The radio frequency module used in daily life, it usually consists of five parts: radio frequency, baseband, power management, peripherals, and software. This article mainly introduces the relationship and difference between the baseband and radio frequency parts.
The main function of the radio frequency part is to transmit the baseband processed signal or to receive and transfer the external signal to the baseband signal. The baseband is generally part of information processing, WIFI serial server which is responsible for processing the signal and passing it to the radio frequency part, or processing the signal received from the radio frequency part. In general, the radio frequency chip is responsible for radio frequency transceivers, frequency synthesis, and power amplification.
The baseband chip is responsible for signal processing and protocol processing. The baseband chip can be considered to include a modem, but it is not limited to a modem but also includes channel codec, source codec, and some signaling processing. The RF chip can be regarded as the simplest up-conversion and down-conversion of baseband modulation signals. The so-called modulation is to modulate the signal to be transmitted onto the carrier wave through certain rules and then send it out through the wireless transceiver. Demodulation is the opposite process. The internal structure of the Semtech baseband chip SX1302 is shown in the figure below.
It can be seen from the figure that the RF front-end chip interacts with the baseband chip through SPI, and the baseband chip interacts with the user’s external equipment through the SPI port.
The radio frequency chip refers to an electronic component that converts radio signal communication into a certain radio signal waveform and sends it out through antenna resonance. It includes a power amplifier, a low-noise amplifier, and an antenna switch. The RF chip architecture includes two parts: the receiving channel and the transmitting channel. When receiving, the antenna converts the electromagnetic wave sent by the base station into a weak AC current signal, which is filtered, amplified at high frequency, and sent to the intermediate frequency for demodulation to obtain the received baseband information.
The transmitting circuit is composed of a transmitting modulator, a transmitting phase detector inside the intermediate frequency; a transmitting voltage-controlled oscillator (TX-VCO), a power amplifier (power amplifier), a power controller (power control), a transmitting transformer, and other circuits. CAN2.0 Communication Module When transmitting, the signal from the baseband is modulated; the modulated signal is processed by the PLL to obtain a radio frequency signal of the required frequency, but this signal is very weak and needs to be amplified by a power amplifier (PA); the amplified signal passes through a filter After filtering, it is transmitted through the antenna. Since the PLL is greatly affected by the oscillation source, the frequency deviation of the external crystal oscillator is highly required. At present, the frequency accuracy of the active crystal oscillator can reach within 1-0.5PPM, which can provide an extremely accurate oscillation source for the PLL.