Mobile phone RF design skills [repost]
1. What is RF?
Answer: RF stands for Radio frequency, which mainly includes wireless transceivers.
2. What are the frequencies of mobile phones in the world today (CDMA, GSM, local telephone, PHS, analog mobile phones, etc.)?
Answer: EGSM RX: 925-960MHz, TX:880-915MHz;
CDMA cellular (IS-95) RX: 869-894MHz, TX:824-849MHz.
3. How should a novice who has just started working in mobile phone RF improve himself?
Answer: First, you should have a systematic understanding of the RF system (such as functionality), and then you can choose some chipsets and study the connectivity among them.
4. What is the role of RF simulation software in mobile phone design and debugging?
Answer: Its purpose is to allow designers to have some understanding of the product to be designed before implementing the design.
5. What is the basic principle when designing the PCB of a mobile phone?
Answer: The basic principle is to minimize EMC.
6. The hardware components of a mobile phone include RF/ABB/DBB/MCU/PMU. What do ABB, DBB and PMU stand for?
Answer: ABB stands for Analog BaseBand,
DBB stands for Direct Baseband, and MCU is often included in the DBB chip.
PMU stands for Power Management Unit. Currently, some mobile phones have PMU and ABB on the same chip. In the future, these chips (RF, ABB, DBB, MCU, PMU) will be integrated into one chip to save cost and size.
7. What are the main functions of DSP and MCU? What is the difference between them?
Answer: In fact, MCU and DSP are both processors, and there is not much difference in theory. However, in actual systems, based on efficiency considerations, DSP generally processes various algorithms, such as channel encoding and decoding, encryption, etc., while MCU processes signaling and communicates with most hardware peripherals (such as LCD, etc.).
8. What should a novice who has just started to engage in RF front-end design pay attention to?
Answer: First, you can choose an RF topic, such as PLL, and learn some basic theories, and then start to design some simple circuits. Only in debugging can you gain some experience, which will help deepen your understanding.
9. What RF simulation software do you recommend and what are its features?
Answer: Agilent ADS simulation software is used for RF simulation. This software supports both discrete RF design and complete system design. For details, please visit the Agilent website.
10. Where can I download the relevant knowledge about mobile phone design solutions, including the major modules, the functions of each module, and the performance requirements of the hardware?
Answer: You can check www.gsmworld.com and www.139130.net, which may be helpful. For TI's wireless solution, you can check wireless communications in www.ti.com.
11. Why does GSM use GMSK modulation, while W-CDMA uses HPSK modulation?
Answer: Mainly due to the GSM and WCDMA standards. If you are interested, you can read some books about digital modulation to understand the advantages and disadvantages of using different digital modulation technologies.
12. How to solve the interference of LCD model to RF?
Answer: During PCB design, LCD wiring can be performed in a single layer.
13. During the design of a mobile phone, in the newly added function, the baseband chip generates noise interference to FM when transmitting data. How to solve this problem?
Answer: Check the PCB design, find the interference source and strengthen isolation.
14. When designing the RF transceiver of a mobile phone, how do you solve the RF interference problem?
Answer: GSM mobile phones work in TDMA mode, and RF transmission and reception are not performed at the same time. The basic principle of reducing RF interference is to strengthen matching and isolation. When designing, it is necessary to consider that the transmitter is in a high-power transmission state, which is more likely to cause interference than the receiver, so the PA matching must be ensured. In addition, the isolation of the RF front-end filter is also an important indicator. The PCB board is generally 6 or 8 layers, and there must be enough ground plane to reduce RF interference.
15. How to eliminate GSM burst interference?
Answer: When PCB wiring, the digital and RF parts must be well isolated, and a good ground plane must be ensured. Some power and signal lines must be effectively filtered by capacitors.
16. How to solve RF power supply interference?
Answer: It is necessary to ensure that the RF power supply has been well filtered. If necessary, separate power supplies can be used for different RF lines.
17. There is an RF application circuit. When the RF part is not working, the CPU and other related peripherals work normally; but when the RF starts working, the CPU ports that are not related to RF are also interfered by sharp pulses. What is the reason? How to overcome such interference?
Answer: It may be that the RF part is not well isolated from the CPU part. Please check the PCB layout.
18. What are the main issues to consider when selecting mobile phone RF chips?
Answer: When selecting RF chips, the following points should be considered:
① RF performance, including reliability.
