JP2010130064A - DeltaSigma MODULATED DA CONVERTER AND DeltaSigma MODULATOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for improving tone quality in a ΔΣ modulated DA converter, while suppressing cost rise as much as possible. <P>SOLUTION: At an audio processing apparatus 10, a digital signal is modulated by a ΔΣ modulator 20 and amplified by a class D amplifier 60 to output to a load 12 such as a speaker. At this point, the output of the class D amplifier 60 is fed back to the ΔΣ modulator 20 indirectly. In order to remove distortion component using a comparatively low speed AD converter as an AD converter needed in the feedback, a class D amplifier emulator 30 is arranged at the ΔΣ modulator 20, wherein the emulator simulates the class D amplifier 60 where distortion generates. In addition, the class D amplifier emulator 30 updates various parameters by learning so that they may become suitable. Thereby, distortion compensation can be performed more effectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a delta-sigma modulation DA converter and a delta-sigma modulator, and includes a delta-sigma modulation DA converter and an input signal that have a class D amplifier and can supply power to a load connected to an output. The present invention relates to a ΔΣ modulator that performs ΔΣ modulation and outputs it to a class D amplifier.

  LCD TVs and other flat-screen TVs are exposed to intense competition, and manufacturers are required to further reduce costs while improving performance. Under such circumstances, audio amplifiers are no exception. In the case of television broadcast waves, with the start of digital broadcasting, most TV circuits are digitized, and audio amplifiers are also required to have devices that receive digital signals. Eventually, digital circuits are integrated into one chip to save space and reduce costs.

  By the way, a ΔΣ modulation DA converter applied to audio and the like is configured by being divided into a modulation section constituted by a digital circuit and a class D amplification section for supplying power. The class D amplifier does not achieve ideal class D amplification due to the dead time, on-resistance of the power switching unit, voltage drop due to power supply impedance, power supply fluctuation due to the influence of other loads, etc., and distortion occurs, resulting in sound quality. There is a problem of causing deterioration.

  FIG. 1 illustrates five types of ΔΣ modulation DA converters currently implemented. FIG. 1A shows an example of the configuration of an initial ΔΣ modulation type DA converter. A digital signal is converted into an analog signal by a DA converter, modulated by an analog ΔΣ modulator, and amplified by a class D amplification unit. ing. The output of the class D amplifier is fed back to the ΔΣ modulator. The ΔΣ modulation DA converter with this configuration is excellent in characteristics, but it is difficult to study a new algorithm for improving power consumption, and the cost is relatively high. There is.

  In the ΔΣ modulation type DA converter of FIG. 1B, the DA converter in the preceding stage of the ΔΣ modulator is omitted, and the ΔΣ modulation DA converter includes a ΔΣ modulator that modulates a digital signal as it is and a class D amplification unit. In this ΔΣ modulation DA converter, the ease of verification of the algorithm is greatly improved, but there is a problem that distortion generated in the class D amplification unit is output as it is.

  In the ΔΣ modulation type DA converter of FIG. 1C, in order to solve the problem of the ΔΣ modulation type DA converter of FIG. 1B, a distortion compensation circuit is provided in the previous stage of the ΔΣ modulator, thereby providing distortion characteristics. Improvements have been made. However, even when this ΔΣ modulation DA converter is employed, there is a problem that, for example, power ripple cannot be sufficiently compensated. In recent years, as a result of the cost reduction of products, the weak point of the power supply ripple resistance of the power supply sometimes becomes apparent.

  In the ΔΣ modulation DA converter of FIG. 1D, in order to solve the problem of the ΔΣ modulation DA converter of FIG. 1C, a ripple removal circuit for power supplied to the class D amplification unit is provided. .

