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WO1993018582A1 - Commande d'amplificateurs - Google Patents

Commande d'amplificateurs Download PDF

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Publication number
WO1993018582A1
WO1993018582A1 PCT/GB1993/000489 GB9300489W WO9318582A1 WO 1993018582 A1 WO1993018582 A1 WO 1993018582A1 GB 9300489 W GB9300489 W GB 9300489W WO 9318582 A1 WO9318582 A1 WO 9318582A1
Authority
WO
WIPO (PCT)
Prior art keywords
amplifier
output stage
signal
current
linear
Prior art date
Application number
PCT/GB1993/000489
Other languages
English (en)
Inventor
Keith Jones
Original Assignee
Keith Jones
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 Keith Jones filed Critical Keith Jones
Priority to AU36437/93A priority Critical patent/AU3643793A/en
Publication of WO1993018582A1 publication Critical patent/WO1993018582A1/fr

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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
    • H03F1/30—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters
    • H03F1/307—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in push-pull 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
    • H03F3/3069—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor the emitters of complementary power transistors being connected to the output
    • H03F3/3071—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor the emitters of complementary power transistors being connected to the output with asymmetrical driving of the end stage

Definitions

  • the invention relates to methods and apparatus for controlling amplifiers, in particular but not exclusively for reducing distortion in electronic audio amplifiers.
  • One particular area of distortion in electronic amplification is caused by temperature effects upon the quiescent current in the amplifier, that is to say changes in ambient temperature (or even heat generated by elements within the amplifier itself) may cause alterations in the operational characteristics of the amplifier.
  • an increase in the temperature of an active component, for example a transistor, in an amplifier will mean that for a given voltage thereacross the component will carry more current.
  • the increase in current passing through the component will lead to a further increase in temperature in the device again increasing the current which can be taken by the device leading, in a cyclical manner, to the effect known as Thermal Run Away.
  • FIG. 1 shows the output stage of a class A-B amplifier to include transistors 10 and 12 emitter coupled to provide an output at 14 to a load 16.
  • the output stage comprising transistors 10 and 12, is driven by a driver 18 passing a signal at 20 across a resistor 22 coupled to the bases of transistors 10 and 12.
  • resistor 22 provides a quiescent bias for transistors 10 and 12 maintaining them conductive.
  • the circuit further includes resistors 24 and 26 coupled in the emitter paths of transistors 10 and 12.
  • the resistors 24 and 26 are shunted by capacitors 28 and 30 as shown in an attempt to keep the impedance of the stage as low as possible.
  • Such an arrangement protects the output stage from the effects of quiescent current variation and in particular from Thermal Run Away effectively by limiting the quiescent or steady state current passing through transistors -10 and 12.
  • this proposal introduces difficulties in the operation of the amplifier and in particular introduces distortion to the output signal provided by the amplifier.
  • the resistors 24 and 26 will react to increase other forms of distortion - particularly that known as Cross Over Distortion (one of the transistors 10 and 12 stops acting as an amplifier before the other transistor 12 or 10 has started to amplify).
  • Cross Over Distortion one of the transistors 10 and 12 stops acting as an amplifier before the other transistor 12 or 10 has started to amplify.
  • Objects of the present invention include the provision of a method of operating an amplifier, and an amplifier, in which flow of quiescent current through the output stage of the amplifier is controlled.
  • the present invention provides a method of operating an amplifier with an output stage to which an input signal is fed to generate an output signal for a load, which method comprises the steps of monitoring current level in the output stage of the amplifier, generating a signal in response to the monitored level and applying the generated signal so as to modify the signal input of the output stage thereby to prevent the quiescent current in that stage falling below a predetermined level.
  • the generated signal may be applied to modify the signal input to the output stage whilst the quiescent current in that stage is above said minimum level will act to maintain said quiescent current at a pre-set level.
  • the invention provides an amplifier having an output stage for providing an output signal to a load in response to an input signal fed thereto, and means for monitoring current in the output stage and generating a control signal which is used to modify the signal to input to the output stage , so as to prevent the quiescent current in the output stage falling below a predetermined level.
