US2206989A - Signal-translating circuit - Google Patents

Description

July 9, 1940. H.'A. WHEELER SIGNAL-TRANSLATING CIRCUIT Filled March 28, 1959 Patented July 9, 1940 PATENT OFFICE 2,206,989 SIGNAL-rmsmmc onwm'r Harold A. Wheeler, Great Neck, N. Y., assig-nor to Hazeltine Corporation, a corporation of Delaware Application March 28,

11 Claims.

This invention relates to signal-translating circuits and. while of generalapplication, it is of particular utility in the line-scanning output circuits of cathode-ray tube television apparatus.

In certain signal-translating systems', it is necessary to transform a signal of any given frequency within a wide range of frequencies or to trans-form a signal having a Wide range of component frequencies, and the transformer circuits utilized for such purposes are frequently such as to produce an undesirable irregularity in the frequency-response characteristic of the system at one or more particular frequencies within the operating range. Further, an undesired transient effect may be caused if the transformed signal comprises a wide range of component frequencies.

Thus, for instance, in a television receiver comprising an electromagnetic scanning circuit, it is desirable to translate a current having a sawtooth wave form which, in effect, comprises component frequencies of a very Wide frequency range. Furthermore, it is frequently desirable to provide the scanning current to the scanning Winding of the system from a vacuum tube through a step-down transformer. In such a system, the circuit comprising the scanning-Winding inherently comprises appreciable shunt capacitance which resonates with the associated circuit inductances and thereby tends to cause irregularities in the frequency-response characteristic of the circuit at one or more particular frequencies with the attendant undesirable effects mentioned above. Also, inherent capacitance coupling the transformer windings of such a system in opposition to their transformer coupling may cause a similar undesirable response but in opposite sense. Similarly, in a television receiver compris-ing an electrostatic scanning circuit, a step-up transformer is frequently utilized between the last vacuum tube in the scanning-signal translating channel and the scanning plates of the cathode-ray tube. In such a circuit also, capacitance across the output electrode of the tube, as well as the inherent capacitive coupling in opposition to the transformer coupling, may cause undesirable responses similar to those mentioned above.

It is an object of the invention, therefore, to provide a signal-translating circuit of the type under discussion which eliminates one or more of the above-mentioned disadvantages of systems of the prior art.

It is a further object of the invention to provide a signal-translating circuit comprising a stepdown transformer for translating scanning currents in a television system utilizing electromagnetic scanning, in which the detrimental effect of capacitance across the scanning windings of the system is substantially eliminated.

It is still another object of the invention to provide a signal-translating circuit comprising 1939, Serial N0. 264,525

a voltage-changing transformer for translating scanning currents in a television system, in which the detrimental effect of capacitance coupling in opposition to the transformer coupling is substantially eliminated.

In accordance with the invention, a signaltranslating circuit for passing a signal comprising a band of frequencies comprises a transformer having closely-coupled primary and secondary windings of substantially different inductances, a terminal circuit connected with the one of the windings of lower inductance, capacitance effectively across the terminal circuit, and capacitance effectively coupling the windings in opposition to their transformer coupling. The capacitances of such a system resonate with resultant inductance of the transformer and of the terminal circuit at a particular frequency within the band and, in accordance with the invention, the capacitances are relatively so proportioned with respect to the inductances of the system as substantially to balance out any irregularity in the coupling characteristic of the translating circuit between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of the said particular frequency of undesired resonance. Either of the above-mentioned capacitances may be comprised, in whole or in part, of inherent circuit capacitance of the signal-translating circuit, or either of the above-mentioned capacitances may be comprised, in whole or in part, of capacitance means added to the circuit to balance out the undesired irregularities in accordance with the invention.

Also in accordance with a preferred embodiment of the invention, the transformer is a stepdown transformer utilized to couple a vacuum tube to the scanning windings of a television signal receiver utilizing electromagnetic scanning. In accordance with another preferred embodiment of the invention, the transformer is a stepup transformer utilized to couple a vacuum tube to the scanning plates of a television receiver utilizing electrostatic scanning, preferably by means of a balanced circuit.

As used in this specification, the term closelycoupled refers to a coefficient of coupling of a higher order of magnitude than that between aircore transformer windings or radio-frequency transformers wherein the coeiiicient of coupling usually does not exceed a few per cent. In other words, in a transformer having closely-coupled primary and secondary windings according to this invention, the windings are as close as physical factors will permit and have a coefficient of coupling of not less than per cent and usually more, such as upwards of 90 per cent.

