Classifications

• • 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
  • H03F3/301—CMOS common drain output SEPP amplifiers
  • H03F3/3016—CMOS common drain output SEPP amplifiers with symmetrical driving of the end stage
  • H03F3/3018—CMOS common drain output SEPP amplifiers with symmetrical driving of the end stage using opamps as driving stages

Definitions

• the present invention relates to a "push / pull" type amplifier, and in particular a Class A audio amplifier, of the type comprising an input and an output, comprising:
• a main amplification branch comprising two amplification transistors anti-series connected between two supply voltages, the output of the amplifier being connected between the two transistors, and
• control circuit for each amplification transistor connected to the input for receiving each input the signal to be amplified.
• the audio amplifiers are classified into several categories, which correspond to different amplification modes leading to performances in terms of power and quality different.
• the class A amplifiers are such that the active amplification elements, consisting of transistors, are constantly on and therefore always operate in linear mode. This makes it possible to obtain a good quality of the output signal but limits the output power.
• Class B amplifiers on the other hand, have amplification elements that operate in linear mode for only half the time and are substantially off the other half of the time. These amplifiers suffer from switching distortions that impair the quality of the amplified signal.
• Class AB amplifiers also exist in which the amplifying elements can switch from an on state to a off state so that the amplifier is effectively class A for low powers, and class B for higher powers. In this case the power of the amplifier is relatively small to have a high linearity.
• class D amplifiers are known in which the transistors operate "all or nothing", and are controlled by a pulse width modulation which depends on the signal to be amplified.
• the power of the amplifier is very high but the signal quality is often poor.
• the object of the invention is to propose a "push / pull" type amplifier which makes it possible to obtain a high power, an amplified signal of good quality and a low static dissipation of energy.
• the subject of the invention is a push / pull amplifier of the aforementioned type, characterized in that the main amplification branch comprises, between each transistor and the output, a non-linear response member and input means, at the input of the control circuit of each transistor, of a signal of nonlinear compensation adapted to impose in the linear response member the flow of a minimum current.
• the amplifier comprises one or more of the following features:
• said non-linear response member is a diode
• said non-linear response member is a MOS transistor
• the means for introducing the non-linear compensation signal comprise:
• a second nonlinear member identical to said nonlinear member connected between a corresponding terminal of said nonlinear member and a current source imposing a current in said second nonlinear member
• a voltage measuring branch connected to the other terminal of the second nonlinear member, which voltage measuring branch is connected to the control circuit for providing said nonlinear compensation signal;
• the means for introducing the non-linear compensation signal comprise: a voltage source having a terminal connected between each amplification transistor and the non-linear response member, and
• a voltage measuring branch connecting the other terminal of the voltage source to the control circuit of the transistor
• the amplifier comprises a linear feedback loop connecting the current output to the input of each control circuit
• the voltage measuring branches and the linear feedback loop are connected together at the input of the control circuit
• the value of the resistance of the voltage measurement loop is at least 100 times greater than the value of the resistance of the linear feedback loop
• each control circuit comprises an operational amplifier whose non-inverting input is connected to the input of the amplifier and whose inverting input is connected to the means for introducing the non-linear compensation signal.
• FIG. 1 is a diagram of the amplification circuit of the "push / pull" type according to the invention.
• FIG. 2 is a view illustrating different currents at different points of the circuit of FIG. 1 and showing non-blocking of the amplification elements.
• the amplifier 10 of the "push / pull" type comprises an input 12 for an audio signal to be amplified and an output 14 for the amplified signal.
• This output 14 is connected to a loudspeaker 16 forming a charge for the amplifier symbolized in the form of a resistor.
• the input 12 of the amplifier is adapted to receive a control voltage whose reference is ground and which comes from a sound reproduction system shown schematically by the generator 17 in FIG.
• the "push / pull” amplifier comprises two amplification transistors 18, 20 of type “MOSFET” connected in anti-series in a main branch amplifier connected between two bus DC voltages V + and V .
• the drain of each transistor 18, 20 is respectively connected to the voltage V + and V" and their sources connected together to the output of amplifier 14.
• each transistor 18, 20 is connected to the output of a control follower circuit 22, 24 each having an operational amplifier 26, 28 whose non-inverting input is connected directly to the input 12 of the amplifier.
• a feedback loop 30, 32 is connected between the output 14 of the amplifier and the inverting output of the operational amplifier respectively 26 and 28.
