US3757155A - Wide bandwidth deflection amplifier - Google Patents

Wide bandwidth deflection amplifier Download PDF

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Publication number
US3757155A
US3757155A US00209842A US3757155DA US3757155A US 3757155 A US3757155 A US 3757155A US 00209842 A US00209842 A US 00209842A US 3757155D A US3757155D A US 3757155DA US 3757155 A US3757155 A US 3757155A
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Prior art keywords
current
sampling
voltage
resistor
deflection
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Expired - Lifetime
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US00209842A
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English (en)
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G Waehner
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RTX Corp
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United Aircraft Corp
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    • 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
    • H03F1/42—Modifications of amplifiers to extend the bandwidth
    • H03F1/48—Modifications of amplifiers to extend the bandwidth of aperiodic amplifiers
    • H03F1/486—Modifications of amplifiers to extend the bandwidth of aperiodic amplifiers with IC amplifier blocks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K6/00—Manipulating pulses having a finite slope and not covered by one of the other main groups of this subclass
    • H03K6/02—Amplifying pulses

Definitions

  • This invention relates to amplifier circuits used for driving an inductive load, and more particularly to amplifiers for driving a magnetic deflection yoke in a CRT display.
  • CRT displays employing magnetic deflection yokes commonly use one of two techniques to drive the yoke.
  • a non-dissipative and inexpensive system currently in use is the resonant energy recovery circuit.
  • This circuit has wide application where a raster is being generated, such as in commercial television, but has no application to display systems where deflection is derived from a stroke generator.
  • a high degree of display linearity is not possible with a resonant energy recovery circuit, primarily because it is an open loop type of circuit.
  • a more flexible system is a magnetic deflection amplifier comprising an operational amplifier which is concurrently responsive to an input voltage and a sampling voltage.
  • the sampling voltage is generated across a small sampling resistor by feeding the deflection current in the yoke through the sampling resistor.
  • An input resistor and a feedback resistor cause the sampling voltage and the input voltage to be compared and the result of the comparison is used to cause the operational amplifier to provide a deflection current in proportion to the input voltage.
  • the waveform of the deflection current in the yoke is a faithful reproduction of the waveform of the input voltage (at the input of the deflection amplifier). For a stroke written display or a display where a very precise raster must be generated, this property is essential.
  • the circuit properties of the yoke which include its inductance and any parasitic circuit parameters associated with the yoke, are important in providing the desired deflection current.
  • a parasitic capacitance (caused by the connection wiring of the yoke, or any other cause) across the yoke causes parasitic current at high frequencies to bypass the yoke and still pass through the sampling resistor, this is particularly important because the parasitic current may cause the sampling voltage to be a poor representation of the deflection current.
  • parasitic capacitance (caused by the connection wiring of the yoke, or any other cause) across the yoke causes parasitic current at high frequencies to bypass the yoke and still pass through the sampling resistor, this is particularly important because the parasitic current may cause the sampling voltage to be a poor representation of the deflection current.
  • parasitic capacitance is an erroneous sampling voltage at high frequencies that causes an erroneous deflection current.
  • bandwidth of the deflection amplifier is usually lower than the desired bandwidth because the frequency dependence of the effects of the parasitic capacitance cause a tendency towards instability at high frequencies.
  • Production of a plurality of similar deflection amplifiers is difficult and costly because slight mechanical construction differences cause differences in the parasitic capacity associated with the yokes of individual deflection amplifiers; this results in a substantial unit to unit variation of the relative stability and high frequency performance between individual deflection amplifiers.
  • a deflection amplifier that is responsive to the voltage provided by a preemphasis network which attenuates the low frequency spectrum of its input voltage while leaving the high frequency spectrum unattenuated.
  • the network thereby compensates for high frequency attenuation caused by the deflection amplifier and causes a flat response to the input voltage.
  • These networks may have little or no effect upon the high frequency performance of a deflection amplifier because high frequency currents that are provided pass through the parasitic capacitor to the sampling resistor, thereby bypassing the yoke.
  • the object of the present invention is to provide an improved deflection amplifier that provides current to an inductive load in response to a deflection voltage.
  • a network which is responsive to the voltage applied to the series combination of an inductive load and a sampling resistor has a transfer function related to the series combination of the inductance of an inductive load and the resistance of the sampling resistor; at high frequencies, the output of the network is coupled to a feedback resistor of an amplifier, providing a bypass for feedback current that results from a voltage developed across the sampling resistor and causing the amplifier to be responsive to the voltage provided by the network and substantially ignore the voltage developed across the sampling resistor.
  • the present invention increases the useful bandwidth of deflection amplifiers and causes the unit to unit performance of similar amplifiers to be more nearly alike than deflection amplifiers known in the prior art.
  • the present invention provides a deflection amplifier which is responsive to the effects of a preemphasis network, since the high frequency effects of parasitic capacitance are substantially ignored.
  • FIG. 1 is a schematic diagram of a deflection amplifier known in the prior art
  • FIG. 2 is a schematic block diagram of a preferred embodiment of the present invention.
  • FIG. 3 is a schematic block diagram of a high frequency equivalent of the present invention.
  • FIG. 4 is a schematic diagram of a first network that has a desired transfer function for use in the embodiment of FIG. 2;
  • FIG. 5 is a schematic diagram of a second network that has a desired transfer function.
  • a deflection amplifier known in the prior art includes an operational amplifier 9 which provides the deflection current to an inductive load, such as a magnetic deflection yoke 10, in response to an input voltage applied to terminals 12.
