| 摘要 |
PROBLEM TO BE SOLVED: To provide a pulse width modulating circuit of novel constitution whose carrier frequency is made nearly constant. SOLUTION: The pulse width modulating circuit 1 charges a first integrating capacitor C1 with a current based upon an audio signal e<SB>S</SB>in a first period T1 (wherein SWs 2 and 3 are ON, and SWs 1 and 4 are OFF), and varies the charging voltage accumulated in the C1 with a constant bias current Ib in a second period (wherein the SWs 2 and 3 are OFF and the SWs 1 and 4 are ON). Further, the pulse width modulating circuit charges a second integrating capacitor C2 with the current based upon e<SB>S</SB>in the T2 and varies the charging voltage accumulated in the C2 with the Ib in a third period T3 (wherein the SWs 2 and 3 are ON and the SWs 1 and 4 are OFF). The time from when the T2 starts until when the voltage across the C1 reaches Vref is detected. The time from when the T3 starts until when the voltage across the C2 reaches Vref is detected. Based upon those times, a pulse signal having a pulse width of the times is generated. COPYRIGHT: (C)2008,JPO&INPIT
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