| 摘要 |
PURPOSE:To reduce the distortion produced in a band pass filter, by passing an input signal through a band pass filter, after the frequency change in the input signal is decreased through the use of a heterodyne circuit. CONSTITUTION:An output of a voltage controlled oscillator VCO1 (frequency f2) and an input signal (frequency f1) applied to an input terminal IN are multiplied at a multiplier 2 to for a signal in frequency f3=f1-f2. When this signal passess through a band filter 4, it becomes a signal in frequency f4=f3'+f2, after it is multiplied with the output of the VCO1. On the other hand, when an output frequency f2 of the VCO1 is controlled so that it can be changed by a.DELTAf proportional to the change DELTAf in the input signal frequency, the f3 becomes as f3= (f1-f2)+(1-a)DELTAf, and the f3' and the f4 are as shown in EquationsIand II. When the a in Equation above is close to 1, an output reducing the harmonic distortion (DELTAf)<n> of the DELTAf can be obtained. |
