| 摘要 |
<p>PURPOSE:To decide the frequency of clocks inputted from the outside by providing a charge pump which outputs a voltage corresponding to the frequency of clock signals and a voltage discrimination circuit which decides the frequency of the clock signals from the output voltage of the charge pump. CONSTITUTION:A charge pump 20 boosts a voltage produced across a capacitor 22 by means of clock signals and inverted clock signals and the boosted voltage is sent to the capacitor of the next stage by means of a transistor 21. By repeating such operation by the number of capacitors, a voltage corresponding to the frequency of inputted clock signal 8 is outputted. A voltage discrimination circuit 30 fetched a signal inputted from the pump 20 and passes the signal through gates 311-31n different in threshold level, of which those having threshold levels lower than the output voltage of the pump 20 output 'L' and those having threshold levels higher than the output voltage output 'H'. By reading the output of the gates 311-31n on a data bus, the frequency of the clock signals 8 is decided. Therefore, the frequency of clocks inputted from the output can be decided and, even when clock signals having a frequency other than a set frequency are inputted, the clock signals can be processed.</p> |
