Note: This article is reprinted from the internet for learning and sharing purposes. If there is any infringement, please contact to delete.
Traditionally, a mobile phone that supports calling, texting, internet services, and APP applications generally consists of five parts: RF section, baseband section, power management, peripherals, and software.
RF: Generally refers to the part responsible for sending and receiving information;
Baseband: Generally refers to the part responsible for information processing;
Power: Generally refers to the power-saving part, as mobile phones are energy-limited devices, so power management is very important;
Peripherals: Generally includes LCD, keyboard, casing, etc.;
Software: Generally includes the system, drivers, middleware, and applications.
In mobile terminals, the most important core components are the RF chip and the baseband chip. The RF chip is responsible for RF transmission and reception, frequency synthesis, and power amplification; the baseband chip is responsible for signal processing and protocol processing. So what is the relationship between the RF chip and the baseband chip?
Relationship Between RF Chip and Baseband Chip
First, let’s talk about history. RF (Radio Frequency) and baseband come from direct English translations. The earliest application of RF was Radio—wireless broadcasting (FM/AM), and this remains the most classic application of RF technology and the radio field to this day.
Baseband refers to signals centered at 0Hz, so baseband is the most fundamental signal. Some also refer to baseband as “unmodulated signals”; this concept was once correct, for example, AM is a modulated signal (no modulation is needed, and the content can be read through sound components upon reception).
However, in the modern communication field, baseband signals usually refer to signals that have undergone digital modulation, with a spectrum centered at 0Hz. Moreover, there is no clear concept that indicates that baseband must be analog or digital; it entirely depends on the specific implementation mechanism.
To get back to the point, the baseband chip can be considered as including a modem, but not limited to a modem; it also includes channel coding/decoding, source coding/decoding, and some signaling processing. The RF chip can be seen as the simplest upconversion and downconversion of the baseband modulated signal.
Modulation refers to the process of modulating the signal to be transmitted onto a carrier wave according to certain rules, which is then sent out through a wireless transceiver (RF Transceiver); demodulation is the reverse process.
Working Principles and Circuit Analysis
RF, short for RF, refers to RF current, which is a type of high-frequency alternating electromagnetic wave, and is an abbreviation for Radio Frequency, indicating electromagnetic frequencies that can radiate into space, with a frequency range of 300KHz to 300GHz. Alternating current that changes less than 1000 times per second is called low-frequency current, while those changing more than 10000 times are called high-frequency current, and RF is such a high-frequency current. High frequency (greater than 10K); RF (300K-300G) is a higher frequency band of high frequency; the microwave frequency band (300M-300G) is an even higher frequency band of RF. RF technology is widely used in the field of wireless communication, and cable television systems adopt RF transmission methods.
The RF chip refers to an electronic component that converts wireless communication signals into certain radio signal waveforms and sends them out through antenna resonance. It includes a power amplifier, low-noise amplifier, and antenna switch. The architecture of the RF chip includes two main parts: the receiving channel and the transmitting channel.
RF Circuit Block Diagram
Structure and Working Principles of the Receiving Circuit
When receiving, the antenna converts the electromagnetic waves sent by the base station into weak alternating current signals, which are filtered, amplified at high frequency, and sent into the intermediate frequency for demodulation to obtain the received baseband information (RXI-P, RXI-N, RXQ-P, RXQ-N); it is then sent to the logic audio circuit for further processing.
This circuit focuses on: 1. Structure of the receiving circuit; 2. Functions and roles of each component; 3. Receiving signal flow.
1. Circuit Structure
The receiving circuit consists of an antenna, antenna switch, filter, high gain tube (low-noise amplifier), intermediate frequency integrated block (receiving demodulator), etc. Early mobile phones had first-level and second-level mixing circuits, aimed at lowering the receiving frequency before demodulation (as shown in the figure below).
Receiving Circuit Block Diagram
2. Functions and Roles of Each Component
1) Mobile Phone Antenna:
Structure: (as shown in the figure below)
There are two types of mobile phone antennas: external and internal; composed of antenna base, helical coil, and plastic casing.
Function: a) During reception, it converts the electromagnetic waves sent by the base station into weak alternating current signals. b) During transmission, it converts the amplified alternating current into electromagnetic wave signals.
2) Antenna Switch:
Structure: (as shown in the figure below)
The mobile phone antenna switch (combiner, duplex filter) consists of four electronic switches.
