US2928001A - Null circuits - Google Patents

Description

March 8, 1960 NULL CIRCUITS Filed D90. 15, 1955 J. F. M CLEAN WW W 3 Sheets-Sheet 1 JIIIS Ii 6 FIG.I FIG 2 5; PRIOR ART 2 PRIOR ART Fl G. 3 6

PRIOR ART I-- I9 l3 IO I'ri mil I2 I; 2-oc( 9 l6 ll FIG. 5

l'" e 20 2| 5 2s 3%; .5 Q3 II II 24 w -o3 FIG. 7 W f 21 29 I FIG. 8 PRIOR ART uvmvrm JOSEPH F. M0 CLEAN FIG. 9 AGENT March 8, 1960 J. F. MCLEAN 2,923,001

' NULL cmcurrs Filed Dec. 15, 1955 5 she ts sneet 2 POWER 69 SUPPLY IOOV.

INPUT AAA! AAAA AAAAAA vvvvvv FIG. I3

,2 INVENTOR.

' l JOSEPH F. MCLEAN F0 F FREQUENCY By AGENT March 8, 1960 J. F. MOCLEAN 2,928,001

7 NULL CIRCUITS File d Dec. 15, 1955 s Sheets-Sheet 3 IN VEN TOR.

JOSEPH F. MQCLEAN AGENT United States Patent NULL CIRCUITS Joseph F. McClean, Goshen, N.Y; I

Application December 15, 1955, Serial No. 553,228

i 13 Claims. (Cl. 250 27) This invention relates to frequency selective networks .and, in particular, to frequency selective networks employing active circuit elements. Further, this invention is primarily concerned with such active frequency selective networks as are characterized by transmission throughout an entire range of frequencies, except for a stop band of relatively small transmission, approaching zero transmission.

Such networks are useful in a manner. comparable to certain passive frequency selective networks of the socalled parallel-T, bridged-T, m-derived and like varieties and will be shown in'the description to follow to offer advantages of an electrical and physical nature over such networks in various applications.

Networks offering relatively narrow regions of small transmission are normally employed under circumstances demanding either rejection of a single undesired compo nent frequency in a waveform, while passing others ideally unattenuated, or for producing incidentalphase altering effects among the several components of a waveform. The latter use is important in so-called COI'I'CC.

tion networks for compensating collateral time delays normally occurring in transmission systems. Depending upon the application, the transmission region, in the neighborhood of the minimum transmission, or null,

frequency may be described as exhibiting gradual slope or steep slope of the curve depicting relative transmission as a function of frequency, the former being-analogous to a condition of low Q-a nd the latter analogous to a condition of high Q in a simple tuned circuit. Simig larly depending'upo'n application, transmission may be described in frequency regions relatively removed from the stop band as (l) uniform, both for frequencies above and frequencies below the stop band, (2) uniform with given gain or attenuation, on one side of the, stop band uniform with a different gain or attenuatio'non the other side of the stop band, (3) non-uniform with at tenuation a function of frequency on one sides of the stop band.

The networks to be described, which incorporate the principles of this invention, will be for conveniencerestricted to the classes (1) and (2) above. However, the principles of this inventionmay apply equally well to networks of class (3.) or to other classes not confined to these three. 1

An object of this invention is to provide a filter network having means for independently controlling null frequency, cut-off frequency and the Q of the network.

filter apparatus of the null type composed of resistance sideor on both 7 Patented Mar. 8, 1960 and but one type of reactance, incombination withactivecircuit elements.

Another particular object is toprovide a compact null circuit suitable for use at low frequencies.

Still another object is to providea high Q filter cir-.

cuit.

Still another object of this invention is to provide a filter circuit utilizing resistance elements and physically small inductance elements together with active elements while achieving the effects commonly attainable with but large inductances. j v

Still other objects and advantages will be in part apparent, and in part pointed out with particularity as the Figure 3 shows schematically a high-pass filter section, H

of the m-derived type.

Figure 4 is a schematic showing ofa form of active network embracing the principles of this invention.

Figure 5 is a schematic showing a second form of active network within the scope of this invention.

Figure 6 is a schematic showing third type of active network within the scope of this invention.

