And the role of the principle of crystal
What is the role of the crystal oscillator role?:
1. Crystal effect: to provide a stable clock signal to the microcontroller to work properly. Principle: two quartz crystal plates plus an electric field, the wafer will produce mechanical deformation of a mechanical force to deform the plate, the plates will generate a corresponding charge, called the piezoelectric effect. If the two plates together with alternating voltage, the wafer will produce mechanical deformation vibration, mechanical shock while this will generate an alternating electric field (relatively small), but when the applied alternating voltage and frequency wafer inherent frequency (decided by its shape and size) are equal, the amplitude of mechanical vibration will increase, resulting in an alternating electric field increases. Called the piezoelectric harmonics.
2. Even remove the crystal oscillation circuit still can, and if those two adjustable capacitor capacitance change can be obtained if a desired frequency, it'll do the crystal: crystals, ceramic resonators, RC oscillation devices and silicon oscillator is suitable for four microcontroller clock source. Application-specific optimization clock source design depends on the following factors: cost, precision and environmental parameters. RC oscillator quick start, the cost is relatively low, but it is usually in the whole temperature and supply voltage range accuracy is poor, vary in the range of 5-50% of nominal output frequency; but in terms of relative RC oscillator based on the crystal and ceramic resonator oscillators typically provide very high initial accuracy and low temperature coefficient.
The role of the crystal in the circuit
1, crystal essential role in digital circuits is to provide a timing control of the standard time. Operation of the digital circuit is based on circuit design, specifically at a time to complete a specific task, if there is no standard time a timing control of the entire digital circuit becomes "deaf" and does not know what time to do things.
2, the role of the crystal is to provide basic clock signal for the system. Usually a system share a crystal, to facilitate the various parts to keep pace. Some group communication system using a different frequency and radio frequency oscillator, and by adjusting the frequency of electronic methods to keep pace.
3, Crystal is usually used in conjunction with a phase locked loop circuit, in order to provide the desired system clock frequency. If different subsystems require clock signals of different frequencies can be used with different phase-locked loop is connected with a crystal to provide.
Principle crystal
Crystal clock circuit element commonly used, the full name is called a crystal oscillator, crystal oscillator in the SCM system is very large role, he combined the internal microcontroller circuit that generates a clock frequency of the microcontroller must perform all MCU instructions are established on this basis, the crystal clock frequencies higher that the processor is running sooner.
Crystal at the resonant state can work with an electrical and mechanical energy transformed into each crystal to provide a stable and accurate single-frequency oscillations. Under normal operating conditions, the absolute accuracy of common crystal frequency up to fifty millionths. Advanced higher accuracy. Some crystal may also be adjusted by the applied voltage frequency within a certain range, known as a voltage controlled oscillator (VCO).
The role of the crystal is to provide basic clock signal for the system. Usually a system share a crystal, to facilitate the various parts to keep pace. Some group communication system using a different frequency and radio frequency oscillator, and by adjusting the frequency of electronic methods to keep pace.
Crystals are usually used in conjunction with a phase locked loop circuit, in order to provide the desired system clock frequency. If different subsystems require clock signals of different frequencies can be used with different phase-locked loop is connected with a crystal to provide.
Figures 1a crystal commonly used three-terminal capacitor (Colpitts) oscillator circuit AC equivalent; actual crystal AC equivalent circuit shown in Figure 1b, where Cv is used to adjust the oscillation frequency, usually with different varactor plus the reverse bias voltage to achieve, which is the mechanism of action of voltage control; Figure 1c after the crystal equivalent circuit replaced crystals. Where Co, C1, L1, RR is an equivalent circuit of the crystal.
And the role of the principle of crystal
Crystal oscillator circuit diagram
Analysis shows that the entire oscillator tank circuit, use Cv to change the frequency is limited: the decision of the oscillation frequency of the entire tank capacitor C = after Cbe, Cce, Cv three capacitors in series and in parallel and then Co and C1 series. It can be seen: C1 smaller, Co larger when Cv changes the entire tank capacitor smaller role. Which can "voltage controlled" frequency range is smaller. In fact, since the C1 is small (1E-15 middleweight), Co can not be ignored (1E-12 middleweight, several PF). So, Cv becomes large, reducing the frequency of the tank have become increasingly small, Cv becomes smaller, increasing the role of the tank frequency is growing. This aspect caused by the nonlinear characteristics of the voltage control, voltage control range the greater, nonlinear more severe; on the other hand, points to the oscillation of the feedback voltage (the voltage on Cbe) are getting smaller, leading to stop vibration. By crystal schematics you should have a general understanding of the role of the crystal and the working process of the bar. Using higher overtone crystal oscillator frequency, the smaller the equivalent capacitance C1; therefore the smaller frequency range.
Microcontroller clock source can be divided into two categories: mechanical resonant clock source devices, such as crystals, ceramic resonators; RC (resistor, capacitor) oscillator. One is Pierce oscillator configuration for crystal and ceramic resonators. Another simple discrete RC oscillator.
With a multimeter to measure whether the method of crystal oscillator: two measuring pin voltage is half the operating voltage of the chip, such as the operating voltage is 51 single + 5V is whether it is about 2.5V. Also, if the crystal tweezers touch another foot, a significant change in the voltage, proved to be the start-up's.
Type Crystal SMD and DIP has a type, that patch and pin type.
Let me talk about DIP: Common sizes HC-49U / T, HC-49S, UM-1, UM-5, which are MHZ units.
Besides SMD: There 0705,0603,0503,0302, there is another four joints and two solder joints. However, the smaller and more expensive, but are small, you can not make a high frequency oscillator.