For a better understanding of the invention, together with other and further objects thereof,

reference is had to the following,v specication taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawing is a circuit diagram, partly schematic, of a complete television signal receiver comprising an electromagnetic line-scanning circuit embodying the invention; Fig. 2 is an electrical equivalent circuit diagram of a portion of the scanning-signal translating channel of Fig. 1; Figs. 3a and 3b are characteristic curves utilized to describe certain operating characteristics of the circuit of Fig. 2; Fig. 4 is a modification of the circuit of Fig. 2 utilized for obtaining relationships for proportioning thecircuit elements of Fig. 1 in accordance with the invention; Fig. 5a illustrates the load voltage of a prior art system similar to that of Fig. 1; Fig. 5b illustrates the load voltage of the system of Fig. 1; Fig. 6 illustrates a modification of the circuit of Fig. 1 to .provide a balanced signal-translating circuit; Fig. 7 illustrates a modification of the signal-translating circuit of Fig. l utilizing a transformer comprising separate primary and secondary windings; while Fig. 8 illustrates a modification of the circuit of Fig. 6 as utilized in the scanning-signal translating channel of a television receiver utilizing electrostatic scanning.

Referring now more particularly to Fig. 1 ofy the drawing, the Vsystem there illustrated comprises a television receiver of the superheterodyne type including an antenna system III, I I connected to a radio-frequency amplifier I2 to which are connected in cascade, in the order named, an oscillator-modulator i3, an intermediate-frequency amplier Ill, a detector I5, a video-frequency amplifier I 6, and an image-reproducing device I l, for example, a cathoderay receiver tube. A pulse-voltage line-frequency generator I8 and a field-frequency generator I 9 are coupled to the output circuit of detector I5 and to the sets of deiiecting windings 2i), 28 and 2l, 2i, respectively, the line-frequency generator I8 being coupled to linedeiiecting windings 20, 20 through a repeated 22, presently to be described. The stages or units I-IQ, inclusive, may allbe of conventional well-known construction so that detailed illustration and description thereof are deemed unnecessary herein. Y

Referring briefly, however, to the general operation of the system described above, television signals intercepted by antenna circuit I0, Ii are selected and amplified in radio-frequency amplifier I2 and coupled to the oscillator-modulator I3, wherein they are converted into intermediatefrequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier Ill and delivered to the detector I5. 'I'he modulation components of the signal are derived by the detector I 5 and the video-frequency signals are supplied to the video-frequency amplifier I 6,

wherein they are further amplified and fromwhich they are supplied in the usual manner to a brilliancy-control electrode of the image-reproducing device I'I. Synchmnizing signals are supplied from detector I5 to the control elements of the generators I 8 and I9. The intensity of the scanning ray Aof device il is thus modulated or controlled in accordance with the video-frequency voltages impressed upon its control electrode in the usual manner. Scanning waves are generated in the line-frequency and field-frequency generators I8, 22, and I8, which are controlled by the synchronizing voltages supplied from detector I5, and applied to the scanning elements of the image-reproducing device I1 to produce electromagnetic scanning elds. thereby to deect the scanning ray in two directions normal to each other so as to trace al rectilinear scanning pattern on the screen and to reconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1 embodying the present invention, there is provided a saw-tooth current generator including a vacuum tube 25 coupled to the output circuit of pulse-voltage generator I8. Therer are included in the output circuit of tube 25 a parallel-connected condenser 26 and resistor 21 effective to develop from the pulse current output of tube 25 a saw-tooth voltage wave, in a manner well understood in the art. This sawtooth voltage is coupled to the input circuit of a vacuum tube 28 through a coupling condenser 29 in order to provide a saw-tooth current through scanning windings 20, 20 from the output circuit of tube 28, the output circuit of tube 28 being coupled to the scanningwindings 20, 28 through a step-down autotransformer including windings 80, 3I The output circuit of vacuum tube 28 may have appreciable inherent capacitances, represented in the drawing by dotted-line condenser 32 across the entire circuit and dotted-line condensers 3l and 38 across the windings 3i and 38, respectively. These inherent capacitances tend to disturb the uniformity of variation of the current through scanning coils 20, 2li, which is detrimental during the trace intervals of the scanning cycle. In order to compensate for the eect of capacitance 32, therefore, there an inductance 33 connected in series with resistor 34 and parallel-connected condenser 26 and resistor 2l in the output circuit of vacuum tube 25.

