US2389025A - Synchronizer for oscillators - Google Patents

Description

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SYNCHRONI ZER FOR OSCILLATORS Filed Jan. 1o. 1942 2 sheets-sheet 1 Z@ f Jr/vrf//wN/z//v 0K 50K 500 RMU/mf MHSTER @msm/rw? Y v f TUBE aff/M701? mm1/ENC),

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SYNCHRONIZER FOR OSCILLATORS I Filed Jan. l0, 1942 2 Sheets-Sheet 2 JVENTOR.

Patented Nov. 13, 1945 SYNCHRQNIZER FOR OSCILLATORS Richard L. Campbell, Maywood, N. J., assigner to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application January 10, 1942, Serial No. 426,322

(Cl. Z50-36) 7 Claims.

With this invention a control tube for an oscillator is operated normally at zero potential, and positive or negative corrective potentials are generated and applied to said control tube dependent upon the direction of frequency correction desired. Also the alternating current signals applied to the control device are balanced out in the output so that it is not necessary to resort to elaborate lter precautions in order to prevent frequency modulation of the master oscillator by either of the controlling signals.

In carrying out this invention, means are provided for comparing two wave forms and deriving from these wave forms a direct current control voltage, depending upon the relative phases between the voltages, and using the produced direct current voltage to actuate a reactance tube for the purpose of holding one of the wave forms in step with the other. The invention will be particularly described in connection with an embodiment thereof which is suitable for causing the 60cycle output of a television synchronizing generator to remain locked in to a 60cycle power line circuit. With this invention there is a gain in stability so that synchronizing generators can be reliably operated. It will be obvious that it has other uses.

Early methods of providing a lock-in to a power line are known. One of these is described in my Patent 2,209,507 in whicha single ended type of detector is used to provide a direct current control voltage for a reactance tube.

By the present invention earlier disadvantages are overcome. For example, spurious reactions from changes in power supply voltage and temperature stability, etc., are overcome or avoided.

This invention makes use of a pair of diodes which detect the outgoing signals in a balanced manner, so that the central operating point for the reactance tube I is that point at which the balanced detector delivers zero output voltage and the balanced detector is arranged so that a phase shift of the sawtooth wave with respect to the sine wave in one direction from this balanced point will deliver a net positive control voltage, while a. phase shift in the other direction will deliver a net negative control voltage. In this way th'e normal operating point for the master oscillator is such that the detector is delivering no voltage, and any hum modulation which would be delivered by the detector is at a minimum at by the reactance tube l.

2 controls a blocking oscillator or other suitable this point, thus obtaining greatest freedom from frequency modulation of the master oscillator.

The invention may be more clearly understood by reference to the accompanying drawings, in which:

Fig. 1 is a schematic diagram showing the circuit of the balanced diode for comparing two wave forms; and

Fig. 2 shows several wave forms illustrating the principles of operation of the invention.

In Fig. 1, the double diode 6H6` has one diode section so connected that it will deliver a negative voltage to the output load circuit and the other diode section so connected that it will deliver a positive detected voltage to the output load circuit. These two voltages are arranged to buck one another, so that the net voltage difference between the two detected signals is delivered to the reactance tube l indicated in'block form after suitable direct current filtering. The synchronizing generator 3 also shown in block form is connected to a master oscillator 2 which generates a sine wave. The oscillating frequency of this master oscillator 2 is controlled to some extent This master oscillator impulse generator in the usual way, which in turn goes through several stages of frequency division to generate a cycle sawtooth wave as indicated by the block 4. It is therefore always a definite sub-multiple of the master oscillator frequency.

By this invention a comparison of this 60cycle sawtooth wave is made with a power line 60cycle sine wave, or some other suitable reference frequency, and a control voltage is generated to be applied to the reactance tube l s0 that the frequency as Well as the phase of the generated sawtooth wave will be locked in and kept locked in with respect to this 60cycle power line. 'I'h'e sawtooth wave is applied through the condenser 6 to the grid 'l of the 6J5 tube, which' is a balanced phase inverter tube delivering a signal of one polarity from its anode circuit through the condenser 9 to the diode plate I0 of the diode GHG and delivering a signal of approximately equal amplitude but of .opposite polarity from its cathode circuit through the condenser I l to the other diode plate I2. The variable resistors i3 and i4 are used to balance or equalize the amplitudes of the sawtooth waves which are applied to the diode plates I0 and I2. Additional cathode-loaded tubes may be inserted when desired in order to balance the system more nearly perfectly.

