WO2005018089A1 - Amplificateur audio de puissance - Google Patents

Amplificateur audio de puissance Download PDF

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Publication number
WO2005018089A1
WO2005018089A1 PCT/IB2004/051438 IB2004051438W WO2005018089A1 WO 2005018089 A1 WO2005018089 A1 WO 2005018089A1 IB 2004051438 W IB2004051438 W IB 2004051438W WO 2005018089 A1 WO2005018089 A1 WO 2005018089A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
noise
pulse
modulated
power output
Prior art date
Application number
PCT/IB2004/051438
Other languages
English (en)
Inventor
Andrea Scenini
Original Assignee
Koninklijke Philips Electronics N. V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N. V. filed Critical Koninklijke Philips Electronics N. V.
Publication of WO2005018089A1 publication Critical patent/WO2005018089A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
    • H03F3/217—Class D power amplifiers; Switching amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/331—Sigma delta modulation being used in an amplifying circuit

Definitions

  • the present invention relates to electric power amplifiers, and in particular relates to an amplifier for converting a digital audio signal into a power output signal and to a method for converting a digital audio signal into a power output signal. It is especially suited for portable electronic audio devices such as portable phones, portable CD players or portable radio receivers. Electronic audio devices require power amplifiers for electronic signals. Earlier audio devices used so-called Class-A or Class-AB power amplifiers. These are analog circuits that consume significant amounts of power and have a low efficiency of typically not more than 60 %. This is disadvantageous, especially for portable electronic audio devices such as portable phones, portable CD players or portable radio receivers, which should be small, light, powerful and power efficient. These disadvantages have been largely overcome by the so-called Class-D power amplifiers.
  • a Class-D amplifier has typically two output transistors that are operated as switches. Its power dissipation is low and its efficiency high - typically 80 to 90 % -, thus requiring less power from the power supply and smaller heat sinks for the amplifier. These are important advantages in portable battery-powered devices.
  • the classical implementation of a Class-D amplifier 101 is shown in Figure 1.
  • An analog input audio signal to be amplified is fed into the amplifier 101 via an input line 102.
  • the amplifier 101 uses a pulse- width-modulation (PWM) configuration, i.e., consists of an analog PWM stage 104 and a power output stage 105.
  • the PWM stage 104 comprises a comparator 143 with two input lines 141, 142.
  • a first input line 141 is for the analog audio input signal.
  • a second input line 142 is connected to an output of a clock 144 generating a reference signal 145, typically a triangle or sawtooth wave, with a reference frequency fk which is much higher than the frequency of the audio input signal.
  • the output of the comparator 143 is used to drive the power output stage 105 comprising two transistors 151 and 152, e.g., metal-oxide- semiconductor field-effect transistors (MOSFETs), which operate as switches.
  • Gate drivers 153 and 154 may be connected in series to the gates of the transistors 151, 152.
  • An output line 106 is for the amplified pulse-width-modulated output signal.
  • a passive low-pass filter (not shown) is typically used for filtering out the reference frequency f R , its harmonics and frequency bands around these frequencies.
  • an amplified analog audio signal is reconstructed that can be used for driving a load, e.g., a loudspeaker (not shown).
  • the load may be a part of the low-pass filter.
  • the disadvantage of the Class-D amplifier 101 shown in Fig. 1 is that the input audio signal must be analog.
  • DECT digital-enhanced-cordless- telecommunications
  • PCM pulse-code-modulated
  • D/A stage normally a high-performance one
  • D/A stage normally a high-performance one
  • the analog PWM modulator 104 must be transferred to the digital domain. It is impossible to simply use a digital PWM since the reference frequency required to generate the modulation signal would become too high.
  • a circuit 101 ' of this type is shown in Figure 2. It consists of a noise-shaping stage 103 comprising a sigma-delta noise shaper 132, and a power output stage 105 as described with reference to Fig. 1. An interpolator 131 is connected in series to the input of the sigma-delta noise shaper 132.