In considering the characteristic of the circuit 22 of Fig. 1, it will be seen that any inherent capacitance 3I across winding 38 resonates with the associated circuit inductances at a particular frequency and\that any inherent capacitance 38 across winding 3i also resonates with the associated circuit inductances at a particular frequency. These two frequencies are, in general, different from each other and from the main resonant frequency of the output circuit of tube 28 as a whole and thereby tend to cause one or more irregularities in the coupling characteristic between generator I8 and scanning windings 20, 2li at frequencies at which such irregularities are not corrected by inductance 33 and, therefore, are detrimental. Therefore, in accordance with the invention, either or both of supplemental condensers 39 and #I0 are included in the circuit of Fig. l in parallel with capacitances 37 and 38, respectively, to balance out any irregularities in the coupling characteristics of the system at frequencies in the vicinity of an undesired resonance.

Reference is now made to Figs. 2-5b, inclusive, in order to show the manner in which the circuit of Fig. 1 is proportioned in order to balance out such undesired resonance. In Fig. 2 there is shown a circuit which is the electrical equivalent of a portion of the circuit of Fig. l. The transformer 30, 3l of Fig. l may be resolved into the uncoupled inductance components La, Lb, and Lm of Fig. 2 in a manner Well understood in the art, in which La-i-Lm is the total primary inductance and Lb-I-Lm is the total secondary inductance. In a closely-coupled transformer, the component Lb may be negative. Windings 20, 28

are represented in the circuit of Fig. 2 by the single inductance Lc, while capacitance Cb replaces capacitances 38 and 20 and capacitance is preferably provided ascenso Cm replaces capacitances 31 and 33 oi' Fig. 1. Capacitance 32 of Fig. 1 is replaced by capacitance Cs in the circuit of Fig. 2.

'I'he general coupling characteristics of the equivalent circuit of Fig. 2 are illustrated by the characteristic curves of Figs. 3a and 3b. Under most conditions, the transformer 30.' 3| and its associated inductances and capacitances has a main or fundamental resonant frequency, producing a major peak in the response characteristic, at a frequency f1, while the leakage inductance of transformer 30, 3| resonating with the associated circuit capacitances produces a minor peak at a frequency fz. The major peak alone is shown by the full-line curve of Fig. 3a and is a response characteristic which may be corrected by the coupling elements 33, 33. 26, and 21 to procure the desired over-all response characteristic from the system. The minor peak X of Fig. 3a is also present if the capacitance Cb in the secondary or low inductance circuit of Fig. 2- is relatively too great. On the other hand, the minor valley Y is present ii' the capacitance Cm of Fig. 2 is relatively too great. If the primary or high inductance side of the circuit of Fig. 2, that is, the side comprising terminals 3, is connected with an external circuit of very i low impedance, the main resonance oi' the transformer coupling system is destroyed and only the peak or valley caused by the spurious resonance of the leakage inductance remains, this circuit characteristic being illustrated in Fig. 3b. v It is, therefore, the purpose of the present invention to proportion the circuit of Fig. 2 in such manner as substantially to eliminate the minor peak X or valley Y.

lf the circuit of Fig. 2 is to balance out the above-mentioned undesired irregularity (peak or valley) in the coupling characteristic, it is necessary to obtain the eiect of no capacitance current flowing from the junction of capacitances Cm and Cb through either of the inductances La and la of Fig. 2. That is, equal capacitive currents should iiow into the junction of Cm and Cb through one of these capacitances and out through the other. In order to derive an expression for proportioning the circuit of Fig. 2 to meet this condition, it is to be compared with that of Fig. 4 where corresponding elements are given identical reference numerals. The condition set forth above is met if the terminals l and 2 of the circuit of Fig. 4 are at the same potential, as driven from terminals 3 and 3, so that no current would flow in a connection between these terminals. The following equations are derived on this basis, in which Ei represents the voltage across condenser Ca and Ea represents the voltage across either inductance Le or condenser Cb under the condition assumed:

from Equations l and 2 the following relation is derived:

A circuit in accordance with that 'of Fig. l and proportioned in accordance with Equation 3 is effective to balance out an undesired irregularity in the coupling characteristics of the system, because the capacitances Cb and Cm, representing condensers 31, 38, 33, and di) are then effective merely to supplement the capacitance C., or condenser 32, across the entire output circuit of tube 23.

The load voltage across scanning windings 20, 20 of Fig. 1, in a circuit in which the undesired irregularity is not balanced out, is illus,- trated by the curve of Fig. 5a. 'I'he effect of the undesired resonance is to produce a transient in tlie load voltage, especially during the early part of the trace interval and immediately following the retrace interval. If the circuit of Fig. 1 is proportioned in accordance with Equation 3, however, the load voltage across scanning windings 20, 20 is in accordance with that illustrated by the curve of Fig. 5b, from which, it is seen, the undesired transient has been eliminated. This'test may be used for adjusting supplemental condensers 39, 40 to secure the desired balance.

