In summary, all real time clock ICs must be clocked by a resonator that can be divided down to 1Hz. The most common is to use an external 32.768kHz crystal, but that limits timekeeping accuracy over temperature. Higher precision can be achieved by embedding the resonator with the RTC device, which features a TCXO to flatten the error curve over temperature. A MEMs-based all-silicon architecture has been developed by Analog Devices that is far more robust than crystal-based designs, allowing the device to be specified not only over temperature but also over the life of the product.