| 摘要 |
PURPOSE:To simplify the constitution and to attain the low cost by providing a switch driven by an edge signal being an output change of a comparator connected to an analog input integration device and an edge signal being an output change of a reference frequency generator and leading a reference current to the integration device. CONSTITUTION:A reference frequency generator OSC generates a square wave of a period T and the wave is fed to a set terminal S of a switch control logic circuit SWC, which is closed by a leading edge signal. The integration device IG adds and integrates an analog input EX and an output current I of a reference current source IS, and a comparator COP detects it when the integration device output reaches zero volt. The detection signal is fed to a reset terminal R of the logic circuit SWC, the switch SW is opened by the trailing edge and only the analog input EX is integrated. Thus, the pulse width of the pulse controlling the switch SW turning on/off the reference current source IS, that is, the pulse width modulation output is subjected to modulation by the analog input EX.
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