| 摘要 |
PURPOSE:To eliminate the distortion component of an FM demodulator which includes an oscillator whose oscillation frequency is determined by controlling a variable capacitor diode, by providing a circuit for canceling a secondary and a tertiary distortion. An element 3 is a comparator and elements 8 and 9 are adders. CONSTITUTION:When input voltage-output frequency characteristics of an oscillator 1 are nonlinear, a demodulation output V1 to the frequency displacement (cospt) of an input is repressented as an approximate equation V1 a1 cospt+a2cos<2>pt+a3cos<3>pt, whose secondary and tertiary distortion components are only removed to obtain V2=cospt. Firstly, the output S1 of a squaring circuit 10 is represented as S1=(V2)<2>=cos<2>pt and the output S3 of a cubing circuit 11 is represented as S3=(V2)<3>=cos<3>pt. When attenuation constants of attenuators 13, 14, and 12 are (k),(l), and (m), the output S7 of an adder 9 is S7= mcospt+kcos<2>pt+lcos<3>pt; when a3=l, a2=k, and a1=m, S7=V1, removing the secondary and tertiary higher harmonic distortions from a demodulated signal. |
