

Frequency Conversion by Means of a 

 Nonlinear Admittance 



C. F. EDWARDS 



(Manuscript received June 20, 1956) 



This paper gives a mathematical analysis of a heterodyne conversion 

 transducer in which the nonlinear element is made up of a nonlinear re- 

 sistor and a nonlinear capacitor in parallel. Curves are given, showing the 

 change in admittance and gain as the characteristics of the nonlinear ele- 

 ments are varied. The case where a conjugate match exists at the terminals is 

 treated. 



It is shown that when the output frequency is greater than the input fre- 

 quency, modulators having substantial gain and bandwidth are possible, 

 but when the output frequency is less than the input frequency, the con- 

 verter loss is greater than unity and is little affected by the nonlinear ca- 

 pacitor. The conditions under which a conjugate match is possible are 

 specified and it is concluded that a nonlinear capacitor alone is the pre- 

 ferred element for modidators and that a nonlinear resistor alone gives the 

 best performance in converters. 



INTRODUCTION 



Point contact rectifiers using either silicon or germanium are used as 

 the nonlinear element in microwave modulators to change an inter- 

 mediate frequency signal to an outgoing microwave signal and in re- 

 ceiving converters to change an incoming microwave signal to a lower 

 intermediate frequency. Most point contact rectifiers now in use behave 

 as pure nonlinear resistors as evidenced by the fact that in either of the 

 above uses the conversion loss is the same. In recent experiments with 

 heterodyne conversion transducers* using point contact rectifiers made 

 with ion bombarded silicon this was found to be no longer true. The 

 conversion loss of the modulator was found to be unusually low and 



* This term is defined in American Standard Definitions of Electrical Terms 

 — ASA C42 — as "a conversion transducer in which the useful output frequency 

 is the sum or difference of the input frequency and an integral multiple of the 

 frequency of another wave". 



1403 



