Differential oscillator

A differential oscillator, comprising:

• a resonator that has at least a first resonance mode and a second resonance mode;
• a differential amplifier circuit configured to oscillate the resonator;
• a filter disposed in parallel to the resonator and the differential amplifier circuit, the filter having a first resonance frequency in the first resonance mode and a second resonance frequency in the second resonance mode, the filter having a lower impedance at one frequency in one of the first resonance frequency and the second resonance frequency than an impedance at one frequency at another in the first resonance frequency and the second resonance frequency, wherein
• the differential oscillator has a negative resistance at a frequency at which the impedance of the filter is higher while the differential oscillator does not have a negative resistance at a frequency at which the impedance of the filter is lower, among the first resonance frequency and the second resonance frequency.