Figure 7 represents schematically one formof passive,

so-called bridged-T filter network.

Figure 8 is a diagram of one form of resistance-capacitance passive networkcornmonly known in the art as a parallel-T circuit.

Figure 9 is a diagram of still another active uetwork based upon the principles of this invention.

Figure lOand Figure 11 are schematic showings of alternative embodiments of active networks based upon the principles of this invention.

Figure 12 is a specific embodiment of the generalized circuit of Figure 4.

Figure 13 is a graphical representation of the filter characteristic of the filter of Figure 12 expressed as Attenuation vs. Frequency.

Figure 14 is a generalized schematic of a circuit corresponding to Figure 4 with inductances employed in place of the capacitances.

Figure 15 is a generalized schematic of a circuit corresponding to Figure 5 with inductances employed in place of the capacitances.

Figure 16 is a generalized schematic of a circuit corresponding to Figure 6 with inductances employed in place of the capacitances.

Figure 17 is a generalized schematic of a circuit correspending to Figure 9 with inductances employed in place of the capacitances.

Figure 18 is a generalized schematic-of a circuit corresponding to Figure 10 with inductanc'es employed in place of the capacitanees.

Figure 19 is a generalized schematic of a circuit corresponding to Figure 11 with inductances employed-in place of the capacitances.

For the purpose of defining the electrical properties of 3 ratio and will be used consistently as so defined in the discussion to follow.

Generically, the passive networks, described herein solely as exhibiting characteristics desirable in filter practice of the former art, may be classed in two' categories;

those employing freely the circuit elements of resistance, capacitance and inductance and those restricted in their composition to resistance and but one kind of reactance. In general, networks of the first, or unlimited, variety are distinguished in the practical sense by greater sharpness, or steepness of slope of the transfer ratio in the vicinity of the frequency of minimum transmission, while practical networks of both types offer in theory the possibility of a true zero of transmission at the null. This latter property is not strictly attainable in some unlimited net- Works due to the finite losses of practical inductances. For this reason, where, in the following complex voltages transfer ratios are developed for such networks, the inductive losses will be neglected and the resultant transmission will appear to permit such perfect nulls.

Referring now to Figure 1, the terminals 1 and 2 taken together comprise input terminals of a network, in which the inductance t and the capacitor are connected in parallel, one end of the combination terminating in the terminal 1 and the second end connecting to a terminal 3 which constitutes one output terminal of the network. The other output connection to the network is made to the common terminal 2 and the network is completed by the resistor 6 connected between the terminals 2 and 3. This network will be recognized as a simple type of antiresonant trap circuit and, if the losses inherent in the inductance 4 are neglected, can be readily shown to exhibit the complex voltage transfer ratio:

Where w represents the angular frequency, 1' is a symbol equal to /1, and p represents the product jw. In this case the co-efiicients of the several terms are given by:

In Figure 2 there is represented a form of so-called m-derived low-pass filter section in which 1 and 2 comprise input terminals, 3 and 2. comprise output terminals, an inductance 4, interconnects the terminals 1 and 3, a capacitor 5, likewise interconnects the terminals 1 and 3, the capacitor 7, is connected between the terminals 3 and 2 and a resistance 6 is also connected between the terminals 3 and 2, completing the network. Once again neglecting the losses inherent in the inductance 4, the complex voltage transfer ratio may be derived:

the symbols j and w respectively being /1 and the angular frequency of'the applied wave and the symbol p again representing their product. The co-eflicients, in terms of the constants of the network, being A similar network is set forth in Figure 3 which represents a high pass filter section of the m-derived type, and in which 1 and 3 comprise respectively input and output terminals. The terminal 2 serves as a common connection for both input and output. The inductance is connected between the terminals 1 and 3, The capacitor 5 is likewise connected between the terminals 1 and 3. The inductance f5 interconnects the terminals 3 and 2 which are also interconnected by the resistance 6 which completes the network. The complex voltage transfer ratio for the network of Figure 3 is found to be:

