21, semiconductor or chip 0.25um, 0.18um, 90nm, 7nm process refers to what? .

These numbers represent the technical nodes that make a semiconductor or chip, also known as process nodes. The actual physical meaning is "half pitch", "physical gate length", "process line width" and so on.

The semiconductor industry usually uses parameters such as "half pitch", "physical gate length (the length of the gate of the MOS tube)" and "junction depth" to describe the integration of the chip, and the smaller these parameters are, the higher the integration of the chip.

For example, a certain chip uses a 90nm process, where the half-pitch is 90nm, and the physical gate length of the transistor is 37nm. Half pitch refers to half of the distance between the interconnection lines inside the chip, that is, half of the lithographic spacing.

Since every new technology node over the years has always been used to manufacture DRAM chips, the latest technology node tends to refer to the half-pitch of DRAM.

In addition, in the technical article there are two expressions similar to the meaning of "half pitch", that is, "line width", "line distance" and "feature size", if the line width is equal to the line distance, then the half pitch is equal to the line width, line distance, they are just different expressions of the same data.

22, green light-emitting diode conduction voltage drop is about how many volts?

About 2V.

23, varactor diode and voltage regulator diode normal working state, should add what kind of voltage: forward, reverse, the former is the latter reverse, the former reverse the latter forward?

Reverse voltage should be added.

24, if an LED indicator does not define the color, red, green, yellow, orange, blue, white you will choose which one, why?

According to the use of habits, the power indicator is red, the signal indicator is green, and these two colors of LED light technology are the most mature and the cheapest.

25, please briefly describe the working principle of TVS transient voltage suppression diode.

When the voltage on the TVS exceeds a certain range, the device quickly switches on, thereby draining the surge energy and limiting the surge voltage to a certain range.

26, What are the two most popular types of programmable logic devices today, and what are the differences between them?

FPGA (Field Programmable Gate Array) and CPLD (Complex Programmable logic Device) are the two most popular types of programmable logic devices today. FPGA is based on lookup table structure, CPLD is based on product item structure.

27, Please list the type of diode you know?

Switching diode (small signal diode), Schottky diode, rectifier diode, voltage regulator diode (Zener diode), transient voltage suppression diode (TVS), varactor diode, light emitting diode (LED).

28. Please briefly explain Kirchhoff's current law (KCL) and Kirchhoff's voltage law (KVL).

Kirchhoff's current law (KCL) states that the current flowing into any circuit node at any time in a lumped circuit is equal to the current flowing out of that node. Kirchhoff's voltage law (KVL) states that the sum of the voltages of any closed branch in a lumped circuit at any time is zero.

29, analog integrated circuit input generally use what circuit: common emitter circuit, common base circuit, differential circuit, common collector circuit?

In order to suppress temperature drift and improve accuracy, differential input circuit is generally used.

30. What is feedback? What is the role of feedback?

Feedback is to recover part or all of the amplifier output signal (voltage or current) to the amplifier input to compare with the input signal (add or subtract), and use the effective input signal obtained by comparison to control the output. Negative feedback can be used to stabilize the output signal or gain, and can also expand the pass band. Especially suitable for automatic control systems. The positive feedback can form oscillations and is suitable for oscillating circuits and waveform generating circuits.

31, the beta parameter of the transistor reflects what ability: current control current, current control voltage, voltage control current, voltage control voltage?

The beta value reflects the ability of the base current to control the collector and emitter current, so it belongs to the ability of the current to control the current.

32, why OD (open leakage) gate and OC (open set) gate output must be added pull resistance?

Because the drain D and collector C are in a high resistance state when the MOS tube and the transistor are turned off, the output has no definite level, and the practical application must pull up to the definite level through the resistance.

33. What are the amplitude and phase conditions of self-excited oscillation produced by the circuit?

The amplitude is obtained under the following conditions: |AF| ≥1

The phase condition is: φA + φF =2nπ (n=0,1,2,...)

34. Please list three typical ESD models.

Human body model (HBM), machine model (MM), charged device model (CDM).

35. Please briefly describe the difference between DC-DC and LDO.

DC-DC achieves basically smooth voltage output through switching chopper, magneto-electric energy conversion of inductance and capacitance filtering.

The output current of the power supply is large, the load capacity is strong, and the conversion efficiency is high, but because of the switching action, there will be high-frequency radiation.

LDO is to achieve a fixed voltage output by adjusting the input and output voltage difference of the transistor or MOS tube. The basic components are the adjustment tube and the voltage reference element. The process of voltage conversion is continuous and smooth, and there is no switching action on the circuit.

LDO circuit is characterized by small output voltage ripple, weak load capacity and low conversion efficiency.

36, what is the general application of charge pump booster circuit? Are charge pumps competent for high current applications, and why?

