Resonant unit, voltage controlled oscillator (VCO) implementing the same, and push-push oscillator implementing a pair of VCOs

A voltage controlled oscillator (VCO) that generates an oscillating signal at an oscillating frequency, the VCO comprising:

• a resonant circuit including:
• a semiconductor substrate, a pair of resonant transmission lines electrically coupled to each other, a coupling transmission line, wherein one of the resonant transmission lines includes an input port and a through port, and another of the resonant transmission lines includes an isolation port and a coupling port;
• the coupling transmission line being connected between the input port of the one of the resonant transmission lines and the coupling port of the another of the resonant transmission lines, the resonant transmission lines each having a length corresponding to a quarter wavelength (λ/4) of twice of the oscillating frequency, the coupling transmission line having a length shorter than the length of the resonant transmission lines, the resonant transmission lines and the coupling transmission line being formed on the semiconductor substrate, and
• a variable capacitor connected to the through port of the one of the resonant transmission lines, the variable capacitor varying capacitance thereof depending on a bias supplied thereto;
• and
• a negative resistance unit including a transistor connected to the input port of the one of the resonant transmission lines,
• wherein the resonant circuit has impedance viewed from the negative resistance unit and the negative resistance unit has impedance viewed from the resonant circuit, the impedance of the resonant circuit in an imaginary part thereof added with the impedance of the negative resistance unit in an imaginary part thereof being substantially zero at the oscillating frequency, the impedance of the resonant circuit in a real part thereof added with the impedance of the negative resistance unit in a real part thereof being negative at the oscillating frequency.

A push-push oscillator, comprising:

• a pair of voltage controlled oscillators (VCOs) each having a resonant circuit and a negative resistance unit,
• wherein each of the resonant circuits in the VCOs includes a semiconductor substrate, a pair of resonant transmission lines electrically coupled to each other, a coupling transmission line electrically connecting the resonant transmission lines, and a variable capacitor connected to the one of the resonant transmission lines, the resonant transmission lines and the coupling transmission line being provided on the semiconductor substrate, the resonant transmission lines each having a length corresponding to a quarter wavelength (λ/4) of twice of the fundamental oscillating frequency, the coupling transmission line having a length shorter than the length of the resonant transmission lines,
• wherein each of the negative resistance units in the VCOs includes a transistor and an output port, wherein the resonant circuits and the negative resistance units have impedance determining a fundamental oscillating frequency of the VCOs;
• wherein the output port of the one of the VCOs is connected to the output port of the other of the VCOs, and
• wherein the push-push oscillator generates oscillation signals of even overtones of the fundamental oscillating frequency and substantially eliminates oscillation signals of odd overtones of the fundamental oscillating frequency.