| 摘要 |
PURPOSE: A digital waveform shaping circuit, a frequency multiplier circuit, and external synchronizing method and circuit are provided to produce a wave form shaping circuit which outputs signals after the wave forms of input signals are shaped to those of duty 50% regardless of whether or not the input signals are of duty 50% and an actual frequency multiplying circuit having a simple construction, which is able to output signals wave forms of which are shaped to those of duty 50%. CONSTITUTION: A waveform shaping circuit from which an input signal, the waveform of which is shaped to a waveform of a duty ratio of 50% whether the input signal has a duty ratio of 50% or not, is output. A duty ratio determining circuit adapted to receive a timing signal generated in a timing signal generating circuit, and determine and designate a timing position for a duty ratio of 50% of a clock signal to be output is provided, which circuit is constituted by a cycle measuring circuit(10) for measuring the length of one cycle in a first cycle which comes at intervals of integral multiples of one cycle T of an input clock signal EXT-CK, an arithmetic circuit(19) adapted to calculate the length of a half cycle on the basis of a value of the above-mentioned cycle, an actual measuring circuit(20) adapted to execute the measurement of the length of a cycle in each of the second cycles in the above-mentioned intervals, and a coincidence circuit(28) adapted to output a coincidence output as a timing position of the duty ratio of 50% when the actual measurement value coincides with the above-calculated value, a clock signal having a pulse width corresponding to the duty ratio of 50% being generated on the basis of a signal synchronous with a leading edge of the input clock signal EXT-CK and the timing position determined and designated in the duty ratio determining circuit(3), the clock signal being then output.
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