Various techniques for improving characteristics by distortion compensation have been proposed. For example, there is a technique for correcting the magnitude of a distortion compensation coefficient in advance while maintaining its phase so that a distortion-compensated transmission signal does not exceed the dynamic range of the DA converter (see, for example, Patent Document 1). .
JP 2001-251148 A

  By the way, in the technique described in Patent Document 1, in principle, only the distortion characteristic related to the causality with the input signal x (t) is corrected. Therefore, in applications where DA converter switching patterns and power supply fluctuations cannot be ignored, such as DA converters that control relatively large power, distortion factors that occur in these applications cannot be corrected. there were. Further, in the technique shown in FIG. 1D, the characteristics of the ΔΣ modulation DA converter can be improved by increasing the power supply ripple, but eventually the cost is increased and the cost of the power supply is reduced. And the cost increase of the ΔΣ modulation DA converter is offset. FIG. 1E shows a ΔΣ modulation DA converter that feeds back the output of the class D amplification unit of FIG. 1B to the ΔΣ modulator. This configuration is ideal, but a high-speed and high-accuracy AD converter is required for feedback. As described above, under the current situation of intense cost competition, the adoption of a high-speed and high-precision AD converter is not practical, and another technique has been demanded.

  In view of the above problems, an object of the present invention is to propose a technique for achieving an improvement in sound quality while suppressing an increase in cost as much as possible in a ΔΣ modulation DA converter.

The apparatus according to the present invention relates to a ΔΣ modulation DA converter. This device includes a ΔΣ modulator including a integrator and a quantizer that converts the output from the integrator to a resolution lower than the resolution of the integrator based on the output from the integrator, and a class D amplifier, and is connected to the output. A delta-sigma modulation DA converter capable of supplying electric power to a load, a class D amplifier emulator for emulating the output of the class D amplifier, and the output of the class D amplifier A feedback unit that generates a feedback signal based on a signal output from the class D amplifier emulator.
The class D amplifier emulator may emulate the distortion characteristics of the class D amplifier.
In addition, the class D amplifier emulator is based on the output of the feedback unit so that the output of the class D amplifier and the output of the class D amplifier are closest to each other. The characteristics may be updated sequentially.
The feedback unit includes an analog filter that filters the output of the class D amplification unit, an AD converter that AD converts the output of the class D amplification unit filtered by the analog filter, and an output of the ΔΣ modulator. May be provided with a digital filter that acquires and filters through a different path from the class D amplifier.
Further, the class D amplification unit emulator, based on the output of the AD converter and the output of the digital filter, outputs the class D amplification unit emulator and the class D amplification unit after conversion in the AD converter. The characteristics of the class D amplifier emulator itself may be updated sequentially so that the output of
The ΔΣ modulator includes a first subtractor that obtains a difference between an output of the class D amplifier emulator and an input to the ΔΣ modulation DA converter, and the integrator includes the first subtractor. May be input.
The class D amplification unit may supply power sufficient to drive a load connected to the output of the class D amplification unit based on the signal of the quantizer.
In addition, the ΔΣ modulation DA converter may include a simulated disturbance generator that artificially generates a disturbance component.
The analog filter may filter only a signal component necessary for distortion component estimation out of the output of the class D amplifier.
The digital filter may filter only a signal component necessary for distortion component estimation out of the output of the class D amplifier emulator.
Moreover, you may provide the calculating means which calculates the difference of the output of the said AD converter, and the output of the said digital filter.
The class D amplifier emulator identifies the parameters of the simulated disturbance generator, the input signal, the output of the quantizer and the causal distortion component, and simulates the distortion characteristics of the class D amplifier. May be.
The parameters of the distortion component include: an output of a second subtractor that obtains a difference between an output of the AD converter and an output of the digital filter, an output of the simulated disturbance generator, the input signal, and the quantum The update of the parameter may converge when the distortion components of the class D amplifying unit and the class D amplifying unit emulator coincide with each other.
Further, the AD converter may be driven at a lower speed than the driving speed of the ΔΣ modulator.
Another embodiment of the present invention relates to a ΔΣ modulator. This apparatus simulates the distortion characteristics of an integrator, a quantizer that converts to a lower resolution than the output of the integrator based on the output from the integrator, and the output class D amplifier, A D-class amplification unit emulator for feedback and output to the integrator; and a simulated disturbance generator for generating a disturbance component in a pseudo manner. The D-class amplification unit emulator is configured such that the output of the D-class amplification unit is AD converted. Based on the difference signal between the later digital signal and the feedback output of the class D amplifier emulator, the signal from the quantizer, and the signal of the simulated disturbance generator, the simulated disturbance generator, the input signal, and the The difference signal between the digital signal after the output of the quantizer and the causal distortion component parameter are identified and the output of the class D amplifier is AD converted and the feedback output of the class D amplifier emulator So that Successively updating the parameter.

