EP1125360A2 - Amplificateur de sortie video - Google Patents

Amplificateur de sortie video

Info

Publication number
EP1125360A2
EP1125360A2 EP99950509A EP99950509A EP1125360A2 EP 1125360 A2 EP1125360 A2 EP 1125360A2 EP 99950509 A EP99950509 A EP 99950509A EP 99950509 A EP99950509 A EP 99950509A EP 1125360 A2 EP1125360 A2 EP 1125360A2
Authority
EP
European Patent Office
Prior art keywords
output
voltage
transistor
current
dynamic
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP99950509A
Other languages
Danish (da)
German (de)
English (en)
Inventor
Erik Albert Jensen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Bang and Olufsen AS
Original Assignee
Bang and Olufsen AS
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 Bang and Olufsen AS filed Critical Bang and Olufsen AS
Publication of EP1125360A2 publication Critical patent/EP1125360A2/fr
Withdrawn legal-status Critical Current

Links

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
    • H03F3/3066—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor the collectors of complementary power transistors being connected to the output
    • H03F3/3067—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor the collectors of complementary power transistors being connected to the output with asymmetrical driving of the end stage
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/189—High-frequency amplifiers, e.g. radio frequency amplifiers
    • H03F3/19—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/148—Video amplifiers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/648—Video amplifiers