The output circuit of tube 28 of Fig. 1 may be balanced with respect to ground. In Fig. 6 there isillustrated a circuit corresponding to a portion il Fig. 1 comprising such a balanced network. Similar circuit elements are given identical reference numerals in the two figures. Ihe principal change which is made in the circuit of Fig. 6 is that each of the elements 30, 31, and 33 of Fig. 1 has been divided into two elements 30'., 31', and 33', respectively, in Fig. 6, the corresponding elements being connected in a balanced relation with respect to winding 3l of the transformer. f

Furthermore, it will be understood that, while an autotransformer has been shown in the circuit of Fig. 1, the invention is equally applicable to a circuit comprising a transformer having separate primary and secondary windings, such a circuit being shown in Fig. 7 where corresponding circuit elements have reference numerals identical to those of Fig. 1, except the high inductance transformer primary winding which is indicated at 30".

It will also be understood that the `invention is equally applicable to a circuit comprising a step-up transformer utilized to couple a vacuum tube to the scanning plates of a television receiver utilizing electrostatic scanning. In Fig. 8 there is illustrated a circuit utilized for this purpose, which is otherwise equivalent to that of Fig. 6. The input and output terminals of the circuit of Fig. 6 have been reversed in the cifcuit of Fig. 8 and the capacitance 32 of Fig. 8 may be comprised, in Whole or in part, of the capacitance of the scanning plates 50 of the image-reproducing device `l1. Winding 3| of Fig. 8 is coupled to the output terminals of a balanced saw-tooth voltage generator 5| of high impedance and either or both of capacitances 39 and 40 may be comprised, in whole or in part, of the output capacitance of the generator and the inherent capacitance of the transformer. In Fig. 8, there is no inductance corresponding to the scanning inductance Le of Fig. 2, so the relation of Equation 3 above is simplified by giving Le an infinite value:

The capacitance 37 and 33 or 31" and 33' in Figs. 1, 6, 7, and 8 providescoupling 'between the primary and secondary circuits of the transformer, together with its directly associated cv!- pacitances or other reactance elements. such as the load inductance 20, -20, has a resonant frquency which is usually much higher than the main resonant frequency of the system.. It is this spurious resonant frequency, denoted fr in Fig. 3, at which the resonance of the lower inductance circuit tends to cause an irregularity in the frequency-response characteristics or a damped transient oscillation. The resonance of this circuit is made ineffective by balancing the circuit capacitances and, if necessary, other impedances in the relations described above. The effect of balancing the capacitances associated with the winding 3i is to nullify the coupling of the transformer at the frequency where this spurious resonance would occur. The coupling 'the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention. y

What is claimed is:

1. A signal-translating circuit for passing a signal comprising. a band of frequencies, said circuit comprising, a transformer having closelycoupled primary and secondary windings of substantially dierent inductances, a terminal circuit connected with the one of said windings of lower inductance, capacitance effectively across said terminal circuit, and capacitance effectively coupling said windings in opposition to their transformer coupling, said capacitances resonating with the resultant inductance of said ,transformer at a frequency within said band, at

which vsuch resonance is undesired, and said capacitances being relatively so proportioned with lower inductance. capacitance effectively across said terminal circuit, and capacitance eifectively coupling said windings in opposition` to their transformer coupling, said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and said capacitances being relatively so proportioned with respect to said inductances as substantially to balance out any irregularity inthe coupling characteristics between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of said frequency ofA undesired resonance.,

3. A signal-translating circuit for passing a signal comprising a band of frequencies, said circuit comprising, a transformer having closelycoupled primary and secondary windings of substantially dierenu inductances, a terminal circuit connected with the one of 'said windings of lower-inductance, capacitance consisting at least partially of inherent circuit capacitance eiectively/across said terminal circuit, and capacitance effectively coupling said windings in opposition to their transformer coupling, said capacitances resonating with the resultant inductance of said transformer and said terminalmcircuit at a frequency within said band at which such resonance is undesired, and-said capacitances being relatively so proportioned with respect to said inductances as substantially to balance out any irregularity in the coupling characteristics between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of said frequency of undesired resonance.

