Voltage-controlled oscillator circuits

A voltage-controlled oscillator circuit formed in a compound semiconductor, the circuit comprising:

• an input configured to receive an input control voltage;
• an odd plurality of delay elements connected in a ring arrangement;
• each delay element connected between first and second defined voltages and comprising:
• a first transistor configured as a variable resistance controlled by the input control voltage;
• and
• a second transistor configured as a voltage pull-down transistor controlled by a preceding delay element.

An amplifier circuit configured to receive a first input pulse-width-modulation signal and output an output pulse-width-modulation signal, the amplifier circuit comprising:

• a first voltage-controlled oscillator configured to receive the first input pulse-width-modulation signal and generate a corresponding first oscillation signal;
• a phase-and-frequency detector configured to receive the first oscillation signal and a reference oscillation signal and output the output pulse-width-modulation signal based on any frequency difference between the first oscillation signal and the reference oscillation signal;
• a feedback path from the output of the phase-and-frequency detector to an input of the first voltage-controlled oscillator, and
• a filter coupled to the input of the voltage-controlled oscillator to filter a carrier component of the first input pulse-width-modulation signal and the output pulse-width-modulation signal.

A voltage-controlled oscillator circuit, the circuit comprising:

• an input node for receiving an input control voltage;
• and
• a plurality of delay elements connected in a ring arrangement;
• wherein the input control voltage is applied to each of the plurality of delay elements;
• and
• wherein the input node presents as a high-impedance input.