Amplitude regulator for crystal oscillator

An electronic device comprising:

• an oscillator circuit portion comprising an inverter having an input terminal and an output terminal, said oscillator circuit portion further comprising a crystal oscillator connected between the input and output terminals of the inverter;
• an amplitude regulator circuit portion arranged to supply a current to the inverter of the oscillator circuit portion, said amplitude regulator circuit portion being arranged to monitor a voltage at the input terminal of the inverter and to vary the current supplied to said inverter in response to said monitored voltage;
• wherein the amplitude regulator circuit portion comprises:
• a trimmable resistor arranged such that the voltage at the input terminal of the inverter is set to an operating point when the supply current provided by the amplitude regulator circuit portion is equal to a threshold value, wherein said operating point is at least partly determined by a selected resistance of the trimmable resistor;
• and
• a current monitor arranged to monitor the current supplied to the inverter during operation and to determine therefrom whether the voltage at the input terminal of the inverter is within a predetermined range;
• wherein the current monitor comprises a current comparator arranged to determine whether the voltage at the input terminal of the inverter is within the predetermined range.