② High integration, requiring fewer peripheral components.
③ Cost factors.
19. How to use mobile phone RF chips to reduce the number of peripheral chips?
Answer: The higher the integration of mobile phone RF chips, the fewer peripheral components are required.
20. Will the RF chip generate electromagnetic interference to the peripheral chips? How to eliminate it?
Answer: It should be said that the RF system will generate electromagnetic interference to other DBBs and ABBs, not just the RF chip. Strengthening RF shielding is an effective measure.
21. In the wireless communication system, should the time domain equalization of the baseband be located after the baseband demodulation and bit synchronization extraction, and the result of each bit extraction should be subjected to time domain equalization before threshold judgment?
Answer: Yes. It needs to be equalized first, and then threshold judgment is made.
22. With the same transmission power, when the frequency is different, does the high frequency (such as 900MHz) have a long transmission distance, and the low frequency (such as 30MHz) has a short transmission distance (in open areas)?
Answer: The wavelength factor should be taken into account. The higher the frequency, the shorter the wavelength. In open areas, the greater the transmission loss, so the transmission distance is shorter.
23. Use timer 1 to generate waveforms. The program is as follows:
LDP #232
SPLK #0Ah, T1PR
SPLK #05h, T1CMPR
SPLK #0000h, T1CNT
SPLK #0042h, GPTCON
SPLK #0D542h, T1CON
Why is there no waveform output on the T1PWM/T1CMP pin?
Answer: You can use the simulation tool to enter the code to debug this problem.
24. "The bandwidth of the front-end filter of the mobile phone receiver is determined by the bandwidth of the receiving frequency. It must ensure that the in-band signal passes with the minimum insertion loss and is not filtered out." Under the condition of being able to effectively receive the signal, for the front-end filter, if the filter bandwidth is relatively wide, the insertion loss of the filter will be small (I don't know if it is the same for SAW), but the in-band noise will increase, and vice versa. So, given the frequency range of the received signal, how should the filter bandwidth be considered to allow the in-band signal to pass with the minimum insertion loss?
A: This problem should be considered from the perspective of system design, including frequency range (sensitivity) and selectivity. A compromise can be made between insertion loss, bandwidth and out of band rejection. As long as the selected value meets the system requirements, it will be fine.
25. Generally speaking, PA and SWITH have a certain ability to suppress stray radiation, but there are certain limitations. How to add other methods to better solve it?
A: The accurate statement should be that the PA matched filter has a certain ability to suppress stray radiation. In addition, a good front-end filter can be selected to enhance out of band suppression.
26. How to choose RF LDO?
A: When choosing LDO, you should consider some of its own characteristics, such as driving current, output noise and ripple rejection.
27. What methods can be used to reduce the power consumption of the RF system when it is in standby mode?
A: You can turn off the RF system during the intervals when listening to network paging information on the mobile phone.
28. The TRF6151 chip launched by TI uses direct frequency conversion technology. Will it cause other problems?
Answer: The TRF6151 chip launched by TI is a single-chip GSM tranceiver, which adopts the zero intermediate frequency receiver structure. Direct frequency conversion technology is now very mature, there is no technical problem, and it is still the mainstream solution.
29. What is the requirement for phase noise at 1k offset, 10kHz offset, and 100kHz offset for GSM handset? When the phase noise of GSM mobile phone is 1k, 10kHz and 100kHz, what conditions need to be met?
Answer: For GSM handset RX it has several architectures to implement: Superheterodyne,near zero-IF,zero-IF,different architecture may have different
LOs requirement and frequency plan,also it's related to the design of filters.
For GSM mobile phone RX, it needs to implement: Superheterodyne,near zero-IF,zero-IF,different architecture may have different LOs requirement and frequency plan,also it's related to the design of filters.
30. The static sound quality of the receiver is very good when the receiving sensitivity is very high, but it is not good when it moves. What may be the reason?
Answer: It may be the influence of fading.
31. What are the key factors that determine whether an RF circuit design can be mass-produced?
Answer: In mass production, the RF performance must be consistent, reliable, stable, non-discrete, and meet the requirements of the production process.
32. In TI's solution, does the DSP software share the same operating system as the MCU software?
Answer: In TI's solution, and even in all solutions, the DSP software cannot share the same operating system with the MCU software. Although they are integrated on a chip, they are independent modules, equivalent to two independent processors.
