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Understanding RF IC chips

2022-03-21T05:55:15.425Z

RF: generally the part that sends and receives information.

Baseband: generally the part of information processing.

Power management: generally the power saving part, as cell phones are energy-limited devices, so power management is very important.

Peripherals: generally include LCD, keyboard, case, etc.

Software: generally includes system, driver, middleware, and application.

In the cell phone terminal, the most important core is the RF chip and the baseband chip. RF chip is responsible for RF transceiver, frequency synthesis, power amplification; baseband chip is responsible for signal processing and protocol processing. So what is the relationship between RF chip and baseband chip?

The relationship between RF chip and baseband chip

RF (Radio Frenquency) and baseband (Base Band) are from the English direct translation. The earliest application of RF is Radio - radio broadcasting (FM/AM), which is still the most classic application of RF technology and even radio field.

The base band is the band center point in the 0Hz signal, so the base band is the most basic signal. Some people also call the baseband "unmodulated signal", and this concept was once correct, for example, AM is a modulated signal (no modulation is needed, and the content can be read by the sounding component after reception).

But for modern communications, baseband signals are usually digitally modulated signals with a spectrum centered at 0Hz. And there is no clear concept that the baseband must be analog or digital, it all depends on the specific implementation mechanism.

To cut to the chase, the baseband chip can be thought of as including the modem, but not only the modem, but also the channel codec, source codec, and some signaling processing. The RF chip, on the other hand, can be seen as the simplest baseband modulation signal upconversion and downconversion.

The so-called modulation, is the need to transmit the signal, through certain rules modulated to the carrier wave above the project let after the radio transceiver (RF Transceiver) to send out, demodulation is the opposite process.

RF Transceiver IC recommended:

TI's CC3220MODASF12MONR

Working principle and circuit analysis

RF RF for short is RF current, is a high frequency AC change electromagnetic wave, for is the abbreviation of Radio Frequency, that can be radiated into space electromagnetic frequency, the frequency range between 300KHz ~ 300GHz. The alternating current that changes less than 1000 times per second is called low-frequency current, greater than 10000 times is called high-frequency current, and RF is such a high-frequency current. High frequency (greater than 10K); RF (300K-300G) is the higher frequency band of high frequency; microwave band (300M-300G) is also the higher frequency band of RF. RF technology is widely used in the field of wireless communication, cable TV system is the use of RF transmission.

RF chip refers to the radio signal communication into a certain radio signal waveform, and through the resonance of the antenna to send out an electronic component, it includes power amplifier, low noise amplifier, and antenna switch. RF chip architecture includes two major parts: receiving channel and transmitting channel.

Translated with www.DeepL.com/Translator (free version)

How to choose an op-amp?

2022-01-25T06:28:47.500Z

Op-amp is the cornerstone of the whole analog circuit design, and choosing a proper amplifier is crucial to achieving the system design specifications.

1. Op-amp supply voltage size and mode selection;

2. op-amp package selection;

3.Op-amp feedback, i.e. VFA (voltage feedback op-amp) or CFA (current feedback op-amp);

4. Op-amp bandwidth;

5. Slew rate size, which determines the full power signal bandwidth;

6. Offset voltage and offset current selection;

7. Offset voltage drift with temperature, i.e. ΔVoffset/ΔT size;

8. Op-amp input impedance selection;

9.Op-amp output drive capability size selection;

10. op-amp quiescent power consumption, i.e. ICC current size selection;

11.Op-amp noise selection;

12. op-amp drive load stabilization time.

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In the design of switching power supply analog circuit, some people simply do not know how to choose the op-amp, what is on hand, maybe you have done so 100 times, are lucky to succeed, but the 101st time what will happen? Some other people are just the opposite, holding the five or six original information to flip around, the result is good to find the dream girl, and can not buy.

Not only do you recommend some commonplace op amps, you can definitely buy them and adapt to most occasions.

1. speed requirements are not high, or DC amplification.

LF441 (single), LF442 (double), LF444 (four), TL084 (four)

(The above op-amp for JFET input, impedance is very high, do not need to consider the impedance balance of the input)

OP07 (single, high-precision, with zero terminal, but the speed is particularly slow, for DC amplification is good)

2. relatively high speed, audio range, multiples of not more than 100: the

LF356 (single), LF353 (double), LF347 (four), TL074 (four)

(The above op-amp for JFET input, impedance is very high, do not need to consider the input impedance balance)

OP27 (single, high precision, with zero terminal, faster than LF356)

NE5534 (for audio amplification, very good sound quality, but low input impedance)

3. High speed

OP37 (unit frequency response 50MHz, but must not be used as a follower! In the closed loop gain of less than 5 will self-excitation)

4. low voltage or single power supply

LM324 (too slow)

Recommend the use of Maxim products

Other special occasions, such as video amplification, ultra-linear amplification, low drift and other requirements, or to look up on the Internet said

"The op-amp you solder on the board is not the ideal op-amp in the textbook!" When designing a circuit, after considering all the issues you have considered, please

Pay attention to the following issues.

