Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
  • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
  • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
  • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
  • H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
  • H03F3/185—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices
• • 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
  • H03F3/211—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only using a combination of several amplifiers
• • 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
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/30—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor
  • H03F3/3001—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor with field-effect transistors
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/45—Differential amplifiers
  • H03F3/45071—Differential amplifiers with semiconductor devices only
  • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
  • H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2200/00—Indexing scheme relating to amplifiers
  • H03F2200/03—Indexing scheme relating to amplifiers the amplifier being designed for audio applications
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45281—One SEPP output stage being added to the differential amplifier

Definitions

• the present invention relates to a high-fidelity audio amplifier with low distortion and high efficiency of the type comprising:
• a reference voltage generator of very high linearity and low output impedance, able to receive as input the audio signal to be amplified
• a power current generator comprising a power voltage generator, the output of which is connected to the output of the reference voltage generator, through a coupling inductance;
• the patent application WO-201 1/107 669 describes the coupling of an analog class A amplifier formed of a reference voltage generator and a class D digital amplifier constituting a power voltage generator, which is coupled at the output of the reference voltage generator by an inductor, with which it then forms a current source.
• the purpose of the combination of a class A amplifier and a class D amplifier is to create an amplifier with very high efficiency and very high linearity.
• the switching losses of the MOS transistors of the class D amplifier are proportional to the switching frequency. For this reason, in practice, this frequency can not exceed significantly 500 kHz for voltages greater than 100 volts.
• the value of the output inductance of the amplifier in class D shall be as small as possible to allow a maximum current scanning rate (referred to as slew rate in English) thus allowing reproduction of the high frequencies of the spectrum. audio.
• slew rate maximum current scanning rate
• the triangular current ripple (or current ripple in English) in the inductance of the class D amplifier is inversely proportional to the switching frequency and inversely proportional to the value of the inductance.
• the high-frequency triangular current is totally absorbed and dissipated by the amplifier Class A analog, which causes significant heat dissipation and decreases system performance;
• the class A amplifier is very stressed when reproducing high frequencies, especially greater than 10 kHz.
• the object of the invention is to improve the current ratio provided by the class A amplifier to the current supplied by the class D amplifier for high frequencies, thus making it possible to reduce the heating of the class A amplifier while increasing the useful bandwidth.
• the subject of the invention is an audio amplifier of the aforementioned type, characterized in that said means for introducing, for its control, at the input of the current generator, a signal representative of the current supplied at the output of the voltage generator of reference, are suitable for introducing, in addition, a signal representative of the produces the value of the coupling inductance and the time derivative of the current supplied to the load.
• the amplifier comprises one or more of the following features:
• the means for introducing, for its control, at the input of the power current generator, a signal representative of the current output by the reference voltage generator comprises a derivative-proportional-integral regulator
• the signal representative of the product of the value of the coupling inductance and the time derivative of the current supplied to the load is the product of the value of the coupling inductance and the derivative with respect to the time of the current supplied to the load from the output;
• the means for introducing, for its control, at the input of the power current generator a signal representative of the current supplied at the output by the reference voltage generator are able to introduce, at the input of the current generator, a signal comprising at the a signal representative of the audio signal to be amplified and the product of the value of the coupling inductance and the time derivative of the current supplied to the load from the output;
• the means for introducing, for its control, at the input of the power current generator, a signal representative of the current supplied at the output by the reference voltage generator are able to introduce, as a signal representative of the current supplied at the output of the reference voltage generator, a signal comprising the product of the value of the coupling inductance and the value of the current supplied at the output of the reference voltage generator;
• said amplifier comprises means for measuring the current supplied at the output of the power voltage generator and means for calculating the value of the coupling inductance as a function of the current supplied at the output of the power voltage generator;
• said amplifier comprises, on the one hand, means for estimating the current supplied at the output of the power voltage generator from the current supplied at the output of the reference voltage generator and a signal representative of the audio signal to be amplified; and, on the other hand, means for calculating the value of the coupling inductance as a function of the current supplied at the output of the power voltage generator;
• said means for estimating the current supplied at the output of the power voltage generator comprise an integration stage of the quotient of the difference of the control signal of the power current generator and the signal representative of the audio signal to be amplified by an estimation.
