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US2185389A - Feedback amplifier filter - Google Patents

Feedback amplifier filter Download PDF

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Publication number
US2185389A
US2185389A US208718A US20871838A US2185389A US 2185389 A US2185389 A US 2185389A US 208718 A US208718 A US 208718A US 20871838 A US20871838 A US 20871838A US 2185389 A US2185389 A US 2185389A
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United States
Prior art keywords
section
coupling
terminals
arms
circuit
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Expired - Lifetime
Application number
US208718A
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English (en)
Inventor
Harold A Wheeler
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.)
BAE Systems Aerospace Inc
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Hazeltine Corp
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Publication date
Application filed by Hazeltine Corp filed Critical Hazeltine Corp
Priority to US208718A priority Critical patent/US2185389A/en
Priority to GB12692/39A priority patent/GB528252A/en
Priority to FR854456D priority patent/FR854456A/fr
Application granted granted Critical
Publication of US2185389A publication Critical patent/US2185389A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/02—Multiple-port networks
    • H03H11/04—Frequency selective two-port networks
    • H03H11/12—Frequency selective two-port networks using amplifiers with feedback

Definitions

  • invention relates to signal-inlog vacuum-tube stares and particularly to such stares oi a. type comprisine a feedback circuit in which the ulter properties of the stage are ⁇ e utilised to incorporate the stage as one oi a series oi conduent iilter networks.
  • the invention comprises a network in which the inocuo pedance characteristics of the feedback stare are matched in the confluent series oi netiii vvorirs with the image impedance characteristics oi other 1
  • vacuo-tube stares comprising feed-bach caffir! cuits have been utilised tor various purposes.
  • stages comprisinp a pair oi terminal circuits and a vacuum-tube coupling means couplinp the terminal circuits in one direction, 2d toeether with an additional coupling means coupiinn the circuits in the opposite directiomhave been utilized as hand-pass selectors in the inter mediate-frequency channel or superheierof.
  • the terminal circuits oi the stage have been indvidually loaded or damped by terminal resistai'ices to provide suitable damping for the stage. hs thus terminated, the ieedbacir stages of the prior it art have had the required damping within the ieedbact stades themselves and have been loosely coupled to adjacent similar stages or to other circuits. li such arrangements are utilized lor passinc a wide band oi irequencies, the width oi the su pass band is limited by the inherent capacitances of the tubes and the circuit elements. Also, the wr or an amplifier comprising such a stage is muterially decreased by the elements provided for individually damping the terminal circuits of the im stese.
  • lt is another object of the invention to provide u, conduent filter network comprising a nlter secu tion including a vacuum-tube coupling in one direction and an additional coupling in the other cation, the stage being matched with adjacent 5@ sections oi the network on an image impedance lt is a iurthcrobiect oi. the invention to provide a confluent filter network comprising an active iiitcr section. as contrasted with a-passive ter section, at least one terminal circuit of' (ci. ira-in) l which is matched with an adjacent section of the network on an imase impedance basis.
  • a filter section comprising a. vacuum-tube coupling in one direction and an additional cou- ..5 pling in the other direction, at least one terminal circuit of the stage being matched on an image impedance basis with an adjacent terminal circuit oi en adjacent lter section to which the stare is coupled in a confluent network.
  • a hlter section comprises a vacuum-tube amplifier stage including terminal circuits, a vacuum-tube couplinu means coupling the terminal circuits in the iorward direction, and a' second vacuum-tube it coupling means coupling the terminal circuits in the backward direction.
  • the input and output terminals of the stage are individually coupled to circuits having constant-lt image impedances.
  • the terminal circuits of the lter section and the E relative transconductances of the vacuum tubes utilized in the stage are so proportioned that the image impedance at each pair of terminals closely matches the constant-Ic image impedance of the adjacent meer section to which a is directly couit pled.
  • the vacuum-tube stage comprises terminal circuits coupled in the forward direction by s. vacuumftube transconductance coupling means4 and .coupled in the backward direction by passive conductance or resistanceV coupling means.
