The automatic gain control circuit senses the amplitude of the oscillation across the crystal and reduces the drive current until the desired amplitude is achieved. This amplitude insures reliable sensing while eliminating all excess current. The result is the absolute minimum current consumption for a given part, crystal, and operating condition. At the same time, excess current is available to support any crystal available. Since the circuit maintains constant amplitude, the drive current required becomes a function of the crystal ESR. If the customer wants the smallest possible foot print, they can choose the smallest surface mount crystal with a high ESR, and Analog Devices will have the drive current to insure oscillation under worse case conditions. If the customer wants the lowest possible power, then they can choose a low ESR crystal, and Analog Devices' part will provide the lowest current consumption on the market. A side benefit of this oscillator design has been a reduction in the minimum operating voltage. Where the last generation RTC would keep time down to 1.3V, the new oscillator has a typical min operation voltage of 1.15V. The real beauty of this solution is that the customer can use a single RTC in different designs requiring different tradeoffs. No longer does the customer have to source different RTCs for different projects.