• the value of the coupling inductance; the means for introducing, for its control, at the input of the current generator, a signal representative of the current supplied at the output of the reference voltage generator and a signal representative of the product of the value of the coupling inductance and the derivative. in relation to the time of the current supplied to the load comprises reintroducing the control signal of the power generator with a predetermined delay at the input of the power generator;
• the value of the coupling inductance is greater than 1 micro Henry and the means for introducing, for its control, at the input of the current generator, a signal representative of the current supplied at the output of the reference voltage generator and a representative signal of the product of the value of the coupling inductance and the time derivative of the current supplied to the load comprise only one means the reintroduction of the control signal of the power current generator with a predetermined delay at the input of the generator of power current.
• FIG. 1 is a circuit diagram of a high fidelity audio amplifier low distortion and very high efficiency according to a first embodiment of the invention
• FIG. 2 is a graph showing the value of the current supplied by the class A amplifier in the absence of the invention and during the implementation of the invention.
• FIGS. 3, 4 and 5 are the electrical diagrams of three embodiments of an amplifier according to the invention.
• the audio amplifier 10 shown in FIG. 1 comprises an input 12 able to receive an analog audio signal to be amplified V in and an output 14 for supplying the amplified signal to which a load formed of a loudspeaker 16 is connected.
• the loudspeaker 16 is connected directly, without any other resistive element, between the output 14 of the amplifier and the ground.
• the input 12 of the amplifier is adapted to receive a control voltage whose reference is the ground.
• the amplifier 10 comprises a reference voltage generator 18 of very high linearity and low output impedance forming a class A amplifier and a power source 19 forming a class D amplifier, the two outputs of which are coupled directly to form the output 14 of the amplifier.
• the power source 19 comprises a power voltage generator 20 and a coupling inductor 22 connected at the output of the voltage generator 20 and through which the voltage generator 20 is coupled to the reference voltage generator 18.
• the coupling inductance is formed of a coil having a low resistance.
• the input of the reference voltage generator 18 is connected to the input 12 of the amplifier, while the output of the reference voltage amplifier 18 is connected directly to the output 14 without the interposition of any resistive element, capacitive or inductive.
• the outputs of the voltage generators 18 and 20 are connected at a coupling point 24, the coupling inductance 22 being arranged between the output of the power voltage generator 20 and the coupling point 24.
• the coupling inductance 22 comprises two series-connected inductors 23A, 23B whose interconnection midpoint is connected to ground by a connection impedance 25.
• the total inductance of the coupling inductance 22 is between 1 micro Henry and 1 milli Henry.
• the power generator 20 is controlled by a control unit 25A.
• the reference voltage generator 18 comprises a voltage amplification stage 26 schematized by a differential amplifier whose non-inverting input is connected directly to the input 12 and whose inverting input is connected to a feedback loop 27 is connected directly to the output of the differential amplifier 26.
• the voltage amplification stage is formed, for example, of an operational amplifier mounted as a voltage follower.
• the reference voltage generator 18 is a class A amplifier having a very high linearity and a low output impedance.
• the output impedance of the reference voltage generator is less than 0.2 ohms.
• the differential amplifier 26 is powered by two direct voltages V + and V and consumes a current denoted respectively I + and I on each of these supply inputs.
• Means for measuring the current consumed 28A, 28B are provided on each of the supply inputs of the differential amplifier 26.
• These means are formed, for example, of current detectors as described in document US Pat. No. 6,937,095. They are capable of providing information representative of the current output by the reference voltage generator, the current i A supplied by the generator 18 being directly related to the current it consumes.
• the outputs of the current sensors 28A, 28B are connected to an adder 30 whose output supplies the current i A consumed by the reference voltage generator and therefore the current supplied at the output of this same amplifier.
