Disclosed is technology related to a signal synthesis apparatus that corrects an offset between a closed loop and an open loop to output a frequency-modulated signal. The signal synthesis apparatus includes a VCO configured to output a frequency signal in response to an input voltage, an energy storage unit configured to output a voltage using stored energy, a VCO input selector configured to connect the VCO to input of the energy storage unit in the case of a closed loop mode and connect the VCO to output of the energy storage unit in the case of an open loop mode, and a digital controller configured to control an operation mode of the VCO input selector and transmit an offset control signal for adjusting an offset of a voltage output from the energy storage unit to the energy storage unit.

A variable frequency oscillator includes an inductance unit having a first inductance, a first variable capacitor coupled across the inductance unit, and a second variable capacitor coupled across a part of the inductance unit. The inductance of the part of the inductance unit coupled by the second variable capacitor is a proportion of the first inductance.

An oscillator includes: an oscillation circuit whose oscillation frequency changes based on a voltage that is applied to a variable capacitance element; and a voltage generation unit that generates the voltage which is applied to the variable capacitance element based on a control signal, in which the voltage that is generated by the voltage generation unit changes nonlinearly with respect to a change in the control signal such that a change in the oscillation frequency with respect to the change in the control signal is adjusted to come close to be linear.