Basic knowledge popularization of RF chips

In wireless communication systems, there are generally four parts: antennas, RF front-end, RF transceiver modules, and baseband signal processors. With the advent of the 5G era, the demand and value of antennas and RF front-end are rapidly increasing. RF front-end is the fundamental component for converting digital signals into wireless RF signals and is also the core component of wireless communication systems.

                 Schematic diagram of wireless communication system structure

According to their functions, the RF front-end can be divided into a transmitting end Tx and a receiving end Rx.

According to different devices, RF front-end can be divided into power amplifier PA (transmitting RF signal amplification), filter (transmitting and receiving signal filtering), low-noise amplifier LNA (receiving signal amplification, reducing noise), switch (different channel switching), duplexer (signal selection, achieving filtering matching), tuner (antenna signal channel impedance matching), etc.

        Schematic diagram of wireless communication system structure

Science popularization of various RF devices

Filter: Select specific frequencies to filter out interference signals

Filter is the most important discrete component in the RF front-end, which allows specific frequency components in the signal to pass through while greatly attenuating other frequency components, thereby improving the anti-interference and signal-to-noise ratio of the signal. At present, acoustic filtering technology is mainly used in the mobile RF market.

According to different manufacturing processes, acoustic filters on the market can be divided into two categories: surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. The SAW filter has a simple manufacturing process and high cost-effectiveness, mainly used for low-frequency filtering below GHz, while the BAW filter has low insertion loss and excellent performance, and can be applied to high-frequency filtering, but the process is complex and the price is high.

Due to the limitations of process complexity, technology, and cost, more RF front-end devices currently use SAW filters under communication standards. But with the increasing penetration rate of 5G, the excellent performance and support for high frequencies of BAW filters will make them the mainstream devices for mobile RF front-end.

Power amplifier PA: amplifies RF signals for transmission

A power amplifier (PA) is the core component of the RF front-end, which uses the current control effect of a transistor or the voltage control effect of a field-effect transistor to convert the power of the power supply into a current that varies according to the input signal.

PA is mainly used for transmission links, which amplifies the weak RF signals of the transmission channel to successfully obtain sufficient power, thereby achieving higher communication quality, stronger battery life, and longer communication distance. The performance of PA can directly determine the stability and strength of communication signals.

With the continuous development of semiconductor materials, power amplifiers have also gone through three major technological routes: CMOS, GaAs, and GaN. The first generation semiconductor material is CMOS, which has mature technology and stable production capacity. The second-generation semiconductor materials mainly use GaAs or SiGe, which have high breakdown voltage and can be used for high-power and high-frequency device applications. The third-generation semiconductor material GaN significantly outperforms GaAs in performance, but at a higher cost. At present, GaAs is mainly used as an amplifier in the civilian mobile market, while GaN has taken the lead in replacing it in some base station applications. GaN will become the main solution for high RF and high power consumption applications in the future.

Low noise amplifier LNA: amplifies the received signal and reduces the introduction of noise

Low Noise Amplifier (LNA) is an amplifier with a very low noise figure. Its function is to amplify the weak RF signal received by the antenna and minimize the introduction of noise. LNA can effectively improve the receiver's receiving sensitivity, thereby increasing the transmission distance of the transceiver. Therefore, the design of a low-noise amplifier is related to the communication quality of the entire communication system.

RF switch: controls the on/off of the circuit to achieve signal switching

The RF switch connects any one or several control logic of multiple RF signals to achieve switching between different signal paths, including switching between receiving and transmitting, switching between different frequency bands, etc., in order to achieve the goal of sharing antennas and channels and saving terminal product costs. RF switches mainly include mobile communication conduction switches, WiFi switches, antenna tuning switches, etc.

Tuner: Impedance matching of antenna

An antenna tuner is an impedance matching network located between the transmission system and the antenna, used to achieve functions such as signal reception, filtering, amplification, gain control, etc., so that the antenna can radiate maximum power at all application frequencies.

Under the 5G/Sub-6 communication standard, the 4x4 downlink MIMO in mobile phones requires each antenna to efficiently support a wider frequency range, and the demand for RF antenna tuners will also increase to improve the radiation efficiency of the corresponding frequency band.

Other RF front-end components

Envelop Tracker (ET)， The envelope tracker is used to improve the efficiency of power amplifiers carrying high peak to average power ratio signals and achieve adaptive power amplification output. Compared with average power tracking technology, envelope tracking technology can enable the power supply voltage of the amplifier to vary with the envelope of the input signal, improving the energy efficiency of the RF power amplifier.

RF Reveiver， That is, RF receiver. In an RF receiver, the RF signal is received by an antenna and then passed through a filter LNA、 The analog-to-digital converter (ADC) performs frequency conversion and demodulation on the signal, and finally forms the baseband signal that enters the baseband. RF receivers are mainly divided into three types: superheterodyne receivers, zero intermediate frequency receivers, and near zero intermediate frequency receivers.