1. output voltage swing

Do not expect the output voltage of a general-purpose op-amp to reach the supply voltage, even if your load resistance is 10M. The output voltage of a general-purpose op-amp

The peak-to-peak value of the general-purpose op amp output voltage is 1~3V different from the power supply.

2. common mode input voltage range

Do not let the potential of the input of your op-amp is very close to its supply voltage, otherwise you will be confused. For example, you choose the

LF347 op amp (most JFET op amps are similar), supply voltage of positive and negative 12V, positive input potential of -11V, negative input of -11.5V, you guess

What will the output be? Perhaps you guessed wrong, is -10V. This is the result of your use of the common mode voltage range beyond. Of course, if you switch to LM324,

there is no such effect. Fortunately, now Maxim and NS have introduced Rail to Rail op amps, their common-mode voltage range and power

Source voltage is the same.

3. output voltage swing rate SR

If you are using an op-amp to amplify high-frequency large-value signals, do not ignore the SR parameter, which represents the maximum change in output voltage per microsecond. For example, the unit bandwidth of uA741 is 1MHz, SR = 0.7V/us, if you connect him as a follower (gain = 1), at this time, if you input amplitude of -5V ~ +5V, frequency of 200KHz square wave, then, the output results must make you disappointed, his output is actually a strange amplitude of only about 2V triangle wave.

Slightly to add:

1. for low potential amplification line, but also take into account the detuning, temperature drift and input noise.

2 for high-precision lines, should pay attention to the common mode rejection ratio, generally speaking, the high common mode rejection ratio of the OP its linearity is better.

3. pay attention to the input resistance, bipolar OP generally in a few hundred K to tens of M.

Op-amp self-excitation may be caused by a variety of:

1. insufficient compensation

For example, OP37 and other op amps, in order to improve the high frequency response, its compensation is small, when the feedback is deeper, self-excitation phenomenon will occur. By measuring the BODE diagram of its open-loop response, we can see that as the frequency increases, the open-loop gain of the op-amp will drop, and if the phase lag is more than 180 degrees before the gain drops to 0db, the closed-loop use is bound to self-excitation.

2. power feed-back self-excitation

From the analysis of the internal structure of the operational amplifier, it is a multi-stage amplifier circuit, the general op-amp is composed of more than 3 stages of circuit, the first stage to complete the high gain amplification and potential shift, the second stage to complete the phase compensation function, the last stage to achieve power amplification. If the internal resistance of the power supply to the op-amp is large, the power consumption of the final stage will cause fluctuations in the power supply, which will affect the work of the front stage circuit and be amplified by the front stage, resulting in greater fluctuations in the rear stage circuit, and so on a vicious circle, resulting in self-excitation.

3. external interference

To be exact, this is not self-excitation, but the phenomenon is similar to self-excitation. The output produces a signal that is unrelated to the input. Because we are in an electromagnetic envelope of the environment, there are 50Hz and 100Hz industrial frequency interference, hundreds of Hz of medium-wave broadcast interference, several MHz of short-wave interference, tens to hundreds of Hz of television broadcast and FM broadcast interference, about 1GHz of wireless communication interference, etc.. If the circuit is not well shielded, the interference will be introduced into the circuit and amplified. If self-excitation occurs in a circuit, the first step is to determine what causes it. The first type of self-excitation occurs when the op-amp is used in closed loop and the gain is low, usually only if the gain is less than 10. In fact, this self-excitation is the best solution,

For some high-speed op amps, the manufacturer's manual will specify the minimum closed-loop gain. In contrast, the latter two cases occur in the case of high gain, which is very important to accurately determine the cause of self-excitation. Relatively speaking, the latter two self-excitation is more difficult to solve, I am not modest to say that only with a certain degree of experience in analog circuit design, it is possible to avoid the occurrence of the above situation. The basic principle is to increase the area of the ground as much as possible, in the op-amp power supply near the pin, must be near the increase in high-frequency bounce capacitors, the use of high-frequency shielding and other methods to eliminate self-excitation, reduce interference.

Applications and Circuits of Photoresistors

2021-07-22T02:27:03.182Z

Photoresistor is one of the photoelectric sensor elements, which is a kind of element made by the photoconductivity effect of semiconductor. The resistance value changes with the intensity of the incident light. Generally speaking, the incident light increases, the conductivity increases, and the resistance value decreases. Generally, the photoresistor body is made into a thin film structure to absorb more light energy. The material used for the photosensitive layer of the photoresistor can be polycrystalline material or single crystal material, and single crystal material can be made into intrinsic type and Doped type.