33. How to reduce spectrum_switch?
Answer: If it is a closed-loop power control, it must be noted that the PA output power detection circuit can meet the GSM dynamic range.
34. The switching frequency of mobile phones is very fast. In the past, the mobile phones we used generally used two phase-locked loops to lock the frequency. Now in the single-chip system, only one phase-locked loop is used, and the N fractional frequency locking technology is adopted. How many seconds is generally suitable for time control?
Answer: The locking time depends on the specific application. Less than 250us can meet the requirements of GPRS Class 12.
35. What problems should be paid attention to in the early and later PCB debugging of the design?
Answer: The power control of burst ramp up and ramp down needs to be adjusted.
36. Can TI provide the source code of MMI?
Answer: In general, TI provides the MMI source code to users together with the source code of some drivers (LCD, etc.). Whether to provide all source codes including MMI, protocol stack and layer1 source code will be determined based on business relationships.
37. How to solve the secondary resonance or multiple resonance of high-frequency LC oscillation circuit?
Answer: The frequency selectivity of the oscillator feedback network can be improved, or the input matching circuit can be used to weaken the harmonics.
Appendix: Related English answer:
You can improve the frequency selectivity of oscillator feedback network or take advantage of the output matching circuitry to attenuate the harmonics.
38. The quality of RF port matching results directly affects the signal quality of the RF link. How to debug these matching circuits the fastest and best?
Answer: Step 1: You can measure the actual S parameters using network analyser based on your board design and input it to the RF simulation SW to get the initial matching network.
Step 2: Based on the simulation result of matching network you can do some further optimization work on your board.
Appendix: Related English answer:
Step 1: You can measure the actual S parameters using network analyser based on your board design and input it to the RF simulation SW to get the initial matching network.
step 2: Based on the simulation result of matching network you can do some further optimization work on your board.
39. When drawing a circuit board for a mobile phone circuit, how to eliminate the influence of DC-DC CONVERTER on the RF circuit?
Answer: You can add capacitors to filter out the influence on the DC line, or you can use a dedicated LDO for the RF line.
40. Can RF reach a maximum distance of 1 km or more?
Answer: This is determined by factors such as RF frequency, transmission power and antenna. It is not a fixed distance.
41. When designing wireless LAN cards, shielding covers are often used to shield the radiation of the RF part. This will increase the cost. Is there any way to use less or even no shielding covers?
Answer:
You can put high power RF signal in the middle layer of PCB and make sure have good grounding to reduce the radiation,but shielding can is still the preferred way to gurantee the stable radiation performance .
42. 10~30mV useful signal: After amplifying 100~120dB, the useful signal reaches a peak-to-peak value of 3V~~4V, but the noise signal also reaches about 300mV, but the actual requirement is that the noise signal is below 20mV. How to solve it? (The problem of the pre-amplification is not obvious, and the contradiction is not prominent. The key is that the problem appears after the last stage of amplification.)
Answer: First please make sure the useful signal has very good SNR before
you input it to amplifiers chain, then you can calculate how much gain and NF you need to get the targeted signal amplitude and noise level, based on this you can choose the right components to design amplifiers chain.
43. When developing the PCB Layou of WLAN, how to match or calculate the line to 50ohm? Answer: The 50ohm matching is determined by the PCB stacking. You can calculate the impedance using
RF simulation tools by setting PCB parameters like layer thickness, line thickness and line width. 44. If the line matching is not good, how to calculate the matching components (L, C) under the network analyzer? A: If there's mismatching you can use network analyser to measure the S-parameters and use LC conponents to compensate the mismatch using Smith chart. 45. When testing the LNA receiving sensitivity in the network room, which point should be the best to test? A: Usually the RX sensitivity is tested, not the LNA sensitivity. 46. In the design of RF circuits such as amplifiers, is it better to separate the signal ground of the tube and the power ground of the bias circuit, or at least separate them on the same layer? A: Generally, there is no need to separate the signal ground and the power ground.
Normally you don't need to seperate the ground of power supply with the ground of amplifier.
47. Many RF PCB layouts do not have large ground areas in the airspace where there are no components and traces. How do you explain this? Should it be different in the microwave frequency band?
Answer:
You can add enough small capacitors on the DC line.