Function: a) Completes the switch between receiving and transmitting; b) Completes the switching of 900M/1800M signal reception.
The logic circuit sends out control signals (GSM-RX-EN; DCS-RX-EN; GSM-TX-EN; DCS-TX-EN) based on the mobile phone’s working state, allowing each path to conduct, ensuring that receiving and transmitting signals do not interfere with each other.
Since mobile phones cannot operate both receiving and transmitting simultaneously in one time slot (i.e., they do not transmit while receiving and vice versa), later models of mobile phones removed two switches from the receiving path, leaving only two transmitting switching switches; the receiving switching task is handled by the high gain tube.
3) Filter:
Structure: Mobile phones have high-frequency filters and intermediate frequency filters.
Function: Filters out other useless signals to obtain pure received signals. Later models of mobile phones are zero intermediate frequency phones; thus, there are no intermediate frequency filters in mobile phones anymore.
4) High Gain Tube (High Frequency Amplifier, Low Noise Amplifier):
Structure: The mobile phone has two high gain tubes: 900M high gain tube and 1800M high gain tube. They are both common-emitter amplifier circuits; later models integrated high gain tubes within the intermediate frequency.
High Frequency Amplifier Power Supply Diagram
Function: a) Amplifies the weak current induced by the antenna to meet the signal amplitude requirements of the subsequent circuit. b) Completes the switching of 900M/1800M receiving signals.
Principle: a) Power Supply: The bias of the base of the two high gain tubes for 900M/1800M shares a path provided by the intermediate frequency simultaneously; the bias of the collectors of the two tubes is sent out in two paths by the intermediate frequency CPU based on the mobile phone’s receiving state command, aiming to complete the switching of 900M/1800M receiving signals.
b) Principle: After filtering to remove other noise, the pure 935M-960M receiving signal is coupled through a capacitor and sent to the corresponding high gain tube, amplified, and then coupled through a capacitor to the intermediate frequency for further processing.
5) Intermediate Frequency (RF Interface, RF Signal Processor):
Structure: Composed of receiving demodulator, transmitting modulator, transmitting phase comparator, etc.; new mobile phones also integrate high gain tubes, frequency synthesis, 26M oscillation, and frequency division circuits internally (as shown in the figure below).
Function:
a) The internal high gain tube amplifies the weak current induced by the antenna;
b) During reception, it demodulates the receiving carrier frequency signal (with the other party’s information) of 935M-960M (GSM) with the local oscillator signal (without information) to obtain the 67.707KHZ received baseband information;
c) During transmission, it modulates the transmitting information processed by the logic circuit with the local oscillator signal into transmitting intermediate frequency;
d) Combines 13M/26M crystals to generate a 13M clock (reference clock circuit);
e) Based on the reference signal sent by the CPU, it generates a local oscillator signal that corresponds to the mobile phone’s working channel.
3. Receiving Signal Flow
When the mobile phone is receiving, the antenna converts the electromagnetic waves sent by the base station into weak alternating current signals, which pass through the antenna switch receiving path, are filtered by the high-frequency filter to remove other useless noise, and obtain the pure 935M-960M (GSM) receiving signal. This signal is coupled through a capacitor to the corresponding high gain tube in the intermediate frequency, amplified, and sent to the demodulator to demodulate with the local oscillator signal (without information) to obtain the 67.707KHZ received baseband information (RXI-P, RXI-N, RXQ-P, RXQ-N); it is then sent to the logic audio circuit for further processing.
Structure and Working Principles of the Transmitting Circuit
During transmission, the transmitting baseband information processed by the logic circuit is modulated into the transmitting intermediate frequency, and the TX-VCO converts the transmitting intermediate frequency signal frequency to 890M-915M (GSM) frequency signal. After being amplified by the power amplifier, it is converted into electromagnetic waves by the antenna.
This circuit focuses on: (1) Circuit structure; (2) Functions and roles of each component; (3) Transmitting signal flow.
1. Circuit Structure
The transmitting circuit consists of a transmitting modulator, transmitting phase comparator; transmitting voltage-controlled oscillator (TX-VCO), power amplifier (PA), power controller (power control), transmitting mutual inductor, etc. (as shown in the figure below).
Transmitting Circuit Block Diagram
2. Functions and Roles of Each Component
1) Transmitting Modulator:
Structure: The transmitting modulator is located within the intermediate frequency, which is equivalent to MOD in broadband networks.
