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 GSM handset 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,near zero-IF,zero-IF,different architecture may have different LOs requirement and frequency plan,also it's 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, and even 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 a closed-loop power control, it must be noted that the PA output power detection circuit can meet the GSM dynamic range.
62. The switching frequency of the mobile phone 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 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.
63. What issues 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.
64. Can TI provide the source code of MMI? A: Generally, TI provides the MMI source code together with some driver (LCD, etc.) source code. Whether all source codes including MMI, protocol stack and layer1 source code are provided will be determined based on business relationship.
65. How to solve the secondary resonance or multiple resonance of high-frequency LC oscillation circuit? A: 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 results directly affects the signal quality of RF link. How to debug these matching circuits fastest and best? A: 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: Based on the simulation results of the matching network, you can do some further optimization work on the board. Appendix: 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. However, the shielding cover is still the first choice to ensure stable transmission performance. You can put high power RF signal in the middle layer of PCB and make sure there is good grounding to reduce the radiation, but shielding can is still the preferred way to gurantee the stable radiation performance. 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, and 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 test the RX sensitivity, 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 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 appliances on the DC line. You can add enough small capacitors on DC line.
76. Are there any amplifier tubes placed in a low-temperature environment for export? Answer: The operating temperature range of the amplifier should be -10-8℃. You can check the parameter table. The regulations above 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) and then down-converts the RF signal 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.
78. What are the components of a general mobile phone RF/IF module? 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 RF head end, 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: 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.
80. 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 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 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.
82. 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.
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. You only need to input the device parameters of the designed circuit. Currently, the more popular RF simulation software 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 in one IC. Does TI currently have a single-chip baseband? Answer: ARM7 and DSP are already integrated in TI's digital baseband chips.
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