Introduction to the Principle of RTC Clock Chips, Crystal Oscillator Selection, and Typical Applications

A clock chip is a high-performance, low-power consumption real-time clock circuit with RAM. It can keep track of years, months, days, weekdays, hours, minutes, and seconds, and has a leap year compensation function. It uses the IIC communication interface to conduct synchronous communication with the CPU/SoC and can transmit multiple bytes of clock signals or RAM data in a burst mode. It has an internally integrated RAM register for temporarily storing data.

The principle of the clock chip is to utilize a crystal oscillator to generate a stable frequency signal and then generate the required clock frequency through frequency division and multiplication circuits. A crystal oscillator is a device that generates electrical signals by the mechanical vibration of a crystal. Its frequency is extremely stable, usually ranging from several hundred thousand to tens of millions of hertz. The clock chip will adjust the frequency of the signal from the crystal oscillator to meet the specific clock frequency requirements.

The clock chip is a microcontroller integrated with a timing function. Its basic structure includes input/output ports, timers/counters, and an interrupt controller. Among them, the input/output ports are used to receive external signals, the timers/counters are used to generate a time reference, and the interrupt controller is used to handle the overflow events of the timers.

1. Input/Output Ports
The clock chip can receive external signals through the input/output ports so as to adjust the system time as needed. For example, it can receive the clock information of a computer or other devices through a serial communication interface (UART, I2C, SPI, etc.), or synchronize the network time through a network interface (such as NTP).

2. Timers/Counters
A clock chip usually has one or more timers/counters integrated internally to generate a time reference. The working mode of the timers/counters is realized through a prescaler and a counter. The prescaler reduces the system clock frequency to an appropriate counter clock frequency, and the counter is used to calculate the elapsed time. When the count value of the timers/counters reaches the set value, an interrupt event will be triggered to notify the system to update the time.

3. Interrupt Controller
To handle the overflow events of the timers, the clock chip also has an interrupt controller. When the count value of the timers/counters reaches the set value, an interrupt request will be sent to the interrupt controller. The interrupt controller will recognize this request and execute the corresponding interrupt service program (ISR), such as updating the system time, awakening tasks waiting to be processed, etc.

4. Update of System Time
When the system time changes, the clock chip needs to perform a series of operations to update the system time. First, it receives new clock information through the input/output ports; then, it uses the timers/counters to calculate the time difference; next, it adds the calculated time difference to the current system time; finally, it notifies other parts of the system that the system time has been updated through the interrupt controller

1. High Precision
The most fundamental characteristic of clock chips is their high precision. Whether it is a quartz clock or an atomic clock, their errors are far smaller than the range of human perception. This enables the clock chip to accurately display the time and meet our various needs for time.

2. Stability
Another important characteristic of clock chips is stability. Due to their high precision, clock chips can maintain a stable working state under various environmental conditions. Whether in high-temperature, low-temperature, humid, or dry environments, clock chips can maintain their accuracy and stability.

3. Low Power Consumption
To ensure the long-term stable operation of clock chips, designers usually try to reduce their power consumption as much as possible. This not only helps to extend the service life of the clock chips but also reduces the energy consumption of electronic devices.

4. Integration
With the development of integrated circuit technology, clock chips are becoming smaller and more powerful in function. Nowadays, clock chips can not only be used for timing alone but also can be integrated into various electronic devices such as mobile phones and computers to provide accurate time display and time management functions.

5. Ease of Use
Although clock chips are powerful in function, they are usually designed to be very simple and easy to use. Users only need to connect and use the clock chips in the correct way to easily obtain accurate time.

 

Differences between Clock Chips and Crystal Oscillators

I. Definitions and Functions of Clock Chips and Crystal Oscillators

1. Clock Chips
Clock chips, also known as timer chips or timing chips, are integrated circuits used to generate pulse signals of specific frequencies. Their main function is to provide a stable clock signal so that electronic devices can operate and communicate according to the predetermined time. Clock chips usually include an internal counter and a divider/multiplier circuit for generating the required clock frequency.



2. Crystal Oscillators
Crystal oscillators, also known as crystal oscillators or quartz oscillators, are components that utilize the piezoelectric effect of quartz crystals to generate precise frequencies. The main function of crystal oscillators is to serve as a stable frequency reference source, providing an accurate time reference for electronic devices. Crystal oscillators are widely used in various electronic devices, such as computers, mobile phones, radio and television, etc.

II. Structure and Working Principles

1. Structure of Clock Chips
Clock chips usually adopt single - in - package (SIP) packaging, with a high level of integration and a small volume. The internal structure mainly includes an input capture circuit, an internal counter, a divider/multiplier circuit, and an output comparator, etc. The working principle of the clock chip is mainly to control the frequency of the output signal through the overflow of the internal counter and the inverted output of the comparator.

