OSCILLATION FREQUENCY CORRECTION CIRCUIT OF RING OSCILLATOR

摘要

PROBLEM TO BE SOLVED: To automatically correct the oscillation frequency of a ring oscillator incorporated in a semiconductor integrated circuit without needing an external oscillator.

SOLUTION: An oscillation frequency correction circuit of the ring oscillator is provided with a delay circuit 2 interposed in an oscillation path of the ring oscillator 1 incorporated in the semiconductor integrated circuit, wherein a plurality of delay elements with delay quantity different from one another are connected in parallel; a frequency detection circuit 3 for receiving an output signal Pr of the ring oscillator 1 and converting the output signal Pr into a plurality of voltage level values obtained by segmentalizing the advance/delay of an oscillation frequency; a capacitor voltage latching circuit 4 for determining logical values according to whether the plurality of a voltage level value outputted by the frequency detection circuit 3 individually exceed a threshold and latching data bits of the determined logical value in each output signal Pr; and a selection circuit 5 for selecting one delay element in the delay circuit 2 as a component of the ring oscillator 1 on the basis of a combination of a plurality of data bits outputted by the capacitor voltage latching circuit 4.

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