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    From the transmission mode, what kinds of electromagnetic waves are transmitted on the transmission line?

    1. TEM wave (transverse electromagnetic wave): Both the electric field and the magnetic field are perpendicular to the propagation direction of the electromagnetic wave.
    2. TE wave (transverse wave): The electric field is perpendicular to the propagation direction of the electromagnetic wave, and there is only a magnetic field component in the propagation direction.
    3. TM wave (transverse magnetic wave): The magnetic field is perpendicular to the propagation direction of the electromagnetic wave, and there is only an electric field component in the propagation direction.

    What are the characteristics of the VGA interface?

    The VGA interface is a D-type interface with a total of 15 pins on it, divided into 3 rows, 5 in each row.
    The VGA interface is the most widely used interface type on graphics cards, and most graphics cards have this interface.

    What are the multiplication instructions and multiply and add instructions?

    ARM microprocessor supports a total of 6 multiplication instructions and multiplication and addition instructions.
    It can be divided into 32-bit operation results and 64-bit operation results.

    What is the input impedance?

    For an antenna to be efficient, the antenna must be impedance matched to the feeder. That is to make the input impedance of the antenna equal to the characteristic impedance of the transmission line. This allows the antenna to obtain maximum power.
    The input impedance of the antenna is the ratio of the voltage to the current at the input terminal of the antenna, which is an important parameter. It depends on the structure and size of the antenna itself. And it is related to factors such as excitation mode, working frequency, and the influence of surrounding objects. It directly determines the matching state between the antenna and the feeder system, which has a great influence on the effective transmission of power.

    How to master the skills of selecting voltage feedback and current feedback op amps?

    First, the same design equations used for voltage-feedback amplifiers apply to current-feedback amplifiers.
    Voltage feedback amplifiers have a fixed gain-bandwidth product, while current feedback amplifiers do not. So you get higher gain and higher bandwidth from a current feedback amplifier.
    The voltage feedback amplifier has two high input impedance nodes. A current feedback amplifier has only a high-impedance non-inverting input, and the inverting input is a low-impedance input.
    Voltage feedback amplifiers have “open loop gain”. Current feedback amplifiers have “open loop transimpedance”.
    Compared to voltage feedback amplifiers, current feedback amplifiers have very wide bandwidths and very high slew rates. Unlike voltage feedback amplifiers, feedback resistors play an important role in the stability of current feedback amplifiers. This limits the choice of feedback resistors (resistor values ​​can be found in the manufacturer’s data sheet) and also limits the value of the gain setting resistors.
    This is just a preliminary introduction to current feedback amplifiers and voltage feedback amplifiers. Current feedback amplifiers provide another powerful option when engineers design circuits. Below is information about current feedback amplifiers and voltage feedback amplifiers. The next time you’re looking for a voltage feedback amplifier, take a closer look at the options you have on hand, and you may be able to find one that suits you better.

    What is the signal of the digital control bus?

    The signal of the digital control bus is made up of Clock, Reset, PWR0, PWR1 driven by the main Powerl208 and the Response generated from the Power604 device.

    What is the basic content of electrical commissioning work?

    1. For complete sets of electrical control equipment and systems, including primary and secondary equipment and various control equipment and devices, adjustment tests during and after installation.
    2. Power on to check the interaction and relationship of all electrical equipment and control devices.
    3. Carry out the adjustment test of the electrical system under no-load and under load according to the requirements of the production process.
    4. Adjust the control equipment so that it can work normally under normal working conditions and excessive working conditions, and check various protection settings.
    5. Review and proofread drawings.
    6. Compile the debugging plan of complex equipment and devices, the test plan of important equipment and the system startup plan.
    7. Technical guidance for participating in some tests.
    8. Responsible for the electrical debugging work and technical guidance of the clearance operation during the start-up process of the whole set of equipment.

    What are the advantages of LED lights compared to halogen lamps?

    • There are two major advantages:
      1. The light source is relatively concentrated. The brightness obtained by lW lighting is equivalent to the brightness of a dozen watts of halogen lamps, so it is relatively power-saving.
      2. The life of LED lamps is longer than that of halogen lamps.

    What are the obvious features of the TDM system?

    The components of each channel inside the multiplexing device have good versatility. Because the components of each channel are mostly the same: the receiving and sending are required to work synchronously, so a good synchronization system is required. Although TDM allows multiple users to share a transmission line resource. But the time slot in TDM mode is pre-allocated and fixed, and each user occupies the time slot exclusively. Not all terminals have data output in every time slot. Therefore, the utilization rate of the time slot is low, and the transmission capacity of the line cannot be fully utilized. Thus, statistical time division multiplexing occurs.

    Principles and advantages of semiconductor lasers:

    Semiconductor lasers are laser diodes, denoted as LDs. It was invented by former Soviet scientist H.Γ. Basov in 1960.
    The structure of a semiconductor laser is usually composed of a P layer, an N layer and an active layer forming a double heterojunction.
    The light emission of semiconductor lasers is based on the principle of stimulated emission of light. Most electrons in a population-inversion distribution state emit photons synchronously when excited by incoming photons. The photons of the stimulated radiation and the incident photons not only have the same wavelength, but also the same phase and direction. In this way, strong emission light is obtained by excitation by weak incident light, which plays a role of light amplification. However, the optical amplifying function alone cannot form optical oscillation. Just like oscillators in electronic circuits, only the amplification function cannot generate electrical oscillations. The positive feedback circuit must also be designed so that the power lost in the circuit is compensated by the amplified power. Similarly, in the laser, the feedback concept of the electronic circuit is also borrowed, and a part of the amplified light is fed back for further amplification. Oscillate and emit laser light. Such instruments used to achieve amplified feedback of light are called optical resonators.
    The advantages of semiconductor lasers are small size, high coupling efficiency, fast response speed, wavelength and size adapted to the size of the fiber, direct modulation, and good coherence.


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