  ADVANTAGE OF THE INVENTION According to this invention, in the delta-sigma modulation type DA converter, the technique which achieves sound quality improvement can be proposed, suppressing a cost increase as much as possible.

  Next, the best mode for carrying out the present invention (hereinafter simply referred to as “embodiment”) will be specifically described with reference to the drawings. First, an outline of the present embodiment will be described. The following audio processing device modulates a digital signal with a ΔΣ modulator, amplifies it with a class D amplifier, and outputs it to a load such as a speaker. At that time, the output of the class D amplifier is fed back to the ΔΣ modulator. At this time, an AD converter is required for feedback to the ΔΣ modulator. However, since a high-speed and high-precision AD converter is difficult to adopt in terms of cost, a relatively low-speed AD converter is used. , Remove distortion components. For this reason, a class D amplifier emulator that simulates a class D amplifier having distortion is provided in the ΔΣ modulator, and the feedback signal generated based on the class D amplifier emulator and a relatively low-speed AD converter. Is used for feedback processing. Furthermore, the class D amplifier emulator updates various parameters to be appropriate by learning, and more effectively realizes distortion compensation.

  FIG. 2 is a functional block diagram illustrating a schematic configuration of the speech processing apparatus 10 according to the present embodiment. The audio processing device 10 is mounted on a display device such as a liquid crystal television.

  As illustrated, the audio processing device 10 includes a ΔΣ modulator 20, a class D amplification unit 60, and a feedback unit 70. A digital signal (also referred to as “original signal S 1”) such as a PCM (pulse code modulation) signal is input from the signal input unit 51 to the audio processing device 10, modulated by the ΔΣ modulator 20, and input to the class D amplification unit 60. Is output. The signal amplified by the class D amplification unit 60 is output to the load 12 such as a speaker through the signal output unit 52. The signal amplified by the class D amplification unit 60 is fed back to the ΔΣ modulator 20 via a feedback unit 70 including an AD converter 74 described later. Each configuration will be specifically described below.

  The class D amplification unit 60 amplifies the signal of the quantizer 24 to a signal that supplies power sufficient to drive the load 12 such as a speaker connected to the signal output unit 52 of the audio processing device 10. .

  The ΔΣ modulator 20 has, as a general circuit configuration for ΔΣ modulation, an integrator 22 and a quantizer 24 that converts the output from the integrator 22 to a resolution lower than the resolution of the integrator 22 based on the output from the integrator 22. The audio signal is quantized into discrete voltage values such as binary and ternary values. Note that the integrator 22 and the quantizer 24 are well-known techniques and will not be described. Further, the integration order of the integrator 22 may be first order or second order or higher. Furthermore, the integrator 22 may be composed of a plurality. Furthermore, a synthesizer 28 is provided before the integrator 22 in order to feed back the output of the class D amplifier emulator 30 to the input side of the integrator 22. The synthesizer 28 calculates the difference between the original signal S1 as a non-inverting input (+) and the output from the class D amplifier emulator 30 as an inverting input (−), and outputs the signal obtained as a result of the calculation to the integrator 22. Output.

  Further, the ΔΣ modulator 20 includes a class D amplifier emulator 30 and a simulated disturbance generator 26 as a characteristic configuration of the present embodiment. The simulated disturbance generator 26 generates a disturbance for estimating a disturbance component. This disturbance is, for example, a sine wave or cosine wave having the same frequency as the power supply fluctuation component of the commercial power supply. In addition, the frequency of the inverter can be set. Below, it demonstrates as a sine wave and a cosine wave.

