Patent ID: 6968168

Claim:
A variable frequency oscillator comprising: an oscillatory circuit for generating a periodic output dependant on the capacitance between a first node and a second node of the circuit, and having a capacitative element connected between the first node and the second node; the capacitative element comprising: a variable capacitance unit, the capacitance of which is variable by means of a voltage applied to a variable capacitance input for varying the frequency of the output; a plurality of trimming capacitances each being selectively connectable to the variable capacitance unit to trim the frequency of the output; a memory for storing information defining one or more sets of the trimming capacitances; and control apparatus coupled to the memory for causing a set of the trimming capacitances to be connected to the variable capacitance unit by the steps of: retrieving from the memory information defining a set of the trimming capacitances; connecting that set of the trimming capacitances to the variable capacitance unit; comparing the voltage at the variable capacitance input with a first preset voltage range; and if that voltage is outside the first preset voltage range, determining, based on the voltage at the variable capacitance input, an adjusted set of the trimming capacitances and storing in the memory information defining that adjusted set of the trimming capacitances.