Function: During transmission, it modulates the transmitting baseband information (TXI-P; TXI-N; TXQ-P; TXQ-N) processed by the logic circuit with the local oscillator signal into the transmitting intermediate frequency.
2) Transmitting Voltage-Controlled Oscillator (TX-VCO):
Structure: The transmitting voltage-controlled oscillator is a three-point oscillation circuit whose output frequency is controlled by voltage; during production, it is integrated into a small circuit board with five pins: power pin, ground pin, output pin, control pin, and 900M/1800M frequency band switching pin. When there is an appropriate working voltage, it oscillates to generate the corresponding frequency signal.
Function: Converts the modulated transmitting intermediate frequency signal from the intermediate frequency modulator into a frequency signal of 890M-915M (GSM) that the base station can receive.
Principle: As it is well known, the base station can only receive frequency signals of 890M-915M (GSM); however, the intermediate frequency modulated signal (for example, the Samsung transmitting intermediate frequency signal of 135M) cannot be received by the base station. Therefore, the TX-VCO is used to raise the frequency of the transmitting intermediate frequency signal to the frequency signal of 890M-915M (GSM) that the base station can receive.
When transmitting, the power supply part sends out a 3VTX voltage to make the TX-VCO work, generating the frequency signal of 890M-915M (GSM) which splits into two paths: a) One path samples back to the intermediate frequency, mixing with the local oscillator signal to generate a transmitting phase frequency signal equal to the transmitting intermediate frequency, which is sent to the phase comparator to compare with the transmitting intermediate frequency; if the frequency oscillated by the TX-VCO does not match the mobile phone’s working channel, the phase comparator will produce a 1-4V jump voltage (a DC voltage with AC transmitting information) to control the capacitance of the variable capacitor inside the TX-VCO, achieving the purpose of adjusting frequency accuracy. b) The other path is sent to the power amplifier, amplified, and then radiated out as electromagnetic waves by the antenna.
From the above, it can be seen that the frequency generated by the TX-VCO is sampled back to the intermediate frequency, generating voltage to control the TX-VCO operation, forming a closed loop that controls frequency phase; thus, this circuit is also called the transmitting phase-locked loop circuit.
3) Power Amplifier (PA):
Structure: Currently, mobile phone power amplifiers are dual-band amplifiers (900M amplifier and 1800M amplifier integrated together), consisting of black glue amplifiers and iron shell amplifiers; different models of amplifiers cannot be interchanged.
Function: Amplifies the frequency signal output by the TX-VCO to obtain sufficient power current, which is then converted into electromagnetic waves by the antenna.
It is worth noting that the power amplifier amplifies the amplitude of the transmitting frequency signal, but cannot amplify its frequency.
Working conditions of the power amplifier:
a) Working Voltage (VCC): The mobile phone power amplifier is powered directly by the battery (3.6V);
b) Ground Terminal (GND): Completes the current loop;
c) Dual-band Amplifier Signal (BANDSEL): Controls the power amplifier to work at 900M or 1800M;
d) Power Control Signal (PAC): Controls the amplification of the power amplifier (working current);
e) Input Signal (IN); Output Signal (OUT).
4) Transmitting Mutual Inductor:
Structure: Two coils with equal wire diameter and turns are placed close to each other, utilizing mutual inductance principles.
Function: Samples the power current from the transmitting amplifier and sends it to the power control.
Principle: When transmitting, the power current passing through the transmitting mutual inductor induces a current of the same magnitude in the secondary, which is then rectified (high-frequency rectification) and sent to the power control.
5) Power Level Signal:
The so-called power level refers to the levels defined by engineers during mobile phone programming, dividing the received signal into eight levels, with each receiving level corresponding to a transmitting power level (as shown in the table below). When working, the CPU determines the distance between the mobile phone and the base station based on the received signal strength, sending out an appropriate transmitting level signal to determine the amplification of the power amplifier (i.e., when the reception is strong, the transmission is weak).
Attached Power Level Table:
6) Power Controller (Power Control):
Structure: An operational comparator amplifier.
Function: Compares the sampled power current signal and the power level signal to obtain a suitable voltage signal to control the amplification of the power amplifier.
Principle: When transmitting, the power current passing through the transmitting mutual inductor induces a current in the secondary, which is then rectified (high-frequency rectification) and sent to the power control; simultaneously, the preset power level signal during programming is also sent to the power control; after internal comparison, a voltage signal is generated to control the amplification of the power amplifier, ensuring that the power amplifier works with moderate current, saving power and prolonging the lifespan of the power amplifier (higher power control voltage results in greater power for the amplifier).
