| 摘要 |
PROBLEM TO BE SOLVED: To make a frequency range of an oscillating circuit wide, to continuously realize the shift of an oscillation frequency, also to simplify a circuit configuration and to realize low power consumption. SOLUTION: Because a ring oscillator is formed by using n stages of a delay stage that consists of variable capacitance elements which comprises nMOS transistors Tn-1 to Tn0 which are connected to a buffer and its output terminal, the capacitance element that constituted each delay stage consists of nMOS transistors Tn-1 to Tn0 whose source and drain are connected to the output terminal of a buffer in common and whose gate is connected to a prescribed bit of a control signal, the size of a transistor is set in accordance with an input bit, a delay time is set in accordance with the control signal by weighting the delay time of each delay stage, and the oscillation frequency of a DCO (digital control oscillator) is controlled in accordance with the control signal when an enable signal ENB of a high level is inputted to a NAND gate NGT, the range of an oscillation frequency of the DCO becomes wide and the frequency shift of an oscillation signal becomes continuous and smooth. |