  • the deflection current flows through a sampling resistor 14 (on the order of one ohm) causing a sampling voltage (proportional to the deflection current) to be developed at a sampling junction 16.
  • the non-inverting input 18 of the amplifier 9 is grounded, which causes a well known phenomena of a virtual ground to be impressed upon the inverting input 20.
  • the sampling voltage causes a feedback current to flow through a feedback resistor 22 (of much greater resistance than the sampling resistor 14).
  • the current into the inputs 18, 20 is negligible; an input resistor 24 provides the path for the feedback current. Negative feedback causes the feedback current to be proportional to the input voltage, which equals the voltage across the input resistor 24.
  • a parasitic capacitor 26 is representative of yoke parasitic capacity and wiring capacity that is associated with the wiring that connects the yoke 10. At high frequencies, a significant parasitic current flows through the parasitic capacitor 26 and through the sampling resistor 14 causing the sampling voltage to be a poor indication of the deflection current (current in the yoke therefore a component of the feedback current is conducted through the resistors 22, 24 that is not associated solely with the deflection current. By contributing to the feedback current, the parasitic capacitor 26 causes the deflection current to be different from the desired deflection current. In the absence of the parasitic capacitor 26, the sampling voltage is truly representative of the deflection current and the Laplace transform of the sampling voltage is given as:
  • the present invention provides a feedback current that would result from the sampling voltage that truly represents the deflection current.
  • the feedback current is provided in response to the sampling voltage; at high frequencies a network provides a bypass for feedback current that results from the sampling voltage, thereby substantially ignoring the sampling voltage, and provides a feedback current in response to the voltage across the series combination of the sampling resistor 14 and the yoke 10.
  • the present invention is predicated upon the knowledge that the effects of the parasitic capacitor 26 is negligible at low frequencies and at high frequencies the current in an inductor is related to the voltage impressed across the inductor, independent of any element in parallel therewith.
  • resistors 22a, 22b are each equal to one half the value of the resistor 22 (FIG. 1).
  • a compensation junction 30 is formed at the juncture of the resistors 22a, 22b and a capacitor 32.
  • the inverting input is at a virm/ ll) where V is the Laplace transform of the compensation voltage.
  • a network 34 has the desired transfer function that provides on a signal line 36 a voltage equal to one half of the sampling voltage in the absence of the parasitic capacitor 26.
  • the capacitor 32 connects the line 36 to the junction 30 so that at high frequencies the compensation voltage is equal to the voltage provided on the line 36; the current through the resistor 22b, provided in response to the sampling voltage, is bypassed to ground.
  • the feedback current (through the resistors 22a, 24) is substantially representative of the deflection current.
  • the frequency above which the capacitor 32 substantially provides the compensation voltage is given as:
  • w is the natural frequency above which the capacitor 32 substantially provides the compensation voltage
  • R is the resistance of the resistor 22
  • C is the capacitance of the capacitor 32.
  • FIG. 3 A high frequency equivalent of the present invention is shown in FIG. 3.
  • the salient features therein are that the current in the yoke 10, the current through the parasitic capacitor 26 and the sampling voltage do not determine the compensation voltage.
  • the transfer characteristics of the network 34 and the voltage at the output 28 substantially determine the compensation voltage and therefore the feedback current through the feedback resistor 22a and the input resistor 24.
  • the network 34 is comprised of resistors 38, 40 and a capacitor 42.
  • the transfer function of this network is given as:
  • the transfer function of the network 34 is of the same form as the desired transfer function and is identical to it if the following relationships exist between the resistors 38, 4t), 14, the capacitor 42 and the yoke es 40 RA 2/RAC42 RM/LXO As is well known to those skilled in the art, an appropriate output impedence of the network 34 is obtained by providing a resistance R, very much less than the parallel combination of the resistances 22a, 22b.
  • a network 3430 consisting of an inductor 441, a resistor 46 and a resistor 48 may be used as an alternative to the network 34".
  • the network 3 k provides the desired transfer function when its components have a relationship to the resistor 14 and the yoke M) which is given as:
  • the network 34a has an appropriate output impedence when the resistance of R is very less than the parallel combination of resistances 22a, 22b.
  • a magnetic deflection amplifier of the type including an operational amplifier which is responsive to an input voltage applied to one end of an input resistor, the other end being connected to an input of said operational amplifier, the output of said operational amplifier providing deflection current and parasitic current to a load including an inductive load in parallel with a parasitic capacitor, and a sampling resistor in series with said load, the deflection current flowing through the inductive load, said load and said sampling resistor having a sampling junction therebetween and a sampling voltage being sustained across said sampling resistor, the improvement comprising:
  • feedback means including a compensation junction, connected from said sampling junction to the input of said operational amplifier for providing a feedback current to said input resistor; and circuit means having an input connected for response to the voltage applied to the series combination of said load and said sampling resistor and having an output connected to said compensation junction, said circuit means having a frequency response characteristic such that at frequencies in excess of those frequencies at which the parasitic current becomes substantial with respect to the deflection current, it provides a current to said compensation junction which is substantially equal to the current which would be provided thereto by said sampling junction if the load were ideal and had no parasitic current, whereby at low frequencies the feedback current is provided substantially in response to the voltage at the sampling junction and at high frequencies a feedback current is provided substantially proportional to the voltage across the series combination of the yoke and the sampling resistor.
  • said feedback means includes a first feedback resistor connected from said sampling junction to said compensation junction and a second feedback resistor connected from said compensation to the input of said operational amplifier and said circuit means comprises:
  • V is the Laplace transform of the voltage applied to the series combination of the inductor and the sampling resistor