  • the main disadvantage of this circuit 101' is the fact that, in order to obtain the same signal-to-noise ratio (SNR) at the input and at the output of the noise-shaping stage 103, a high oversamplmg ratio K is needed, ending with a high switching frequency of the output MOSFETs 151, 152.
  • SNR signal-to-noise ratio
  • K oversamplmg ratio
  • Eq. (1) has to be modified to take into account the noise-shaping effect.
  • the power amplifier shall be small, light, powerful and power efficient; its bitstream frequency shall be so low that it can be processed by the MOSFETs in the output stage.
  • Advantageous embodiments of the invention are defined in the dependent claims.
  • the invention is based on the idea to depart from the classical Class-D amplifier, to adopt its advantageous qualities and to improve its characteristics by remaining in the digital domain. This is achieved by introducing the following steps: 1.
  • the N-bit-long PCM input signal is upsampled by an inte ⁇ olator and noise shaped by a sigma-delta noise shaper.
  • the noise-shaped signal is used as an input for a digital PCM/PWM converter.
  • the output signal of the PCM/PWM converter is fed into a power output stage.
  • the amplifier according to the invention for converting a digital audio signal into a power output signal comprises a noise-shaping stage for noise-shaping the digital audio signal, thus providing a pulse-code-modulated noise-shaped signal; a PCM/PWM converter stage for converting said pulse-code-modulated noise-shaped signal into a pulse-width-modulated signal; and a power output stage for converting said pulse-width-modulated signal into a power output signal.
  • the method according to the invention for converting a digital audio signal into a power output signal comprises the steps of noise-shaping the digital audio signal, thus providing a pulse-code-modulated noise-shaped signal; converting said pulse-code-modulated noise-shaped signal into a pulse-width-modulated signal; and converting said pulse-width-modulated signal into a power output signal.
  • Fig. 1 shows a block diagram of a classical Class-D power amplifier according to the prior art.
  • Fig. 2 shows a block diagram of an improved Class-D power amplifier according to the prior art.
  • Fig. 3 shows a flow diagram of the method according to the invention.
  • Fig. 4 shows a block diagram of the power amplifier according to the invention.
  • the method according to the invention is schematically illustrated in the flow diagram of Figure 3.
  • the block diagram of the power amplifier 1 according to the invention is shown in Figure 4.
  • the PCM audio input signal is supposed to have N bits and a sampling frequency f s . This input signal is fed via an input line 2 into a first, noise-shaping stage 3 of the power amplifier 1.
  • the noise-shaping stage 3 comprises an inte ⁇ olator 31 for upsampling the sampling frequency to K-fs, where K is the oversampling ratio.
  • the noise-shaping stage 3 further comprises a sigma-delta noise shaper 32 which reduces the quantization noise in the audio band by pushing the quantization noise out of the audio band towards higher frequencies.
  • the noise-shaped signal has then M bits, with 1 ⁇ M ⁇ N, and a sampling frequency K-fs. In other words, the noise-shaping stage 3 increases the sampling frequency, decreases the number of bits and reduces the noise in the audio band.
  • the noise-shaped signal is fed via an input line 41 into a second, PCM/PWM converter stage 4.
  • This stage 4 comprises a counter 44 which provides on a reference input line 42 a reference signal with a reference frequency f R , and a comparator 43 for comparing the PCM input signal with the counter signal.
  • the reference frequency must be at least f > 2 M -K-fs.
  • the PWM signal on a PWM output line 46 is then used to drive a power output stage 5, just like in a conventional Class-D amplifier.
  • the output stage 5 comprises two gate drivers 53, 54 connected in series to two transistors 51, 52, respectively, which are preferably MOSFETs.
  • a numerical example will be considered for the power amplifier 1 according to the invention, comprising a 2 nd order noise shaper 32.
  • M 6 bit at the noise-shaper output
  • K 18.
  • the invention is suitable for all devices that require an audio power output stage and high efficiency, e.g., portable electronic audio devices.
  • CMOS complementary metal-oxide-semiconductor
  • the amplifier is as much as possible digital; the "analog" part is limited to the design of the output MOSFETs and their gate drivers.
  • the amplifier can be made small, light, powerful and power efficient. This is achieved by processing the PCM input signal in the digital domain.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

