US2229705A - Means and method of amplifying electric wave energy - Google Patents

Description

Jan. 28, 1941.

MEANS AND METHOD OF AMPLIFYING ELECTRIC WAVE ENERGY 7 Filed March 1'7, 1958 an 10 -|Fo C 26 g I 15 15 {RM FFiIIIIIIiI Ftgui *Il w J8 INVENTOR.

K. RATH 2,229,705 I Patented Jan. 28, 1941 UNITED STATES MEAN S AND METHOD OF AIVIPLIFYING ELECTRIC WAVE ENERGY Karl Bath, New York, N. Y., assignor to Radio Patents Corporation, New York, N. Y., a corporation of New York Application March 11, 1938, s ri l No. 196,394

v 8 Claims.

The present invention relates to electric frequency discriminating systems or networks and methods of operating the same for use as filters, compensating or equalizing circuits, tone control, and other purposes well known.

More particularly the invention is concerned with systems or networks of the above character comprising one or more amplifiers such as electron discharge valves employing inverse or negative feedback or signal degeneration for selected predetermined frequencies or ranges of frequencies in such a manner as to obtain a desired resultant frequency response characteristic of the amplifier or associate circuit connected therewith.

Accordingly, an object of the invention is to obtain a desired frequency response characteristic of a single amplifier stage by use of inverse or negative feedback.

Another object is .to obtain a desired frequency response characteristic of a single amplifier stage normally having a broad frequency response by utilizing selective inverse or negative feedback.

Still a further object is the provision of an amplifier with intercoupling input and output elements normally producing a substantially broad frequency response and means for modifying the response characteristic of the amplifier by selective inverse or negative feedback to obtain a resultant response characteristic of any desired shape.

The above and further objects and advantages of the invention will become more apparent from the following detailed description taken with reference to the accompanying drawing forming part of this specification and wherein;

Figures 1, 3, 5, 6, and 7 show single electron valve amplifier stages embodying selective inverse feedback according to the invention.

Figures 2, 4 and 8 show frequency response curves explanatory of the function and operation of the circuits according to Figures 1, 3 and 7 respectively.

Like reference characters identify like elements throughout the different views of the drawing.

With the above objects in view, the invention in its general aspect contemplates the provision of a common return impedance for the grid and anode circuits of an amplifying valve to normally provide a degenerative or inverse feedback for the current or potential variations impressed upon the input circuit of the valve, and frequency discriminating elements or networks connected to said common impedance on the one hand and to one or more points in either the input or output circuit of the valve on the other hand thereby to suppress or reduce the effect of" inverse feedback for predetermined frequenciesor ranges of frequencies and resulting in an amplification and passing of these frequencies to the outpu circuit in such a manner as to obtain a desired E resultant input-output frequency response characteristic of the amplifier of any desired shape to suit any existing requirements.

The advantages of inverse feedback such as high operational stability, freedom from inter-1 ll) e e low n ise level, indep nd nce o l e characteristics, etc., are well known. In the prior art systems employing negative or inverse feedback, these advantages could not be fully realized without material loss of amplification due to the fact that all frequencies passed by the amplifier were subjected to the inverse feedback action; thereforeto obtain any amplification the degree of feedback had to be limited to prevent the loss of amplification caused thereby. By the improvements according to the present invention, a high degree of inverse feedback or degeneration is employed for all frequencies to which the amplifier is normally responsive and only the desired frequencies are by-passed around the inverse feedback impedance resulting in increased stability and efficiency and other desirable advantages.

