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Vmari'z'n Greenspan June 13, 1957 M. GREENSPAN ErAL 2,796,522 CRYSTAL-CONTROLLED RELAXATION OSCILLATOR Filed Aug. 21, 1953 INVENTOR vMari‘z'n Greenspan M v .r I Carroll E. Ybc/u'eyy - - - Y .BY ’ AGENT , , 2,796,522 United States a atent {C Nice Patented June 18, 1957 1 2 1It is another object of the present invention to provide 2,796,522 a crystal controlled relaxation oscillator, the output of which is relatively insensitive to variations in circuit CRYSTAL-CONTROLLED RELAXATION parameters even at high division ratios. OSCELLATOR *It is another object of the present invention to pro Martin Greenspan and Carroll E. Tschiegg, Silver Spring, vide a relaxation oscillator in which the voltages along Md, assignors to the United States of America as rep the ?at portion of the capacitor discharge curve are made resented by the Secretary of Commerce to vary considerably from instant to instant. Application August 21, 1953, Serial No. 375,841 1It is another object of the present invention to pro 10 vide a relaxation oscillator in which an oscillatory volt 4 Claims. (Cl. 250—36) age with a constantly increasing amplitude is superim (Granted under Title 35, U. S. Code (-1952), see. 266) posed on the grid voltage of the oscillator tube or tubes. Further provision is also made to crystal stabilize the frequency of this oscillatory voltage. The invention described herein may be manufactured 15 and used by or for the Government of the United States 'It is a'further object of the present invention to in for governmental purposes without the payment to us of crease the frequency stability of relaxation oscillators any royalty thereon in accordance with the provisions of when working along the steep portion of the timing wave 35 United States Code (1952) section 266. form. It is another object of the present invention to pro The present invention relates to relaxation oscillators 20 and in particular to a method and apparatus for stabiliz vide a multivibrator in which the various phases of an ing the frequency of relaxation oscillators ‘by means of asymmetrical output wave are locked in by a piezoelec a piezoelectric crystal. trical crystal. ‘In the prior art numerous attempts have been made In accordance with the preferred embodiment of the to stabilize the frequency of various types of relaxation 25 present invention there is provided a multivibrator, the oscillators. in the case of the ‘blocking oscillator, Mar’ output frequency of which is synchronized with a har rison, Patent No. 1,919,795, provides a crystal-stabiliz monic or subharmonic of a piezoelectric crystal. The ing circuit. However, since the division ratios obtain piezoelectric crystal is coupled into the grid circuit of able with this circuit were rather small and the range the multivibrator, the crystal and the tube acting as a of frequencies limited, the circuit was not widely used. 30 crystal oscillator immediately prior to the ?ring of the In the case of multivibrators, which are inherently fre tube in whose grid circuit the crystal is coupled. In addi quency ‘unstable, stability has been provided by syn tion to the crystal oscillator the circuit resonates as a chronizing the frequency by means of an oscillatory volt low-Q amplitude-unstable oscillator, whose frequency is age coupled into the circuit from an external oscillator. locked on some harmonic or subharmon‘ic of the crystal The use of an external oscillator of necessity increased 35 frequency. Because the low-Q oscillator is amplitude the complexity of the circuits. unstable, successive oscillations of this circuit will pro The primary cause of frequency instability of relaxa duce output voltages of increasing amplitude, the ?ring of tion oscillators arises from the fact that the time of ?r the tubes of the multivibrator being controlled by one of ing of the oscillator tube is controlled by the rate of these voltage peaks. Since the amplitude of these peaks discharge of a capacitor in the grid circuit of the tube. is increasing rapidly, particularly during the period just As long as the ?ring of the tube takes place at a voltage before ?ring, the circuit can easily differentiate between which lies along the steep portion of the discharge curve, successive voltage peaks. the frequency stability is acceptable. However, if the Other uses ‘and advantages of the invention will be frequency is varied so that ?ring of the oscillator tube come apparent upon reference to the speci?cation and is to occur at a voltage which lies along the ?at portion 45 drawings. of the discharge curve, the frequency stability becomes {Figure 1 is a circuit diagram of a crystal-controlled very poor. ,This is due to the fact that along the ?at ‘blocking oscillator. portion of the discharge curve the variation in voltage Figure 2 is a series'of reproductions of pictures taken from instant to instant