Design of fiber LED driver circuit

In the development of an array signal processing system, since the array antenna must be placed in an open area around the array, and the array signal processing unit is located at the center of the circular display antenna, this requires an array signal processing unit and a microcomputer located 1 to 2 km away. Perform duplex communication. In order to reduce the proportion of data transmission time in the overall system processing time index, the data transmission rate is required to be not less than the E1 (2.048 Mb/s) rate, and the communication link is required to be safe and reliable. Through the analysis of the cold storage installation of various data communication technologies, we finally selected the fiber-optic keyway and achieved satisfactory results.

1, copper media data link analysis

Since high data transmission rate and long communication distance are required at the same time, it is difficult to meet the index requirements without coding and modulation in the copper medium link, but the high-speed modem is not only expensive, but also the time-consuming handshake process of both parties requires random real-time. The field where the data is transmitted will obviously not be applicable. Most importantly, traditional copper dielectric links generate both electromagnetic interference signals and are susceptible to electromagnetic interference, and are less susceptible to EMC (electromagnetic compatibility) and EMI (electromagnetic interference) standards.

2. Analysis of fiber link

In people's traditional impression, it is uneconomical for fiber to be used for short-distance communication, but it has the incomparable advantages of copper media bonding: 1 fiber-optic link neither emits electromagnetic waves nor is it affected, there is no interference between fibers. The bit error rate is greatly reduced. Designers do not have to consider the environmental noise that may be coupled in; 2 fiber provides electrical isolation between the two sides of the communication link, and the shop eliminates problems caused by different ground potentials between long-distance devices. At the same time, the designer no longer has to worry about impedance matching; 3 fiber optic transmitter can use digital modulation drive circuit. The digital baseband signal can be directly driven by the fiber optic transmitter as long as it is simply line coded.

Now, the price of fiber optic devices has dropped sharply compared with the past. In the future, as the price of wire ropes rises and the price of fiber optic devices drops further, people will not consider the price factor first when choosing fiber. Therefore, we comprehensively consider the rate and distance indicators, select the appropriate type of fiber, transceiver and its drive circuit, can obtain high-performance price ratio fiber communication key, which is the focus of this paper.

3. Choice of optical fiber communication devices

A basic fiber-optic communication system is very simple: an LED transmitter converts an electrical signal into an optical signal and couples it into a transmission fiber. The optical signal passes through the fiber to the optical receiver, which restores the received optical signal to its original state. Electrical signal output.

Fiber optic cable selection: In general, quartz glass fiber is used for long-distance communication links due to its low loss and high bandwidth. For example, Ethernet and FDDI standards specify multimode 62.5/125μm quartz glass fiber. These fine-core fibers require high-precision connectors to reduce coupling losses, and for industrial applications, low-cost cables and connectors are required. Therefore, 1 mm POF (Plymer Optical Fibers) and 200 μm HCS (Hard Clad Silica) fibers are the best choice, and they all belong to step-index multimode fibers.