Ten Daily Electronic Common Sense-Section 32

What are the series of Altera CPLDs?

Altera’s CPLDs include MAX 9000, MAX 7000, MAX 3000A and MAX II series.

What is the temperature rise time of the sensor?

Sometimes the operation of the sensor is unstable before and after the power is turned on, so there is a large drift.

At this time, the heat inside the sensor has not yet reached the normal value, so the operating point changes. Such drift is temporary and eventually disappears by itself, and the time required to reach a normal state is called the heating time.

How to design UHF RFID anti-metal tag antenna?

• The design principles of the UHF RFID anti-metal tag antenna are as follows.
  1. Impedance matching of tags Adjust the antenna and its feed structure to achieve conjugate matching between the antenna impedance and the chip impedance.
  2. Tag gain The advantage of UHF RFID technology is that the tag has a longer reading distance. Therefore, metal-resistant tags cannot be sacrificed at the expense of read distance.
  3. The directionality of the label The label has good directionality, preferably the hemisphere on the metal surface has omnidirectional characteristics, so that the reader can accurately read the label at different angles.
  4. The size of the tag In order to meet the needs of practical applications, the area of the tag antenna is required to be as small as possible and the thickness of the tag is as thin as possible.
  5. The cost of the label In order to reduce the cost, on the one hand, the material of the label is required to be cheap, and on the other hand, the manufacturing process of the antenna is required to be simple. The manufacturing process of the antenna is simple, and the antenna is required to have a simple plane structure.

What are the common fieldbuses?

1. Foundation field bus (Fieldbus Foundation, FF)
2. Process Field Bus (Process Field Bus, PROFIBUS)
3. Local operation network (LonWorks)
4. Addressable Remote Transducer Data Path (HART)
5. Control local area network

What is the role of the inverter?

The inverter is one of the most important parts of the inverter. The main function is to convert the rectified output direct current into alternating current with adjustable frequency and voltage under the control of the control circuit. The most widely used inverter is the three-phase bridge inverter circuit.

Briefly describe the design of the underlying driver of the RTL8019AS network?

The driver program of RTL8019AS includes the initialization program of the chip, the program of receiving data and the program of sending data. The controller sends and receives data with the internal RAM as the core.
RTL8019AS has two internal RAMs, one 16KB RAM, used to store forwarded data; the other is 328 RAM. The 16 KB storage area is paged, each 256 bytes is called a page, and there are 64 pages in total. This RAM is used in programming to store received or sent data packets.
Since the RTL8019AS receives or transmits in units of pages, even if a page is not completely filled with data, the next packet of data cannot continue to use this page, and only a new page can be used. And the data is stored continuously by page, the 16KB RAM can be configured by the user, part of it is used to store the received data packet, part of it is used to store the sent data packet, but the addresses cannot be interleaved. 
The user accesses the 16KB RAM through DMA, which is a dual-port RAM. Dual port means that the RAM is connected by two sets of buses, and the controller performs DMA access to the internal RAM through bus a.
In order to distinguish the two kinds of access from the host and the chip, this kind of access is called local DMA access; while the RAM access performed by the CPU through bus b is called remote access. Users do not have to worry about conflict between the two accesses, and there is an arbitration mechanism inside the chip to prevent conflicts. And because the remote access operation on the CPU side is much slower than the local DMA access, there is no need to wait for the timing, and it can be performed at the same time as the local access without affecting each other. 
The driver writes the packaged data to be sent into the chip according to the specified format, and starts the sending command, and the data is sent out. After the same chip receives the physical signal, it restores it to data, stores it in RAM according to a certain format, and informs the main program.

What are the advantages of vacuum photocells?

The advantages of vacuum photocells are: in a wide range of light intensity, the input light intensity is proportional to the output current, the measurement accuracy is high, and the disadvantage is low sensitivity.

What is the transport layer?

The transport layer defines the type of connection between hosts, and whether and how acknowledgments are sent. From a usage perspective, there are only two protocols to choose from at this layer: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

What is the main purpose of the limiter circuit?

The main purpose of the limiter circuit is to limit the amplitude of the signal, protect the input stage of the op amp and improve the speed of change of the output voltage.

What are the logic signal generators?

The logic signal generator can be divided into pulse signal generator and pattern generator. The pulse signal generator drives a small number of square wave or pulse wave output, and the pattern generator generates digital patterns of many channels.