Referring to Figure 1 of the drawing which shows a single resistance-coupled amplifier stage 39 employing inverse or negative feedback accord-. ing to the invention, item 10 represents an amplifying valve of standard construction in the example shown comprising a cathode l I which may be a directly or indirectly heated cathode, a grid I2 and an anode or plate l3. The anode is con-v nected to the cathode through a load impedance, in the example shown, a resistance M in series with a source of high potential for supplying the anode current of the valve such as battery [5 40 shunted by a by-pass condenser l5 and a common cathode return or negative feedback impedance, in the example shown, a resistance 16. Item I! is a coupling condenser connected between the anode and the output terminal c, -th e v other output terminal 41 being connected to the lower grounded end (ground l8) of the inverse or degenerative feedback resistance I61 Input wave energy which may be of audio, intermediate or high frequency is impressed upon an input 59 impedance such as resistance l9 across the input terminals a.-b. The impedance l9 has its upper terminal connected to the grid 12 and its we terminal to the wer o sround endor the resistance 15 throug a p ur li y of enqenser is 20 arranged in series. The junction points between the condensers 20 are connected through impedances such as resistance elements 2| in the example shown to the cathode, while the lower terminal of the input impedance I9 is connected to the cathode through an additional resistance 2|. There is further provided in the example shown a} resistance 22 connected between the upper terminal of the feedback resistance I 6 and the cathode shunted by a by-pass condenser 23 to provide proper operating grid biasing potential for the valve in a manner well understood. In an arrangement of this type the condensers 20 and resistance elements 2| form a high-pass filter connected across the common return or inverse feedback resistance IE on the one hand and terminated by the resistance 2| on the other hand which latter is preferably of the same value as the resistance It. As a result, the amplified high frequency components of an input signal Wave across the common return resistance IE will be passed by the high pass filter and produce across the terminating resistance 2| voltage variations corresponding to these frequencies Which voltages being applied in series with the grid circuit will oppose the input signal wave voltages of the same frequency which will therefore become degeneratedby this inverse feedback. The amplified lower frequency components however will be passed directly to the cathode or upper terminal of the inverse feedback resistance [6 and will therefore not be degenerated resulting in these lower frequency components to be amplified and transmitted to the output circuit connected to terminals cd.

In Figure 2 there is shown a frequency response curve of an amplifier according to Figure 1. Curve A represents the frequency response (output current or potential across c--d in suitable units such as 'db. units as a function of the frequency f of the input potential impressed upon ab) of the amplifier without the inverse feedback arrangement which is characteristic of a resistance coupled amplifier as shown and comprises a broad band of operating frequencies. Curve B shows the response characteristic with the inverse feedback system embodied in the amplifier as described and resulting in a low pass efiect with a cut-off frequency shown at in. In order to improve the sharpness of this cutoff in Figure 1, induction coils may be provided in place of the resistances 2| or of both the resistances 2| as well as the resistances l6 and 2|. It is further understood that any other type of amplifying valve such as a screen grid or pentode valve may be provided in place of a three element valve shown for illustration. Furthermore, it is understood that in place of a battery as an anode potential source, the space current for the tube may be supplied from a potentiometer'or a battery eliminator in common use in amplifier systems.

Referring to Figure 3 there is shown a system similar to Figure 1 wherein the filter associated with the inverse feedback resistance l6 is of the low pass type comprising resistance elements 2| serially inserted in the grid circuit in series with a further condenser 24 of large capacity and condensers 20 connected between the junction points of the resistance elements 2| and the cathode or upper terminal of the inverse feedback resistance 6. In this-manneran inverse response curve, i. e. a curve of the high-pass type, 'is obtained by an arrangement according 75 to Figure 3. This is shown by curve C in Figure 4, other details being substantially similar to the previously described circuit.

Referring to Figure 5, this is substantially similar to Figure 1 and differs therefrom merely by the fact that the resistance elements 2| are connected to different taps on the inverse feeds back resistance Hi. The response characteristic of this circuit'is substantially similar to the characteristic of the circuit of Figure 1 and shown in Figure 2.

Referring to Figure 6, this shows a circuit of the type according to Figure 3 and differs from the latter by the connection of the condensers 20 to variable taps of the cathode return or inverse feedback resistance Hi. The function and operation of this circuit is substantially similar to the circuit of Figure 3 and the response characteristic obtained is of substantially the same type as shown in Figure 4.

Referring to Figure 7, there is shown a further modification of a system according to the invention wherein a plurality of condensers 26 are connected between the cathode and different taps on the output or load resistance l4 thereby forming a low pass filter in the output circuit. There is further shown in Figure 7 the connection of the input terminal b to a point of positive potential of the anode source l5 to compensate for excessive steady or quiescent operating grid bias produced by the voltage drop through the inverse feedback resistance 6 to obtain a most favorable operating point on the valve characteristic. The tapped off portion of the source I5 is by-passed by a condenser l5".

