Ring oscillator having selectable number of inverter stages

A ring oscillator comprising:

• an inverter group including first to N-th inverters (N is an odd number satisfying N.gtoreq.3) connected in series;
• power supply detecting means receiving a power supply voltage for outputting a power supply detection signal on the basis of the value of said power supply voltage;
• and
• switching means for determining the number K of inverters (K is an odd number satisfying 1.ltoreq.K.ltoreq.N) forming a loop in said inverter group on the basis of said power supply detection signal to feed back the output of the K-th inverter to the input of the first inverter and provide the output of the K-th inverter in the form of an oscillation signal.

A ring oscillator comprising:

• an inverter group including first to N-th inverters (N is an odd number satisfying N.gtoreq.3) connected in series;
• a shift register serially receiving serial input data for outputting storage data having said serial input data in parallel in the form of a plurality of shift output signals;
• and
• switching means for determining the number K of inverters (K is an odd number satisfying 1.ltoreq.K.ltoreq.N) forming a loop in said inverter group on the basis of said plurality of shift output signals to feed back the output of the K-th inverter to the input of the first inverter and provide the output of the K-th inverter in the form of an oscillation signal.

An ring oscillator comprising:

• an inverter group including first to N-th inverters (N is an odd number satisfying N.gtoreq.3) connected in series for feeding back the output of the N-th inverter to the input of the first inverter and providing the output of the N-th inverter in the form of an oscillation signal;
• first current amount control means receiving a first control voltage for changing the amount of current flowing in some of said N inverters forming said inverter group on the basis of said first control voltage;
• and
• second current amount control mean receiving a second control voltage for changing the amount of current flowing in some others of said N inverters forming said inverter group on the basis of said second control voltage.