RINGING TONE GENERATING CIRCUIT AND SMALL-SIZED RADIO EQUIPMENT AND SELECTIVE CALL RECEIVER EMPLOYING THE CIRCUIT

摘要

PURPOSE:To facilitate the miniaturization of the circuit by setting variably a duty cycle of a ringing tone signal generated by a ringing tone signal generating means by a duty cycle variable means in response to the information generated by a sound volume designation means. CONSTITUTION:When a possessor of a selective call receiver sets a call sound volume to a large sound volume with a sound volume designation switch 9, a large count corresponding to the duty cycle in response to the large sound volume is fed from a ROM 64 to a comparator 65. That is, the duty cycle of a ring tone signal is set variably in response to the setting state of the sound volume designation switch 9 to vary the sound volume of ringing tone sounded from a speaker 8. Thus, it is not required to provide resistors or switches difficult for large scale circuit integration to vary the driving current of the speaker 8 and the ringing tone generating circuit is integrated with large scale efficiently and the circuit is made small. Moreover, the number of components is decreased, the component management is facilitated and the manufacture of the circuit is simplified.