An oscillator circuit (702; 802) comprising: first and second resonator terminals (710, 712; 810, 812) for connecting to respective terminals of a resonator (704; 804); a first inverting amplifier (706; 806) having an input is coupled to the first resonator terminal (710;810); a second inverting amplifier (708;808) having an input coupled to the second resonator terminal (712;812); a first switch (730; 830), a second switch (732; 832), a first AC coupling capacitor (714; 814) and a second AC coupling capacitor (718; 818); wherein in a first mode of the operation the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to the second resonator terminal (712;812) and the output of the second inverting amplifier (708;808) is coupled by the second switch (732;832) to open circuit, or the output of the second inverting amplifier (708;808) is coupled by the second switch (730;830) to the first resonator terminal (710;810) and the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to open circuit; and in a second mode of operation the first AC coupling capacitor (714;814) is coupled in series between the output of the first inverting amplifier (706;806) and the second resonator terminal (712;812) by the first switch (730;830) and the second AC coupling capacitor (718; 818) is coupled in series between the output of the second inverting amplifier and the first resonator terminal by the second switch, the oscillator circuit further comprising a controller configured to compare an operational parameter of the oscillator circuit (702; 802) to a switchover threshold, and switch the oscillator circuit (702; 802) from the first mode of operation to the second mode of operation when the operational parameter exceeds the switchover threshold. first and second resonator terminals (710, 712; 810, 812) for connecting to respective terminals of a resonator (704; 804); a first inverting amplifier (706; 806) having an input is coupled to the first resonator terminal (710;810); a second inverting amplifier (708;808) having an input coupled to the second resonator terminal (712;812); a first switch (730; 830), a second switch (732; 832), a first AC coupling capacitor (714; 814) and a second AC coupling capacitor (718; 818); wherein in a first mode of the operation the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to the second resonator terminal (712;812) and the output of the second inverting amplifier (708;808) is coupled by the second switch (732;832) to open circuit, or the output of the second inverting amplifier (708;808) is coupled by the second switch (730;830) to the first resonator terminal (710;810) and the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to open circuit; and in a second mode of operation the first AC coupling capacitor (714;814) is coupled in series between the output of the first inverting amplifier (706;806) and the second resonator terminal (712;812) by the first switch (730;830) and the second AC coupling capacitor (718; 818) is coupled in series between the output of the second inverting amplifier and the first resonator terminal by the second switch, the oscillator circuit further comprising the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to the second resonator terminal (712;812) and the output of the second inverting amplifier (708;808) is coupled by the second switch (732;832) to open circuit, or the output of the second inverting amplifier (708;808) is coupled by the second switch (730;830) to the first resonator terminal (710;810) and the output of the first inverting amplifier (706;806) is coupled by the first switch (730;830) to open circuit; and in a second mode of operation the first AC coupling capacitor (714;814) is coupled in series between the output of the first inverting amplifier (706;806) and the second resonator terminal (712;812) by the first switch (730;830) and the second AC coupling capacitor (718; 818) is coupled in series between the output of the second inverting amplifier and the first resonator terminal by the second switch, the oscillator circuit further comprising a controller configured to compare an operational parameter of the oscillator circuit (702; 802) to a switchover threshold, and switch the oscillator circuit (702; 802) from the first mode of operation to the second mode of operation when the operational parameter exceeds the switchover threshold.