• the control unit 25A comprises a linear regulator 32 receiving as input the current i A being connected at the output of the adder 30.
• the regulator 32 comprises a linear amplification stage 34, a bypass stage 36 and an integration stage 38 each connected in parallel and receiving as input a value representative of the sum of the currents i A consumed by the reference voltage generator. 18.
• the outputs of 34, 36 and 38 are connected to an adder 40 of the control unit 25A.
• the regulator 32 is able to output a signal representative of the current supplied by the reference generator 18.
• the regulator 32 is an integral proportional regulator (PI) integrating only a linear amplification stage 32 and an integration stage 38 without a bypass stage 36.
• the regulator 32 is a stage of derived integral proportional type (PID) comprising the three stages 34, 36 and 38.
• the summator 40 is connected by another input to the input 12, via a linear amplification stage 42 to receive the musical signal V in to be amplified.
• the power current generator 19 and therefore the power voltage generator 20 are adapted to receive as input a combination of the audio signal to be amplified V in from the input 12 and a value representative of the current i A consumed by the reference voltage generator 18.
• the power voltage generator 20 is formed in the example considered of a differential amplifier 50 mounted as a follower, and whose inverting input is connected directly to the output by a feedback loop 51. Its non-inverting input is connected to the output of the control unit 25A formed from the output of the adder 40 through a delay stage 54.
• the differential amplifier 50 consists of a class D amplifier, that is to say an amplifier of the "push / pull" type comprising, according to its amplifier branch, two transistors. MOSFET “mounted anti-series, these two transistors being driven according to a pulse width modulation law.
• the impedance 22 consists of an inductance, a resistance or a combination of both.
• the two transistors are controlled according to a sigma / delta law.
• the power voltage generator 20 consists of a class A or class AB amplifier.
• the coupling inductance 22, whether it is a coil or a resistor has a module less than ten times the load module, namely the loudspeaker 16, in the frequency range useful.
• the inductor 22 used in the case of a class AB amplifier to form the power generator 19 is less than 10 ⁇ .
• the coupling inductance has a value less than 100 ⁇ .
• control unit 25A of the current generator 19 comprises means 60 for introducing, for its control, to the input of the current generator 19, in addition to the signal representative of the current supplied at the output of the generator of reference voltage 18, a signal S L representative of the value of the coupling inductance 22.
• the output of the means 60 is connected to an input of the adder 40 for taking into account the signal S L.
• these means 60 are connected at the input to a stage 62 for measuring the current I D supplied at the output of the power voltage generator 20 and flowing through the coupling inductance 22.
• stage 62 is connected to an adder 64 of stage 60 whose other input is connected the output of the adder 30 for receiving the intensity a i output from the voltage generator 18..
• the intensity Î L OAD supplied to the load 16 at the output 14 of the amplifier is obtained the intensity Î L OAD supplied to the load 16 at the output 14 of the amplifier, this intensity being equal to the sum of the intensity i A supplied at the output of the voltage generator and the intensity i D output from the power current generator 19.
• the output of summer 64 is connected to a bypass stage with respect to time 66 capable of outputting ⁇ L0AD.
• This output is connected to a multiplier 68, whose other input terminal is connected to a stage 70 for supplying a value L (i D ) of the coupling inductance 22 as a function of the current i D passing therethrough.
• This stage 70 comprises an input adapted to receive the intensity D passing through the inductor 22, this input being connected to the measurement stage 62.
• the unit 70 is formed for example of a table of pre-recorded values suitable for providing at the output the value L (i D ) of the inductor 22 as a function of the intensity flowing in this inductance.
• the output of the calculation unit of the value of the coupling inductance 70 is connected to an input of a multiplier 72, whose other input is connected to the output of the adder 30.
• the output of the multiplier 72 is connected to the regulator input 32, allowing the regulator 32 to receive as input a signal representative of the current i A supplied at the output of the reference voltage generator 18, a signal Li A representative of the product of the value of the coupling inductance 22 and the current A i output from the reference voltage generator 18.