With 1', w and p defined as before, the several co-efficients for the circuit of Figure 3 become:

ent common passive combinations of the three circuit parameters of resistance, inductance and capacitance which have in their practical embodiments useful electrical properties. Although the ideal performance permitted by their respective complex voltage transfer ratios is not possible with physically realizable inductances, in many applications losses of the reactive elements can be curtailed to a degree permitting a close approximation of the ideal. v In other applications, however, it is not possible to achieve sufi'iciently good components to produce the performance desired. For example, when, in the course of designing such passive networks for operation at lower and lower frequencies, a point is reached where inductors of reasonable size, Q and cost become difficult to produce, the passive networks discussed, as well as those offering similar transfer ratios, do not provide a solution. It is thus an object of this invention to provide alternative networks, composed of resistance and but one type of reactance, in conjunction with active circuit elements, which not only overcome the practical shortcomings of passive networks, containing resistance and both types of reactance, but also to provide such active networks capable of the theoretical infinite-Q performance of non-realizable passive networks.

Figure 4 is one form of active network embodying the principles of this invention, in which: the terminal 1 provides a means for connecting a source of input voltage, in association with the common terminal 2; the terminal 3 in association with the common terminal 2 forms a means for observing the output voltage. The elements 9, 10, 11, 12 and 19'having the respective gain constants k k k k k are active unilateral translating devices whose common characteristic is their ability to repeat at their output terminals voltages applied to their respective input terminals such voltages modified only by the said dimensionless proportionality constants k k k k k and exhibiting the dual properties of relatively high input impedance and relatively low output impedance with respect to theimpedances coupled to their terminals, as observed in the vicinity of the so-called cut-off frequency of the entire network. The active devices 9 and 19 are mutually fed from the input terminal 1. The resistance 13 is connected between the output of the device 19 and the input of the device 10. The capacitor =16 is similarly connected from the output of the device .9 to the input of the device 11. A capacitor 14 is connected to the input of the device '10 and the remaining terminal of the capacitor 14 is joined to the resistance 15, the remaining terminal of the latter being connected to the input side of the device 11. A resistance 17 connects from the output side of the device 10 to the input side of the device 12 which is also connected to one end of .the capacitor 18. The opposite terminal of the capacitor lAnalysisof the circuit, of FigureAfor the, complex voltagetransfer ratio reveals the expression: T r

and upon the fulfilhnent of the condition:

R c, =.R,c,='Rc

the above-reduces to the. form:

E 'E+BP+DP the symbols jand w defined 'as before, the several coefficients become:

Thus, by proper selection of the circuit parameters R,

' lossless reactances was requiredto produce ;a perfect null in the examples given, no-such restriction :exists for the embodiment of this invention in Figure 4, provided only that the condition R CiR C stated above is fulfilled.

Figure is another embodiment of the principles of this invention whose circuit is in all respects vsave one identical to that of the circuit of'Figure 4 and whose component parts bear identicalinumbers. Whereas in thecircuit of Figure 4. the capacitor 14 .is terminated at the output connection of the active device 12 in the circuit of Figure 5 the capacitor ,14 is terminated instead at :the common circuit terminal 2, The form of the transfer equation is unchanged and the co-efiicientsof the several terms are unchanged, with the exceptionof thesecond denominator'term co-eificient, which becomes:

Figure 6 is a representation of still another "circuit employing the principles of this invention, identical in all respects save one to the circuit of Figure 4 and whose component parts are identical and bear identical numbers in the drawing as those comprising the circuit of Figure 4. Whereas in the circuit of Figure 4 the resist: ance 15 is terminated at one end at the output connection of the device 12 in the vcircuit of Figure 6 the resistance15- is connected instead to the common circuit terminal 2. The form of the transfer equation given for the circuit of Figure 4 applies equally to the'equation for the complex voltage transfer ratio of the circuit of Figure 6 and the co-efficients of the terms, except for the co-eificient of the second denominator termsare'identi cal. The second denominator terms co-efilcient is found to be:

In practice the circuits of the several drawings, Figure 4, Figure 5 and Figure 6 difier in performance only'in the conceivable minimum value of the co-efiicient B. vAn examination of the mathematical effects of control over the magnitude of the said co-efiicient B reveals that this co-efiicient controls the steepness of the plottedivoltage transfer ratio curve in the vicinity of the null, i.e., the sharpness of 'the'null, such eifect appearingininverse of the co-efficient, B.

