PURPOSE:To decrease the deterioration to nonlinear type amplification, by producing the frequency modulation signal in spectrum shape through almost continuous switching of the frequency and the phase at the switching circuit. CONSTITUTION:The signal of logic ''1'' is always given to the input of the first stage of the shift register 14 from the terminal 16. Shift operation is made for the delay circuit 13 with the output pulse of the shift pulse generator 17 in unit delay time tau. Each output signal of the registers 14, 151-156 corresponding to tauo+Ktau (where; tauo=mtau, K=1, 2...6) for the delay time from the circuit 13 is selected at the switching circuit 18 and fed to the output terminal 9. The signal at the terminal 9 is fed to the reset circuit 19 to form reset pulse and the circuit 13 is reset with the pulse. The circuit 18 is switched for control through the switching control circuit 21 in response to the modulator input from the input terminal 6.
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