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An electronic circuit comprising a resonant circuit formed from an inductive component in parallel with a capacitive component;

• wherein the capacitive component is a varactor;
• wherein the electronic circuit is arranged for a differential signal and wherein the electronic circuit comprises:
• a first resonant circuit formed from an inductive component in parallel with a varactor;
• and
• a second resonant circuit formed from an inductive component in parallel with a varactor;
• and
• wherein the first resonant circuit is arranged for receiving a positive part of the differential signal and the second resonant circuit is arranged for receiving a negative part of the differential signal.

A differential circuit having a first positive arm and a second negative arm;

• wherein the first positive arm comprises at least one first reactive component and the second negative arm comprise at least one second reactive component;
• further comprising:
• an active circuit, the active circuit arranged to increase the ac voltage difference across the first reactive component by changing the current at an input to the first reactive component and the current at an output of the first reactive component by equal and opposite amounts, and the active circuit arranged to increase the ac voltage difference across the second reactive component by changing the current at an input to the second reactive component and the current at an output of the second reactive component by equal and opposite amounts;
• wherein a third reactive component is connected between the input of the first reactive component and the input of the second reactive component;
• and wherein a fourth reactive component is connected between the output of the first reactive component and the output of the second reactive component.