  • et i phase-shifting circuit may beassociated with. the backward coupling. means, the amount oi phase shirt being proportioned to e'ect regeneration just suillcient to compensate, at the cutoff frequency, for the losses caused by the sell-conductance or other dissipation in the terminal circuits and coupling means of the stese. The result is to maintain the sharpness of cutoi! which would be obtained in a nlter if the nlter had no inherent dissipation.
  • Fig. 1 of the drawings is a simplified circuit diagram of a low-pass ampliiler illter of the invention, an image impedance of the vacuum-tube feedback section of which is matched with that of an adjacent circuit to form a confluent series of sections;
  • Figs. 2te-2e, inclusive are graphs illustrating certain theoretical characteristics of the feed-back stage of Fig. 1;
  • Fig. 3 is a simplified circuit diagram of a feedback lter similar to that of Fig. 1 except that a conductance feedback circuit is provided in the feedback section of the network;
  • Fig. 4 is a circuit diagram of a band-pass amplifier ilter corresponding in type to the low-pass lter of Fig. 1;
  • Figs. 5 and 6 are circuit diagrams of different types of conuent amplier filters of the invention, each comprisingl two feedback sections.
  • a vacuum-tube amplifier stage comprising one of a conuent series of iilter sections.
  • the stage comprises input terminals 8, 8 and output terminals 1, 1 across which are coupled, respectively, condensers C1 and C2,
  • the terminal circuits are coupled in the forward direction by a unidirectional coupling means primarilyv transconductive, such as a vacuum tube I and are coupled with opposite polarity in the backward direction by a vacuum tube II.
  • Sources of operating potentials (not shown) and other electrodes such as screen grids, if desired, are provided for tubes I0 and II in a conventional manner.
  • the image impedance of the circuit between the input terminals t, 6 is indicated by Z'.
  • Vacuum tube I I is so connected as to have eifectively a positive transconductance in contrast to the ordinary negative transconductance of a vacuum tube; that is, the output circuit of vacuum tube II is taken from ascreen circuit.
  • Figs. 2a'2e represent certain theoretical characteristics of thel feedback ampliiier iilter section of Fig. 1,' each of the ilgures having frequency as the abscissae.
  • Fig. 2a represents the impedance of the feedback amplifier filter section of Fig. 1 on 'either side, with the other side on short'circuit:
  • Fig. 2b shows the' the feedback amplier illter section.
  • the upper and lower 4dotted-line curves of Fig. 2e show the actual phase shift for a stage having, respectively, negative and positive forward transconductance. It will be understood that the characteristic curves of Figs. 2a-2c, inclusive, are equally applicable at either the input terminals 6, 6 or the output terminals 1, 1.
  • the feedback amplifier filter section has input and output image impedances which exactly conform to constant-Ic mid-shunt image impedances.
  • the system may, therefore, be connected in a conuent series of networks on an image impedance basis with other similar amplifier stages or with filter sections having the constant-Ic form of image impedance.
  • the low-pass amplifier filter stage shown has a cutoff frequency:
  • Resistor R' representing the image impedance of both circuits connected at the terminals 8, 6, and resistor R", representing the image impedance of both circuits connected at the terminals 8, 8, or terminating resistors to match such image impedances, have the values:
  • this image impedance ratio is unity in a low-pass iilter network.
  • the amplifier filter section of the invention is an active section, the image impedance ratio of the circuit of Fig. 1 can have any desired value.
  • the gain of the amplifier filter section of Fig. 1, which is the voltage ratio when connected between equal impedances, is:
  • phase shift of a filter section varies over a range of 180 degrees over the pass band. It will be seen from the phase-frequency curves of Fig. 2e that the phase of the low-pass lan output circuit, as in the case of tube II in Fig. l, is one way of securing a negative transconductance. Other means for accomplishing this are two conventional tubes coupled in cascade in the normal manner, or a. phase-reversing transformer utilized with a. normal tube having a negative transconductance.
  • the tubes utilized in the iilter networks oi the invention have a very small anode conductanceI which is a property of high-mu tubes, such as screen-grid tubes or high-mu triodes. if the ampliiier filter section is designed for operation at very high frequencies, the tubes must be shielded against internal capacitive coupling and in such cases the use of screen-grid tubes is essential.