  As shown in the figure, the class D amplifier emulator 30 includes an output of the quantizer 24 (S2), an output of the simulated disturbance generator 26 (S3), and an original signal S1 (to be described later, an AD converter) input to the signal input unit 51. Using the input d3) as an input signal, the parameters of the causal distortion component and those signals (S1 to S3) are identified, and the behavior of the class D amplifier 60 is simulated. The above parameters are sequentially updated based on the output (S3) of the simulated disturbance generator 26, the original signal S1, the output (S2) of the quantizer 24, and the error signal S4 output from the combiner 76 of the feedback unit 70. . When the distortion components of the class D amplification unit 60 and the class D amplification unit emulator 30 match, the parameter update converges. The configuration and mathematical model of the class D amplifier emulator 30 will be described later.

  The feedback unit 70 includes an analog filter 72, an AD converter 74, a combiner 76, and a digital filter 78. The analog filter 72 passes only a necessary signal component out of the output of the class D amplifier 60 and outputs it to the AD converter 74.

  The AD converter 74 converts the analog signal that has passed through the filter 72 into a digital signal and outputs the digital signal to the synthesizer 76.

  The digital filter 78 passes only a necessary signal component of the signal output from the class D amplifier emulator 30 and outputs it to the combiner 76.

  The synthesizer 76 calculates the difference using the signal from the AD converter 74 as the non-inverting input (+) and the output of the class D amplifier emulator 30 via the digital filter 78 as the inverting input (−), and calculates the result. The error signal S4 is output to the class D amplifier emulator 30.

Next, an outline of a mathematical model of processing of the class D amplifier emulator 30 will be described. The general formula of the mathematical model is expressed by the following formulas (1) to (6). Here, the class D amplification unit emulator 30 outputs y ₁ (t) as the output of the class D amplification unit 60, y ₂ (t) as the output of the class D amplification unit emulator 30, and the class D amplification unit 60 and the class D amplification unit. the error of the emulator 30 is taken as e (t), (4) 2 squared such time integral of the error is minimized, the steepest descent method parameters a ₁ ~a _n error e (t) represented by the formula To learn and update. In equation (5), a _i (t) is the current parameter, and a _i (t + 1) is the updated parameter. Further, although the steepest descent method, which is a basic method, is exemplified as a parameter learning method, naturally, a genetic algorithm or other learning method may be used.

Next, based on FIG. 3 and the following formulas (7) to (12), a specific configuration and mathematical model of the class D amplifier emulator 30 will be described. Here, it is assumed that the output of the class D amplifier emulator 30 has a distortion model represented by the following equations (7) to (12).

The class D amplifier emulator 30 includes a sine wave first disturbance wave d1 (equation (7)) and a cosine wave second disturbance wave d2 (equation (8)), which are simulated disturbance signals from the simulation disturbance generator 26. , The absolute value (formula (9)) of the AD converter input d3 that is the original signal (input signal) S1, the quantizer output d4 (formula (10)) that is the output from the quantizer 24, and a feedback unit The error signal e from the synthesizer 76 of 70 is acquired as an input, and an emulator output signal y ₂ (t) expressed by the equation (11) is output after a predetermined calculation process described later.

  More specifically, as shown, the class D amplification unit emulator 30 includes a class D amplification simulation parameter update controller 42, a class D amplification simulation output calculator 44, a class D amplification simulation parameter unit 46, It has. The class D amplification simulation parameter update controller 42 calculates the absolute value of the first disturbance wave d1 in equation (7), the second disturbance wave d2 in equation (8), and the AD converter input (input signal) d3 in equation (9). The value, the quantizer output d4 of the equation (10), and the error signal e from the synthesizer 76 of the feedback unit 70 are acquired.

In the above equation (11), the portion indicated by “a ₁ · d ₁ + a ₂ · d ₂ ” corresponds to the power fluctuation component due to the sine wave and cosine wave having the same frequency as the commercial power supply as described above. Further, a portion indicated by “a _3. | D ₃ |” corresponds to a voltage drop component due to the power source impedance of the signal source of the original signal S1. Furthermore, the portion indicated by “a ₄ · d ₄ ” corresponds to the gain fluctuation.