The usefulness of the described circuits of Figure 4,

'Figure'S and Figure 6 is not limited to the stimulation of drawings of Figure .1, Figure 2 and Figure 3 which, it

has been noted, are capable of true nulls only when theoretically composed of lossless reactances in whole or in part. Such circuits embracing the principles of this invention may also be employed in lieu of those types of passive circuits which, though constituted of realizable reactances and their accompanying losses or resistive components, are, by virtue of special design characteristics capable of producing true nulls. .An e'xampleof a class of networks capable of true nulls is the so-called bridged-T network of Figure 7.

Referring to Figure 7,'the terminals 1 and 2 constitute input'terminals to a network, the terminal 2 being common .to both input and output. The output terminals 3 and 2 provide access to the output voltage, e which appears when the driving,.or input, voltage is applied to the input terminals. The inductance 20 is connected between the terminals 1 and Stogether with itsloss re-' sistance 21 here representedas a physical resistance in series with the said inductance 20. The capacitor 22 is connected at its one end to the terminal 1 and at its second terminus to the capacitor 23 and to the resistance 24. The remaining terminal of the capacitor 23 is connected to the circuit output terminal 3 and the circuit is completed by'the connectionof the resistance 24 to the common terminal 2.

The solution for the complex voltage transfer ratio of the circuit of Figure 7 is of the form:

, where the symbols 1' and w represent-V-l and the angular frequency respectively, and the several co-efiicients are as follows:

Thus it is seen that the circuits of Figure 4, Figure 5 and Figure 6 comprised of active circuit elements, re

sistance and but one itype'of reactance, may also be given performance characteristics similar to passive circuits, employing resistance and both types of reactance known to the art asbridged-T circuits, with the additional property, as respects the active network, of simple control of circuit Q and the possibility of realizing cir- :,cuit Qs in excess ofithe capabilities of the passive networks.

Referring now to Figure 8, the drawing illustrates a common type of null circuit of the prior art, known as a parallel-T. Again the network is provided in the drawing with input terminals 1 and 2 of which 2 is a terminal common. to both input and output and with output terminals 3 and 2. The resistance 25 is connected to the input terminal 1 at its one juncture and to the capacitor connected at its far end to the common'circuit 2. The

circuit is completed by the junction of the remaining ends of the resistance (Aland the capacitor 29 to each other and to the output terminal 3. Itis found upon ere analysis that the complex voltage transfer ratio for this circuit is given by the equation:

Z 1 +1 2 2) 2102 (CZZRIRZ) -j 1 1 CZFRZ) r '8' 55' and capacitor 56. ,The voltage appearing at the common junction of the two components 55""and 56' is which equation reveals that the parallel-T network exhibits a real null when the real and imaginary parts of the numerator respectively are zero, a condition requiring that R1C1=R2C2.

In Figure 9 is shown a network within the scope of this invention, which, while resembling the parallel-T in many respects, possesses characteristics which render it markedly difierent and superior in performance and utility to that of the said parallel-T circuit. Circuit ele ments in the Figure 9 bear like numbers as those in the Figure 8 and are connected in like manner with the following exceptions: the addition of an active unilateral translating device 31, which has the attributes of such devices as previously described herein, so that its input is connected to the circuit output terminal 3 and its output terminal forms a common junction with the capacitor 26 and the resistance 28 said terminals of the said capacitor 26 and resistance 28 being those terminals connected in the circuit of Figure 8 to the common ter minal 2.

Analysis of the circuit of Figure 9 reveals a complex voltage transfer ratio:

in turn applied tothe grid of cathode follower tube 57.,

The capacitor 64-resistor 69 arm of the network corresponding to resistor 15 and capacitor 16 is driven in like fashion with the voltage across resistor 63. The junction of capacitor 64 andresistor 69 is-connected to the grid of cathode follower tube 61.

A resistance 5Q-capacitance 60 branch is connected between the respective cathodes of cathode follower tubes 57 and 61, the junction of resistor 59 and capacitor 60 being connected to the grid of cathode follower tube 70, whose cathode provides output voltage through the"D.C. blocking capacitor 67. The output voltage may be derived from output terminals 72. The grid of cathode follower tube 66 is connected to the variable tap of resistor 71 permitting a selected portion of the output voltage to be applied between the junction of capacitor 56 and resistor 59. The generalized circuit of Figure 4 terminates at terminal 3 which point is also shown in Figure 12.