The load circuits in the cathodes I5 and I6 of the diode GHG are also balanced as indicated by the resistors I1 and I8, and the condensers I8, 20 and 2l.

'I'he application of balanced sawtooth waves of opposite polarities to the two diodes and the balanced load circuits in the cathodes of the diodes cause one sawtooth wave to generate a signal at the point 25 which is opposed by the detected signal from the other sawtooth wave. A sine wave voltage suitably isolated by the 500,000 ohm resistors 26 and 21 is inserted in a balanced manner in the double diode 6H6 so that the diode plates I and I2 are driven by avoltage wave form which is the sum of the sawtooth and the sine wave, and the wave forms at the diode plates will chang their shapes and consequently their energy content in the positive excursion portion of the cycles as the phase of the sawtooth shifts with respect to the phase of the sine wave.

This will be more clearly understood by reference to Fig. 2, in which the section A shows the sine wave form, and the three divisions of section A represent three columns, the first column showing the conditions where the sawtooth wave form has its rapid return occurring at the 180 phase point of the sine wave, the second column has the sawtooth wave rapid return occurring at the 270 phase point of the sine wave, and the third column has the rapid return of the sawtooth occurring at the 360 phase point of the sine wave. The wave forms at B show the sawtooth waves applied from the lower cathode circuit of the 6J5 tube to the plate I2. The amplitude ratio between the signals at A and B may be adjusted by means of the variable resistors I3 and I4. The wave forms at A are illustrative of the signals that are delivered by the 60-cyc1e input 30 and the transformer 3i to the conductor 32 that is connected between the resistors 26 and 21 at one end and the resistors I1 and I8 at the other end.

Both the wave forms A (Fig. 2) and the wave forms B represent the signals before mixing has taken place. The circuits are so arranged that the voltages are added in the respective network, so that a summation voltage is actually applied to the plate I0 and the plate I2 of the diode 6H6. On Fig. 2 the wave forms designated as A+B are the wave forms which are applied to the diode plate I2 of the diode 6H6.

These wave forms represent the signals which are being applied to the diode before considering the conductance of the diode. The diode passes current, however, when the plates I0 and I2 become positive with respect to the cathodes I5 and I6. When the diode is passing current a further network of resistors I1 and I8 is shunted across these wave forms of A+B, causing the positive excursions of the wave forms to be attenuated or reduced in aplitude according to the newly applied lower impedance of the load circuit. In practice, this simply means that the energy content of the positive excursion portion of the wave forms shown at A+B are the controlling factors in determining how much direct current voltage is generated in the detector circuit of the cathode load of tube 6J5.

The other diode plate I0 has a sawtooth wave form applied to it from the upper or plate circuit of the 6J5 tube, which is represented by the diagrams at C of Fig. 2, which, by mixing with the wave forms A in the three phases mentioned. result in the three wave forms shown at A14-.C in Fig. 2.

The diode plate I2 has its cathode I6` grounded, and therefore develops its detected signal essentially as a plate output diode, the rectified voltage appearing across the resistor 21 through the transformer secondary 3| and across the resistor I8 to ground. When the plate I2 of the diode 6H6 draws current with respect to the cathode Ii, this plate stores a charge in the condenser 20 so that the point 30 becomes negative with respect to ground, thus preventing momentarily any further flow of current in this diode. When the wave form of A+B again returns to its negative portion this condenser 20 will hold a negative charge for a time, thus giving the normal detector action. On the other hand, the diode IIJ-I5 is connected with part of its effective load circuit in the plate III network and part of the effective load circuit in its cathode I5 network, so that when the plate IIl starts to conduct, the cathode I5 will become positive with respect to the point 30, developing a voltage across the resistor I1 which is retained by the action of the condenser I9. The resistors I1 and I8 are connected in series, so that these opposing voltages are added to one another, and whichever voltage is the larger will determine the net voltage delivered to the connection 25 and on through the filtering stages 26 to the reactance tube I.