Then, (11) the first to fourth parameters _a 1 ~a ₄ expressions are sequentially updated, will be focused are learned.

Therefore, the class D amplification simulation parameter update controller 42 includes a first disturbance wave d1, a second disturbance wave d2, an AD converter input d3, a quantizer output d4, and an error signal e from the combiner 76 of the feedback unit 70. (t) to the original, calculates the update amount Δa ₁ ~Δa ₄ of the first to fourth parameters _a 1 to a4 shown in equation (12), and outputs the class D amplifier simulating parameter section 46.

Class D amplifier simulating parameter section 46, the update amount Δa ₁ ~Δa ₄ of the first to fourth parameters _a 1 ~a ₄ obtained from the D-class amplification simulating parameter update controller 42, the above-mentioned (5) The updated parameter a _i (t + 1) is calculated with respect to the current parameter a _i (t) by applying the equations (6) and (6), and is output to the class D amplification simulation output calculator 44 together with the signals d1 to d4 To do.

  The class D amplification simulation output calculator 44 executes the calculation represented by the above equation (11) based on the output of the class D amplification simulation parameter unit 46, and the result of simulating the class D amplification unit 60 is fed back to the feedback unit. 70 and the synthesizer 28 before the integrator 22.

  In the speech processing apparatus 10, such parameter updating is sequentially executed, and when the output error e (t) of the class D amplifying unit 60 and the class D amplifying unit emulator 30 becomes 0, convergence is achieved. That is, as a result of learning by the class D amplification unit emulator 30, the distortion components of the class D amplification unit 60 and the class D amplification unit emulator 30 match, and the indirect feedback shown here is a direct feedback. It functions in the same way, and disturbances such as distortion components and power supply ripple caused by the class D amplifier 60 are effectively compensated.

  As described above, according to the present embodiment, since feedback is performed by the AD converter 74, disturbances such as power supply ripple and distortion components peculiar to the class D amplifier 60 can be indirectly fed back. Further, in the case of direct feedback, a high-speed AD converter is necessary. However, since this method does not require a high-speed AD converter, a feedback system can be constructed at a relatively low cost. Furthermore, since the entire ΔΣ modulator 20 including the integrator 22 and the quantizer 24 can be realized by digital signal processing, the compatibility with the digital broadcast receiver system is high. For the same reason, various methods can be examined by development using an FPGA (Field Programmable Gate Array), and development efficiency is remarkably improved. Furthermore, since the ΔΣ modulation algorithm is entirely composed of a digital circuit, the algorithm can be studied without being restricted by design restrictions specific to analog ICs such as drift noise. Furthermore, even when the distortion characteristics of the class D amplification unit 60 change due to changes over time, for example, the class D amplification unit emulator 30 updates the parameters again to appropriate parameters through learning. It can correspond to.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of these components, and such modifications are also within the scope of the present invention.

It is the figure which showed the five types of (DELTA) (Sigma) modulation type | mold DA converter based on a prior art. It is a functional block diagram which shows schematic structure of the audio processing apparatus based on embodiment. It is a functional block diagram which shows schematic structure of the class D amplification part emulator based on embodiment.

Explanation of symbols

10 Audio processing device (ΔΣ modulation DA converter)
20 ΔΣ modulator 22 Integrator 24 Quantizer 26 Simulated disturbance generator 28 Synthesizer 30 Class D amplifier emulator 42 Class D amplification simulation parameter update controller 44 Class D amplification simulation output calculator 46 Class D amplification simulation parameter Unit 51 signal input unit 52 signal output unit 60 class D amplification unit 70 feedback unit 72 analog filter 74 AD converter 76 synthesizer 78 digital filter

Claims (15)