In operation the three R-C time constants are made equal (R C =R C =R C ),where R is the resistance in ohms and C is the capacitance in farads. The

where the symbol k is a constant representing the gain of the active device 31 and the symbols 1', w and p are as previously defined. The vnumerator of the latter expression is identical in all manner with that of the transfer equation of the parallel-T circuit of Figure 8 thus the conditions necessary for a transmission null are also identical. it will be noted that the interposition of the active device 31 serves to modify the co-efiicient of the first and second order denominator terms in w and 12, such that increasing k serves to reduce the magnitude of these co-eflicients, having the physical significance of increasing the sharpness or rapidity of change of transmission in the vicinity of the null.

Figure 10 and Figure ll are modifications of the circuit of Figure 9 in a manner analogous to the relationship of the circuits of Figure 6 and Figure 5 to the circuit of Figure 4. Analysis of the circuits of Figure 10 and Figure 11 reveal transfer equations identical in form to the transfer equation applying to the circuit of Figure 9 and-differing from it only as respects the interrelation between the active gain factor k and the co-eflicients of the first and second order denominator terms.

While I have elected'to show generalized schematic circuits so as to make the basic concepts of this invention readily understood, I wish it to be appreciated that the practical embodiments corresponding thereto may be built in accordance with standard engineering practice. By Way of example, the circuit of Figure 4 has been implemented in Figure 12. The other generalized circuits may be translated in a like manner. It should be noted that while I have chosen to show triode vacuum tubes as the translating device, I regard the use of other translation devices within the scope of this invention.

Referring now to Figure 12, a pair of input terminals 50 have connected thereto a D.-C. blocking capacitor 51, which is in turn connected to the grid of cathode follower tube 53; this corresponds to terminal 1 of Figure 4. Resistor 52 serves as a grid resistor and potentiometer resistor 54 the cathode resistor. This cathode follower stage serves as a matching and isolating stage and repeats across low impedance resistor 54, the A.-C. signal, applied to high impedance input terminals 50.

A second cathode follower stage utilizes tube 68 driven from a variable tap of potentiometer 54. The resistor 13 and capacitor 14 of Figure 4 are shown as resistor all) value of M is controlled by thertap setting of potentiometer 54- and the Q is adjusted by means of the tap,

setting. of potentiometer 71.

In practice particular filter characteristics are realized by the cascading of so-called filter sections, each ,of

which contributes important properties to the aggregate performance. Thus, by way of example, it is. common to compose a filter of one or more sections of the socalled constant-k or similar typesuch sections con tributing continuingly greater attenuation with frequency removal from the pa-ssband-combined with one or'more sections of m-derived or related types; The said inderived sections contribute the desired property of rapid attenuation beyond cut-0d in the region of frequenciesv In preparing sections of the constant-k or like type, con-' trol is ordinarily exercised over the cut-off frequency. the rate of attenution per octave of frequency departure in the stop band and the peaking, or Q factor, in the immediate vicinity of cut-off. In nz-derived or like sections control is available to the designer over .the' above properties and, in addition, over the null, or maximum attenuation, frequency.

Referring in; particular to the'network of Figure 4. and.

the corresponding general expression for the complex voltage transfer ratio thereof and also to the passive.

networks of Figure 2 and Figure 3 and the respective expressions for their complex voltage transfer ratios, it is apparent that said expressions are all identical as respects the frequency-containing terms and differ only as respects the several dimensionless co-efficients. Thus, specifically, to simulate entirely the voltage transfer-ratio of the low-pass network of Figure 2 by means of the network of the present invention shown in FigureA, one

need adjust the resistances, ,capacitances and gain con,

stants of thelatter to produce. co-e'fficients A, BQD, E

and G identical to those of the networkof Figure 2 maybe conveniently adjusted, for example, by manipulation of the respective gain constants k and k for simulation of circuit m. Further inspection will reveal that the conventionally defined cut-off frequency of the simulating circuit is controlled entirely by the coefficients D and 'E, which in turn are conveniently adjustable by manipulation of respective resistances and capacitances of the network. Lastly, the peaking or Ql factor of the simulation is tied to duplication of the co-eflicient B, which may be adjusted, without affecting prior adjusted cut-01f and null, by manipulation of the gain constant k In an exactly parallel procedure it may be shown that complete simulation of thepassive high-pass network of Figure 3 may be had also by proper control of the design constants of the network of Figure 4 of. this invention. 7 a