  • the generated control signal may be fed to the input of the output stage.
  • the monitoring means is preferably located in the current path of the output stage remote from the signal path.
  • the monitoring means is desirably operable to modify the quiescent current in the output stage whilst that current is below the predetermined level to maintain the quiescent current at said desired pre-set level.
  • the monitoring means is with advantage arranged to be substantially disabled if current in the output stage of the amplifier exceeds a second predetermined level.
  • Means may be provided for isolating the control signal generated by the monitoring means from alternating signals.
  • the monitoring means includes a resistive or other linear element in the current path of the output stage across which a control voltage is developed, which control voltage is used to modify the signal" input to the output stage so as to prevent the quiescent current in the output stage falling below said second predetermined level.
  • the control voltage is preferably used to effect negative feedback and maintain the quiescent current in the output stage at said desired pre-set level.
  • the monitoring means may further include, in parallel with the resistive or other linear element, an element having a non-linear response to an applied potential which non-linear element is operable to provide substantially zero resistance to current flow should the voltage across the resistive or other linear element exceed a predetermined value.
  • One amplifier embodying the invention comprises a pair of amplifying elements coupled together and to respective potential voltage supplies, and wherein the output of the amplifier is taken from the coupled amplifying elements, wherein the circuit coupling at least one of the amplifying elements to a potential voltage supply includes a shunted pair of linear and non-linear elements across which is generated the control voltage applied to the input signal fed to said amplifying elements.
  • This embodiment may be implemented by a pair of transistors the emitters of which are coupled together and the collectors of which are coupled to respective potential voltage supplies, wherein the output of the amplifier is taken from the coupled emitters of the two transistors, and wherein the collector circuit of at least one of the transistors includes a shunted pair of linear and non-linear elements across which is generated the control voltage applied to the input signal fed to the bases of said transistors.
  • the or each of shunted pair of linear and non- linear_elements respectively may comprise a resistor and a diode.
  • the bases of the emitter-coupled transistors are preferably coupled across biasing means to which the input signal is applied; the biasing means may comprise a resistor.
  • the input signal is advantageously applied to the resistor coupling the bases of the emitter-coupled transistors via the: base-collector path of a further transistor to the emitter of which is applied the control voltage developed across the said at least one shunted pair of linear and non-linear elements.
  • the input signal may also advantageously be applied to the resistor coupling the bases of the emitter- coupled transistors via the base-collector paths of two further transistors to the emitters of which are applied control voltages developed across shunted pairs of linear and non-linear elements in the respective collector circuits of each of the emitter-coupled transistors.
  • the or each path carrying a control voltage to the emitter of the or each further transistor includes means for reducing AC feedback; said means for reducing AC feedback may be provided by a resistor in the emitter path of the or each further transistor and a capacitor coupling the or each emitter to a respective supply rail.
  • the control voltage is preferably operable to effect change in the generating conditions of the output stage.
  • FIG. 2 schematically illustrates the method and apparatus of the present invention.
  • Figure 3 illustrates a first amplifier embodying the invention.
  • FIG. 4 illustrates a further amplifier embodying the present invention
  • Figure 5 illustrates another amplifier embodying the present invention.
  • Figure 2 schematically shows the output stage of an amplifier coupled between positive and negative voltage supply rails 100 and 102, in particular having coupled thereacross two output devices 104 and 106.
  • devices 104 and 106 are Bi-polar transistors (although any other form of active amplifying device e.g. Field Effect Transistors S.C.R or the like may be used).
  • the emitters of the devices 104 and 106 are coupled as shown and provide an output at 108 to a load 110.
  • a transistor 112 is fed to the base of a transistor 114 the collector of which is coupled to positive supply rail 100 by a voltage divider 116, 118; whilst its emitter is coupled to a current monitoring device 120 in the collector path of the transistor 106.
