT2 signal is combined with the output voltage of the CMOS inverter 142 that is positively fed back by the resistor R5, and has a voltage waveform as shown in FIG. 7C (HIS signal). The HIS signal is compared with a reference voltage (1.5 V in the present embodiment) in the comparator 123 and converted into a binary PWM signal. The output PWM signal is power-amplified via the output voltage of the driver 141 and the CMOS inverter 142, and then is supplied to the speaker 11 as a load through the low-pass filter 10 to drive the speaker.
[0036]
Therefore, according to the present embodiment, with respect to the data format of 1-bit data, the PWM amplifier which is excellent in power consumption efficiency by eliminating the conventionally used 1-bit D / A converter and analog low-pass filter. Can be configured at low cost.
[0037]
As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and includes a design and the like within a range not departing from the gist of the present invention. It is. For example, in the embodiment of the present invention, before supplying 1-bit digital data to the integration circuit, a primary low-pass filter is provided to remove noise outside the audio band. However, the present invention is not limited to this. A low-pass filter may be provided.
[0038]
In the embodiment of the present invention, DSD is exemplified as 1-bit data that can be directly input. However, the present invention is not limited to this, and any data having a 1-bit data format may be used. In the embodiments of the present invention, the power supply of the circuit is described as a single power supply (VCC-GND). However, it is needless to say that the present invention can be applied even if the power supply of the circuit is a dual power supply (± VCC-GND).
[0039]
【The invention's effect】
As described above, according to the present invention, since a 1-bit data can be directly input and a PWM output can be obtained, a low-cost digital audio PWM amplifier with a simple circuit configuration can be provided. There is an effect that can be. Further, since a feedback circuit is provided between the output of the drive circuit and the input of the integration circuit, the distortion rate of the audio output can be improved.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an outline of the present invention.
FIG. 2 is a diagram showing a configuration of a PWM amplifier according to the present invention.
FIG. 3 is a circuit configuration diagram of a PWM amplifier according to the present invention using a separately excited PWM modulation circuit.
FIG. 4 is a diagram showing a circuit configuration of a CMOS inverter.
FIG. 5 is a circuit configuration diagram of a PWM amplifier according to the present invention using a self-excited PWM modulation circuit.
FIG. 6 is a diagram showing voltage waveforms at various parts of a PWM amplifier according to the present invention using a separately excited PWM modulation circuit.
FIG. 7 is a diagram showing voltage waveforms at various parts in a PWM amplifier according to the present invention using a self-excited PWM modulation circuit.
FIG. 8 is a diagram showing voltage waveforms at various parts of a PWM amplifier according to the present invention using a self-excited PWM modulation circuit when there is no input to an integration circuit.
FIG. 9 is a configuration diagram relating to a conventional example.
FIG. 10 is a configuration diagram of a PWM amplifier according to a conventional example.
[Explanation of symbols]
1 ... ΔΣ modulation circuit, 2 ... 1 bit D / A, 3 ... analog LPF, 4 ... PWM amplifier, 5 ... input terminal, 6 ... triangle wave signal generator, 7 ... ..Comparator, 8 ... drive amplifier, 9 ... pulse amplifier, 10 ... LPF, 11 ... load, 21 ... multiplexer, 22 ... 1-bit input PWM amplifier, 23 ... Integration circuit, 24: output driver, 25: DSD I / F circuit, 101, 102, 103, 104, 105: resistor, 111, 112, 113 ... capacitor, 121 ... Operational amplifier, 122 comparator, 131 inductor, 141 driver, 142 CMOS inverter, 151 input terminal, 152 PMOS transistor, 153 NMO S transistor, 154... Output terminal,

Claims (2)

A PWM amplifier including a PWM modulation circuit that modulates digital audio data into a PWM signal and a drive circuit that power-amplifies the PWM signal, wherein the PWM modulation circuit directly inputs 1-bit digital audio data; A PWM circuit comprising: a comparison circuit that compares an output signal of the integration circuit with a reference triangular wave signal and outputs the PWM signal. 2. The PWM amplifier according to claim 1, further comprising a feedback circuit between an output of the drive circuit and an input of the integration circuit.

Images