| 摘要 |
PURPOSE: A circuit for modulating pulse width using an ossillator is provided to enable an accurate PWM circuit using a frequency of a slow oscillator by using delay occurring when forming a ring oscillator. CONSTITUTION: In a circuit of modulating pulse width, a ring oscillator(20) produces a TAP signal using the delay between an oscillator frequency and a signal between an inverter and a buffer. A TAP counter(22) produces the phase count value by counting phase tap signals corresponding to the oscillator frequency of the ring oscillator(20) A ring count converter(24) produces a ring count value at the rising edge of the clock using the TAP signal and the phase count value. A resolution generator(26) produces a resolution by subtracting the ring count value a clock earlier from the current ring count value. Space converters(28,29) converts the starting and end points of the pulse into ring count values to be used inside. Adders(32,33) add ring count values with offset values. Edge generators(30,31) produces edges selecting one of the TAP signals. An XOR gate produces the final pulse using the output of the edge generators(30,31).
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