Portable telephone set

DETAILED DESCRIPTION Accordingly, it is an object of the invention to provide a portable telephone set with which the user's voice can be heard easily by the other party even if the noise around the user is loud while the set is used with the volume of sound increased.
A portable telephone set according to the invention comprises: a demodulating circuit for demodulating a signal from a base station to output a demodulated signal; a first signal processing unit for amplifying the demodulated signal to output a first amplified signal; an earphone for converting the first amplified signal into a sound; a microphone for converting a sound into a signal; a second signal processing unit for amplifying the signal from the microphone to output a second amplified signal; a modulating circuit for modulating the second amplified signal to output a modulated signal; a volume control unit for increasing the amplification degrees of the first and second signal processing units to perform a volume increasing process in accordance with the user's selection; a band limiting circuit for limiting to the voice band the sound input through the microphone; and an S/N determining circuit for comparing the level of the signal from the microphone and the level of a signal from the band limiting circuit.
The volume control unit is rendered inoperative if the S/N determining circuit judges that the ratio of the level of the signal from the microphone to the level of the signal from the band limiting circuit has exceeded a predetermined range during the operation of the volume control unit.
Even while the volume increasing process is performed, the amplification degree of the first signal processing unit decreases automatically if the ambient noise is loud relatively to the user's voice.
This inhibits the user from speaking excessively low.
At the same time, the amplification degree of the second signal processing unit decreases.
This prevents the ambient noise from being heard loudly by the other party.
The volume control unit may be rendered operative if the S/N determining circuit judges that the ratio of the level of the signal from the microphone to the level of the signal from the band limiting circuit has decreased to a predetermined range while the volume control unit is inoperative