PCB Tech - Teflon PCB with FM Technology in Mobile Communication System

Teflon PCB with FM technology in mobile communication system.Frequency modulation (FM) is the most common analog modulation skill in mobile communication system

Teflon PCB modulation is the process of processing the coding information of signal source to make it suitable for transmission. Generally speaking, this means that the baseband signal (source) is transformed into a band communication signal with a very high frequency relative to the baseband frequency. This band communication signal is called modulated signal, and baseband signal is called modulated signal. Modulation can be accomplished by changing the fluctuation, phase or frequency of the high frequency carrier with the fluctuation of the signal. Demodulation is the process of extracting the baseband signal from the Teflon carrier for the predetermined receiver (sink) to process and understand.

This chapter describes various modulation techniques used in Teflon mobile communication systems. It includes the analog modulation scheme for the first generation mobile communication system and the digital modulation scheme for the present and future systems. Because digital modulation has many advantages and has been used to replace the traditional analog system, this chapter focuses on the digital modulation plan. However, because the imitation system is still widely used, and will continue to exist, so first introduce the imitation modulation. This chapter describes many practical FM techniques, receiver architectures, planning tradeoffs, and their functions under different channel loss types.

Frequency modulation (FM) is the most common analog modulation skill in mobile communication system. In frequency modulation, the fluctuation of modulated carrier signal remains unchanged, while the frequency changes with the change of modulated signal. In this way, the FM signal contains all the information in the carrier phase or frequency. As we will see later, as long as the admission signal reaches a certain minimum value (FM threshold), the admission quality will be improved nonlinearly. In AM, there is a linear relationship between the quality of the Teflon PCB received signal and the energy of the received signal. This is because am superimposes the fluctuation of the modulated signal on the carrier, so that the amplitude modulated signal contains all the information in the fluctuation of the carrier. FM has many advantages over am, which makes FM better choice in many mobile communication applications.

FM has better anti noise function than AM. Because the FM signal shows the change of frequency rather than the fluctuation, the FM signal is less susceptible to the influence of atmosphere and impulse noise, which will form the fluctuation of receiving signal. In addition, in FM, because the change of signal fluctuation does not carry information, as long as the received FM signal is above the FM threshold, the impact of sudden noise on FM system is not as great as that on am system. In the last article, we explained how the small-scale fading leads to the agility and wavering of the received signal. It can be seen that FM has better anti fading function than am. In addition, in FM system, we can make a trade-off between bandwidth and anti noise function. Different from am system, FM system can get better signal noise function by changing the modulation index, which is the occupied bandwidth. We can see that under certain conditions, the signal-to-noise ratio (SNR) of the FM system can be increased by 6dB every time the bandwidth is doubled.

Perhaps the most important reason why FM system is superior to am system is that it can exchange bandwidth for SNR. However, AM signals occupy less bandwidth than FM signals. In the modern am system, because the in band pilot tone is transmitted together with the standard AM signal, its sensitivity to fading has been greatly improved. The modern AM receiver can monitor the pilot tone and adjust the gain quickly to compensate the fluctuation of the signal.

Because the envelope of FM carrier does not change with the modulation signal, FM signal is a constant envelope signal. In this way, regardless of the fluctuation of the signal, the power of FM signal transmission is fixed. And the constant envelope of the transmission signal allows the use of class C power amplifier in RF power amplification. In amplitude modulation, because it is necessary to adhere to the linear relationship between the signal and the fluctuation of the transmitted signal, it is necessary to use low-power amplifiers such as linear class A or class B.

When planning a portable user terminal, the power of the power amplifier is a very important issue because the battery life is closely related to the power of the power amplifier. The power of a typical class C amplifier is 70%, that is to say, 70% of the DC signal power at the end of the amplifier circuit is converted into the RF signal power. The rate of class A or class AB amplifier is only 30 ~ 40%, which means that the operation time of constant envelope FM modulation with the same battery is twice as long as that of AM method. FM has a property called the capture effect. The capture effect is the direct result of the rapid progress of nonlinear admission quality with the increase of admission power. If two signals of the same frequency band appear on the FM receiver, the stronger one will be accepted and demodulated, and the weaker one will be discarded. This inherent ability to select the strongest signal and discard other signals makes the FM system have a strong ability to resist co channel interference, and can provide better reception quality. On the other hand, in AM system, all disturbances are accepted together, so it is necessary to remove the disturbance after demodulation.

Although FM system has many advantages over AM system, it also has disadvantages. In order to show its advantages in noise reduction and capture effect, FM system needs to take up more bandwidth (usually several times of AM) in the transmission medium. And the FM transmitter and receiver are more complex than AM system. Although the frequency modulation system can tolerate the nonlinearity of certain types of signals and circuits, it is necessary to pay special attention to its phase characteristics. Both AM and FM can be demodulated by low-cost uncorrelated demodulator. Am can be demodulated easily with envelope detector, while FM can be demodulated with frequency discriminator or skew detector. Am can demodulate by product detector. In this case, the function of AM is better than FM in weak signal condition because FM signal is only useful when it is above the threshold.

In conclusion:Teflon PCB modulation is the process of processing the coding information of signal source to make it suitable for transmission.