534 BELL SYSTEM TECHNICAL JOURNAL 



Among the first serious efforts to utilize the piezoelectric effect in electrical 

 circuits were those of Alexander McLean Nicolson who used rochelle salt 

 crystal in the construction of devices for the conversion of electrical energy 

 into sound and vice versa. He constructed loudspeakers and microphones 

 during several years of study prior to the publication of his work^^ in 

 1919 — ideas now being used extensively in phonograph pickups, micro- 

 phones and sound producers. Nicolson also was the first to use a piezo- 

 active crystal to control the frequency of an oscillator. His patent^, 

 applied for in 1918, shows a circuit which he operated successfully in 1917. 

 The first actual use of resonators of quartz is attributed to P. Langevin^^- ^^, 

 who drove large crystals in resonance in order to generate high-frequency 

 sound waves in water for submarine signaling and depth sounding. 



The Quartz Crystal Controlled Oscillator 



The first comprehensive study of the use of quartz crystal resonators 

 to control the frequency of vacuum tube oscillators was made by Walter G. 

 Cady in 1921 and published by him in April, 1922^^. This was the step 

 which initiated a most extensive and intensive research of the properties of 

 quartz crystal and into methods for its use in numerous fields requiring a 

 stable frequency characteristic. 



The extent and importance of this research are well indicated by the 

 number of investigators and published contributions to the art. Among 

 these, a paper by A. Scheibe^^ in 1926 lists 28 articles on the subject, along 

 with a description of his own extensive studies. Two years later Cady 

 published a bibliography^^ on the subject, including 229 separate references 

 to papers and books and 84 patents in various countries. R. Bechmann in 

 1936 published a review of the quartz oscillator^^ including 26 references to 

 other original contributions in that field alone. More recently there comes 

 at the end of Cady's 1946 book^*^ on 'Tiezoelectricity", a bibliography of 

 57 books and 602 separate published articles on this subject. By any 

 measure this represents a great amount of detailed effort for a single subject 

 in so short a time — ^just about a quarter of a century. Of this great amount 

 of material, it is feasible to review only a small number of the outstanding 

 ideas relative to the evolution of the quartz crystal clock. 



The first published quartz-controlled oscillator circuit is reproduced in 

 Fig. 8A from Cady's 1922 article. In this oscillator the ''direct" and 

 ''inverse" piezoelectric effects were employed separately, making use of 

 two separate pairs of electrodes; The output of a three-stage amplifier 

 was used to drive a rod-shaped crystal at its natural frequency through 

 one pair of electrodes making use of the "inverse" effect, while the input to 

 the amplifier was provided through the "direct" effect from the other pair. 