  • the circuit oi Fig. 3 is, in general, similar to the circuit oi Fig. l and similar circuit elements have been given identical reference numerals.
  • the coupling provided by vacuum tube ii ci Fig. l, oi opposite polarity to the couv pling oi vacuum tube it, has been replaced by a dit primarily conductive coupling.
  • This conductive coupling is obtained by means of a resistor it connected directly between the anode and the grid oi vacuum tube it.
  • Ii the conductance Gs oi" the feedback circuit comprising resistor it is much less than the transconductance gm ci' vacnum tube it, the operation oi the circuit ci Fig.
  • Ii is in all respects similar to that of the circuit oi' Fig. i. vl'he ampliier nlter section of Fig. 3 has the characteristic oi a mid-shunt constant-7c image impedance across each of condensers C1 and f G2 similar to that across corresponding elements in the circuit oi? iilig. l.
  • the following additional equations erpress the edective transconductances in the circuit oi' ilig. 3:
  • Ga (s) lin Fig. 'i there is shown a bandiiiter arnplifier section ci the invention connected in a titl continent network with age impedance matching.
  • the circuit is generally similar to the circuit ci the low-pass iilter oi tig. l and similar circuit elements have been given identical reierence numerals.
  • a comprises an inductance lin connected in parallel with condenser C1, and an inductance in connected in parallel with condenser Cz.
  • the rst amplier hlter section comprises a shunt reactive arm including a series-connected inductance 22 and condenser it and a second shunt reactance arm comprising a condenser 2 I.
  • These shunt reactance arms are coupled in the forward direction by the vacuum tube 2t and are coupled in the backward direction with opposite polarity by a conductance coupling with the addition of series inductances 25 and it, resistor it being replaced by resistors it', I5".
  • a condenser 2l is connected from the Junction between inductances 2t and it and the low-potential terminal of condenser 2t.
  • Grid-leak resistor it is provided for vacuum tube it, while the resistance of its load circuit is represented by resistor 29.
  • resistor 29 Across the input terminals of the circuit o lFig. 5 is connected a resistor it matching the image imped ance between the terminals and which is nearly constant over the pass band.
  • the second amplier filter section of the circuit ci Fig. 5 comprises a shunt capacitance armconsisting of a condenser it and a shunt arm including a series-connected inductance 3E and condenser it.
  • the shunt arm comprising condenser tt and the shunt arm comprising series-connected inductance it and condenser it are coupled by vacuum tube t? and are coupled in the backward direction ywith opposite polarity by a resistor tu.
  • a grid leal; it 'is provided for vacuum tube t?, while resistor dit represents the resistance in the output circuit ci' vacuum tube iii. Across the output terminals of the conduent network oi Fig.
  • Inductance element it provided in the shunt reactance ⁇ arm of the input circuit of vacuum tube 2t completes an mderlved termination having an image impedance which matches the constantresistance til.
  • im ductance tti is provided for the same reason in series with condenser lit; that is, to complete an 11i-derived termination for the output circuit of the amplifier lter section comprising tube ti which more closely matches thel impedance ot the sections oi' the invention coupled in cascade in a confluent band-pass lter network.
  • first amplifier filter section of Fig. 6 comprises a shunt reactance arm including the secondary winding of transformer 56 and a shunt reactance arm comprising the primary winding 53 of transformer 52.
  • is coupled in a. forward direction to winding 53 by a vacuum tube 54 and is coupled in the backward direction with opposite polarity by a c-ircuit comprising seriesconnected resistor 55 and condenser 56.
  • the electrode capacitances of tube 54 represented by condensers 5
  • the primary winding'i of transformer 50 is tuned by a shunt condenser 58 across which is coupled a.
  • the circuit of the second amplifier filter section of Fig. 6 is in all respects similar to the first amplifier filter section described above, and comprises a vacuum tube 64 coupling the secondary winding 6
  • a shunt condenser 68 is connected across the secondary winding 69 of transformer 62 to which is coupled resistance 'I0 representing the impedance of the succeeding circuit to which the output terminals of the filter network are coupled.
  • the inherent input and output capacitances of vacuum tube Glare represented respectively by condensers 6I" and 68'. l
