VARIABLE FREQUENCY MODULATION CIRCUIT

摘要

PURPOSE:To obtain a stable modulation output against a voltage reduction and temperature change by using a DC component and an AC component subjected to temperature compensation based on a stabilized reference voltage so as to control the modulation and a modulation frequency of an FM converter. CONSTITUTION:A stabilized reference voltage VREF1 whose low voltage level is stabilized is obtained from a power supply voltage Vcc, and a DC component transistor (TR) Q13 subjected to temperature compensation based on said reference voltage and an AC component TR Q12 subjected to temperature compensation based on the reference voltage stabilize the oscillation frequency (modulation frequency) and the modulation of the Fm modulator 2. Then the voltage reduction characteristic is improved and the temperature change in the output current of the TR Q13 constituting the DC component control system and of the TR Q12 constituting the AC component control system is compensated to improve the temperature characteristic. Moreover, an input signal Vin is fed directly to a base of a TR Q10 through DC coupling so as to eliminate the need for a DC block coupling capacitor.