Ring oscillator having wide frequency range

A ring oscillator comprising:

• a plurality of delay cells coupled in a loop to generate an oscillation frequency,
• wherein each delay cell comprises:
• a transconductance circuit configured to receive first differential input signals from the preceding delay cell, invert the first differential input signals, and output differential output signals, which are delayed by a predetermined time through the inversion, to first and second output nodes;
• an inversion-rate control circuit connected to the transconductance circuit and configured to vary an inversion rate of the first differential input signals in response to a first control signal provided from an exterior;
• an active load circuit configured to receive second differential input signals from the delay cell preceding by two stages and provide an active load to the transconductance circuit;
• and
• an output-rate control circuit configured to vary an output rate of the differential output signals, which are generated from the transconductance circuit, in response to a second control signal provided from the exterior,
• wherein the output-rate control circuit comprises:
• third and fourth PMOS transistors cross-coupled to each other between a power source voltage and the first and second output nodes;
• and
• first and second switches configured to turn the third and fourth PMOS transistors on/off in response to the second control signal.