| 摘要 |
PURPOSE:To attain a power amplifier to an analog and a digital input signal with high efficiency by providing a means switching selectively an analog or digital input signal selectively so as to amplify the analog or digital signal switchingly. CONSTITUTION:When the input signal fed to an analog input terminal 11 is an analog signal such as an audio signal, a changeover switch (SW) 24 is switched to the position of the analog input mode to turn on SWs 22, 23 and the switching amplifier circuit 13 is selected. Thus, the signal is subjected to a pulse width modulation by a modulator 15 and amplified with high efficiency by using the circuit 13. When the input signal fed to a digital input terminal 21 is a digital signal, the SW 24 is switched into the digital mode to turn off the SWs 22, 23 to disconnect the modulator 15 and the negative feedback circuit 19. Then the signal is sent to the circuit 13 directly or via the digital converter 26. Thus, the analog and digital input is subjected to the power amplification with high efficiency.
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