What are the main application scenarios of photoresistors?

Visible light photoresistors are widely used in automatic control such as the automatic extinguishing of dirty beacon lights, railway signal lights, street lights and other lighting systems, which are mainly used in switching circuits. It is required that the resistance of the photoresistor changes with the light, the better, that is, the resistance change multiple should be higher. It is also used as photoelectric counter, mechanical "position detector" and automatic protection device, automatic water supply of faucet and automatic water stop device after people leave, photoelectric potentiometer, automatic exposure device of camera, etc.

The application field of infrared technology is very extensive. It has now become a technology that the world military attaches great importance to. Because infrared technology can work at night and can detect targets through smoke, it has received great attention and is widely used in night combat, reconnaissance and camouflage. For example, the current infrared forward-looking device used for reconnaissance can detect people, vehicles, cooking fires in the jungle, and other camouflaged targets on the ground from an altitude of about 1,500 meters. Most of this pretense is array elements. Reconnaissance satellites with infrared photography carry out reconnaissance from space. Even when taking pictures in the monitored area, no one has no vehicles, but the heat radiation produced by people or vehicles a few hours ago can leave traces on the film. The infrared camera can determine the position of tanks and military vehicles, which can be identified from an altitude of 230 kilometers

A target that can't be found by visible light. Infrared radar and infrared communication are also widely used.

Infrared technology can be used in industry to detect thermal joints of electrical equipment, heat setting and temperature control of cotton and polyester, furnace temperature measurement, infrared baking, detection of train hot shafts, and so on. It can also be used for infrared gas analysis, which uses the characteristic absorption of various gases in different infrared bands for component determination. Compared with general chemical analysis methods, it is sensitive, accurate, fast and can be continuously measured for automatic control. It is also widely used in metallurgy, chemical industry, fertilizer, environmental protection, etc.

Because temperature affects the physical, chemical and physiological processes of crops and soil, and affects the growth cycle and yield of crops, in agriculture, infrared technology is used mainly through the thermal infrared radiation of the crop itself and the ability of the crop to absorb or reflect infrared radiation. Measure the temperature of crop leaves to observe crop growth, detect pests and diseases, and accurately grasp drought conditions.

In forestry, infrared technology can be used to draw forest distribution maps and determine forest quality, fire sources, pests and diseases, etc. If the forest fire infrared detector is placed on the commanding height of the forest area, the surrounding forest area can be monitored instead of the construction observation, and forest fires that cannot be detected by the artificial observation can be found.

Infrared technology is mainly used to detect and monitor water and air pollution in terms of environmental protection.

In medicine, according to the infrared radiation emitted by the skin surface of the patient, an image of the infrared radiation distribution of the patient is formed by an infrared detector and an appropriate display system to reflect the changes in the skin temperature of the patient's surface. When comparing the radiation images, information about the pathological state can be obtained. It can diagnose diseases such as early cancer, arthritis, arterial disease and so on.

In addition, thermal infrared detectors are also used to measure the surface temperature of oceans, rivers, and lakes, survey water sources, and survey geothermal in dry areas.

Photoresistor application circuits

1. Photoresistor dimming circuit

The picture shows a typical light-controlled dimming circuit. Its working principle is: when the surrounding light becomes weak, the resistance value of the photoresistor RG increases, so that the partial voltage added to the capacitor C rises, and the thyristor conducts. The increase of the pass angle achieves the purpose of increasing the voltage at both ends of the illuminating lamp. On the contrary, if the surrounding light becomes brighter, the resistance value of RG decreases, which causes the conduction angle of the thyristor to decrease, and the voltage at both ends of the illuminating lamp also decreases at the same time, which makes the light dim, thereby realizing the control of the light illuminance.

Note: The rectifier bridge in the above circuit must give a DC pulsating voltage, and it cannot be filtered by a capacitor to become a smooth DC voltage, otherwise the circuit will not work normally. The reason is that the DC pulsating voltage can not only provide the basic conditions for the zero-crossing shutdown of the thyristor, but also enable the charging of the capacitor C to start from zero in each half cycle, and accurately complete the synchronous phase shift triggering of the thyristor.

2. Photoresistive light control switch

The light-controlled switch circuit with relay control output with photoresistor as the core component has many forms, such as self-locking bright excitation, dark excitation and precise bright excitation, dark excitation, etc. Several typical circuits are given below.

The figure is a sophisticated dark excitation delay relay switch circuit. Its working principle is: when the illuminance drops to the set value, the inverting terminal potential of the op amp IC rises due to the increase in the resistance of the photoresistor, and its output stimulates VT to be turned on, and the excitation current of VT makes the relay work, and the normally open contact is closed. The normally closed contact is disconnected to realize the control of the external circuit.