The charge pump achieves voltage boost by charging and discharging the capacitor through the switch, because the circuit has no inductive element to store energy, the driving capacity is weak, and can only be used in small current situations.

37. What are the conventional EMC test items?

1) Conducted emission interference test

2) Radiation emission interference test

3) Conducted interference immunity test

4) Radiation interference immunity test

5) ESD immunity test

6) Electrical fast transient pulse group immunity test

7) Surge immunity test

8) Power frequency magnetic field immunity test

9) Harmonic and flicker test

10) Voltage drop, short-time interruption and voltage change immunity test

38, please list the electrical safety certification standards of electronic products you know?

39. Which six hazardous substances are restricted by the RoHS directive in electronic and electrical equipment?

Limit the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE), six hazardous substances.

40. Please explain the working principle of WatchDog.

The watchdog has two important signals: clock input and reset output. When the circuit works, the CPU sends a clock signal to the guard dog, that is, to feed the dog.

If the system fails and the CPU cannot send a continuous clock signal, the watchdog outputs a reset signal to the CPU to reset the system.

41, transistor basic amplifier circuit has a common emitter, common set, common base three kinds of connection, please describe the characteristics of these three basic amplifier circuit.

Common emission: The common emission amplifier circuit has the function of amplifying current and voltage, the input resistance is centered, the output resistance is larger, and the frequency band is narrow, which is suitable for general amplification.

Common set: The common set amplifier circuit only has the effect of current amplification, the input resistance is high, the output resistance is low, and the voltage follows the characteristics, and it is often the input stage and the output stage of the multistage amplifier circuit.

Common base: The common base circuit only has voltage amplification, the input resistance is small, the output resistance and voltage amplification times are comparable to that of the common radio circuit, and the high frequency characteristics are good, which is suitable for wide-band amplification circuit

42. What are the inter-stage coupling modes of multistage amplifier circuits? Which coupling mode has the most serious circuit zero deviation? Which coupling mode can realize impedance transformation?

There are three coupling modes: direct coupling, resistance-capacitance coupling, transformer coupling. Direct coupled circuit zero drift is the most serious, transformer coupled circuit can achieve impedance transformation.

43, noun explanation: coupling, decoupling, bypass, filtering.

Coupling: A cross link between two otherwise separate circuits or between two otherwise separate parts of a circuit. Energy can be transferred from one circuit to another, or from one part of the circuit to another.

Decoupling: Prevents the exchange or feedback of energy from one circuit to another, preventing unpredictable feedback that affects the normal operation of the next amplifier or other circuits.

Bypass: The high-frequency component of the signal mixed with the high-frequency signal and the low-frequency signal is filtered out through the electronic component (usually a capacitor), allowing only the low-frequency signal to be input to the next level, without the need for the high-frequency signal to enter.

Filtering: Filtering is the operation of filtering out the specific band frequency in the signal, which is an important measure to suppress and prevent interference.

What is competition and adventure?

In the logic circuit, because the input signal of the gate passes through different delays, the time to reach the gate is inconsistent, which is called competition. The phenomenon that the output produces a burr (momentary error) due to competition is called risk-taking.

45, What is the difference between passive filter and active filter?

The passive filter is composed of passive components R, L and C, which are designed to shunt the harmonic current of the corresponding frequency with very low impedance at a certain frequency, and its behavior mode is to provide passive harmonic current bypass channel.

Passive filters can be divided into two main categories: tuned filters and high-pass filters. Passive filter has the advantages of simple structure, low cost and high operational reliability, and is widely used as passive harmonic control scheme. Active filter consists of active device (such as integrated operational amplifier) and R, C, no inductor L, small size, light weight.

An active filter is actually an amplifier with a specific frequency response. The open loop voltage gain and input impedance of the integrated OP amplifier are high, and the output resistance is small, which can amplify and buffer the voltage after forming the active filter circuit. The integrated amplifier bandwidth is limited, so the active power filter's operating frequency is not high.

46, what are the parts of the PLL?

It is composed of phase discriminator, loop filter and voltage-controlled oscillator, and some PLL also has a 1/N frequency divider.

47, What is the voltage range of RS-232C standard logic 0 and logic 1? What are the operating levels of CAN and RS485 transceivers?

The RS-232C electrical standard is negative logic, the voltage range of logic 0 is +5V~+15V, and the voltage range of logic 1 is -5V~-15V.

CAN transceiver operating level is 5V, RS485 transceiver operating level is 3.3V.

48, noun explanation: UART, USRT, USART.

UART: UniversalAsychronous Receiver/Transmitter, universal asynchronous receiver/transmitter, capable of asynchronous communication.