By exactly similar procedures it may be shown that i the networks of this invention, Figure andqFigure 6,

may be employed to exactly simulate in respect to complex voltage transfer ratio the passive networks described by Figure 2 and Figure 3 as well .as those of Figure 1, Figure 7, Figure 8 and other networks.

When employed in lieu of the cited conventional passive networks and others generically similar, certain advantages accrue which make such substitution particularly advantageous: (l) The restriction of circuit elements to resistance-capacitance (or resistance-inductance) combinations and the corollary elimination of one form of reactance make possible physical realization of properties not possible with conventional networks. Example: complete realization of low-frequency filter designs normally prohibitive or impossible to achieve using inductances; (2) independent control over the separate properties of null frequency, cut-oif frequency and peaking (Q) not possible because of the physical interdependence of critical network properties in the latter. Example: the peaking of conventional passive filters is inextricable tied, in some cases, to the physical limitations of Q in inductors, limiting the possibility of modifying this important property in the finished filter; (3)

cuit;.a first two terminal-resistor having one of said terminals' connected in series with said first translation device output circuit; a second translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the other of said terminals of said first resistor; a second two-ten terminal of said first reactance and said input circuit being connected in parallel with said first translation device input circuit; a fourth translation device having a I terminals of said second resistor; a third two-terminal high impedance input circuit and a low impedance output circuit, said input circuit being connected .to the other terminal of said first reactance; a second two-terminal reactance having one of said terminals connected to said fourth translation device output circuit and the other of said terminals connected tothe other of said connected to the other said terminal of said third reactance; and means for feeding back a portion of the output signal to a portion of said apparatus isolated from said input signal introducing means by one of said translation devices.

2. Theapparatus of claim 7 wherein said reactances are capacitors. I Y

3. A frequency sensitive apparatus comprising in com- Q bination: a first translation device having a high impedance input circuit and a low impedance output circuit; a first two-terminal resistor having one of said terminals connected in series with said first translation device output circuit; a second translation device having a separation of the problem of achieving a suitable overall voltage transfer ratio in a section or in an entire filter from impedance conditions, either at input or output, or at intermediate points among said sections. Design of passive resistance-inductance-capacitance filters is not possible without close simultaneous attention'to'impedances as well as to voltage transfer. Impedance considerations frequently impose severe limitations upon the attainable voltage transfer properties.

A typical attenuation curve with reference to frequency is shown in Figure 13.

In Figures 14 to 19 I have shown inductances substituted for the capacitances of the equivalent filters of Figures 4, 5, 6, 8, 9, 1i) and ll.

In order to make readily apparent the substituted components, they have been identified as inductance 26L in place of capacitor 26 and inductance 27L in place of capacitor 27, etc.

While I have disclosed what is at present considered the bmt mode for carrying out the invention, it will be obvious to those skilled in the art'that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modificahigh impedance input circuit and a low impedance output circuit, said input being connected to the other of said terminals of'said first resistor; a second two-terminal resistor having one of said terminals connected tosaid second translating device output circuit; a first two-ter- I minal reactance; a third translation device having a high impedance input circuit and a low impedance output'circuit, said output circuit being connected to one terminal of said first reactance and said input circuit being connected in parallel with said first translation device input circuit; a fourth translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the other terminal of said first reactance; a second two-terminal reactance having one of said terminals connected to said a fourth translation device output circuit and the other of said terminals connected to the other of said terminals of said second resistor; a third two-terminal reactance having one terminal connected to the common junction of said first resistor and said second translation device input circuit; .a third two-terminal resistance having one terminalconnectedto the common junction of said first reactance and said fourth translating device input cirtions as fall within the true spirit and scope of the inpedance input circuit and a'low impedance output circuit; a fifth translation device having a high impedance input circuit and a lowimpedance output circuit, said input circuit being connected to the common junction of said second resistor and said second reactance, said output circuit being'connected so as to provide a signal to at least one of said other terminals of said third reactance and said third resistor associated frespectively with said second and fourth translation device input circuits; means for introducing a signal to said first'and third translation device input circuits and means for deriving a signal from said apparatus. j