  • Current monitoring device 120 monitors the quiescent current in the collector path of transistor 106 and provides a voltage which is fed to the emitter of the transistor 114. In the steady state - with no signal or an invarient signal fed to the base of transistor 114 - a stable voltage is be developed across resistor 118. This acts to provide the quiescent or bias current required by transistors 104 and 106 to maintain their operation. This current is monitored by device 120 and any increase in the collector current of transistor 106 will cause the current monitoring device 120 to increase the voltage at the emitter of transistor 114.
  • the current monitoring device ' - ⁇ will, in response to changes in the collector current of transistor 106 act to generate a voltage fed to the emitter of 114 which will maintain the quiescent current in the output stage of the amplifier at a generally desired, pre-set, level.
  • the current monitoring device 120 is arranged, should an alternating current signal be applied to input 112, to be effectively disabled.
  • FIG. 3 illustrates one implementation of the device 120 in accordance with the invention. Parts of the
  • the signal input to the amplifier at 112 is fed to the base of transistor 114 via a capacitor 122 coupled to the negative supply rail 102 by
  • any constant current source could be used at this position to ensure that a steady quiescent or steady state voltage is applied to the base of transistor 114 to cause this transistor to develop
  • the monitoring circuit 120 (shown within the dotted lines) comprises a resistor 128 and diode 130 coupled in parallel in the collector path of transistor 106.
  • the current monitoring device 120 presents an impedance to current flow in the collector path of transistor 106 which is essentially linear when that current flow is near or below a first predetermined level. It will be seen that as current flow through transistors 104 and 106, and therefore in the collector path " of transistor 106 increases, the voltage across resistor 128 will increase driving the voltage at the emitter of transistor 114 up. As the steady state voltage at the base of transistor 114 is constant, the collector current through transistor 114 reduces and the voltage across resistor 118 also reduces. This in turn acts to reduce current flow through transistors 104 and 106.
  • the current monitoring device 120 acts to provide negative feedback controlling the quiescent current in the output stage of the amplifier.
  • resistors 132 and 136 and capacitor 134 provide alternating current isolation of the signal from the current monitoring device 120 to the emitter of transistor 114. These components, however, will also reduce, to an extent, the effectiveness of the arrangement in controlling quiescent current changes caused by temperature variations.
  • This control may be restored by modifying the amplifier such as is shown in Figure 5.
  • the emitter circuit of transistor 114 includes the arrangement shown in Figure 4 - that is to say the current monitoring device 120 and AC isolation elements 132 and 134 and emitter bias resistor 136 as shown. Between resistors 140 and 142 a further tap is taken to the base of a transistor 114' the emitter circuit of which includes a current monitoring device 120* including a resistor 128* and diode . ,130', AC isolation elements 132' and 134* as shown and an emitter bias resistor 136'.
  • any variation in the collector current of transistor 106 will be mirrored by an equivalent variation in the collector current in transistor 104 the variation in potential voltages applied to the emitter of transistors 114 by monitoring device 120 will be substantially equal to the variation in potential applied to the emitter of transistor 114' by monitoring device 120'.
  • transistor(s) 114 may be replaced by any amplifying or voltage level shifting device operable to achieve the desired effects. Such devices may comprise thermionic valves. Unipolar or Bipolar devices; for example including FET's, MOSFET's and transistor SCR's.
  • the resistor 118 may be replaced with any suitable device, which will generate sufficient potential voltage across its terminals to provide bias for the desired transistors 104 and 106.
  • the resistor may be replaced by any suitable combination of resistive, resistive/semiconductor or semiconductor/semiconductor elements or by a constant current source.
  • embodiments of the invention provide a current monitoring device operable to maintain the quiescent current level in the output stage of an amplifier above a predetermined level - and which moreover provides feedback tending to drive that quiescent current level to a pre-set desired level.
  • the monitoring means furthermore has a reduced, substantially zero, effect when a varying signal is applied to the amplifier.
  • the current monitoring circuit effectively provides two stage control of current flow in the output stage of the amplifier.