is almost in?nitesimal. In order from the face of a cathode-ray-oscilloscope, showing the ‘for a tube to ?re at exactly the same potential during 50 various wave forms obtained on the grid of the oscillator each cycle and therefore at the same time the tube tube. characteristics would have to remain just about constant Figure 3 is a circuit diagram of a multivibrator which which, of course, is impossible. is crystal controlled. -It is the primary object of the present invention to Figure 4 is a reproduction of pictures taken from the provide a simple method of and apparatus for crystal 55 face of a cathode-ray-oscillo'scope, showing the wave stabilizing the frequency of various types of relaxation form at the output of the multivibrator. oscillators. %It should be noted that the use of a crystal to stabilize It is another object of the present invention to provide rblocking oscillators is not speci?cally claimed in this appli for crystal stabilization of relaxation oscillators having cation, but the explanation of that circuit is included for high division ratios. the purpose of developing the overall concepts involved. it is another object of the present invention to pro The crystal~controlled .blocking oscillator is speci?cally vide crystal-controlled relaxation oscillators in which the claimed in co-pending application No. 376,770, ?led on frequency of the oscillator is synchronized with the fre August 26, 1953, by Moody C. Thompson, Jr., now quency of the crystal. U. S. Patent 2,761,971. ‘It is another object of the present invention to provide 65 Referring to Figure 1, the tube 11 has its cathode 12 crystal-controlled multivibrators in which the frequency grounded and its plate 13 connected through one wind of the oscillator is synchronized with the frequency of ing 14 of the pulse transformer 16 to the B+ supply. the crystal. ' The grid 17 of the tube is connected through another Another object of the present invention is to provide winding 18 of the pulse transformer and through the crystal-controlled relaxation oscillator-s which require 70 variable capacitor 19 to ground. The capacitor 19 is only very minor modi?cations of the conventional oscil shunted by the ?xed capacitor 21 and the series combina lator circuit. ‘ ’ ' tion of the ?xed resistor 22 and variable resistor 23. A 2,790,522 3 4 third winding '24 of the transformer 16 has one terminal 2. The overall shape of the wave is controlled by the dis connected to ground and the other terminal connected charge or exponential curve of the capacitor. Superposed through the crystal 26 to ground. on the capacitor-discharge Wave is the characteristic fre Assuming initially that the blocking oscillator has just quency voltage of the low-Q oscillator (curve 1‘) which, as ?red, the grid 17 is instantaneously driven very highly can be seen, builds up cycle by cycle. The curve g rep positive and then very sharply negative. The negative resents the grid potential at which the tube will ?re, there bias on the grid shuts oif the tube, and this negative charge by producing an output pulse from the blocking oscillator. is stored in the capacitors 19 and 21, thereby maintaining It will be noted that the magnitude of each positive peak, the tube in the biased-off condition. However, the such as h and 1', increases considerably over the prior posi capacitors gradually discharge through the resistors 22 10 tive peak and therefore makes it possible to differentiate and 23, and the potential on the grid 17 rises along the between one pulse and the next succeeding or prior pulse exponential discharge curve of the capacitors. When even when operating on the ?at portion of the timing wave the grid has reached a potential at which the tube can form. again ?re, a large pulse is given out by the oscillator, The frequency of the blocking oscillator is’ controlled by the grid again being instantaneously driven very highly 15 varying the discharge time of the capacitor 19. Rough positive and then very highly negative. Owing to the adjustments may be made by varying the value of resistor very tight coupling of the pulse transformer the crystal 23. This oscillator was found to have a high degree of ‘and tube combine to form an oscillator which will oscil frequency stability at even large division ratios. late for a brief period before the ?ring of the blocking It will be noted in the above analysis that several volt oscillator. Initially the crystal is caused to ring as the ages are applied to the grid-to-cathoclecircuit of the tube. result of the large output pulse supplied to it but since These voltages include a crystal oscillator voltage and a the tube is biased almostto cutoff by the large negative low-Q oscillator voltage, both of which appear in the charge stored across the capacitors 19 and 21, thetube aforementioned grid-to-cathode circuit.
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