PIEZOELECTRIC CRYSTALS IN OSCILLATOR CIRCUITS 



181 



where again Rl is assumed small compared to 



1 



cooLi — 



OJoCl COo(Co 



I T 



+ C.)J 



and Wo is considered a constant. 



Equation (12.32) shows that in order to obtain a large amplitude yp 

 should be large and $o should be small. With this in mind equations (12.33) 



pMC-)oC3 



Fig. 12.15 — Functions from which the activity variations (A) are determined as the 

 plate circuit capacitance is varied. Crystal connected grid to cathode 



and (12.34) may be analyzed to determine the relation between the circuit 

 components and amplitude. It is found that for maximum amplitude 



Cg and Ri should be small, 

 C4 should be large, 

 Cz has an optimum value, and 

 Rg should be large. 



As to the plate circuit, the amplitude is maximum when 



R. 



1 



oooL'i 



C00C2 . A plot of ^ and $0 + — is shown in Fig. 12.15. The difference 



between these two curves is a measure of the amplitude and is shown by 



curve ,1 . Oscillations can exist only where \}/ lies over $0 + "^ • The sharp- 



Rg 

 ness of \p varies considerably with the value of Rp and the resistance of the 

 L2 — Co circuit. The latter is disregarded for simpHcity. Here again the 



