Horizontal oscillation circuit capable of changing frequency

A semiconductor integrated circuit having an oscillation circuit, comprising:

• a phase comparing circuit which compares a phase of an input signal with a phase of a reference signal, said phase comparing circuit outputs a signal corresponding to a phase difference between the input signal and the reference signal;
• a filter circuit which generates a first control signal from the output signal which is supplied from said phase comparing circuit;
• and
• a voltage-controlled oscillator which oscillates a signal in accordance with the first control signal applied from said filter circuit, said voltage-controlled oscillator having a plurality of inverter circuits and being configured to change a center frequency by varying an amount of delay of the inverter circuits in accordance with a second control signal corresponding to the frequency of the input signal.

A method of generating an oscillating signal, comprising:

• comparing a phase of an input signal with a phase of a reference signal and outputting a signal corresponding to a phase difference between the input signal and the reference signal;
• filtering the signal output in the preceding step to generate a first control signal;
• and
• applying the first control signal to a voltage controlled oscillator having a plurality of delay elements to vary a delay of each of the delay elements based on the first control signal;
• changing a center frequency of the voltage controlled oscillator by varying an amount of delay of the delay elements in accordance with a second control signal corresponding to the frequency of the input signal;
• and
• outputting an output signal of the voltage controlled oscillator at a center frequency determined by said second control signal.