Definitions

  • a video output amplifier is a video output amplifier.
  • the invention relates to a video output amplifier for conversion of an intensity signal consisting of a static and a dynamic component into a control voltage for an electron gun in a cathode ray tube, comprising a first voltage supply with a voltage corresponding to the operating characteristics of the cathode ray tube, an input terminal for the video signal and an output terminal for the control voltage. It is a purpose of the invention to provide a video output amplifier of this type in which the power loss is reduced considerably in comparison to known constructions in order that particular cooling means, such as cooling fins, may be avoided.
  • Cathode ray tubes are in general use in television receivers as well as in monitors for computer installations or personal computers, and video output amplifiers are used for driving such CRTs.
  • Video output amplifiers are known and in practice comprise an output stage, the output terminal of which delivers a control voltage which is intended to control an electron beam in a CRT by modulating a suitably high voltage on the cathode.
  • the bandwidth of the output signal is up to 5 MHz in generally known circuits for television. Discussions regarding television in the present text may be directly transferred to monitors and other equipment with a ca- thode ray tube.
  • the control voltage may be divided into two components: a static or only slowly varying component which contains the momentarily static intensities and slower intensity variations, and a dynamic component which contains the fast intensi- ty variations.
  • the input signal to the video output amplifier is provided by a signal processing circuit with output voltages in the range from +1 V to +6 V, while the output signal from the video output amplifer correspondingly is in the range +150 V to +50 V which means that a video output amplifier for use in connection with television must have a supply voltage in the range +200 V.
  • the fastest intensity variations in the output signal are ca . 100 V and occur in the course of ca.
  • the power loss in a class-A output stage is high.
  • the comparatively high quiescent current combined with the high supply voltage cause the total power loss in the output stage to be high, and it becomes necessary to utilise external cooling means, such as cooling fins.
  • external cooling means such as cooling fins.
  • the bandwidth of the video signal increases to e.g. 10 MHz, which is necessary in flicker-free television, where the deflection frequency is doubled
  • the power loss is correspondingly increased in a class-A output stage, and it is hence still more desirable to reduce the quiescent current in the output stage.
  • a class-B output stage where an improvement may be obtained.
  • One measure of the improvement may be the degree of increase in the proportion between the bandwidth of the video signal and the power loss of the video output amplifier used, and in class-B there is in practice obtained a halving of the power loss for a given bandwidth.
  • Another mea- sure of the improvement may be expressed as the reduction of the area below a curve which represents power drained from the voltage supply during a prescribed time function for the driving.
  • An advantageous embodiment is particular in that the base of the output transistor is driven via the collector of a further transistor, the base of which is connected to reference voltage at a low voltage level, and the emitter of which is supplied with the static component of the control signal as a current from a driver amplifier.
  • the control signal for the static component is lifted to the correct base bias voltage for the output transistor.
  • the dynamic component is predominantly supplied via a coupling capacitor.
  • a further particular embodiment is characterised in that the operating point for the further transistor is adjusted so that further to the static component it additionally supplies rectified dynamic components to the base of the output tran- sistor for the control of its dynamic output current for charging any stray capacitances present.
  • a further particular embodiment is characterised in that a second output transistor is driven in such a way that the discharge current is drawn out of stray capacitances present during negative jumps in the dynamic signal component.
  • the second output transistor is biased such that it does not draw any appreciable quiescent current.
  • a power limiting circuit In particular the large difference between peak power and quiescent power may necessitate the use of a power limiting circuit, because a video signal which contains many contrast jumps, such as white noise on the input terminal, would be able to overload a circuit which due to the large power savings according to the invention has been made less bulky and with weaker cooling means. Ordinary signals would not be influenced by such a power limiting circuit.
  • a further particular embodiment is characterised in that a continuing large number of fast and strong dynamic intensity variations activate a current limiting function which limits the dynamic control currents to one or both output transistors, such that the maximum average power loss is limited to a level where there is no need for particular cooling means.
  • FIG. 1 is a schematic block diagram for video circuits comprising an output amplifier with a high supply voltage according to prior art
  • Fig. 2 shows an embodiment according to the invention
  • Fig. 3 shows an embodiment with a changed driver stage and an output buffer stage
  • Fig. 4 shows a test signal which has been used to determine the power consumption in different amplifier constructi- ons
  • Fig. 5 shows the modelling of the power consumption from the voltage supply to a known construction based on a class-A amplifier
  • Fig. 6 shows the modelling of the power consumption for a construction according to the invention.
  • Fig. 1 is shown a block diagram for a part of a television receiver or video monitor.
  • those signals are processed which are to drive the individual electron guns in a CRT.
  • Amplification of the signals for use at the CRT in block 3 occurs in three identical video output amplifiers 2 to the colours R, G, and B.
  • the CRT is driven at the cathode, but with suitable bias voltages and a phase reversal of the output signal it can e- qually be a control grid which is driven.
  • the G signal from the circuit 1 is taken to the base of the driver transistor DTr which obtains its current from a low voltage supply. From the emitter an in-phase signal is taken to the output transistor TR which obtains it current supply from a relatively high voltage via a collector resistor Re, corresponding to the requirements of the CRT.
  • the local components required by a practical circuit for adjusting the operating point of the driver transistor are not shown.
  • the operating range of the video output amplifier is in practice adjusted by an adjustment by means of an adjustment in the signal pro- cessing circuit in block 1, in the form a manual "cut-off" adjustment during manufacture or by means of a control loop so that it corresponds to the CRT used. In this construction both the DC or slowly varying component and the high frequency content are transferred.
