| 摘要 |
PURPOSE:To modulate a carrier signal even if this carrier signal has been already modulated, by obtaining four-phase signals orthogonal to one another from the carrier signal to be modulated and synthesizing respective signals after AM-modulating them by modulation signals of orthogonal phases. CONSTITUTION:A carrier signal to be modulated has the phase shifted by a 90 deg. hybrid circuit, and obained output signals are inputted to 180 deg. hybrid circuits respectively to obtain signals of phases orthogonal to one another. Four signals obtained in this mannr are synthesized after AM modulation to obtain an FM modulation wave. That is, an output (f) of a voltage control oscillator VCO which oscillates in accordance with a modulation signal im is made into two signals having phases shifted from each other by 90 deg., and respective signals have frequencies divided by flip-flops and have phases detected by a signal (f') of the accurate f/2, thus obtaining AM modulation signals X1, X2, Y1, and Y2. Consequently, since an AFC loop is digitized, athe operation is accurate, and the circuit is simplified, and thus, the circuit is made into an IC easily. |