• These loops respectively comprise a resistor 34, 36 of the same value. This resistance is chosen relatively low value, preferably less than 1 MOhms and for example equal to 330 Ohms.
• the main amplification branch comprises, between the source of each transistor 18, 20 and the output 14 of the amplifier, a non-linear member 38, 40 and means 42, 44 provide a reference value of the voltage across the non-linear member for the introduction of a non-linear compensation signal adapted to ensure the circulation in the non-linear member 38, 40 of the main amplification branch of a predetermined value current.
• the non-linear members 38, 40 are each formed of a diode.
• the anode of the diode 38 is connected to the source of the transistor 18 and its cathode is connected to the output 14.
• the anode of the diode 40 is connected to the output 14 and its cathode is connected to the source of the transistor 20.
• the means for introducing a compensation signal 42, 44 are integrated in the feedback loop 30, 32 of the operational amplifiers 26, 28.
• This diode 46, 48 is connected to the drain of each transistor 18, 20 in an orientation identical to that of the corresponding diode 38, 40. Its other end is connected to a current source 50, 52 of opposite directions imposing through the diode 46, 48 associated with a constant current of low intensity preferably less than 100 milliamps and by example of 10 milliamperes.
• the diode 46 has its anode connected to the anode of the diode 38, its cathode being connected to the current source 50 while the diode 48 has its cathode connected to the cathode of the diode 40, its anode being connected to the current source 52.
• a coupling resistor 54, 56 respectively connects the cathode of the diode 46, and the anode of the diode 48 to the feedback loop respectively 30, 32 of the operational amplifiers 26, 28. These resistors are suitable for injecting into the feedback loop 30, 32 the voltage across the diodes 46, 48.
• the other terminal of the resistors 54, 56 is connected to the non-inverting input of the operational amplifiers 26, 28.
• the presence of the diodes 38 and 40 which constitute non-linear members prevents the intensity in the transistors 18 and 20 from being zero, whatever the output current of the amplifier. Indeed, when the current passes essentially through one of the transistors, the other transistor has an intensity therethrough which is non-zero and converges to a current value equal to that of the current source 50, 52, because the regulation imposed by the counter-reaction loop on the current flowing in the non-linear element in the main amplification branch.
• the diodes 46, 48, traversed by the currents imposed by the current sources 50, 52 provide the reference role for correcting the control circuits of the transistors 18, 20 through the feedback loop 32, 34 a value compensation circuit guaranteeing the circulation in the diodes 38, 40 of the main branch of amplification of a minimum current.
• the resistor 54, 56 is much greater and in particular at least a hundred times greater than the value of the resistors 34, 36.
• the value of the resistors 54, 56 is for example equal to 100 kOhms.
• the diodes 46, 48 and the current sources 50, 52 are replaced by a voltage source arranged in place of the diodes 46, 48, the diodes 38, 40 remaining in place as well as the resistors 54, 56. In this case, the current flowing through the transistors 18, 20 converges to zero without ever reaching this value.
• the current sources 50, 52 are retained and the diodes 38, 40, 46, 48 are each replaced by a MOSFET transistor whose gate is connected to the drain.
• a MOSFET transistor whose gate is connected to the drain.
• Such a transistor then has a non-linear response, such as a diode thus ensuring operation of the circuit as in the previous embodiments. It can be seen in FIG.
• the current flowing in the diodes 38 and 40 illustrated by the curves 238 and 240 has, over half of the period of the signal illustrated by 240A, a substantially sinusoidal shape and on the other half of the period illustrated by 240B, a continuously differentiable portion of between 2 and 15 milliamps, without this value never vanishing, which guarantees the absence of blocking of the transistor in series with the diode.
• Such an amplifier thus allows to have a high power while ensuring a good quality of the output signal, none of the transistors never being blocked and a low static dissipation of energy.
• reference diodes 46, 48 traversed by an imposed current allows the current to be fixed through diodes 38, 40 and therefore transistors 18 and 20 without knowing the temperature evolution curves of the diodes used.
• Such an amplifier is particularly suitable for high fidelity but also finds application in any type of amplifier requiring a high linearity such as a radio amplifier, a medical imaging amplifier or a source amplifier.

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• Power Engineering (AREA)
• Amplifiers (AREA)

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• 2010
  • 2010-03-16 US US13/582,312 patent/US9257949B2/en not_active Expired - Fee Related
  • 2010-03-16 WO PCT/FR2010/050470 patent/WO2011107670A1/fr active Application Filing
  • 2010-03-16 EP EP10716397A patent/EP2543140A1/de not_active Withdrawn
  • 2010-03-16 JP JP2012555461A patent/JP5647272B2/ja not_active Expired - Fee Related
  • 2010-03-16 KR KR1020127025632A patent/KR20130053394A/ko not_active Application Discontinuation
  • 2010-03-16 CN CN201080066545.2A patent/CN102906999B/zh not_active Expired - Fee Related
  • 2010-03-16 BR BR112012022178A patent/BR112012022178A2/pt not_active Application Discontinuation

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