Voltage-controlled crystal oscillator with extended range

A voltage-controlled crystal oscillator circuit with expanded frequency range, said voltage-controlled crystal oscillator comprising

• a crystal oscillator circuit having an input terminal and an output node, said crystal oscillator circuit generating at said output node a signal having a frequency f.sub.ref responsive to a voltage at said input terminal;
• a phase-locked loop having an input node connected to said output node of said crystal oscillator and an output node, said phase-locked loop generating a signal at said output node having a frequency f.sub.o, said phase-locked loop having a first divider circuit dividing said f.sub.ref frequency by a first variable integer M and a second divider circuit dividing said f.sub.o frequency by a second variable integer N;
• and
• a look-up table for M and N values connected to said first and second divider circuits, said look-up table varying M and N responsive to said input terminal voltage;
• whereby said voltage-controlled crystal oscillator circuit has an increased frequency range.

A method of expanding the frequency range of a voltage-controlled crystal oscillator, said method comprising

• generating a first signal at a first frequency f.sub.ref from an oscillating crystal having a fundamental frequency, said first frequency varying about said fundamental frequency in response to a tuning voltage;
• multiplying said first frequency by a factor M/N, where M and N are integers, to generate a second signal at a second frequency;
• and
• varying M and N when said tuning voltage exceeds a predetermined voltage range;
• whereby a widened frequency range about said second frequency is generated.