| 摘要 |
PURPOSE:To prevent a noise amount outputted from a loudpspeaker from being increased considerably at a place where the radio wave is weak in a portable telephone set. CONSTITUTION:When an electric field strength detected by an electric field strength detection circuit 435 is higher than a prescribed strength, a received signal is given to expander circuit 431 by changeover switches 433, 434 and a switch control section 436. Thus, in this case, the received signal is expanded by an expansion ratio corresponding to a compression ratio and the sound quality is improved. When the electric field strength is smaller than the prescribed strength on the other hand, the received signal is given to a bypass circuit 432. Even when the level of noise included in the received signal is high, the noise is not amplified. As a result, remarkable increase in the noise amount due to the existence of an expander circuit 431 at a weak radio wave is prevented. |