3. Transmitting Signal Flow
When transmitting, the transmitting baseband information (TXI-P; TXI-N; TXQ-P; TXQ-N) processed by the logic circuit is sent to the transmitting modulator in the intermediate frequency, modulated with the local oscillator signal into the transmitting intermediate frequency. Since the intermediate frequency signal cannot be received by the base station, the TX-VCO is used to raise the frequency of the transmitting intermediate frequency signal to the frequency signal of 890M-915M (GSM) that the base station can receive. When the TX-VCO operates, it produces the frequency signal of 890M-915M (GSM) which splits into two paths:
a) One path samples back to the intermediate frequency, mixing with the local oscillator signal to generate a transmitting phase frequency signal equal to the transmitting intermediate frequency, which is sent to the phase comparator to compare with the transmitting intermediate frequency; if the frequency oscillated by the TX-VCO does not match the mobile phone’s working channel, the phase comparator will produce a 1-4V jump voltage to control the capacitance of the variable capacitor inside the TX-VCO, achieving the purpose of adjusting frequency accuracy. b) The other path is sent to the power amplifier, amplified, and then radiated out as electromagnetic waves by the antenna. To control the amplification of the power amplifier, when the power current passes through the transmitting mutual inductor, the induced current in the secondary is rectified (high-frequency rectification) and sent to the power control; simultaneously, the preset power level signal during programming is also sent to the power control; after internal comparison, a voltage signal is generated to control the amplification of the power amplifier, ensuring that the power amplifier works with moderate current, saving power and prolonging the lifespan of the power amplifier.
Current Status of Domestic RF Chip Industry Chain
In the RF chip field, the market is mainly dominated by overseas giants, with major overseas companies including Qorvo, Skyworks, and Broadcom; domestically, no company can independently support the IDM operation model, mainly consisting of Fabless design companies. Domestic enterprises have formed a “soft IDM” operation model through collaboration in design, foundry, and packaging stages.
In terms of RF chip design, domestic companies have made achievements in 5G chips and have certain shipping capabilities. RF chip design has a high threshold, and with RF development experience, the development of subsequent advanced RF chip categories can be accelerated. Currently, companies with RF chip design capabilities include Unisoc, Weijie Chuangxin, Zhongpu Micro, ZTE, Rapoo Technology, Huahong Design, Jiangsu Juxin, Aistek, etc.
In terms of RF chip foundry, Taiwan has become the largest compound semiconductor chip foundry in the world, with major foundries including Win Semiconductors, Advanced Wireless Semiconductor, and Global Communication. Domestically, only Sanan Optoelectronics and Haiwei Huaxin have begun to venture into compound semiconductor foundry. Sanan Optoelectronics has the most comprehensive layout in the country, with GaAs HBT/pHEMT and GaN SBD/FET process layouts, currently collaborating with over 200 domestic enterprises and institutions, with more than 10 types of chips passing performance verification and about to enter mass production. Haiwei Huaxin, a subsidiary of Hitech High-tech Holdings, is a joint venture with China Electronics Technology Group Corporation No. 29 Institute, currently possessing GaAs 0.25um PHEMT process capabilities.
In terms of RF chip packaging, the increase in frequency for 5G RF chips leads to a greater impact of connecting wires on circuit performance; during packaging, it is necessary to reduce the length of signal connecting wires. Additionally, power amplifiers, low noise amplifiers, switches, and filters need to be packaged into one module, reducing volume while facilitating use by downstream terminal manufacturers. To minimize the parasitics of RF parameters, Flip-Chip, Fan-In, and Fan-Out packaging technologies need to be adopted.
During Flip-Chip and Fan-In/Fan-Out packaging, there is no need to connect signals through gold wire bonding, which reduces parasitic electrical effects caused by gold wire bonding and improves chip RF performance; entering the 5G era, high-performance Flip-Chip/Fan-In/Fan-Out combined with SIP packaging technology will be the future packaging trend.
Flip-Chip/Fan-In/Fan-Out and SIP packaging belong to advanced packaging, which has much higher profitability than traditional packaging. Domestic listed company Changdian Technology formed a complete Flip-Chip+SIP technology packaging capability after acquiring Xingke Jinpeng.
Note: This article is reprinted from the internet for learning and sharing purposes. If there is any infringement, please contact to delete.
[RF Information][RF Introduction][Chip Filter]