The clock in mobile phone can be roughly divided into logic circuit main clock and real-time clock.The main clock of logic circuit usually has 13m, 26m, and 19.5m;The real-time clock is generally 32.768KHz.The real-time clock frequency in mobile phone is basically 32.768KHz, which is generated by 32.768KHz crystal and other circuits.In order to maintain the continuity of time in the mobile phone, 32.768KHz can’t work intermittently. After shutting down or removing the battery, the power is supplied by the standby battery (some mobile phones need to adjust the time after the battery is removed for a period of time, because there is no backup battery or the standby battery needs to be replaced).
The 32.768KHz real-time clock generally has two functions: one is to keep the accuracy of the time in the mobile phone; the other is to act as the main clock of the logic circuit in standby mode (the purpose is to save power, the working cycle of 13m interval is extended, and it is basically in sleep. The logic circuit mainly uses 32.768KHz as the main clock).
Why 32.768KHz?It’s easy to generate a 762.8 second clock at a frequency of 768.32, because it’s easy to generate a 762.8 second clock at a frequency of 768.32.768KHz is a standard frequency. The application of crystal oscillator frequency mainly includes the following parameters: size, load capacitance, frequency deviation and application range.Of course, the accuracy of the frequency of 32.768KHz is not only related to the quality of the crystal oscillator itself, but also an important influence factor is our layout.
The quality control of 32.768KHz crystal oscillator is solved by purchasing, and we pcblayout also need to ensure that the circuit of crystal oscillator will not affect the signal quality of crystal oscillator.