4. .A frequency sensitive apparatus comprising-in combination: a first translation device having a high impedance input circuit and a low-impedance. output cir- 7 11 cuit; a first two-terminal resistor having one of said terminals connected in series with said first translation device output circuit; a second translation device having a high impedance input circuit and a low impedance output circuit, said input being connected to the other of said terminals of said first resistor; a second two-terminal resistor having one of said terminals connected to said second translating device output circuit; a first two-terminal reactance; a third translation device having a high impedance input circuit and a low impedance output circuit, said output circuit being connected to one terminal of said first reactance and said input circuit being connected in parallel with said first translation device input circuit; a fourth translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the other terminal of said first reactance; a second two-terminal reactance having one of said terminals connected to said fourth translation device output circuit and the other of said terminals connected to the other of said terminals of said second resistor; a third two-terminal reactance having one of said terminals conected to the common junction of said first resistor and said second translation device input circuit and the other of said terminals comprising a common input-output terminal for said apparatus; a third two-terminal resistor having one terminal connected to said fourth translation device input circuit; fifth translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the common junction of said second resistor and said second reactance and said output circuit connected to the other said terminal of said third resistor; means for introducing a signal to said first and third translation device input circuits and means for deriving an electrical signal from said apparatus.

5. A frequency sensitive apparatus comprising in combination: a first translation device having a high impedance input circuit and a low impedance output circuit; a first two-terminal resistor having one of said terminals connected in series with said first translation device output circuit; a second translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the other of said terminals of said first resistor; a second two-terminal resistor having one of said terminals connected to said second translating device output circuit; a first twoterminal reactance; a third translation device having a high impedance input circuit and a low impedance output circuit, said output circuit being connected to one terminal of said first 'reactance and said input circuit being connected in parallel with said first translation device input circuit; a fourth translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the other terminal of said first reactance; a second two-terminal reactance having one of said terminals connected to said fourth translation device output circuit, and the other of said terminals connected to the other of said terminals of said second resistor; a third two-terminal reactance having one terminal connected to the common junction of said first resistor and said second translation device input circuit; a third two terminal resistance having one terminal connected to said fourth translation device input circuit and said other ofsaid terminals comprising a common input-output terminal of said apparatus; a fifth translation device having a high impedance input circuit and a low impedance output circuit, said input circuit being connected to the common junction of said second i stor and said second reactance, said output circuit being connected to the other of said terminals of said third reactance; means for introducing an electrical signal to said first and third translation device input circuits and means for deriving an electrical signal from aid apparatus.

6. A' frequency sensitive apparatus 'for producing an output signal difiering from an input signal including signal input means and means for deriving an output signal comprising: a first branch circuit, interconnecting said signal input means and said signal output means, including at least one translation device having a high input circuit impedance and a low output circuit impedance and a plurality of resistors in cascade; a second branch circuit in parallel with said first branch circuit comprising at least one translation device having a high impedance input and low impedance output circuit and a plurality of reactances in cascade; and a feedback circuit including a translation device, having a high input circuit impedance and a low output circuit impedance in cascade with an impedance element, said feedback circuit being interposed between said means for deriving an output signal and an intermediate portion of one of said branch circuits.

7. A frequency sensitive apparatus for producing an output signal differing from an input signal, including a two terminal signal input circuit means, including a first terminal and a second terminal, and a two terminal signal output circuit means, including a third terminal and said second terminal, comprising: two branch circuits, one of said branch circuits including a plurality of resistor elements connected in cascade between said first and'third terminals and the other of said branch circuits including a plurality of reactance elements con nected in cascade between said first and third terminals so that said branch circuits are in parallel; a signal feedback circuit connected between said third terminal and a point on one of said branch circuits between a pair of said cascaded elements of said branch circuit, said signal feedback circuit including an element of the type included in the other'of said branch circuits anda translation device having a high impedance'input circuit and a low impedance output circuit, said last named element being connected in cascade between said one branch circuit and said translation device output circuit; a signal coupling circuit including said translation device connected between said signal output means, and a point on said other branch circuit between a pair of said cascaded elements of said other'branch circuit; and an element of the type included in the said one branch circuit connected in series with said signal coupling circuit.