48. Are there any amplifier tubes placed in low-temperature environments for export?
Answer: The operating temperature range of the amplifier should be -10-8℃. You can check the parameter table, and the above regulations should be the same.
For amplifier it should have its working temperature range like -10-85c, you can check the datasheet,it should have this specification.
49. How does a mobile phone RF IC process signals?
Answer: When the RF/IF IC receives a signal, it receives the signal from the antenna (about 800Hz~3GHz) and then down-converts it to baseband after amplification, filtering and synthesis, and then processes the baseband signal; when the RF/IF IC transmits a signal, it up-converts the baseband below 20KHz, converts it into a signal within the RF band, and then transmits it.
50. What parts does a general mobile phone RF/IF module consist of?
Answer: A general mobile phone RF/IF module consists of three units: wireless reception, signal synthesis and wireless transmission. The wireless reception unit consists of a radio frequency head, a mixer, an intermediate frequency amplifier and a demodulator; the signal synthesis part includes a distributor and a phase-locked loop; and the wireless transmission unit consists of a power amplifier, an AGC amplifier and a modulator.
51. What are the components and main functions of a mobile phone baseband processor?
Answer: The common mobile phone baseband processor is responsible for data processing and storage. The main components are DSP, microcontroller, memory (such as SRAM, Flash) and other units. The main functions are baseband encoding/decoding, sound encoding and voice encoding.
52. How to understand the radio frequency, intermediate frequency and baseband of mobile phones?
Answer: The basic structure of the mobile phone can be divided into three parts: radio frequency (RF), intermediate frequency (IF) and baseband (BF) according to the processing of different frequency signals. The radio frequency is responsible for receiving and transmitting high-frequency signals, and the baseband is responsible for signal processing and storage. The intermediate frequency is the intermediate bridge between the radio frequency and the baseband, so that the signal can be smoothly converted from a high-frequency signal to a baseband signal.
53. The final transmission frequency of the mobile phone is 890--915Mhz. Is this an FM wave or an AM wave? When testing the radio frequency part of a GSM mobile phone using GMS modulation, why is a fixed frequency of 902.4Mhz used during testing?
Answer: GMSK modulation refers to Gaussian minimum shift keying, which is digital modulation. To some extent, it can be understood as frequency modulation, but the frequency change is carried out in a discrete (discontinuous) manner, while frequency modulation is purely analog modulation, and the frequency change is continuous.
From 890MHZ to 915MHZ, there is a total of 25MHZ bandwidth, and the channel spacing is 200KHZ (i.e. 0.2MHZ). There are 125 uplink channels in total. It is impossible to test all 125 channels during testing. Usually, three representative frequency points (channels) are selected, two on both sides and one in the middle. 902.4MHZ happens to be the middle channel.
54. What are the English expressions for mobile phone test items: RF carrier power, time/power envelope, phase error, and receiving report level?
Answer: RF carrier power: RF Carrier Power; time/power envelope: Time/Power Template; phase error: Phase Error; receiving report level: RSSI.
55. What are the more popular RF simulation software now?
Answer: Generally speaking, manufacturers of RF devices have such software. For example, EIC's products have such software. You only need to input the device parameters of the designed circuit. Currently, the more popular RF simulation software includes: HP-ADS, ADS, microwave office, Ansoft, etc.
56. Mobile phones are mainly composed of baseband and RF. Many IC manufacturers now have single-chip products for RF. At the same time, the baseband also integrates DSP and ARM cores in one IC. Does TI currently have a single-chip baseband?
Answer: TI's digital baseband chip currently integrates ARM7 and DSP.
57. What is the requirement for phase noise at 1k offset, 10kHz offset, and 100kHz offset for GSM handset? What conditions need to be met when the phase noise of a GSM phone is 1k, 10kHz, and 100kHz?
Answer: For GSM handset RX it has several architectures to implement: Superheterodyne,near zero-IF,zero-IF,different architecture may have different
LOs requirement and frequency plan,also it's related to the design of filters.
For GSM handset RX, it needs to implement: Superheterodyne close to zero intermediate frequency (zero-IF). Different architectures have different zero intermediate frequencies. Loss requirements and frequency plans, which are related to the design of filters.
58. The static sound quality of the receiver is very good when the receiving sensitivity is very high, but it is not good when it moves. What may be the reason?