• V V in + L ⁇ LD is therefore a perfect estimator of the voltage to be supplied to the generator 20 to maximize the ratio -.
• the class A reference voltage generator 18 provides no current; in practice, the class A reference voltage generator merely provides a weak current intended to correct small imperfections in the implementation of each of the elementary functions (differentiator, integrator, L 22 value, etc.).
• the circuit according to the invention makes it possible to in addition, on the one hand to modulate the value of L used in the calculation of the estimator of the voltage to be supplied to the power voltage generator 20 as a function of the current passing through it, and secondly to modulate the gain of the feedback of the servocontrol by the non-linear function connecting the value of L (i D ) to its current i D passing through it, in order to to be able to maximize the gains of the servocontrol for any value of the current passing through the inductor 22 and to avoid having to designate a ratio 2 for the gain margin during the design of the amplifier only to take account of the 50% decrease the value of the coupling inductance L on the current peaks.
• the peak current of the Class A amplifier is only 150 milliamps (bottom curve) instead of the 1500 milliamps of the state of the art shown in the top curve of Figure 2.
• the dissipation in the Class A amplifier is then divided by about ten which breaks down as follows:
• the embodiment variant illustrated in FIG. 3 is devoid of measurement unit 62 of the current i D supplied at the output of the power voltage generator.
• This unit 62 is replaced by a unit 82 for estimating the current i D supplied at the output of the power voltage generator 20.
• the estimator 80 includes a first input connected at the output of the linear amplification stage 42 to receive the musical signal V in to be amplified.
• the second input is connected at the output of the control unit 25A of the power supply generator 19. This input is connected to a delay unit 84 identical to the delay unit 54.
• the unit output 84 is connected to a subtractor stage 86 whose other input is connected to the output of the linear amplification stage 42 to receive the musical signal V, M to be amplified.
• the subtractor 86 is able to calculate the difference between the control signal input to the power generator 19 delayed by a delay ⁇ and the musical signal V, M to be amplified.
• the output of the subtractor 86 is connected to the input of a divider 88 whose other input is connected to a unit 90 for calculating the value of the coupling inductance 22 as a function of the intensity passing therethrough.
• This divider 88 is able to divide the difference resulting from the subtractor 86 by the calculated inductance L.
• This quantity is introduced into an integrator 92 whose output provides an estimate of the intensity i D supplied by the reference voltage generator 20.
• the output of the integrator 92 is also connected to the input of the unit 90. estimating the value of the coupling inductance L in order to output the inductance therefrom as a function of the estimated intensity i D.
• the estimator operates here by integrating the estimated potential difference at the edges of the coupling inductance 22 and uses the current or previous value of the estimator to non-linearly calculate an estimate of the L-value as a function of the current. D through.
• the estimator 80 of the current i D is found, but the output of this estimator is no longer used at the input of the control unit 25A but only for the determination of the value L of the inductor 22 as a function of the current flowing therethrough.
• the summator 64 of Figures 1 and 3 is deleted. This is made possible since reverse integration and derivation operations are performed in units 92 and 66.
• the value L of the coupling inductance is assumed not to depend on the intensity i D through it. This is made possible since the inductance 22 is assumed to have an oversized coupling inductance value in current and for which the magnetic saturation phenomena are negligible. Alternatively, the inductor 22 can be made without the use of ferromagnetic materials (air inductance) or have a gap in its magnetic circuit. Magnetic saturation phenomena are considered negligible when they are less than 10% saturation.
• An oversized coupling inductance has a value between 0.1 ⁇ and 100 ⁇ for a current of 50A.
• the control block is simplified and the adder 40 receives as input only the control signal delayed by a delay ⁇ by the retarder 84.
• the value representative of the current supplied by the reference voltage generator introduced into the PID regulator 32 is given by the difference of the potentials measured across the inductance 22 and a complementary resistance disposed between the coupling point 24 and the output 14 according to the assembly described in the document FR 2 873 872.

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• 2014
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