Method and apparatus for controlling oscillation frequency

A method for determining a bias current of a quartz oscillator, comprising:

• defining a plurality of bias current values;
• supplying in sequence the plurality of bias current values to the quartz oscillator;
• determining the oscillation frequency of an output signal at the output of the quartz oscillator corresponding to each bias current value;
• determining the bias current values having a valid oscillation frequency in the output signal of the quartz oscillator;
• and
• fixing as a bias current of the quartz oscillator an algebraic average of the bias currents determined to have a valid oscillation frequency in the signal output of the quartz oscillator.

An apparatus for determining a bias current of a quartz oscillator for generating an output signal, the apparatus comprising:

• a ramp signal generator having an input coupled to an output of the quartz oscillator and an output on which is generated a ramp signal in response to the quartz oscillator output signal;
• a voltage comparator comparing the ramp signal to a reference voltage and generating a comparison output signal;
• a control logic circuit having an input for receiving the comparison output signal from the comparator, the control logic circuit configured to generate a bias current control signal at an output thereof responsive to the comparison output signal of the comparator;
• and
• a current generator having an input for receiving the bias current control signal from the control logic circuit and for generating a bias current signal to the quartz oscillator;
• wherein the control logic circuit is further configured to determine the bias current of the quartz oscillator by:
• generating a plurality of bias currents having a prefixed value;
• supplying the plurality of bias current values to the quartz oscillator;
• verifying the oscillation frequency of an output signal generated by the quartz oscillator for each of the plurality of bias current values;
• storing the bias current values determined to have valid oscillation frequencies in the output signal of the quartz oscillator;
• and
• determining as a bias current of the quartz oscillator the algebraic average of the bias current determined to have valid oscillation frequencies at the output signal of the quartz oscillator.