In Figure 8 there is shown the frequency response curve for the circuit according to Figure 7. Curve A shows the response curve for the amplifier without the feedback arrangement. which corresponds to the curve characteristic of a resistance coupled amplifier. Curve D is the characteristic of the filter I4, 26 per se and curve E the resultant input-output response characteristic of the amplifier.

It will be evident from the above that the invention is not limited to the specific circuit arrangements and methods described for illus tration but that the novel concept and principle of the invention are susceptible of numerous variations and modifications coming within the] broader scope and spirit of the invention as defined in the appended claims. The specification and drawing are accordingly to be regarded in an illustrative rather than in a limited sense. I I claim:

1. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, coupling impedance means connected between the alternating potential reference point of the system and said grid and anode, respectively, a degenerative impedance connected between the cathode and the alternating potential reference point, said degenerative impedance being designed to present substantially equal impedance to all frequency components of the energy to be translated, and means to provide a plurality of circuit paths having different frequency discriminating characteristics between different points of said degenerative impedance and at least one point of one of said coupling impedance means, thereby to cause varying portions of said degenerative impedance to form a common effective cathode return path for said input and output impedance means for components of different frequency of the energy being translated.

2. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side connected to said grid, output circuit impedance means connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of said system, and means to provide a plurality of circuit paths having different frequency discriminating characteristics connected between the low potential side of said input impedance means and different points of said degenerative resistance, thereby to cause varying portions of said degenerative resistance to form an effective common cathode return path of said input and output impedance means for components of different frequency of the energy being translated.

3. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, an input circuit connected to said grid, a first output impedance connected to said anode, a second degenerative impedance connected between the cathode and the alternating potential reference point of the system, said degenerative imedance being effective in normally substantially equally reducing the amplifying gain for all frequency components of the energy being translated, and means to provide a plurality of circuit paths having difierent frequency discriminating characteristics connected between at least one point of said impedances and different points of the other impedance, thereby to cause varying portions of said degenerative impedance to form an effective common cathode return path for said input and output impedance means for components of different frequency of the energy being translated.

4. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side operatively connected to said grid, output impedance means connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of said system, a further impedance connected between the low potential side of said input impedance and the cathode, and a frequency discriminating network comprising series and parallel impedance elements having different impedance characteristics dependent upon frequency, said series elements being connected between the low potential side of the input impedance and a point of said degenerative resistance relatively remote from the cathode, and said parallel elements being each connected between a junction point of said series elements and a point of said degenerative resistance relatively close to the cathode, thereby to cause varying portions of said degenerative resistance to form an effective common return path for said input and output impedance means for high and low frequency components, respectively, of the energy being translated.

5. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side operatively connected to said grid, an output circuit connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of said system, a further impedance connected between the low potential side of said input impedance means and the cathode, and a frequency discriminating network comprising a plurality of capacity elements in series connected between the low potential side of said input impedance means and said reference point, and a plurality of resistance elements each connected between a junction point of said capacity elements and a point of said degenerative resistance remote from said zero reference point.

6. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side operatively connected to said grid, an output circuit connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of the system, a further impedance connected between the low potential side of said input impedance means and the cathode, and a frequency discriminating network comprising a plurality of series resistances connected between the low potential side of said input impedance means and said reference point, and a plurality of capacity elements, each connected between one junction point of said resistance elements and a point of said degenerative resistance remote from said reference point.

7. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side operatively connected to said grid, an output circuit .connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of said system, a further resistance connected between the low potential side of said input impedance means and the cathode, and a frequency discriminating network comprising a plurality of capacity elements in series connected between the low potential side of said input impedance means and said reference point, and a plurality of resistance elements each connected between a junction point of said capacity elements and the cathode.

8. In a translation system for electric wave energy, an amplifying tube comprising a cathode, an anode and at least one control grid, input impedance means having its high potential side operatively connected to said grid, an output circuit connected to said anode, a degenerative resistance connected between the cathode and the alternating potential reference point of the system, a further resistance connected between the low potential side of said input impedance means and the cathode, and a frequency discriminating network comprising a plurality of series resistance elements connected between the low potential side of said input impedance means and said reference point, and a plurality of capacity elements each connected between one junction point of said resistance elements and the cathode.

KARL RA'I'H.

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