Answer: It may be the influence of fading.
59. What are the key factors that determine whether an RF circuit design can be mass-produced?
Answer: In mass production, the RF performance must be consistent, reliable, stable, without discreteness, and meet the requirements of the production process.
60. In TI's solution, does the DSP software share the same operating system with the MCU software?
Answer: In TI's solution, as in all solutions, the DSP software cannot share the same operating system with the MCU software. Although they are integrated on one chip, they are independent modules, equivalent to two independent processors.
61. How to reduce spectrum_switch?
Answer: If it is closed-loop power control, it is necessary to pay attention to the PA output power detection circuit to meet the GSM dynamic range.
62. The switching frequency of mobile phones is very fast. In the past, the mobile phones we used generally used two phase-locked loops to lock the frequency. Now in a single-chip system, only one phase-locked loop is used, and N fractional frequency locking technology is adopted. How many seconds is generally suitable for time control?
Answer: The locking time depends on the specific application. Less than 250us can meet the requirements of gprs class 12.
63. What should be paid attention to in the early and later stages of PCB debugging?
Answer: The power control of burst ramp up and ramp down needs to be adjusted.
64. Can TI provide the source code of MMI?
Answer: Generally, TI provides the source code of MMI to users together with the source code of some drivers (LCD, etc.). Whether all source codes including MMI, protocol stack and layer1 source code are provided will be determined based on business relationships.
65. How to solve the secondary resonance or multiple resonance of high-frequency LC oscillation circuit?
Answer: You can improve the frequency selectivity of oscillator feedback network or take advantage of the output matching circuitry to attenuate the harmonics.
Attachment: Related English answer original text:
You can improve the frequency selectivity of oscillator feedback network or take advantage of the output matching circuitry to attenuate the harmonics.
66. The quality of RF port matching directly affects the signal quality of RF link. How to debug these matching circuits the fastest and best?
Answer: Step 1: You can use a network analyzer to measure the actual S parameters based on the circuit board design and input them into the RF simulation SW to obtain the initial matching network.
Step 2: You can do some further optimization work on the board based on the simulation results of the matching network.
Attachment: Related English answers:
Step 1: You can measure the actual S parameters using network analyser based on your board design and input it to the RF simulation SW to get the initial matching network.
step 2: Based on the simulation result of matching network you can do some further optimization work on your board.
67. When drawing a circuit board for a mobile phone circuit, how can you eliminate the impact of DC-DC CONVERTER on the RF circuit?
Answer: You can add capacitors to filter out the impact on the DC line, or you can use a dedicated LDO for the RF line.
68. Can the farthest RF transmission reach 1 km or more?
Answer: This is determined by factors such as RF frequency, transmission power and antenna. It is not a fixed distance.
69. When designing a wireless LAN card, a shielding cover is often used to shield the radiation of the RF part. Doing so will increase the cost. Is there any way to use less or even no shielding cover?
Answer: High-power RF signals can be placed on the middle layer of the PCB and ensure good grounding to reduce scattering. 70. 10～30mV useful signal: After amplification of 100～120dB, the useful
signal reaches a peak-to-
peak value of 3V～~4V, but the noise signal also reaches about 300mV, but the actual requirement is that the noise signal is below 20mV. How to solve it? (The problem of pre-amplification is not obvious, and the contradiction is not prominent. The key is that the problem appears after the last stage of amplification.) Answer: First,
ensure that the useful signal has a very good signal-to-noise ratio, and then input it into the amplifier chain. Then calculate the gain and NF required to obtain the target signal amplitude and noise level. Finally, select the appropriate device to design the amplifier chain based on these data.
First please make sure the useful signal has very good SNR before you input it to amplifiers chain,then you can calculate how much gain and NF you need to get the targeted signal amplitude and noise level, based on this you can choose the right components to design amplifiers chain.
71. When developing PCB Layou for WLAN, how do you match or calculate the line to 50ohm?
Answer: The 50ohm matching is determined by the PCB stackup.
You can calculate the impedance using RF simulation tools by setting PCB parameters like layer thickness, line thickness and line width.
72. If the line is not well matched, how do you calculate the matched components (L, C) under the network analyzer?
Answer: If the line is not matched, you can use a network analyzer to measure the S parameters and use LC components with the help of the Smith chart to compensate for the mismatch.
