Capacitor arrangement for oscillator

An adjustable capacitive circuit, comprising:

• a first node;
• a second node;
• a plurality of capacitive branch circuits, each including a respective set of capacitors and configured and arranged to
• in an enabled mode, contribute a first amount of capacitance between the first and second nodes and
• in a disabled mode, contribute a second lesser amount of capacitance between the first and second nodes;
• an initialization circuit configured and arranged to, for each of the plurality of capacitive branch circuits that is disabled,
• in a first mode, couple the set of capacitors of the capacitive branch circuit to a respective reference voltage in response to the capacitive branch circuit being disabled, and
• in a second mode, uncouple the set of capacitors of the capacitive branch circuit from the respective reference voltage;
• and
• an additional switch coupled to couple the second node and the reference voltage, wherein the additional switch is configured to stay disabled at all times.

A method for operating an LC circuit including an adjustable capacitive circuit and an inductive circuit connected in a circuit loop, the method comprising:

• enabling a subset of a plurality of capacitor branch circuits in the adjustable capacitive circuit and disabling other ones of the plurality of capacitor branch circuits, each of the plurality of capacitor branch circuits including a respective set of capacitors and configured and arranged to provide a first capacitance between first and second nodes when enabled and provide a second lesser capacitance between the first and second nodes when disabled;
• in a first mode,
• disabling oscillation of the LC circuit by opening a switch in the circuit loop,
• for each of the plurality of capacitive branch circuits that is disabled, using an initialization circuit in the adjustable capacitive circuit to couple the set of capacitors in the capacitive branch circuit to a respective reference voltage, and
• charging the capacitive circuit by providing a charge voltage across the LC circuit;
• and
• in a second mode, enabling the oscillation of the LC circuit by closing the switch in the circuit loop, wherein the charge on the capacitive circuit causes the LC circuit to oscillate with a single-ended peak-to-peak amplitude equal to the charge voltage of the capacitive circuit nearly instantaneously after the oscillation is enabled, wherein a parasitic capacitance is introduced in the adjustable capacitive circuit using a switch that stays open at all times.