  • the amplifier in the active range of the CRT must be both linear and have a large bandwidth, the transistor TR is driven in class-A.
  • Fig. 2 is seen an embodiment of the invention in the form of a G video output amplifier comprising the supply voltage indicated as 200 V, an input terminal and an output ter- minal for driving the CRT.
  • the input signal is fed via a summing resistor R2 to the positive terminal of a voltage follower ICl, which i.a. provides a low impedance driver stage for the output transistor TR3 via the coupling capacitor C4.
  • ICl is also the driver stage for the dyna- mic component to TR2.
  • ICl receives its power from a low voltage supply which is not shown.
  • the emitter of transistor TR3 is connected directly to the voltage supply, and the output voltage is taken from the collector.
  • the same signal is taken to negative feed-back via the resistor R3 to the point of summation on the positive input terminal of the voltage follower ICl.
  • the supply voltage is at signal ground, and the transistor TR3 may hence dynamically be seen as a "grounded emitter” .
  • the transistor TR1 converts the output voltage from the driver stage ICl into a control current which is taken to the base of transistor TR3.
  • the operating point of TRl may be adjusted by means of R8 and RIO, so that the control current contains both the static control current and the rectified part of the dynamic control current required by TR3 , whereby non- intended reversals of charge of C4 are avoided.
  • the output transistor TR3 delivers the required DC current to maintain the DC potential on the output terminal.
  • TR3 delivers the charging current to the stray capacitances (in the order of 15 pF) during positive voltage steps, because it draws the discharge current out of the stray capacitances.
  • TR2 is provided with a signal from the dri- ver stage ICl via the coupling capacitor C3.
  • Dl, R17 and R18 establish a temperature compensated bias on the basis of TR2.
  • the bias and R18 are determined so that the quiescent current in TR2 is maintained in the order of 1 mA mentioned and such that the bias on the base of TR2 may be influenced in the ne- gative direction by the increasing control current which appears during many fast intensity variations.
  • control current to T2 is limited and hence the dynamically determined power losses in order that no need for special cooling means arises.
  • C3 is adjusted so that the time constant for the power limiting becomes large enough so that short series of fast intensity variations within a frame do not cause limiting.
  • the skilled person will fit linearising resistors in suitable places as well as current limiting resistors.
  • a practical circuit would comprise a cut-off control loop, the function of which does not interfere with the present invention.
  • ICl may advantageously be connected so that it provides a given voltage amplification, which gives a possibility of elevating the upper cut-off frequency of the video output amplifier.
  • Fig. 3 a video output amplifier according to the invention which is essentially identical in its function to that described with respect to Fig. 2. The difference is that the voltage follower ICl is replaced by the emitter follower TR6 with the emitter resistance R4 , and that there is added a buffer stage in the output consisting of the two transistors TR5 and TR4 with the zener diode D2. Furthermore there is shown a connection BCFB for beam current feedback. In case the requirement for amplification and bandwidth is moderate it is sufficient to use an emitter follower TR6 as a driver.
  • a discrete transistor amplifier with a certain voltage amplification as a driver in stead of the emitter follower TR6 , and it may be further advantageous to comprise a limiter function in the transistor amplifer in such a way that the control current for TR3 is limited in the same way that the control current to TR2 is limited, cf . the description concerning Fig. 2. It may be advantageous to include a buffer stage in the output of the amplifier, in particular if there is already a cut-off transistor, in that the dynamic power losses may be distributed among four transistors rather than among only two. In the circuit of Fig.
  • TR4 functions as a cut-off transistor most of the time, where the slowly varying beam currents from the CRT are taken through TR4 to the video signal processing circuit via the terminal marked BCFB.
  • TR4 functions as a buffer, because a part of the stray capacitances are discharged via TR4 and D2 to ground.
  • the zener voltage on D2 is chosen such that the beam current is fed to the video signal processing circuit and not to ground. It is obvious that other voltage limiter circuits may perform the same function.
  • TR5 is without cur- rent most of the time but it acts as a buffer during fast positive intensity variations where it charges a part of the stray capacitances.
  • Fig. 4a a test signal which is used in modelling a 5 MHz amplifier.
  • the signal consists of two pulses with risetimes of ca. 100 ns , in that the pulses start from black and reach 50% and 100% maximum signal.
  • the total duration of the test signal is ca. 3.5 ⁇ s, and it may be provided repetitively from a signal generator.
  • the voltage amplitude on the input is 1 V and 2 V, respectively.
  • the corresponding output signal is shown in Fig. 4b and goes from an output voltage of 160 V and falls during the two pulses to 110 V and 55 V, respectively.
  • the signal is hence in reverse phase with respect to the input signal and is intended for cathode control of the CRT.
  • Fig. 4a a test signal which is used in modelling a 5 MHz amplifier.
  • the signal consists of two pulses with risetimes of ca. 100 ns , in that the pulses start from black and reach 50% and 100% maximum signal.
  • the total duration of the test signal is ca.
  • 5 is shown the power consumption from the voltage supply of a 5 MHz output stage in class-A during the pulses, and it will be noted that the quiescent power is 1 W (black) , and that the power consumption rises to 2 W (50% intensity) and 3.5 W (max. intensity) during the pulse cycle. As a mea- sure of the power consumption it may be judged that the area below the curve is 6.5 ⁇ Ws, i.e. the energy consumed during a pulse cycle. The power taken from the low voltage power supply is not taken into consideration.
  • Fig. 6 is similarly shown the power consumption from the voltage supply of a 5 MHz output stage according to the invention. It is seen that the quiescent power consumption is ca. 0.25 W and that the power consumption is very low during the whole cycle, except where the output voltage (Fig. 4b) is intended to rise with a steep flank towards the quiescent value. Hereby power surges of 1.7 W and 3.2 W, respectively, are obtained. These peaks are hence up to 12 times the quiescent power consumption.
  • the area below the curve may be jud- ged to be 0.3 ⁇ Ws, i.e. an improvement of more than 20 times with respect to prior art expressed as a class-A stage. In a practical amplifier 8-10 times may be obtained.
  • the power taken from the low voltage power supply is not taken into consideration in this case either.
  • Video output amplifiers according to the invention will be suitable for integration due to the small power consumption.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