2. Structure of Crystal Oscillators
Crystal oscillators usually use quartz crystals as resonant elements, which are encapsulated in a small cylindrical ceramic tube. Quartz crystals have high stability and reliability, so crystal oscillators are widely used in electronic devices. The structure of crystal oscillators mainly includes quartz crystals, capacitors, resistors, and electrodes, etc. The working principle of crystal oscillators is mainly to generate a high - frequency voltage signal in a sine waveform through the piezoelectric effect of quartz crystals, and then filter and regulate the voltage through capacitors and resistors, and finally output a stable clock signal.

III. Comparison of Performance Indicators of Clock Chips and Crystal Oscillators

1. Performance Indicators
There are certain differences in performance between clock chips and crystal oscillators, mainly manifested in the following aspects:
(1) Precision: The precision of crystal oscillators is usually higher than that of clock chips because quartz crystals have higher resonant stability. This means that crystal oscillators can provide more accurate clock signals.
(2) Volume and Power Consumption: Due to the single - chip integrated circuit design, clock chips have a smaller volume and relatively lower power consumption. However, because crystal oscillators need to use quartz crystals and corresponding packaging materials, they have a relatively larger volume and higher power consumption.

2. Comparison between Clock Chips and Crystal Oscillators
Generally speaking, clock chips and crystal oscillators have their own advantages and disadvantages. Crystal oscillators have high precision and stability and are suitable for occasions with high requirements for clock signals. Clock chips, on the other hand, have lower power consumption and are suitable for applications in electronic devices. In practical applications, users can choose the appropriate products according to their own needs.

 

Introduction to the Precision Range of Clock Chips

The precision of clock chips is mainly affected by two factors: crystal oscillator frequency and temperature compensation. Crystal oscillator frequency refers to the frequency of the quartz crystal oscillator inside the clock chip, usually measured in hertz (Hz). The higher the crystal oscillator frequency, the higher the precision of the clock chip. Temperature compensation refers to the sensitivity of the temperature sensor inside the clock chip to changes in ambient temperature. Through temperature compensation, the stability and precision of the clock chip can be improved.

According to the standards of the International Electrotechnical Commission (IEC), the precision of clock chips is divided into the following levels:
1 ms (millisecond - level): The clock chip updates the time every 1 millisecond, with an error of no more than 1 millisecond. This type of chip is often used in applications with high requirements for time precision, such as high - precision timers and real - time data acquisition.

10 ms (microsecond - level): The clock chip updates the time every 10 milliseconds, with an error of no more than 0.1 milliseconds. This type of chip is often used in general timing applications, such as household appliances and office equipment.

1 μs (microsecond - level): The clock chip updates the time every 1 microsecond, with an error of no more than 0.01 microseconds. This type of chip is often used in applications with high requirements for time precision, such as communication equipment and precision instruments.

1 ns (nanosecond - level): The clock chip updates the time every 1 nanosecond, with an error of no more than 0.001 nanoseconds. This type of chip is often used in applications with extremely high requirements for time precision, such as aerospace and biomedicine.

Others: Besides the above - mentioned levels, there are also some special clock chips, such as GPS receivers with higher precision and atomic clocks.

 

Why is 32.768 kHz the Commonly - used Crystal Oscillator Frequency in Circuit Design?

The most commonly - used frequencies of crystal oscillators are 32.768 kHz, 77.503 kHz, 60.003 kHz, 40.003 kHz and 12 MHz, 14 MHz, 16 MHz, 24 MHz in MHz, etc., which are widely used in various electronic products.

32.768K is the most commonly used frequency and is indispensable in daily life. 32.768 kHz is relatively easy to divide the frequency so as to generate a 1-second clock frequency, because 32,768 is equal to 2 to the power of 15. The clocks that display the time on the watches, mobile phones, and computers we use every day are all derived from it.

32.768 kHz is a standard frequency. The application of crystal oscillator frequencies mainly involves the following parameters: size, load capacitance, frequency deviation, and application range. According to the size and shape, they are mainly divided into through-hole and surface-mount types. The through-hole types mainly include 2×6, 3×8, 49s, etc., and there are many types of surface-mount ones. Depending on the design of each company, there are numerous available models.

In a clock system, the second is an important unit of time. One second corresponds exactly to 1 Hz. If we want to improve the accuracy of time, this 1 Hz must be precise. As we know, in the digital world, there are only two possibilities: 0 and 1. Now let's look at a calculation:

2 to the power of 15 equals 32,768, which is equal to 32.768K.

The 15th power of 2 is exactly 32,768. Conversely, if we divide the clock frequency of 32.768K fifteen times, the resulting frequency will be exactly 1 Hz.