  • each amplifier filter section of Fig. 6 is similar to the operation ofthe circuit of Fig. 3, rendering a further description thereof unnecessary.
  • the feedback circuits of Fig. 6 are tapped down on their respective transformer windings in order that a lower value of resistance may be utilized in the feedback circuits and for the purpose of reducing the capacitive coupling associated with the resistance elements. It will be seen that the circuit of Fig. 6 provides a means for coupling two vacuum-tube amplifier filter sections in cascade, there being minimum dissipation within the filter stages.
  • the circuit of each of the amplifier filters ⁇ of Fig. 6 is similar to that of Fig. 4 in that each relates to a band-pass filter. However, the feedback coupling paths ofthe amplifier filters of Fig.
  • of transformer 62 is much less than would be required to couple conventional vac- .uum-tube amplifier stages. If Aw is the width of the pass band and wo is the mean frequency of the pass band, the required coupling is,
  • a Wave filter network comprising a first filter section having a predetermined image impedance at one end and an active second filter section comprising input and output pairs of terminals, a reactance arm individual to and. coupled to each of said pairs of terminals, unidirective coupling means betweensaid arms primarilyitransconductive in the direction of coupling, and means coupling said arms with opposite polarity in the other direction, whereby said second filter section has a predetermined pass band and a predetermined image impedance across one of said pairs of terminals, said one of said pairs of terminals being coupled to said end of said first filter section, said coupling means being so proportioned with respect to the reactive constants of said arms that the image impedance of said second filter section matches the image impedance of said first section at their junction.
  • a wave filter network comprising a first filter section having a predetermined image impedance at one end and an active second filter section comprising input and output pairs of terminals, a reactance arm individual to and coupled to each of said pairs of terminals, unidirective coupling means between said arms primarily transconductivein the direction of coupling, coupling means primarily conductive coupling said arms with opposite polarity in the other direction, whereby said second filter section has a predetermined pass band and a predetermined image impedance across one of said pairs of terminals, said one of said pairs of terminals being coupled to said end of said first filter section, and said coupling means beingl so proportioned with respect to the reactive constants of said arms that the image impedance of said second filter section matches the image impedance of said first section at vtheir junction.
  • a wave filter network comprising a first filter section having a predetermined image impedance at one end and a second active filter section comprising input and output pairs of terminals, a reactance arm individual to and coupled to each of said pairs of terminals, unidirective coupling means between said arms primarily transconductive in the direction of coupling.
  • coupling means primarily transconductive coupling said arms with opposite polarity in the other direction, whereby said second section has a predeterminedv pass band and a predetermined image impedance across one of said pairs of terminals, said one of said pairs of terminals being coupled to said end of said first filter section, and said coupling means being so proportioned with respect to the reactive constants of said arms that said image impedance of said second filter section matches said image impedance of said first filter section at their junction.
  • a low-pass filter network comprising a first filter section having a predetermined image impedance at one end and a second active filter section comprising input and output pairs of terminals, a shunt reactance arm individual to andcoupled to each of said pairs of terminals and comprising shunt capacitance, said reactance arms having coupling means between said arms primarily transconductive in the direction of'v coupling, means coupling said arms with opposite polarity in the opposite direction, whereby said iii n.so
  • arenoso 4 Sind section h a predetermined pass band and a predetened image impedance across one oi said pairs oi terminals.
  • said one oi said pairs oi terminals being coupled to said end of said t st nlter section, and said coupling means beina so proportioned with respect to the reactive constante oi said arms that said image impedance oi said second dlter section matches the image impedance ci said ilrst filter section at their iunction.