L'invention concerne des amplificateurs de sortie permettant à des tubes cathodiques de fournir une vitesse de montée élevée, ainsi que des amplificateurs classiques de catégorie A à haute consommation au repos en raison de la combinaison de la tension d'alimentation élevée au courant de repos nécessaire. Selon l'invention, le courant de repos est principalement constitué du courant continu de rebouclage sur le dispositif de sortie (TR3), et son électrode de commande est attaquée grâce à un transistor (TR1), caractérisé par un potentiel de référence à la base, et dont l'émetteur reçoit la composante statique du signal de commande destiné au tube cathodique. Selon un mode de réalisation, la consommation de courant de repos représente 10-15 % de la consommation d'un amplificateur correspondant de catégorie A, et le dispositif de refroidissement requis peut être considérablement réduit.
EP99950509A 1998-10-23 1999-10-22 Amplificateur de sortie video Withdrawn EP1125360A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DKPA199801371 1998-10-23
DK137198 1998-10-23
PCT/DK1999/000579 WO2000025420A2 (fr) 1998-10-23 1999-10-22 Amplificateur de sortie video

Publications (1)

Publication Number Publication Date
EP1125360A2 true EP1125360A2 (fr) 2001-08-22

Family

ID=8104128

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99950509A Withdrawn EP1125360A2 (fr) 1998-10-23 1999-10-22 Amplificateur de sortie video

Country Status (3)

Country Link
EP (1) EP1125360A2 (fr)
AU (1) AU6326399A (fr)
WO (1) WO2000025420A2 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2002339600A1 (en) * 2001-11-22 2003-06-10 Koninklijke Philips Electronics N.V. Image display apparatus and high voltage driver circuit
EP1353440B1 (fr) * 2002-04-12 2009-12-16 STMicroelectronics Limited Etage de sortie classe AB pour un amplificateur à gamme de tension de sortie égale à la tension d'alimentation

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4097815A (en) * 1975-04-09 1978-06-27 Indesit Industria Elettrodomestici Italiana S.P.A. Amplifying circuit
US4114109A (en) * 1975-04-09 1978-09-12 Indesit Industria Elettrodomestici Italiana S.P.A. Amplifying circuit
US4293875A (en) * 1980-01-03 1981-10-06 Telegram Communications Corp. Wide bandwidth video amplifier
US5546048A (en) * 1992-09-04 1996-08-13 Hitachi, Ltd. Amplifier and display apparatus employing the same
US5661436A (en) * 1996-04-19 1997-08-26 Eastman Kodak Company High bandwidth video output amplifier circuit for high resolution cathode ray tube image displays

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0025420A2 *

Also Published As

Publication number Publication date
WO2000025420A2 (fr) 2000-05-04
AU6326399A (en) 2000-05-15
WO2000025420A3 (fr) 2000-07-27

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