| 摘要 |
PURPOSE:To obtain a highly efficient amplifier characteristic while eliminating the effect of a pulse obstacle by using the amplifier at the AM radio reception while the amplifier is switched to an analog amplifier in a switching amplifier applying pulse width modulation to an analog signal. CONSTITUTION:When an input signal fed to an input terminal 11 is an analog signal such as an audio signal, a switch driving section 25 throws changeover switches (SW) 22, 23 to the switching amplifier circuit 13 to disconnect an analog amplifier circuit 26. Thus, the analog signal is amplified by an input stage 12 and subject to pulse width modolation at a modulator 15 by a carrier signal sent from a carrier signal generator 14, amplified by a pulse width amplifier 16 and on/off-control by a switch driving section 17. Moreover, when the input signal fed to the terminal 11 is an analog signal for AM radio, the switches SWs22, 23 are thrown to the position of the analog amplifier circuit 26. Thus, the radio interference at AM radio reception is excluded to amplify the analog signal such as audio signal with high efficiency.
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