Patent ID: 8130048

Claim:
A local oscillator in which three or more differential non-inverting delay circuits are connected in series, an output of a first of the three or more differential non-inverting delay circuits at an end is fed back, with polarity changed, to an input of a second of the three or more differential non-inverting delay circuits at a beginning to form an oscillation ring, and a frequency signal is extracted from the first of the three or more differential non-inverting delay circuits to an outside, wherein equal numbers of variable capacitance elements, having capacitance values that are separately controlled according to a logic value of a corresponding bit of a delay control signal that is in a one-to-one relation with an oscillation frequency, are connected in parallel among differential outputs of the differential non-inverting delay circuits excluding the first of the three or more differential non-inverting delay circuits, and bits of the delay control signal are connected in a one-to-one relation to the equal numbers of the variable capacitance elements arranged on respective output sides of the three or more differential non-inverting delay circuits, in a relation in which delay control signals continuous in terms of frequency are not connected to the equal numbers of the variable capacitance elements arranged on an output side of one of the three or more differential non-inverting delay circuits, wherein the local oscillator is a digitally controlled oscillator configured to perform oscillation operation according to a control code that indicates an oscillation frequency generated from phase information detected in an all digital phase locked loop, and the delay control signal is a thermal code generated by converting the control code.