Direct frequency modulation apparatus which modulates frequency by applying data-dependent voltage to control terminal of voltage-controlled oscillator without mediacy of PLL, and communication system

摘要

A direct frequency modulation apparatus modulates frequency by applying a transmission data-dependent voltage to the control terminal of a voltage-controlled oscillator without the mediacy of a phased-locked loop. The direct frequency modulation apparatus is set such that the temperature dependencies of a terminal voltage in PLL locking and a modulation voltage in an open state correspond to that of a varicap diode.