Multi-phase oscillators

An apparatus, comprising:

• a first oscillator having first oscillator terminals;
• a second oscillator having second oscillator terminals;
• and
• a first circuit having first inputs and first outputs, the first inputs coupled to the first oscillator terminals, the first outputs coupled to the second oscillator terminals, the first circuit including a first transformer coupled between the first inputs and the first outputs;
• and
• a second circuit having second inputs and second outputs, the second inputs coupled to the second oscillator terminals, the second outputs coupled to the first oscillator terminals, the second circuit including a second transformer coupled between the second inputs and the second outputs.

An apparatus, comprising:

• a first oscillator having first oscillator terminals;
• a second oscillator having second oscillator terminals coupled to the first oscillator terminals;
• and
• a frequency multiplier circuitry coupled to the first and second oscillators, the frequency multiplier circuitry including a harmonic extraction circuit.

An apparatus comprising:

• a first oscillator circuit having a first terminal and a second terminal;
• a second oscillator circuit having a third terminal and a fourth terminal;
• a first circuit having a first positive input, a first negative input, a first positive output, and a first negative output, the first positive input coupled to the first terminal, the first negative input coupled to the second terminal, the first positive output coupled to the third terminal, and the first negative output coupled to the fourth terminal;
• and
• a second circuit having a second positive input, a second negative input, a second positive output, and a second negative output, the second positive input coupled to the fourth terminal, the second negative input coupled to the third terminal, the second positive output coupled to the first terminal, and the second negative output coupled to the second terminal.

A system comprising:

• an oscillator circuit, comprising:
• multiple bulk acoustic wave (BAW) oscillator circuits each having respective oscillator terminals and a respective center tap terminal, each of the multiple BAW oscillator circuits configured to provide respective first signals having a first frequency at the respective oscillator terminals;
• and
• a first circuit having an input and an output, the input coupled to the center tap terminals of the BAW oscillator circuits, and the first circuit configured to provide a second signal at the output, the second signal having a second frequency higher than the first frequency;
• and
• a second circuit having a clock input coupled to the output of the first circuit.