US2245722A - Coupling network - Google Patents

Coupling network Download PDF

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Publication number
US2245722A
US2245722A US267384A US26738439A US2245722A US 2245722 A US2245722 A US 2245722A US 267384 A US267384 A US 267384A US 26738439 A US26738439 A US 26738439A US 2245722 A US2245722 A US 2245722A
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Prior art keywords
frequency
inductance
grid
resistance
coupling
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Expired - Lifetime
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US267384A
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English (en)
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Rust Noel Meyer
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RCA Corp
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RCA 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
    • H03F1/50—Modifications of amplifiers to extend the bandwidth of aperiodic amplifiers with tubes only

Definitions

  • This invention relates, to electrical networks suitable for use as inter-stage coupling networks in electron-discharge tube amplifiers and has for its main object to provide improved amplifiers of substantially uniform response over a wide frequency range, adaptedfor use at high frequencies, and of relatively high amplification having regard to the performance in other respects.
  • the invention is of wide application but two important applications are (1) to video signal amplifiers in high fidelity television apparatus and (2) to high frequency amplifiers.
  • the present invention seeks to reduce or avoid these limitations and defects.
  • an electrical network suitable for use as an inter-stage coupling network in an electron discharge tube amplifier, is a four terminal network having an input terminal and an output terminal effectively common and comprisestwo resistances one between the input terminals and. the other between the output terminals, an inductance in shunt across each resistance and a coupling condenser connected between a tapping point on one. inductance and a. tapping point. on the. other.
  • each of the inductances thus comprisesin effect, a series coil (on one side of.
  • Fig. 1- illustrates diagrammatically one embodiment of. the invention asap plied to an amplifier'for longand medium broad-- cast wave bands
  • Fig. 1a is the electrically equivalent circuit of Fig. 1
  • Figs. 2a, 2b and 2c illustrate the design development of a coupling network according to the invention.
  • the amplifier comprises two pentodes I, Z'each having its cathode 3 or 4 earthed through the usual capacity shunted bias resistance combination 5' or 6.
  • Input is applied between the first grid 1 of the pentode I and earth and output is taken from between the anode 8 of the pentode 2 and earth.v
  • The. suppressor grids 9 and H) are connected to their respective cathodes and the screen grids II and I2 are positively biased as in the customary way.
  • the network between the two stages is in accordance with this invention and, in describing the network, reference letters. which identify individual elements and also represent their values, will be used in order to facilitate understanding of the design description to be given later.
  • the coupling network comprises an inductance Ll in series with a condenser C in series with another inductance LI in series in the order stated between the anode of the first valve and the first grid of the second.
  • the positive terminal of a source of anode potential is connected to the anode of the first pentode through a resistance R and is also connected to the anode side of the condenser C through an inductance L2.
  • a source of grid bias is connected to the first grid of the second pentode through a resistance R and also. to the grid side of the condenser C through. a second inductance L2.
  • the condenser C' may, for theoretical purpose, be regarded as consistingof two condensers C2.:in series each equal to.2C.' and.
  • the stray capacities maybe regarded as con sisting oftwo condensers; Cl. connected across: thezrespective resistancesR at the; anodeuofthe r first valve and the control grid of the second.
  • Figure 1a which is the electrically equivalent circuit of Figure 1.
  • a small trimmer condenser shown in broken lines in Figure 1a may be used to supplement one of the condensers CI but this will usually not be required.
  • This network may be regarded as a back-toback compound line impedance transformer made up of two similar compound sections terminated (by resistances R) at both ends. Since a pentode is a high impedance valve aseparate anode resistance R is connected between the anode of the first valve and the source of anode potential but if the first valve were a triode or other valve of internal impedance R the separate anode resistance could be omitted. Similarly, as regards the grid termination, if the operating frequency were so high that the grid impedance was (due to electron transit time effects) low enough, a separate grid terminating resistance R could be dispensed with.
