CMOS VCO with implicit common-mode resonance

A method for providing an oscillator with common-mode resonance, the method comprising:

• providing a first oscillator circuit comprising a first cross-coupled transistor pair and a second oscillator circuit comprising a second cross-coupled transistor pair, wherein the first cross-coupled transistor pair includes a first transistor and a second transistor, a gate node of the first transistor directly connected to a drain node of the second transistor and a gate node of the second transistor directly connected to a drain node of the first transistor, wherein the first transistor and the second transistor are NMOS transistors, and wherein the second cross-coupled transistor pair includes a third transistor and a fourth transistor, a gate node of the third transistor directly connected to a drain node of the fourth transistor and a gate node of the fourth transistor directly connected to a drain node of the third transistor, wherein the third transistor and the fourth transistor are PMOS transistors;
• and
• coupling the first oscillator circuit to the second oscillator circuit via a joint tank circuit,
• wherein providing the joint tank circuit comprises:
• providing a differential coupled pair of inductors including a first node, a second node, a third node, and a fourth node, the first node and the second node coupled with a pair of first capacitors to ground potential;
• and
• coupling one capacitor of a pair of second capacitors between the first node and the second node of the differential coupled pair of inductors that are respectively coupled to drain nodes of the first NMOS transistor and the second NMOS transistor of the first cross-coupled transistor pair, and another capacitor of the pair of second capacitors being coupled between the third node and the fourth node of the differential coupled pair of inductors that are respectively coupled to drain nodes of the third PMOS transistor and the fourth PMOS transistor of the second cross-coupled transistor pair, and
• wherein each of the first oscillator circuit and the second oscillator circuit is configured to allow tuning of a respective common mode resonance frequency (FCM) to be at twice a respective differential resonance frequency (FD) by adjusting a ratio of capacitance values of the pair of the first and second capacitors.

A communication device comprising:

• a radio-frequency (RF) transceiver comprising one or more local oscillators,
• the one or more local oscillators comprising at least one oscillator with common-mode resonance, wherein the at least one oscillator with common-mode resonance comprises:
• a first oscillator circuit comprising a first cross-coupled transistor pair including a first transistor and a second transistor, a gate node of the first transistor directly connected to a drain node of the second transistor and a gate node of the second transistor directly connected to a drain node of the first transistor, wherein the first transistor and the second transistor are NMOS transistors;
• and
• a second oscillator circuit comprising a second cross-coupled transistor pair including a third transistor and a fourth transistor, a gate node of the third transistor directly connected to a drain node of the fourth transistor and a gate node of the fourth transistor directly connected to a drain node of the third transistor, the second cross-coupled transistor pair being coupled to the first oscillator circuit via a joint tank circuit, wherein the third transistor and the fourth transistor are PMOS transistors,
• wherein the joint tank circuit comprises:
• a differential coupled pair of inductors including a first node, a second node, a third node, and a fourth node, the first node and the second node coupled with a pair of first capacitors to ground potential;
• and
• a pair of second capacitors, one capacitor of the pair of second capacitors being coupled between the first node and the second node of the differential coupled pair of inductors that are respectively coupled to drain nodes of the first NMOS transistor and the second NMOS transistor of the first cross-coupled transistor pair, and another capacitor of the pair of second capacitors being coupled between the third node and the fourth node of the differential coupled pair of inductors that are respectively coupled to drain nodes of the third PMOS transistor and the fourth PMOS transistor of the second cross-coupled transistor pair, and
• wherein each of the first oscillator circuit and the second oscillator circuit is configured to allow tuning of a respective common mode resonance frequency (FCM) to be at twice a respective differential resonance frequency (FD) by adjusting a ratio of capacitance values of the pair of the first and second capacitors.