To a load connected to the output, comprising a ΔΣ modulator comprising a integrator and a quantizer for converting to a resolution lower than the resolution of the integrator based on the output from the integrator, and a class D amplifier A ΔΣ modulation DA converter capable of supplying power,
A class D amplification unit emulator for emulating the output of the class D amplification unit; a feedback unit for generating a feedback signal based on the output of the class D amplification unit and the output of the class D amplification unit emulator;
A ΔΣ modulation DA converter characterized by comprising:   The ΔΣ modulation DA converter according to claim 1, wherein the class D amplifier emulator emulates distortion characteristics of the class D amplifier.   Based on the output of the feedback unit, the class D amplification unit emulator adjusts the characteristics of the class D amplification unit emulator so that the output of the class D amplification unit emulator and the output of the class D amplification unit are closest to each other. The ΔΣ modulation DA converter according to claim 1, wherein the ΔΣ modulation DA converter is sequentially updated.   The feedback unit includes an analog filter for filtering the output of the class D amplification unit, an AD converter for AD converting the output of the class D amplification unit filtered by the analog filter, and an output of the ΔΣ modulator. 4. The ΔΣ modulation DA converter according to claim 1, further comprising a digital filter that acquires and filters through a path different from the class D amplification unit. 5.   Based on the output of the AD converter and the output of the digital filter, the class D amplification unit emulator outputs the output of the class D amplification unit emulator and the output of the class D amplification unit after conversion in the AD converter. 5. The ΔΣ modulation DA converter according to claim 4, wherein the characteristics of the class D amplifier emulator itself are sequentially updated so as to be closest to each other. The ΔΣ modulator includes a first subtractor that obtains a difference between an output of the class D amplification unit emulator and an input to the ΔΣ modulation DA converter,
The ΔΣ modulation DA converter according to claim 1, wherein an output of the first subtracter is input to the integrator.   7. The class D amplification unit supplies power sufficient to drive a load connected to the output of the class D amplification unit based on a signal of the quantizer. ΔΣ modulation type DA converter.   The ΔΣ modulation DA converter according to claim 1, wherein the ΔΣ modulation DA converter includes a simulated disturbance generator that artificially generates a disturbance component.   9. The ΔΣ modulation DA converter according to claim 5, wherein the analog filter filters only a signal component necessary for distortion component estimation out of the output of the class D amplification unit. 10.   10. The ΔΣ modulation DA converter according to claim 5, wherein the digital filter filters only a signal component necessary for distortion component estimation from the output of the class D amplifier emulator. 10. .   11. The ΔΣ modulation DA converter according to claim 5, further comprising arithmetic means for calculating a difference between an output of the AD converter and an output of the digital filter.   The class D amplifier emulator identifies parameters of the simulated disturbance generator, input signal, and output of the quantizer and causal distortion components, and simulates the distortion characteristics of the class D amplifier. The ΔΣ modulation DA converter according to any one of claims 8 to 11, characterized in that   The parameters of the distortion component include: an output of a second subtractor that obtains a difference between an output of the AD converter and an output of the digital filter, an output of the simulated disturbance generator, the input signal, and the quantizer The parameter update converges when the distortion components of the class D amplification unit and the class D amplification unit emulator coincide with each other. ΔΣ modulation type DA converter.   14. The ΔΣ modulation DA converter according to claim 1, wherein the AD converter is driven at a lower speed than a driving speed of the ΔΣ modulator. An integrator;
A quantizer for converting the output from the integrator to a lower resolution than the output of the integrator, based on the output from the integrator;
A class D amplifier emulator that simulates the distortion characteristics of the output class D amplifier and outputs the feedback to the integrator;
A simulated disturbance generator that artificially generates a disturbance component;
With
The class D amplification unit emulator includes a difference signal between a digital signal after the output of the class D amplification unit is AD converted and a feedback output of the class D amplification unit emulator, a signal from the quantizer, and the simulation Based on the signal from the disturbance generator, the parameters of the simulated disturbance generator, the input signal, the output of the quantizer and the causal distortion component are identified, and the output of the class D amplification unit is converted to the AD converter. The ΔΣ modulator is characterized in that the parameter is sequentially updated so that a difference signal between the digital signal after being processed and the feedback output of the class D amplifier emulator becomes small.

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