In certain clock-making applications, and in the case of electronic devices that do not operate permanently, but have to be activated from time to time, according to the current time, it is desirable to have a time reference, the energy consumption of which is as low as possible. This is especially the case for portable devices powered by an independent power source such as a battery.
In conventional time references, the output of the time base rarely provides a signal having a duty cycle corresponding to the exact symmetry of the pulse signal (duty cycle of 50%) and the voltage swing of which extends from one potential to the other of the power supply lines of the circuit (expressed as “rail to rail” swing). It is then necessary to mount a divider by two after the time base to accurately adjust the duty factor of the pulse signal.
In applications dedicated more specifically to radio communication and featuring the activation function mentioned above, two time references are conventionally used, namely a low energy reference based most commonly on a 32 kHz watchmaker's type quartz resonator to ensure synchronization on the current time and another very accurate time reference, the time base of which produces, at the cost of greater consumption, a high frequency, greater than 10 MHz for example, to create a narrowband communication channel for exchanging information with one or more other devices equipped with compatible transmission/reception equipment.
Such an arrangement with two time references leads to a greater complexity (controlling the starting of the high frequency oscillator) and entails the use of two bulky quartz resonators.