Therefore the diode I2-I6 as connected tends to deliver a negative signal derived from the wave forms A+B to the point 30, and thence to the reactance tube I. The diode III-I5 tends to deliver a positive signal derived from the wave forms A+C to the point 30, and thence to the reactance tube I. By a comparison of the wave forms A+B at the three phase relations plotted with the wave forms A+C at the corresponding phase positions, it can be seen that the positive energy in the wave form designated byreference character 40 (Fig. 2, A+B) is approximately the same as the positive energy shown in the crosshatched region of the wave form designated by reference character 5I. The reversal in shape of the wave forms is not serious, since the diode detectors have a low frequency detecting filter in their cathode circuits and. the output load responds essentially to the energy in these wave forms. But the Wave form of reference character 4I contains more energy in its positive excursion than the wave form 40, and the wave form 50 at this same phase relation contains less energy than the ywave form 5I. Since wave form 4I delivers a negative detected signal and wave form 5II delivers a positive detected signal, it can be seen that at the phase relation of the negative detected signall will predominate in magnitude, and a net negative voltage will be delivered to the terminal 30 (Fig. l). This negative voltage, applied to the reactance tube I, tends to slow down the master oscillator 2, causing the sawtooth wave to tend to shift back toward the 270 phase point.

On the other hand, if the master oscillator 2 is running too slowly, the phase relation of the sawtoothv with respect to the sine wave may be, as illustrated (right hand end of Fig. 2, A and C) at 360. In this case the energy in the positive cross-hatched portion oi 52 is seen to be larger than the energy in the positive cross-hatched portion of 42, and the diode I0-I 5, to which the wave form of A+C is fed, will deliver positive control signal which predominates in magnitude and thus increases the master oscillator frequency momentarily, causing the phase of the sawtooth Wave to shift back toward the 270 point to an intermediate phase angle which is the position of equilibrium.

If the master oscillator 2 is on the correct frequency which can be determined by closing the switch 33, then opening the switch 33 will connect the balanced detector control circuit and the sawtooth wave will beat against the sine wave thus generating a control voltage which will shift the master oscillator frequency until the phase relation is at the low stable point. This point corresponds to the 270 diagram, Fig. 2, where it can be seen at once that the positive cross-hatched energy of wave form 40 (Fig. 2, A+B) is equivalent to the positive cross-hatched energy of wave form I (Fig. 2, A+C), and therefore the output net voltage will be neither positive nor negative and will be balanced for control voltage, and furthermore will be balanced for any surge voltages from power supplies or from other voltages which might otherwise get on through the integrating filter.

There will be another condition in which .the wave form of A+B (Fig. 2) in its positive portion will have the same energy as the wave form A-l-C in its positive portion, but this other condition is at a phase relation such that the detected voltage will tend to throw the frequency farther oi the correct value rather than toward its correct value. With this circuit it is found that the master oscillator may be held in step over a phase relation from 180 to 360 of the sine wave.

This is adequate for many applications, but in some cases it may be desirable to lcause the 60- cycle sine wave from the power line to control directly a sawtooth wave form and then utilize the same balanced detector circuit to compare the power line sawtooth with the synchronizing generator sawtooth, thus making it possible to iind a stable control point for phase angles essentially anywhere within the 360, as can be done with this invention.

The principles of this balanced detector circuit can be used for comparing other types of wave forms with one another for control purposes, such as locking-in the switch oscillators of a television receiver with respect to incoming synchronizing pulses or for controlling the oscillator of a frequency modulated transmitter with reference to a crystal oscillator.

While specific values are shown on the circuit diagram, it is well understood that the principles of operation of the circuit are not confined to any speciflc input signal amplitudes, and the values of the circuit components may be changed very widely and still yield satisfactory performance.

What is claimed is:

1. A synchronizer for an oscillator, comprising two diodes, means for. applying impulses in phase opposition from said oscillator to the anodes of said diodes, and means to apply low frequency since wave impulses in parallel between the plates and cathodes of said diodes, one of said cathodes being connected to -ground and the other one to said oscillator.

2. The device of claim l, in which resistors are connected in series between said anodes.

3. The device of claim 1, in which resistors are connected in series between said cathodes.

4. The device of claim 1, in which two resistors are connected in series between the anodes of said diodes and two capacitors are connected in series between the cathodes of said diodes.

5. The device of claim 1, in which two resistors are connected in series between the anodes of said diodes and two capacitors are connected in series between the cathodes of said diodes and two resistors in series are connected in parallel with said capacitors.

. 6. The device of claim 1, in which a capacitor is connected between said other one of said cath-4 odes and ground.

7. In a synchronizer for an oscillator, a balanced phase inverter comprising a vacuum tube having its grid connected to said oscillator, diodes having their plates connected respectively to opposite sides of said inverter whereby signals from said oscillator are connected in phase opposition to said diodes, one of said diodes having its cathode grounded, balanced load circuits connected to the cathodes of said diodes, means to apply a low frequency sine wave voltage in phase to the plates of said diodes, and a connection from said balanced load circuits to saidoscillator whereby the frequency of said oscillator'is controlled.

RICHARD L. CAMPBEIL.

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