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

Abstract

L'invention concerne un procédé de commande d'un amplificateur, et un amplificateur présentant un étage de sortie recevant un signal d'entrée et générant un signal de sortie, qui de plus consiste à surveiller le courant de repos de l'étage de sortie et à commander l'entrée de l'étage de sortie en réponse au niveau surveillé pour éviter que le courant de repos ne tombe au dessous d'un niveau prédéterminé. La surveillance du courant s'effectue dans le chemin du courant de l'étage de sortie distant du chemin du signal et fait en sorte qu'une tension soit fournie négativement à l'entrée de l'étage pendant que le courant de repos de l'étage est inférieur à un second niveau prédéterminé, de manière à maintenir le courant de repos dans l'étage à un niveau pré-réglé. L'amplificateur décrit comprend une paire de transistors à couplage par les émetteurs dont les collecteurs sont couplés à des pôles d'alimentation en courant continu; le circuit collecteur de l'un ou des deux transistors comprend une paire d'éléments linéaire (résistifs) et non-linéaire (diode) pontés à travers lesquels la tension de retour se propage. Le signal d'entrée est fourni aux bases des transistors par une résistance excitée via le ou les chemins base-collecteur d'un ou de plusieurs transistors à l'émetteur desquels (de chacun) la tension de retour est appliquée. Le chemin, ou chaque chemin, portant la tension de retour comprend une résistance et un condensateur est prévu pour coupler l'émetteur de l'autre ou de chaque autre transistor à un pôle d'alimentation respectif, pour isoler en courant alternatif le dispositif.
PCT/GB1993/000489 1992-03-11 1993-03-09 Commande d'amplificateurs WO1993018582A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU36437/93A AU3643793A (en) 1992-03-11 1993-03-09 Controlling amplifiers

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9205295.0 1992-03-11
GB929205295A GB9205295D0 (en) 1992-03-11 1992-03-11 Controlling amplifiers

Publications (1)

Publication Number Publication Date
WO1993018582A1 true WO1993018582A1 (fr) 1993-09-16

Family

ID=10711918

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1993/000489 WO1993018582A1 (fr) 1992-03-11 1993-03-09 Commande d'amplificateurs

Country Status (2)

Country Link
GB (1) GB9205295D0 (fr)
WO (1) WO1993018582A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0720354A3 (fr) * 1994-12-28 1998-12-09 Thomson Consumer Electronics, Inc. Circuit de polarisation d'étage de sortie avec efficacité et stabilité améliorées
EP1638205A1 (fr) * 2004-09-16 2006-03-22 Deere & Company Circuit d'attaque
WO2010071876A1 (fr) * 2008-12-19 2010-06-24 Qualcomm Incorporated Amplificateur de classe ab muni de circuits résistifs de rétablissement du niveau zéro

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1033704A (en) * 1962-10-01 1966-06-22 Marconi Wireless Telegraph Co Improvements in or relating to transistor amplifiers
DE2822037B1 (de) * 1978-05-20 1979-11-15 Braun Ag Schaltungsanordnung zur Regelung des Arbeitspunktes bei einem Gegentakt-B-Verstaerker

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1033704A (en) * 1962-10-01 1966-06-22 Marconi Wireless Telegraph Co Improvements in or relating to transistor amplifiers
DE2822037B1 (de) * 1978-05-20 1979-11-15 Braun Ag Schaltungsanordnung zur Regelung des Arbeitspunktes bei einem Gegentakt-B-Verstaerker

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 6, no. 55 (E-62)(727) 16 April 1981 *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0720354A3 (fr) * 1994-12-28 1998-12-09 Thomson Consumer Electronics, Inc. Circuit de polarisation d'étage de sortie avec efficacité et stabilité améliorées
KR100405223B1 (ko) * 1994-12-28 2004-02-25 톰슨 콘슈머 일렉트로닉스, 인코포레이티드 빔주사속도변조구동기회로
EP1638205A1 (fr) * 2004-09-16 2006-03-22 Deere & Company Circuit d'attaque
WO2010071876A1 (fr) * 2008-12-19 2010-06-24 Qualcomm Incorporated Amplificateur de classe ab muni de circuits résistifs de rétablissement du niveau zéro
CN102257727A (zh) * 2008-12-19 2011-11-23 高通股份有限公司 具有电阻式电平移位电路的ab类放大器
KR101269349B1 (ko) * 2008-12-19 2013-05-29 퀄컴 인코포레이티드 저항성 레벨-쉬프팅 회로를 구비한 클래스 ａｂ 증폭기
US8536947B2 (en) 2008-12-19 2013-09-17 Qualcomm Incorporated Class AB amplifier with resistive level-shifting circuitry

Also Published As

Publication number Publication date
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