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Details Of Television Scanning (AREA)
US00209842A 1971-12-20 1971-12-20 Wide bandwidth deflection amplifier Expired - Lifetime US3757155A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US20984271A 1971-12-20 1971-12-20

Publications (1)

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US3757155A true US3757155A (en) 1973-09-04

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Application Number Title Priority Date Filing Date
US00209842A Expired - Lifetime US3757155A (en) 1971-12-20 1971-12-20 Wide bandwidth deflection amplifier

Country Status (5)

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US (1) US3757155A (enExample)
JP (1) JPS4871129A (enExample)
CA (1) CA980459A (enExample)
FR (1) FR2165686A5 (enExample)
GB (1) GB1407287A (enExample)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4142134A (en) * 1977-06-27 1979-02-27 United Technologies Corporation Direct integration yoke driver for a high speed alphanumeric display system
US4293802A (en) * 1979-12-19 1981-10-06 International Business Machines Corporation Transresonant deflection yoke operations
US20190102586A1 (en) * 2017-09-29 2019-04-04 Tyco Fire & Security Gmbh Anti-theft pedestal suspension system

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5529988Y2 (enExample) * 1973-06-22 1980-07-17
FR2407606A1 (fr) * 1977-10-25 1979-05-25 Thomson Csf Amplificateurs de balayage a grande bande passante, notamment utilises dans des consoles graphiques a balayage cavalier et consoles ainsi obtenues
DE4431344A1 (de) * 1994-09-02 1996-03-07 Hoechst Ag Wäßrige Dispersionen für Klebstoffe

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4142134A (en) * 1977-06-27 1979-02-27 United Technologies Corporation Direct integration yoke driver for a high speed alphanumeric display system
US4293802A (en) * 1979-12-19 1981-10-06 International Business Machines Corporation Transresonant deflection yoke operations
EP0031032B1 (en) * 1979-12-19 1985-10-02 International Business Machines Corporation Cathode ray tube display system deflection yoke operating above its resonant frequency
US20190102586A1 (en) * 2017-09-29 2019-04-04 Tyco Fire & Security Gmbh Anti-theft pedestal suspension system

Also Published As

Publication number Publication date
JPS4871129A (enExample) 1973-09-26
FR2165686A5 (enExample) 1973-08-03
GB1407287A (en) 1975-09-24
CA980459A (en) 1975-12-23

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