Cet amplificateur (1) de conversion de signaux audionumériques en signaux de puissance de sortie comprend un étage (3) de mise en forme du bruit avec un convertisseur sigma-delta (32) pour mettre en forme les signaux audionumériques et donner ainsi des signaux mis en forme à modulation par codage d'impulsions. Un étage convertisseur subséquent (4) à modulation par codage d'impulsions ou à modulation d'impulsions en largeur convertit les signaux mis en forme à modulation par codage d'impulsions en signaux à modulation d'impulsions en largeur. Un étage subséquent de puissance de sortie (5) convertit les signaux à modulation d'impulsions en largeur en signaux de puissance de sortie. Cet amplificateur de puissance (1) est autant que possible numérique. Il est petit, léger, puissant et a une faible consommation d'énergie. Il est particulièrement approprié pour des dispositifs audio électroniques portatifs tels que des téléphones cellulaires.
PCT/IB2004/051438 2003-08-18 2004-08-10 Amplificateur audio de puissance WO2005018089A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP03102575.2 2003-08-18
EP03102575 2003-08-18

Publications (1)

Publication Number Publication Date
WO2005018089A1 true WO2005018089A1 (fr) 2005-02-24

Family

ID=34178577

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2004/051438 WO2005018089A1 (fr) 2003-08-18 2004-08-10 Amplificateur audio de puissance

Country Status (1)

Country Link
WO (1) WO2005018089A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1028524A1 (fr) * 1999-02-11 2000-08-16 STMicroelectronics S.r.l. Amplificateur de puissance à modulation de largeur d'impulsion avec une entrée pour un signal numérique
EP1050971A2 (fr) * 1999-05-07 2000-11-08 Motorola, Inc. Méthode et appareil pour produire un signal modulé en largeur d'impulsion
US6414613B1 (en) * 2000-01-05 2002-07-02 Motorola, Inc. Apparatus for noise shaping a pulse width modulation (PWM) signal and method therefor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1028524A1 (fr) * 1999-02-11 2000-08-16 STMicroelectronics S.r.l. Amplificateur de puissance à modulation de largeur d'impulsion avec une entrée pour un signal numérique
EP1050971A2 (fr) * 1999-05-07 2000-11-08 Motorola, Inc. Méthode et appareil pour produire un signal modulé en largeur d'impulsion
US6414613B1 (en) * 2000-01-05 2002-07-02 Motorola, Inc. Apparatus for noise shaping a pulse width modulation (PWM) signal and method therefor

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
ANTUNES V M E ET AL: "Harmonic distortion reduction in multi-level PWM modulators for audio power amplifiers", IECON-2002. PROCEEDINGS OF THE 28TH. ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY. SEVILLA, SPAIN, NOV. 5 - 8, 2002, ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY, NEW YORK, NY : IEEE, US, vol. VOL. 1 OF 4. CONF. 28, 5 November 2002 (2002-11-05), pages 852 - 857, XP010633268, ISBN: 0-7803-7474-6 *
R.E. HIORNS, J.M. GOLBERG, M.B. SANDLER: "Realizing an all digital Power Amplifier", 89TH CONVENTON OF THE AUDIO ENGINEERING SOCIETY, 21 September 1990 (1990-09-21), LOS ANGELES, XP002304267 *
SMEDLEY K M: "Digital-PWM audio power amplifiers with noise and ripple shaping", POWER ELECTRONICS SPECIALISTS CONFERENCE, PESC '94 RECORD., 25TH ANNUAL IEEE TAIPEI, TAIWAN 20-25 JUNE 1994, NEW YORK, NY, USA,IEEE, 20 June 1994 (1994-06-20), pages 566 - 570, XP010549387, ISBN: 0-7803-1859-5 *

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