4. A signal-translating circuit for passing a signal comprising a band of frequencies, said cir- .cuit comprising, a transformer having closelycoupled primary and secondary windings of substantially diierent inductances, a terminal circuit connected with the one of said windings of lower inductance, capacitance effectively across said terminal circuit, and capacitance consisting at least partially of inherent circuit capacitance eiectively coupling said windings in opposition to their transformer couplingVsaid. capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and said capacitancesbeingrelatively so proportioned with respect to said inductances as substantially to balance out any irregularity in terminal circuit, capacitance consisting of inherent circuit capacitance effectively coupling said windings in opposition to their transformer coupling, said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and additional capacitance effectively in parallel with one of said mst-mentioned capacitances and of such value as substantially to balance out any irregularity in the coupling characteristics between said terminal circuit and said winding of greater inu ascenso ductance at frequencies in the vicinity of said particular frequency of undesired resonance.

6. A signal-translating circuit for passing a signal comprising a band of frequencies, said circuit comprising, a transformer having closely-coupled prima-ry and secondary windings of substantially different inductances, a terminal circuit connected with the one of said windings of Tower inductance, capacitance consisting of inherent circuit capacitance effectively across said terminal circuit, capacitance consisting of inherent circuit capacitance effectively coupling said windings in opposition to their transformer coupling, said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and additional capacitance effectively in parallel with said capacitance across said terminal circuit and of such value as substantially to balance out any irregularity in the coupling characteristics between said terminal circuit and said winding oi' greater inductance at frequencies in the vicinity of said particular frequency of undesired resonance.

7. A signal-translating circuit for passing a signal comprising a band of frequencies, said circuit comprising, a transformer having closelycoupled primary and secondary windings of substantially different inductances, a terminal circuit connected with the one of said windings of lower inductance, capacitance consisting of inherent circuit capacitance effectively across said terminal circuit, capacitance. consisting of inherent circuit capacitance effectively coupling said windings in opposition to their transformer coupling, said capacitances tending to resonate with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and additional capacitance effectively in parallel with said capacitance effectively coupling said windings in opposition to their transformer coupling and of such .value as substantially to balance Vout any irregularity in the coupling characteristics between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of said particular frequency of undesired resonance.

8. A signal-translating circuit comprising, a. transformer having closely-coupled primary and secondary windings of substantially different inductances, said winding of greater inductance `having a self-inductance Liri-Lm, said winding of less inductance having a self-inductance Ln-l-Lm, and said primary and secondary windings having mutual inductance Lm, a capacitance Cb effectively across said winding of less inductance, and a capacitance Cm effectively coupling said windings in opposition to said transformer coupling, where the circuit parameters are as defined in the specification. said capacita-nces resonating with the resultant inductance of said transformer at a frequency at which such resonance is undesired, said inductancesand 'capacitances being proportioned in accordance with the relation:

Ct L.,

whereby any irregularity in the coupling characteristics between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of said frequency is substantially balanced out.

9. A signal-translating circuit comprising, a transformer having closely-coupled primary and secondary windings of substantially different inductances, said winding of greater inductance having a self-inductance Lu-l-Lm, said winding oi' less inductance having aself-inductance Lb-l-Lm, and said primary and secondary windings having mutual inductance Lm, a terminal circuit of inductance Le connected with said winding of less inductance, a capacitance Cb effectively across said terminal circuit, and a capacitance Cm eiectively coupling said windings in opposition to their transformer coupling, where the circuit parameters are as defined in the specification, said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency at which .such resona-nce is undesired, and said inductances and capacitances being proportioned in accordance with the relation:

whereby any irregularity in the coupling characteristics between said terminal circuit and said winding of greater inductance at frequencies in the vicinity of said frequency is substantially balanced out.

l0. A signal-translating circuit for passing a signal comprising a band of frequencies, said circuit comprising, an autotransformer having a plurality of windings connected in series. a terminal circuit connected with those of said windings that are common to the primary and secondary circuits of the transformer, capacitance effectively in parallel with said terminal circuit, and capacitance effectively in parallel with the others of said windings. said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and said capacitances being relatively so proportioned with respect to said inductances as substantially to balance out any irregularity in the coupling characteristics between said terminal circuit and said others of said windings at frequencies in the vicinity of said particular frequency of undesired resonance.

ll. A signal-translating circuit for passing a signal comprising a band of frequencies, said circuit cornprising, a transformer having separate but closely-coupled primary and secondary windings of substantially different inductances, a terminal circuit connected with the one of said windings of lower inductance, capacitance eectively across said terminal circuit, and capacitance e'ectively coupling said windings in opposition to their transformer coupling, said capacitances resonating with the resultant inductance of said transformer and said terminal circuit at a frequency within said band at which such resonance is undesired, and said capacitances being relatively so proportioned with respect to said inductances as substantially to balance out any irregularity in the coupling characteristics between said terminal circuit and said winding of higher inductance at frequencies in the vicinity of said particular frequency of undesired resonance.

HAROLD A. WHmlER

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