US2305743A - Amplifier - Google Patents

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Publication number
US2305743A
US2305743A US332819A US33281940A US2305743A US 2305743 A US2305743 A US 2305743A US 332819 A US332819 A US 332819A US 33281940 A US33281940 A US 33281940A US 2305743 A US2305743 A US 2305743A
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United States
Prior art keywords
transformer
impedance
frequency
output
amplifier
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Expired - Lifetime
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US332819A
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English (en)
Inventor
Six Willem
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Hartford National Bank and Trust Co
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Hartford National Bank and Trust Co
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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

Definitions

  • ⁇ be considered as approximately ohmic resistances so that matching is obtained if the transformation ratio of each of these corresponds to the square root of the ratio of the resistances to be matched.
  • impedance of the amplifier as measured between the terminals of the primary winding of the input transformer,
  • An amplifier which has an output transformer transformed in the above manner into a lowpass filter is particularly useful in connection with a negative feed-back by which, as is well known, non-linear distortion in the amplifier can be avoided.
  • the negative feed-back voltage is taken from the output circuit of an amplifier comprising an output transformer, phase diswinding capacities of the transformer may be neglected.
  • the input and output impedances of the amplifier can no longer be considered as ohmic.
  • the main object of my invention is to provide means by which the influence ⁇ of the leakageinductance and of the winding capacity of the input transformer or the output transformer, or both transformers of amplifiers, can be removed in the frequency-range to be transmitted, so that in this frequency-range the'input impedance or output impedance or both impedances of the amplifier always conserves an ohmic character.
  • a low-pass filter of the v,r-type has an image .impedance in the transmission range which is an ohmic resistance.
  • This resistance ⁇ is substantially constant in a considerable 'part of that range, but increases in the vicinity of the cut-off frequency.
  • This phase displacement may attain such a high value that the negative feed-back passes into back-coupling which may cause self-oscillation of the amplifier.
  • thevalue of the negative feed-back will vary-also at the higher frequencies.
  • phase of the l negative feed-back will of course vary, but also describe the same in more detail with reference to the accompanying drawings, in which:
  • Figure 1 is a schematic diagram of e. line amplifler
  • FIG. 2 is a schematic diagram of the line amplifier of Fig. 1 with equivalent circuits shown for the transformers,
  • Fig. 3 is a vschematic diagram of the line amplifier of Fig. 1 with equivalent circuits of the transformers at the higher frequencies
  • Fig. 4 is a graph showing the relationship between imag'e impedance and frequency
  • Fig. 5 is a schematic diagram of an. amplifier with negative feed-back and embodying the invention
  • Fig. 6 is a schematic diagram of an output circuit of an amplifier according to the invention.
  • Fig. 7 is a schematic diagram of an output circuit of an amplifier according to the invention and combining voltage feed-back and current feed-back,
  • Fig. 8 is an equivalent circuit for the ampilier of Fig. 7, and
  • Fig. 9 is a phase diagram of the circuit of Fig. 8.
  • the line amplifier shown in Figure 1 is connected between two transmission lines I and 6 and comprises a first amplifying tube i and an output tube 2 which has an internal resistance R2.
  • One or more amplifying tubes (indicated by the reference numeral 50) may be connected between theamplifying stages represented by tubes i and 2.
  • the amplifying tube I has an input circuit including an input transformer 3, which has a transformation ratio 1m, of such a value that the grid-cathode impedance of the tube I, which is determined by a resistance R1, is matched to the impedance of transmission line 4 whose impedance may be represented approximately by an ohmic resistance R.
  • condensers having values of (F1/nzl and C11/m2 are connected in parallel with the primary winding of the input transformer and in parallel with the secondary winding of the output transformer respectively.
  • the input transformer 3 and the output transformer 5 are thus transformed into low-pass filters.
  • a circuit such as shown in Fig. 2 is obtained.
  • the reference letters L1 and Le represent the primary leakage inductance and the secondary leakage inductance respectively
  • M1 represents the mutual inductance
  • n1 the transformation ratio of the input transformer 3.
  • the reference letters La and L4 indicate the primary leakage inductance and the secondary leakage inductance respectively
  • Mz indicates the mutual. inductance and n2 indicates the transformation ratio of the output transformer 5.
  • the image impedance Z,r of the lowpass filter may be represented -by the expression:
  • R is the nominal value of the image impedance which corresponds to the impedance of the transmission line l.