If there's mismatching you can use network analyser to measure the S-parameters and use LC conponents to compensate the mismatch using Smith chart.
73. When testing the LNA receiving sensitivity in the network room, which test point should be selected as the best?
Answer: Usually the RX sensitivity is tested, not the LNA sensitivity.
74. In the design of RF circuits such as amplifiers, should the signal ground of the tube and the power ground of the bias circuit be separated, or at least separated on the same layer?
Answer: Generally, there is no need to separate the signal ground and the power ground.
Normally you don't need to seperate the ground of power supply with the ground of amplifier.
75. Many RF PCB layouts do not have a large area of ground in the airspace, that is, where there are no components and traces. How to explain this? Should it be different in the microwave frequency band?
Answer:
You can add enough small capacitors on DC line.
76. Are there any amplifiers that are placed in low temperature environment for export?
Answer: The working temperature range of the amplifier should be -10-8℃, you can check the parameter table, the above regulations should be the same.
For amplifier it should have its working temperature range like -10-85c, you can check the datasheet,it should have this specification.
77. How does the RF IC of a mobile phone process signals?
Answer: When the RF/IF IC receives a signal, it receives the signal from the antenna (about 800Hz~3GHz) through amplification, filtering and synthesis, and then downconverts the RF signal to baseband, followed by baseband signal processing; and when the RF/IF IC transmits a signal, it upconverts the baseband below 20KHz, converts it into a signal within the RF band, and then transmits it.
78. What are the components of a general mobile phone RF/IF module?
Answer: Generally, the RF/IF module of a mobile phone consists of three units: wireless reception, signal synthesis and wireless transmission. The wireless reception unit consists of a RF head, a mixer, an IF amplifier and a demodulator; the signal synthesis part includes a distributor and a phase-locked loop; the wireless transmission unit consists of a power amplifier, an AGC amplifier and a modulator.
79. What are the components and main functions of a mobile phone baseband processor?
Answer: Common mobile phone baseband processors are responsible for data processing and storage. The main components are DSP, microcontroller, memory (such as SRAM, Flash) and other units. The main functions are baseband encoding/decoding, sound encoding and voice encoding.
80. How to understand the RF, IF and baseband of a mobile phone?
Answer: The basic structure of a mobile phone can be divided into three parts: RF (RF), IF (IF) and baseband (BF) according to the processing of different frequency signals. RF is responsible for receiving and transmitting high-frequency signals, baseband is responsible for signal processing and storage, and IF is the intermediate bridge between RF and baseband, so that the signal can be smoothly converted from high-frequency signals to baseband signals.
81. The final transmission frequency of the mobile phone is 890--915Mhz. Is this an FM wave or an AM wave? When testing the RF part of a GSM mobile phone using GMSK modulation, why is a fixed frequency of 902.4Mhz used during the test?
Answer: GMSK modulation refers to Gaussian minimum shift keying, which is digital modulation. To some extent, it can be understood as frequency modulation, but the frequency change is carried out in a discrete (discontinuous) manner, while frequency modulation is purely analog modulation, and the frequency change is continuous.
From 890MHZ to 915MHZ, there is a total of 25MHZ bandwidth, and the channel spacing is 200KHZ (i.e. 0.2MHZ). There are a total of 125 uplink channels. It is impossible to test all 125 channels during the test. Usually, three representative frequency points (channels) are selected, two on both sides and one in the middle. 902.4MHZ happens to be the middle channel.
82. What are the English expressions for the mobile phone test items: RF carrier power, time/power envelope, phase error, and reception report level?
Answer: RF Carrier Power: RF Carrier Power; Time/Power Template: Time/Power Template; Phase Error: Phase Error; Received Report Level: RSSI.
83. What are the more popular RF simulation software now?
Answer: Generally speaking, manufacturers of RF devices have such software. For example, EIC's products have such software. Just input the device parameters of the designed circuit. The more popular RF simulation software currently include: HP-ADS, ADS, microwave office, Ansoft, etc.
84. Mobile phones are mainly composed of baseband and RF. Many IC manufacturers now have single-chip products for RF. At the same time, the baseband also integrates DSP and ARM cores into one IC. Does TI currently have a single-chip baseband?
Answer: ARM7 and DSP are currently integrated in TI's digital baseband chips.
Original author: JimY
Source: Feiyang Technology Network
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