| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a PLL having desired frequency characteristics even if processes for manufacturing a semiconductor integrated circuit are varied. <P>SOLUTION: The semiconductor integrated circuit includes a PLL and a control unit 9, wherein the PLL includes a phase/frequency comparator 1, a loop filter 3, a voltage controlled oscillator (VCO) 8 and a frequency divider 6, and the VCO (8) includes a voltage/current converter (VIC) and a ring oscillator. In response to a control voltage Vc, the VIC generates a control current for setting an operational current of the ring oscillator. The control unit 9 switches the PLL into an open-loop calibration operation period and a closed-loop ordinary operation period. During the ordinary operation period, the predetermined control voltage Vc is supplied to the VCO and a frequency of the VCO is set to a predetermined frequency. During a frequency measurement of the VCO set to a state where a reference voltage V<SB>REF</SB>at a level approximately equal to the control voltage Vc is supplied during the calibration operation period, the control unit 9 sets a value of an operation parameter T of the VIC 81 so that the frequency of the VCO becomes approximately equal to the predetermined frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT |
