The application of crystal oscillator in Bluetooth module
Bluetooth is a wireless technology that supports short-range communication, typically around ten meters. By utilizing Bluetooth levels, communication between mobile communication terminals can be effectively simplified, making data transmission faster and more efficient. The common Bluetooth products in the market are widely used in electronic products such as computers, mobile phones, and entertainment devices, among which the most common is mobile phones.
Most smartphones have a Bluetooth function when you open the settings tool. The introduction of Bluetooth technology into smartphones is a major breakthrough for electronic products. On Bluetooth devices, there is a small surface mount crystal oscillator that provides a stable working clock pulse frequency. Without this small surface mount crystal oscillator, the entire Bluetooth system would not be able to function and become inactive. So, what is a crystal oscillator?
Crystal oscillator, also known as quartz crystal resonator, is a basic structure that involves cutting thin sheets from a quartz crystal at a certain azimuth angle, then coating a silver layer on the corresponding surface of the thin sheet and polarizing it to form two electrodes. Each electrode is soldered with a lead wire and enclosed in a metal shell to form a crystal oscillator. It has an important characteristic that if it is powered on, it will produce mechanical oscillation; On the contrary, if mechanical force is applied to it, it will generate electricity, and this characteristic is called electromechanical effect. Crystal oscillators have a characteristic that their oscillation frequency is closely related to their shape, material, cutting direction, etc. Due to the very stable chemical properties of quartz crystals, their thermal expansion coefficient is very small, and their oscillation frequency is also very stable. The geometric dimensions can be made very precise, so their resonance frequency is also very accurate.
Crystal oscillators are usually divided into two categories: active crystal oscillators and passive crystal oscillators, and in terms of appearance, crystal oscillators can be further divided into patch type crystal oscillators and plug-in type crystal oscillators. The crystal oscillator that can be used in Bluetooth products is the surface mount crystal oscillator. For a small number of products, plug-in crystal oscillators can also be used to save costs and provide sufficient space on the circuit.
The crystal oscillator that can be used in Bluetooth products is generally in the 3225 package, which is also the most commonly used package. There are also packages in the 2520 package, but they are not very commonly used because the cost is higher than that of the 3225 package. Common frequencies include 3225/12MHz, 3225/16MHz, 3225/24MHz, 3225/26MHz, 3225/32MHz, etc. The most commonly used package is the 26M package in the 3225 package. This package is also widely available and is the most commonly supplied package by manufacturers and suppliers. The commonly used load capacitors for these frequencies are 7PF, 9PF, 12PF, and 20PF, with 9PF being the most widely used load.
The Bluetooth surface mount crystal oscillator has an important electrical parameter, which is frequency error, also known as frequency accuracy. Currently, there are three types of frequency errors circulating in the market: ± 10PPM, ± 20PPM, and ± 30PPM. ± 10PPM is the most stable and reliable, and there is a certain price difference compared to 30PPM error. Generally, manufacturers will choose 10PPM error crystal oscillators.
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