  • Zoa is the image impedance from the low impedance end of the section
  • Zob is the image impedance from the high impedance end of the section
  • Z0 is the geometric mean impedance
  • a television I. F. amplifier for one video side band was constructed to the same circuit as above described.
  • the single side band range was 1.5 megacycles, themid-band frequency being 5.3 megacycles so that the band was 5.3:.75 megacycles.
  • the valves were pentodes with a mutual conductance of 3 milli-amperes per volt and the following component values were used:
  • the attenuation outside the pass range and adjacent the cut off frequencies may increase as rapidly as possible, egg. to eliminate a strong interfering signal adjacent the desired frequency spectrum.
  • This may be achieved by so designing the shunt arms of the network (other than shunt arms representing shunt capacities due to valves and strays) to be series resonant at the unwanted frequency or frequencies or, in general, at frequencies just outside the cut-off frequencies.
  • the values of the inductance and capacity in each series-resonant shunt arm is so chosen that the net reactance at the log-midfrequency are as required by the above described design principles.
  • Figures 2a, 2b and 2c illustrate the design development of such a network with series resonant shunt arms from what may be termed the prototype network, Figure 2a showing the prototype, Figure 2b an equivalent circuit and Figure 2c the final network.
  • Figure 2a shows the prototype
  • Figure 2b an equivalent circuit
  • Figure 2c the final network.
  • actual values of inductance, capacity and resistance are indicated in these figures in micro-henries, micro-microfarads and ohms respectively.
  • the prototype filter of Figure 2a has a log mid-frequency of megacycles and a band width of :2 megacycles.
  • the shunt capacities of 20 acids. include valve capacities and strays.
  • the two halves of the filter are symmetrical about the line AB each half constituting a compound section, the two sections being back-to-back.
  • FIGs 2a, 2b and 20 A represents the anode of valve l and G the control grid of valve 2.
  • a coupling network between a pair of vacuum tubes for extending the frequency range in which uniform amplification is obtained over that obtainable with the conventional resistancecapacity coupling network comprising a resistance connected in the anode circuit of the first tube, a second resistance connected in the grid circuit of the second tube, a first inductance, a coupling capacity and a second inductance connected between the anode side of the first resistance and the grid side of the second resistance, and a pair of additional inductances, one connected between the low potential end of the first resistance and the junction between the first inductance and the coupling condenser, and the other connected between the low potential end of the second resistance and the junction between the second inductance and the coupling condenser.
  • an interstage coupling network comprising in combination, an output anode resistor, an input grid resistor, an inductance connected in shunt across each of said resistors, and a coupling condenser.
  • inductances being subdivided by said points of connection that the portions which together with the coupling condenser are serially connected between the highpotential ends of the anode and grid resistors combine with the stray capacities effectively in shunt across the anode and grid resisters to increase the response at high frequencies, and the remaining inductance portions have such values relative to the coupling condenser as to increase the response at low frequencies.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microwave Amplifiers (AREA)
  • Amplifiers (AREA)
US267384A 1938-04-14 1939-04-12 Coupling network Expired - Lifetime US2245722A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB11571/38A GB514304A (en) 1938-04-14 1938-04-14 Improvements in or relating to electrical networks suitable for use as inter-stage coupling networks in electron discharge tube amplifiers

Publications (1)

Publication Number Publication Date
US2245722A true US2245722A (en) 1941-06-17

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BE (1) BE433827A (en))
GB (1) GB514304A (en))

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511185A (en) * 1946-08-03 1950-06-13 Du Mont Allen B Lab Inc Constant band width coupling circuit
WO1999044256A1 (en) * 1998-02-27 1999-09-02 Schreuders Ronald C Balancing apparatus for signal transmissions

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511185A (en) * 1946-08-03 1950-06-13 Du Mont Allen B Lab Inc Constant band width coupling circuit
US6031432A (en) * 1997-02-28 2000-02-29 Schreuders; Ronald C. Balancing apparatus for signal transmissions
WO1999044256A1 (en) * 1998-02-27 1999-09-02 Schreuders Ronald C Balancing apparatus for signal transmissions

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Publication number Publication date
GB514304A (en) 1939-11-06
BE433827A (en))

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