The present invention relates to compounds of formula I . An automatic transimpedance gain control and DC cancellation control feedback circuit includes variable impedance circuitry. The operation of interest may be a save-to-disk operation during a battery operated computer shutdown or a shutdown procedure for a personal digital assistant, for example. The method may further include setting a capacitance of a variable capacitor coupled to the resonator in order to compensate for temperature-dependent and process-dependent frequency variation of the oscillator based on the ambient temperature and the process-based compensation.