Compared with structured light and binocular stereo vision, what are the advantages of ToF technology?

2021-04-28T09:59:20.190Z

Phone withTof function

Time of Flight (ToF), Structured Light (Structured Light), and Stereo Vision (Stereo Vision) together form the current three mainstream technology routes for 3D imaging and sensing. Among them, the 3D structured light solution is the most mature and has been widely used in industrial 3D vision. ToF has become a more promising solution on the mobile side by virtue of its own advantages.

What are the advantages of ToF?

One of the technical means available to realize 3D solutions at present is to imitate human eyes. Therefore, the development trend of mobile phones is from monocular to more and more cameras. Mobile phone monoculars cannot meet the development of some of our applications, so mobile phone developers will use more The camera is used to simulate the depth scene, and the biggest change we see is the change from single camera to dual camera, that is, simulating the eyes of a person and realizing the extraction of depth information.

Binocular Stereo Vision technology began in the mid-1960s. It is based on the parallax principle and uses imaging equipment to obtain two images of the measured object from different positions. By calculating the position deviation between the corresponding points of the image, To obtain the three-dimensional geometric information of the object. After decades of development, stereo vision has become more and more widely used in the fields of robot vision, aerial surveying and mapping, reverse engineering, military applications, medical imaging and industrial inspection.

The way to realize binocular stereo vision is relatively simple and close to human perception. But it has a big disadvantage, that is, it cannot extract the depth data very accurately. For example, we have no way of knowing how many meters or centimeters an object is from us through our eyes. Binocular stereo imaging systems often suffer from performance degradation when the scene lacks features, so they have not been used in smartphone imaging. For example, in the case of facing a flat and smooth surface of a wall, the 3D information captured by a stereo imaging system is usually incomplete or inaccurate.

This introduces another 3D technology, namely 3D structured light. This technology uses a near-infrared laser to project light with certain structural characteristics to the object, and a special infrared camera collects and obtains the three-dimensional structure of the object, and then performs in-depth processing and imaging of the information through calculations. In terms of structured light contrast with binoculars, accurate distance information can be obtained, and depth information can be obtained with only one imaging. It has the advantages of low energy consumption and high imaging resolution, and can achieve high security in security, so it is widely used Used in scenes such as face recognition and face payment. However, the recognition distance of structured light technology is relatively short, and it is only suitable for short distances, between 0.2 meters and 1.2 meters, so that its application is limited to the front camera of mobile phones.

TOF (Time of Flight) technology is a 3D imaging technology that was only applied to mobile phone cameras in 2018. It transmits continuous infrared light pulses of a specific wavelength to the target, and then a specific sensor receives the light signal from the object to be measured, and calculates The flight time or phase difference of the light round-trip, so as to obtain the depth information of the target object. TOF lens is mainly composed of light-emitting unit, optical lens and image sensor. Its recognition distance can reach 0.4 meters to 5 meters. TOF technology has the characteristics of strong anti-interference and higher FPS refresh rate, so it can perform better in dynamic scenes. In addition, TOF technology has a small amount of depth information calculation, and the corresponding CPU/ASIC calculation amount is also low, so the requirements for the algorithm are lower.

Although ToF has some technical shortcomings, such as relatively low 3D imaging accuracy and depth map resolution, high power consumption, etc., compared with structured light and binocular technology, it has a wider range of adaptation, covering from short distances to farther distances. Long distance, and it can also extract very accurate depth information.

Li Jia, engineer from Utmel Electronic, concluded that ToF has the following technical advantages:

High quantum efficiency CCD scheme @940nm light wavelength, with good outdoor performance
Can solve the mutual interference problem of multiple machines in the same scene
High resolution
Low power consumption
Narrow pulse, high speed, global exposure, low noise interference
Long detection distance

Conclusion

ToF sensor is superior to structured light and stereo vision. First of all, ToF has only two components, structured light and stereo vision have 3 to 4. In addition, ToF does not require a baseline, ensuring a compact shape and no baseline calibration, while also improving durability and reducing production costs. Finally, ToF does not need to use complex image recognition algorithms, saving a lot of power consumption. In short, compared with other 3D technologies, ToF technology is smaller, cheaper and more durable.

In the future, most smartphones will be equipped with one or two 3D cameras, 3D face authentication will become the de facto standard for secure mobile payments, and realistic augmented reality technology will push mobile games to a new stage.

Not only that, ToF technology will also be applied in smart factories and smart homes, such as household appliances, which require sweepers with clear obstacle images. In addition, the technology can also be used in access control systems for buildings and even private residences.