USRT: UniversalSychronous Receiver/Transmitter, universal synchronous receiver/transmitter, capable of synchronous communication.

USART: UniversalSychronous Asychronous Receiver/Transmitter, universal synchronous asynchronous receiver/transmitter, can complete asynchronous and synchronous communication.

49, the serial port asynchronous communication of the character frame format consists of which parts?

It consists of four parts: start bit, data bit, parity bit and stop bit.

50. Please briefly describe the difference between USBHOST, USB Slave and USB OTG.

USB HOST is a host that implements control functions and can also access data, such as a computer PC. USB HOST A USB host can be connected only to a USBSlave device.

USB Slave is the slave device, belongs to the controlled device, can input and output data, such as U disk, mobile hard disk, MP3, MP4, mouse, keyboard, game controller, network card, printer, card reader and other USB devices.

USB OTG, the full name of which is USBOn-The-Go, is a direct control and transmission device. It can be used as either USB HOST or USB Slave to control master and slave switchover through ID signals.

51, please list the logic level you know.

Low speed: RS232, RS422, RS485, TTL, CMOS, LVTTL, LVCMOS, ECL, PECL, LVPECL

High speed: LVDS, GTL, PGTL, CML, HSTL, SSTL

52, please list the differential balance level interface that you know.

RS422, RS485, RJ45, CAN, USB, LVDS.

53, What are the three elements of electromagnetic interference?

Electromagnetic interference sources, interference propagation paths and interference sensitive devices.

54. Please explain what crosstalk and ringing are.

Crosstalk: Crosstalk means that a signal is disturbed by other signals, and the principle of action is electromagnetic field coupling. The mutual inductance and capacitance between signal lines can cause noise on the line. Capacitive coupling causes coupling current, while inductive coupling causes coupling voltage.

Ringing: Because the impedance of the signal line itself does not match, the signal is reflected and superimposed, so that the signal appears oscillating waveform.

55, What are the signals that you encounter that need to control the single-ended impedance of 50 ohms and 75 ohms? What signals do you encounter that require a differential impedance of 90 ohms, 100 ohms, 120 ohms?

The general high frequency signal lines are 50 ohms to 60 ohms. 75 ohms is mainly a video signal line. The differential impedance of the USB signal line is 90 ohms, and the differential impedance of the Ethernet differential signal line is 100 ohms. The differential impedance of RS422, RS485 and CAN differential signals is 120 ohms.

56, the difference line has two principles: equal length and equal distance. But in the actual wiring may not be able to fully meet the two, then ask is equal length priority or equal distance priority?

The difference signal is the intersection of the rising edge and the falling edge of the signal as the signal change point, and the unequal length of the line will make this intersection offset, which has a greater impact on the timing of the signal, and also introduces the common mode component into the differential signal, reducing the quality of the signal and increasing EMI.

The impact of a small range of unequal distances on the differential signal is not very large, although the spacing inconsistency will lead to changes in the differential impedance, but because the coupling between the difference pair itself is not significant, so the impedance change range is also very small, usually within 10%, only equivalent to a reflection caused by a hole, which will not cause significant impact on signal transmission.

57. Why should the reference ground plane of the high-frequency signal line be continuous (that is, the high-frequency signal line cannot cross the island)?

The reference ground plane provides the signal return path to the high-frequency signal line, and the return path is best kept close to the signal line to minimize the area of the current loop, which is conducive to reducing radiation and improving signal integrity.

If the reference ground plane is discontinuous, the signal will find its own minimum path, and this return path may be superimposed with other signal loops, resulting in mutual interference. Moreover, the high frequency signal across the island will make the characteristic impedance of the signal produce special changes, resulting in signal reflection and superposition, resulting in ringing phenomenon.

58, What is semi-cured tablet?

The semi-cured sheet is the dielectric material and bonding material in the PCB, composed of glass fiber and epoxy resin, and the dielectric constant is about 4.0~4.5. At normal temperature, the semi-cured sheet is solid, and when heated at high temperature, the semi-cured sheet gelatinizes the upper and lower sides of the copper foil, and the semi-cured sheet becomes the middle medium.

59, What is through hole, blind hole and buried hole? How large can the aperture be made of mechanical holes, and how small must the aperture be made of laser holes? Can the laser micro-hole be directly punched on the component pad? Why?

The through hole is the through hole that runs through the entire PCB, the blind hole is the through hole that is connected from the PCB surface to the inner layer, and the buried hole is the through hole that is buried in the inner layer of the PCB.

The processing capacity of most PCB manufacturers is like this: holes greater than or equal to 8mil can be made of mechanical holes, and holes less than or equal to 6mil need to be made of laser holes. For micro holes less than or equal to 6mil, when the drilling space is not enough, part of the hole is allowed to play on the PCB pad.