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What are the types of linear integrated circuits?

Linear integrated circuit is an integrated circuit based on amplifier. The word "linear" means that the response of the amplifier to the input signal usually presents a linear relationship. Later, this kind of circuit includes many nonlinear circuits such as oscillator, timer and data converter, as well as the circuit combining digital and linear functions. Because the information processed involves continuously changing physical quantities (analog quantities), people also call this kind of circuit analog integrated circuit.   A new development in linear circuits is the use of MOS technology to manufacture audio filters. Its principle is switched capacitor method, that is, the capacitor is alternately connected to different voltage nodes in the circuit with a switch to transmit charges, so as to produce equivalent resistance. This technology is especially suitable for MOS process (see switched capacitor filter). On the other hand, due to the application of analog sampling technology, MOS technology has been able to produce high stability operational amplifiers and high-precision digital to analog and analog to digital converters. The combination of these two technologies opens up a broad prospect for the large-scale integration technology of analog information processing and communication equipment subsystems.   In terms of manufacturing process, most linear integrated circuits are manufactured by standard bipolar process. In order to obtain high-performance circuits, some modifications or additional manufacturing processes are sometimes made on the basis of standard processes, so as to make various components and devices with different performances on the same chip.   According to the functions and applications of circuits, linear integrated circuits can be roughly divided into:   General circuit, including operational amplifier, voltage comparator, voltage reference circuit and regulated power supply circuit;   Industrial control and measurement circuit, including timer, waveform generator, detector, sensor circuit, phase-locked loop, analog multiplier, motor drive circuit, power control circuit, analog switch;   Data conversion circuit, including digital to analog converter, analog to digital converter, voltage frequency converter;   Communication circuit, including telephone communication circuit and mobile communication circuit;   Consumer circuits, including television circuits, video recorder circuits, and audio circuits. In fact, there are many other circuits, such as medical circuits such as cardiac pacemakers.   On the other hand, due to the increasing development of large-scale integration technology and computer-aided design and measurement technology, the design of linear circuits is developing from traditional standard units to custom integrated circuits with complex functions.

What is FPGA field programmable gate array

  Field programmable gate array (FPGA) is the product of further development on the basis of programmable devices such as pal (programmable array logic) and gal (general array logic). As a semi custom circuit in the field of application specific integrated circuits (ASIC), it not only solves the shortcomings of custom circuits, but also overcomes the shortcomings of the limited number of programmable devices. The mainstream manufacturers of field programmable gate array FPGA chips include Xilinx, Altera, lattice and MICROSEMI, of which the first two have a total market share of 88%. Field programmable gate array FPGA is a semiconductor device composed of configurable logic block (CLB) matrix connected through programmable interconnection. FPGA can be reprogrammed according to the required application or functional requirements after manufacturing. This feature is the key to the difference between FPGA and ASIC. You can customize FPGA devices for specific design tasks. Although there are also one-time programmable (OTP) FPGAs on the market, most of them are based on SRAM and can be reprogrammed as the design evolves. Field programmable gate array FPGA has a very mature and wide range of applications in the aerospace, military, telecommunications fields. Taking the telecommunication field as an example, in the stage of all-in-one telecommunication equipment, FPGA is applied to network protocol parsing and interface conversion because of its programming flexibility and high performance. In the nfv scenario, FPGA based on the general server and hypervisor can achieve a 5-fold performance improvement of the network element data plane, and can be managed and arranged by the openstack cyborg hardware acceleration framework. In terms of chip design, we need to focus on rationality in algorithm design to ensure the final completion effect of the project, and put forward a solution to the problem according to the actual situation of the project, so as to improve the operation efficiency of FPGA. After the algorithm is determined, the module should be constructed reasonably to facilitate the later code design. In the code design, we can use the pre designed code to improve work efficiency and reliability. Write the test platform, carry out the code simulation test and board debugging, and complete the whole design process. Unlike ASIC, FPGA has a short development cycle. It can change the hardware structure in combination with the design requirements. When the communication protocol is immature, it can help enterprises quickly launch new products and meet the needs of non-standard interface development.

How to realize the frequency synchronization of crystal oscillator?

Crystal oscillators can help electronic systems provide frequencies for synchronous operation, as frequency references or to achieve accurate timing. In microprocessor-based systems, there are several different frequency signals used to execute instructions, move data into and out of memory, and external communication interfaces. A simple embedded controller may have a clock frequency of several MHz, while microprocessors in personal computers usually expect an input frequency of 15 MHz. This will multiply internally to provide the frequency of the CPU and other subsystems. Other components in the system may have their own frequency requirements. In addition to providing the basic requirements of the specified frequency, the oscillator may have to meet other requirements depending on the application requirements of the product. For example, many product applications require extremely precisely defined frequencies. This is particularly important for systems that need to communicate with other devices through serial or wireless interfaces. Accuracy is usually measured in parts per million (PPM). At the same time, the trimming circuit can be based on resistance capacitance (RC) or inductance capacitance (LC) networks. These devices are relatively simple and can change the frequency in a wide range. However, designing an accurate RC oscillator or LC oscillator requires the use of expensive precise components. Even so, they cannot meet the highest accuracy and stability required by many product applications. Crystal oscillators (usually quartz) can also be used as resonant components. Cut the crystal into two parallel crystal planes and deposit metal contacts on them. Quartz has piezoelectric effect, which means that when the crystal is placed under pressure, voltage will be generated on its crystal surface. On the contrary, when voltage is applied to the crystal, the crystal will also change its shape.

How does the common mode choke solve the problem of common mode interference?

Common mode chokes, also known as common mode inductors, are coils symmetrically wound on a closed magnetic ring in opposite directions and with the same number of turns. It is often used to filter common mode electromagnetic interference, suppress the outward radiation and emission of electromagnetic waves generated by high-speed signal lines, and improve the EMC of the system. In practical applications, it is generally to add common mode inductance to the differential signal line. Signal interference is mainly divided into common mode interference and differential mode interference. There are two forms of voltage and current changes when they are transmitted through wires, which we call "common mode" and "differential mode". In addition to these two wires, there is usually a third conductor, which is "ground". There are two kinds of interference voltage and current: one is that two wires are used as round-trip lines respectively; The other is that two wires are used as the going path and the ground wire is used as the return path. The former is called "differential mode" and the latter is called "common mode". Usually, the electrical appliances we use are two-wire, a live wire [2] (L) and a zero wire (n). The zero wire is considered as the neutral line of three-phase electricity, and there is also a ground wire called ground wire. The interference between zero line and live line is called differential mode interference, and the interference between live line and ground line is called common mode interference. Usually, on the line, the differential mode component and common mode component of the interference voltage exist at the same time, and because of the imbalance of the line impedance, the two components will transform into each other in transmission. Then, how does the common mode choke solve the problem of common mode interference? The principle of common mode inductance suppressing common mode interference is also very simple. According to the right-hand screw rule, when two coils with the same magnetic ring winding in the opposite direction pass through two voltages with the same polarity and equal amplitude, the magnetic flux generated is superimposed with each other, and the inductive reactance is: xl=wl, which is very large. The magnetic flux generated by the differential signal cancels each other.