Bluetooth Low Energy physical layer tws earbuds controls

tolerance
A tolerance is given when a device is manufactured. Generally speaking, the more precise the tolerance, the more expensive the equipment. For radio, the main tolerance can be determined by frequency accuracy. Even if the radio is designed to transmit at 2402MHz, the actual operating frequency may be 2401850MHz or 2402150MHz, which is the center frequency tolerance for sending a message. For Bluetooth Low Energy, the center frequency tolerance of the entire message is +150kHz. The reason why the center frequency deviates is that it is generally obtained by multiplying a crystal of a known frequency. The frequency of the crystal oscillator is usually 16MHz. If you want to get 2400MHz, you need to multiply the frequency by 150 times. Any deviation of the crystal will also be amplified and reflected in the transmit frequency. For example, if the actual frequency of the crystal data is 160001MHz, the center frequency will deviate from the ideal frequency by 150kHz. We call this crystal an error of 62ppm, or 62 parts per million. Typically, a low-cost crystal that is used in large quantities can have an error below about 50ppm. www.bjbjaudio.com   <a style="opacity:0.0;color:#ffffff">tws earbuds controls</a>

Another very important indicator is the drift of the center frequency during packet transmission. Drift can be caused by heat build-up while the chip is operating. As heat builds up, the radio's internal frequency drifts slightly. During the sending of a Bluetooth low energy packet, the drift is not allowed to exceed 50 kHz. That is to say, when starting to send a message, if the center frequency is 2402.000MHz, the center frequency should be between 2401950MHz and 2402050MHz during the sending process. At the same time, the maximum drift rate of the frequency cannot exceed 400Hz/us. www.bjbjaudio.com

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Receiver sensitivity
When building a receiver, a very important question is; how good is it. Measuring the receiver's sensitivity quantifies the problem: how sensitive the receiver is to detect wireless signals from other devices. Sensitivity is usually measured in dBm, which is a very small unit. Bluetooth Low Energy stipulates that the sensitivity of the receiver should be higher than -70dBm. In other words, the receiver must work properly when it receives 00000001mW of electromagnetic energy. However, noise is always present. There is no point in just detecting the signal if it can't be decoded correctly. Therefore, in practice, the receive sensitivity threshold is defined under an acceptable bit error rate (BER) condition. Bluetooth Low Energy has chosen a bit error rate of 0.1%. Controllers that support Bluetooth low energy have receiver sensitivity of -90dBm, or 1pW. This is an incredibly small amount of energy detectable from band noise, which results in an objective communication distance, as explained in the next section. www.bjbjaudio.com   <a style="opacity:0.0;color:#ffffff">tws earbuds controls</a>          <a style="opacity:0.0;color:#ffffff">tws earbuds controls</a>