  • n band-pass ter network comprising a first ter section having a predetermined image impedce at one end and an active second lter section comprising input and output pairs oi ternals, a parallel-resonant shunt a individual to and coupled to each oi said pairs of terminals, unidirective coupling means between said arms rimarilv transconductive in the direction of coupg, me coupling withopposite polarity said arms in the other ection, whereby said second section has a predetermined pass band and a predetermined ge impedance across one oi said pairs oi terminals, said one oi said pairs oi terals being coupled to said end of said niet nlter section, and said coupling means being so proportioned with respect to the reactive constants ci said arms that the image impedance ci said second dlter section matches the image impedance oi said nrst section at their junction.
  • wave dites network comprising a nrst ter section having a mid-shunt constant-lt impedance at one end and an active second nlter section comprising input and output pairs oi' tenais, a reactance t, i o l individual to and coupled to each oi said pairs oiteals, unidirectire coupling means between said arms primarily trconductive in the direction oi coupling, means coupling said arms with opposite polarity in the other direction.
  • said second nlter section has a predetermined pass band and a mid-shunt constant-lc image impedance across each oi said pairs of te als, one ci said pa s oi teinals being coupled to said end oi said t nlter section, said coupli means being so proportioned with respect to the reactive constants of said arms that the image impedance oi said second utter section matches the im ance oi id nrst @lier-econ attheir junction-and said image imp si ci said second section ve a constant ratio substantially dit., iereht we unity.
  • a iowss hlter network a t ter between said arms in one direction consisting primarily oi transconductance gis in the clis rection of coupling, unidirective coupling means of opposite polarity between said arms in the other direction consisting primarily of transconductance Q21, whereby said second'iilter section has a cutod frequency Y and whereby said second section has a constant-k mid-shunt image impedance across one of said pairs of terminals, said one oi said pairs of ter minals being coupled to said end of said first nlter section, and said coupling means being so proportioned with respect to the reactive constants of said arms that said image impedance of said second lter section matches the image impedance oi said first illter section at their junction.
  • an active filter section comprising input and output pairs ci terminals, a reactance arm individual to and coupled to each oi said pairs oi' terminals, unidirec-a tive coupling means between said arms in one direction primarily transconductive in the direction of ⁇ coupling, coupling means of opposite polaritts between said arms in the other direction, an mderived termination for said lter section comprising one of said arms, whereby said' lter section has a predetermined cutoil.' frequency and a predetermined constant image impedance across one of said pairs of terminals over said band, and a constant resistance circuit 'connected across said one of said pairs oi terminals.
  • an active lter section comprising input and output pairs ci terminals, a reactance arm individual to and coupled to each oi saidpairs oi terminaladirective coupling means in one direction between said arms primarily transconductive in the direction ci' coupling, and coupling means primarily conductive coupling said arms with opposite polarity in the other direction, an "in-derived termination for said lter section comprising one of said arms, whereby said Filter section has a predetermined cutoti frequency and a predetermined constant image impedance across one oi said pairs of terminals over said band, and a constant resistance circuit connected across said one of said pairs oi terminals.
  • an active filter section comprising input and output pairs of terminals, a reactance arm individual to and coupled to each oi said pairs of terminals, dlrective coupling means in one direction between said arms primarily transconductlve in the direction or coupling, and me coupling said arms with opposite polarity in the vother direction, one oi' said arms consisting oi a series-connected inductance and condenser, whereby' said section has a predetermined cutod frequency and a sub stantially constant resistive image impedance across the pair of terminals to which said one oi said arms is coupled, and a constant resistance circuit connected across said -ntioned pair oi terminals.
  • An active lter section comprising input and output rs oi terminals. areactance arm dit dit
  • directive coupling means in :one direction between said arms primarily transconductive in the direction of coupling, and coupling means primarily conductive coupling said arms in the other direction with opposite polarity, phase-shifting means included in said .con-