  • Fig.4 shows the image impedance Z.r as a function of the frequency f. and from the curve thereof it appears that the image impedance, in a very broad frequency-range below the cut-of! frequency fo, is approximately constant with a nomnal value R and then increases with the frequency.
  • a condenser can be connected in parallel with the secondary winding of the output transformer 5 so that a capacity C2 lies 'between the output terminals U1 and U2 in the diagram shown in Fig. 3, and that a low-pass filter is formed also'in the output circuit of the amplifier.
  • This filter is likewise proportioned so that the output impedance of the amplifier in the frequency range to be amplified is matched to the impedance R of the transmission line 6.
  • Fig. 5 shows an amplifier with voltage feedback and comprises two stages including amplifying tubes I and 2 interconnected by a network 1.
  • the primary winding of the input transformer 3 and the secondary winding of the output transformer 5 are shunted by condensers C1 and Cz respectively,
  • the amplitude of the back-coupled voltage induced in the winding 8 be maintained constant in the entire transmission band of the low-pass filter constituted by the output-transformer. This can be ensured by giving the capacity connected in parallel with the primary winding a'larger value, preferably equal to 2Cz.
  • the outputcircuit of the amplifying tube v2 is connected in the manner shown in Fig. 6 in which the same reference characters Vare used to indicate the same parts of Fig. 5.
  • the impedance Z measured between the primary terminals of the output-transformer 5 is now constituted by the image impedance Z1r and the impedance of a condenser Cz connected in parallel therewith.
  • the voltage feedback may advantageously be combined with a current feedback, and this will be explained with reference to Fig. 7.
  • the negative feedback consists of two components i. e. a voltage which is set up across the winding 8 and depends on the voltage set up across the primary winding of the output transformer 4, and a voltage which is set up across the resistance 9 and depends on the current traversing the primary winding.
  • phase-variations of the entire degeneratively back-coupled voltage with respectto frequencies lying outside the frequency-range are such that the negative feed-back never can pass into a back-coupling, as will be appreciated from the equivalent circuit shown in Fig. 8 and the corresponding phase-diagram shown in Fig. 9.
  • the impedance measured between the terminals of the primary winding ofthe output-transformer is represented by the image impedance Z1r of the low-pass filter.
  • Z1r the image impedance of the low-pass filter.
  • the voltage induced in the winding 8 corresponds to the voltage set up across the primary winding so that the entire degeneratively back-coupled voltage ei corresponds to the sum of the voltage across the impedance Z and the voltage drop across the resistance Ru which corresponds, to the resistance 9.
  • This resultant impedance Zn is indicated in the diagram shown in Fig.
  • the impedance Z1r is capacitative.
  • the value of this capacitative impedance decreases with the frequency.
  • the phase-angle of the total impedance Zz abruptly varies by an angle 4 which decreases with an increasing frequency.
  • the phase-angle of the degeneratively lback-coupled voltage varies in exactly the same manner.
  • the angle i is always smaller than 90; consequently the phase angle of the degeneratively back-coupled voltage always remains smaller than but decreases with an increasing frequency to thereby prevent the negative feedback from passing into a back-coupling.
  • an output transformer in said output circuit and provided with primary and secondary windings, current feedback means controlled by the current traversing said primary winding, and capacities connected in parallel with said windings, said capacities and the leakage inductance of the transformer forming a low-pass filter of the r type having a cut-off frequency corresponding at least to the highest frequency to be amplied.
  • an output transformer in said output circuit having a one-toone transformer ratio and being provided with a primary Winding and a secondary winding, a capacity connected in parallel with the secondary winding, and a capacity connected in parallel with the primary winding and having a value about twice the value of the first capacity,.
  • said capacities and the leakage inductance of the transformer forming a lowpass lter of the 1r type having a cut-olf frequency corresponding at least to the highest frequency to be amplified.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US332819A 1939-04-22 1940-05-01 Amplifier Expired - Lifetime US2305743A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2305743X 1939-04-22

Publications (1)

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US2305743A true US2305743A (en) 1942-12-22

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US332819A Expired - Lifetime US2305743A (en) 1939-04-22 1940-05-01 Amplifier

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US (1) US2305743A (xx)
NL (1) NL97706B (xx)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2721260A (en) * 1950-10-09 1955-10-18 Du Mont Allen B Lab Inc Television input circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2721260A (en) * 1950-10-09 1955-10-18 Du Mont Allen B Lab Inc Television input circuit

Also Published As

Publication number Publication date
NL97706B (xx)

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