8. The apparatus of claim 7 wherein translating devices are interposed between each of said branches, and said signal input means, said translating devices being characterized by a high impedance input circuit and a low impedance output circuit.

9. The apparatus of claim 7 wherein translating devices having high input impedance circuits and low impedance output circuits are interposed between said branch circuits and said signal input means and between succeeding cascaded elements in each of said branch circuits.

10. A frequency sensitive apparatus for producing an output signal differing from an input signal includ ing signal input means and means for deriving an output signal comprising: a first branch circuit, interconnecting said signal input means and said signal output means, including at least one translation device, having a high input circuit impedance and a low output circuit impedance, and a plurality of resistors in cascade; a second branch circuit in parallel with said first branch circuit comprising at least one translation device, having a high impedance input and a low impedance output circuit, and a plurality of reactances in cascade; and a feedback circuit comprising a translation device having a high impedance input circuit and a low impedance output circuit in cascade with an impedance element, said feedback circuit being interposed between said means for deriving an output signal and a point common to a plurality of said reactances in said second branch circuit so termediate portion of one of said branch circuits.

11. A frequency sensitive apparatu's for producing an output signal differing from an input signal including signal input means and means for deriving an output signal comprising; arfirst branch circuit interconnecting said signal input means and said signal output means including at least one translation device having a high input circuit impedance and a low output circuit impedance and ajplurality of resistors in cascade; a second branch circuit in parallel withsaid first branch circuit comprising at leastone translationdevice having a high,

impedance inputiand low impedance output circuit and .f y

a plurality of reactances in cascade; and a feedback circuit comprising a translation device having a high impedance input circuit anda low impedance output cir-' cuit in cascade; with an impedance element, said feedback circuit being interposed between said means for deriving an output signal and appoint common to a plurality of said resistors in said first branch circuitso as'to feed back a portion of said output signal to an inter-- mediate portion of one of said branch circuits.

1 :14 a said meansjfior deriving an output signal and an intermediate portion of one of'said branch circuits.

13. A frequency sensitive apparatus for producing an output signal differing from an input signal including signal input" means and, means for deriving angoutput signal comprising: a first branch circuit interconnecting said signal input means and said signal output means including at least one translation device, having a high input circuit impedance and a low output circuit imedance anda plurality ofresistors in cascade; a second branch circuit in parallel with said first branch circuit comprising at least one translation-device, having a high impedance input and low impedance output circuit, and

a plurality of reactances in cascade; and a feedback cir- 12. A frequency sensitive apparatus for producing an device having a high impedance input circuit and alow impedance output circuit in cascade with an impedance element, said feedback circuit being interposed between r having a high impedance input-circuit and a low i111 pedance output circuit interposed betweenza pair of said reactances; and a feedback circuit including a translation cuit comprising a two-terminal reactance, a' two-terminal resistance and a translation device having a high im-' pedance input circuit and a low impedance output circuit, said input circuit being connected to said means for'deriving an output signal and said output circuit connected to one terminal of eachof said two-terminal resistance and said two-terminal reactance,the other said terminal of said resistance being connected to a pointcommon to a plurality of said reactances and the other said terminal of-said'reactance being connected to a point common to a plurality of said resistancesfor feeding back a portion of said output signal "to intermediate portions of said branch circuits.

References Cited in the file ofthis patent UNITED STATES PATENTS 3 2 ,341,067 Wise Feb. 8, 1944 2,565,497 'Harling .1. Aug. 28, 1

. 2,581,456, Swift Ian. 8, 1952 2,658,993 Seeley Nov. 10, 1953 2,672,529 Villard Mar. '16, 1954 2,692,343 Spiro --Oct. 19, 1954 2,756,283 Bach July 24, 1956 Sziklai. r Nov. 20, 1956'

Images