Degeneration for a wideband voltage-controlled oscillator

A voltage-controlled oscillator (VCO) comprising:

• a tank circuit coupled to a pair of nodes, the pair of nodes including a first node and a second node;
• a first cross-coupled transistor pair of a first transistor type, a drain terminal of a first transistor of the first cross-coupled transistor pair connected to the first node of the pair of nodes, a drain terminal of a second transistor of the first cross-coupled transistor pair connected to the second node of the pair of nodes, and a source terminal of the first transistor of the first cross-coupled transistor pair and a source terminal of the second transistor of the first cross-coupled transistor pair connected to a third node;
• a second cross-coupled transistor pair of a second transistor type, a drain terminal of a third transistor of the second cross-coupled transistor pair connected to the first node of the pair of nodes, a drain terminal of a fourth transistor of the second cross-coupled transistor pair connected to the second node of the pair of nodes, and a source terminal of the third transistor of the second cross-coupled transistor pair and a source terminal of the fourth transistor of the second cross-coupled transistor pair connected to a fourth node;
• and
• means for providing differential degeneration to the VCO, comprising:
• a first inductor connected between the third node and a supply voltage;
• a second inductor connected between the fourth node and a ground;
• and
• means for providing a degeneration capacitance having a degeneration capacitance value selected from multiple capacitance values, the means for providing the degeneration capacitance connected to the third node and the fourth node.

A voltage-controlled oscillator (VCO) operating method comprising:

• generating an oscillating signal having a fundamental frequency using a VCO, the VCO comprising:
• a tank circuit;
• a first cross-coupled transistor pair of a first transistor type, drain terminals of the first cross-coupled transistor pair being connected to the tank circuit, and source terminals of the first cross-coupled transistor pair connected to a first node;
• and
• a second cross-coupled transistor pair of a second transistor type, drain terminals of the second cross-coupled transistor pair of the second transistor type being connected to the tank circuit, and source terminals of the second cross-coupled transistor pair connected to a second node;
• presenting a frequency-dependent impedance to the source terminals of the first and second cross-coupled transistor pairs using a resonant circuit, the resonant circuit comprising:
• a first inductor connected between the first node and a supply voltage;
• a second inductor connected between the second node and a ground;
• and
• a capacitor connected between the first node and the second node, the capacitor comprising a switched degeneration capacitor hank configured to provide a degeneration capacitance value selected from multiple capacitance values based on a degeneration-tuning control signal,
• wherein the resonant circuit is tuned to resonate at a frequency that is approximately twice the fundamental frequency.

A frequency synthesizer apparatus, comprising:

• a phase locked loop (PLL) synthesizer comprising:
• a reference oscillator configured to generate a reference frequency signal;
• and
• a voltage-controlled oscillator (VCO) configured to generate an output signal having a frequency that is controlled at least partially by the reference frequency signal, the VCO including a degeneration network that is configured to degenerate phase noise in the output signal of the VCO in response to a degeneration-tuning control signal, the degeneration network comprising a degeneration capacitor bank that is configured to tune the degeneration network in relation to the frequency of the VCO;
• and
• a control signal generator configured to provide:
• a band-selection control signal to select an inductance value from multiple inductance values provided by a switched inductor network included in the VCO, the selected inductance value determining a frequency band of operation for the frequency synthesizer;
• a coarse-tuning control signal and a fine-tuning control signal to set the frequency of the output signal of the VCO;
• and
• the degeneration-tuning control signal to tune the degeneration network to provide at least one differential degeneration signal to reduce the phase noise in the output signal of the VCO.