  • phaseshifting means comprising inductance in series with said conductive coupling means and capacitance in shunt therewith effective to provide regeneration at the cutoff frequency of said section just suiiicient to compensate for dissipation in said section, whereby said section has a predetermined cutoff frequency and a predetermined image impedance across'one of said pairs of terminals.
  • a band-pass filter comprising a plurality of coupled filter sections with image impedance matching at their junctions, each of two of said sections comprising a transformer having primary and secondary windings, transoonductive coupling means comprising a vacuum tube having inherent input and output capacitances coupling thesecondary winding of one of said transformers with the primary winding of the other of said transformersvcoupling means of opposite polarity in the other direction between said two last-mentioned windings, the coupling eect of said coupling means being proportioned with respect to the reactive constants of said transformers to provide constant-k mid-shunt image impedances across said capacitances and a predetermined pass band for said filter, said image impedances matching the image impedances of adjoining ones of said sections.
  • a band-pass filter comprising a plurality of coupled lter sections with image impedance matching at their junctions, each of two of said sections comprising a transformer having primary and secondary windings, transconductive coupling means comprising a vacuum tube having inherent input and output capacitances coupling the secondary winding of one of said transformers with the primary winding of the other of said transformers, coupling means of oppoindividualoto and coupled to each of said pairs- 'site polarity in the other' direction between said two last-mentioned windings, said couplingI ⁇ means comprising a'resistor coupled between points of said two.l lastmentioned windings, the coupling eiect of said coupling means being proportioned with respect to the reactive constants of said transformers to provide constant-1c mid-shunt image impedances across said capacitances 'and a predetermined pass band for said filter, said image impedances matching the image impedances of adjoining ones of said sections.
  • a wide band iilter network comprising a first filter section having a predetermined image impedance at one end and an active lter section comprising input and output pairs of terminals, two capacitive shunt arms coupled to said terminals and having unidirective coupling means between said arms primarily transconductive in the direction of coupling, said coupling means comprising a vacuum tube having input and output capacitances, one of said capacitances of said tube comprising the capacitance of a full-shunt element of said iilter network, and means coupling said arms with opposite polarity in the other direction, whereby said section has a predetermined pass band and a predetermined image impedance across said one of said arms, said one of said pairs of terminals being coupled to said end of said first iter section, and said coupling means being so proportioned with respect to the reactive constants ot said arms that the image impedance of said second filter section matches the image impedance of said first iilter section at their junction.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Networks Using Active Elements (AREA)
  • Filters And Equalizers (AREA)
US208718A 1938-05-09 1938-05-09 Feedback amplifier filter Expired - Lifetime US2185389A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US208718A US2185389A (en) 1938-05-09 1938-05-09 Feedback amplifier filter
GB12692/39A GB528252A (en) 1938-05-09 1939-04-27 Feed-back amplifier filter
FR854456D FR854456A (fr) 1938-05-09 1939-05-08 Filtre de bande

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Application Number Priority Date Filing Date Title
US208718A US2185389A (en) 1938-05-09 1938-05-09 Feedback amplifier filter

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US2185389A true US2185389A (en) 1940-01-02

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2605358A (en) * 1946-01-30 1952-07-29 Leland K Neher Low pass filter
DE1127401B (de) * 1953-06-08 1962-04-12 Western Electric Co Aktives UEbertragungssystem

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB0313781D0 (en) * 2003-06-13 2003-07-23 Sepura Ltd Amplifier impedance matching

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2605358A (en) * 1946-01-30 1952-07-29 Leland K Neher Low pass filter
DE1127401B (de) * 1953-06-08 1962-04-12 Western Electric Co Aktives UEbertragungssystem

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FR854456A (fr) 1940-04-16
GB528252A (en) 1940-10-25

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