Design and Application of USB signal transmission through optical fiber

Because the USB signal of the computer is transmitted by cable, the communication distance is difficult to extend, generally not more than 30 meters. The scheme in this paper overcomes the shortcomings of USB signal short distance transmitted by existing cables, so as to provide a circuit for transmitting USB signal through optical fiber, so that the communication distance of USB is increased to several thousands of meters.

1. Implementation Principle

This scheme is a circuit for transmitting USB signals through optical fiber. It is used in pairs and represents three States of the USB data cable respectively through three levels of full light, half light, and dark light intensity, when the light intensity is the lowest) represents the idle status of the USB data cable. One side that sends the USB signal first changes the USB data status first, and its status changes through the optical fiber transmission to the receiving circuit of the other side to generate a descent edge or rising edge) to trigger a monostable circuit, the output control of this monostable circuit allows the USB signal "receive/Send. One side that sends the USB signal first changes the USB data status first, and its status changes through the optical fiber transmission to the receiving circuit of the other side to generate a descent edge or rising edge) to trigger a monostable circuit, the delay time of the monostable circuit is the time when one frame of data is transmitted by USB.

2. Implementation Method

2.1 convert USB signal D + and D-) to Optical Fiber Transmission Signal

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To convert USB signal D + and D-) into Optical Fiber Transmission Signal-laser diagram. USB signal detection circuit 1) converts D + and D-to "or" gate output DOR1 and differential comparator output rcv1. One-to-two controllable three-state Buffer 2) controls the logic "pass" and "end" through the control end EN ". When EN = "0", the data centers are DOR1 and RCV = RCV1. However, when EN = "1", the data centers and RCV are in high-resistance state. Laser emission driving circuit 3) converts the Dors and RCV into three types of laser intensity: Bright, semi-bright, and dark ). Laser receiving circuit 4) restores the received three laser intensity light, half light, and dark to three States: D + and D. Laser receiving circuit 4) One of the outputs H state changes trigger a single steady delay circuit 5 ). (5) the output EN is usually when the USB signal is idle) is "0". When the input H is down, it is changed from "1" to "0 ") the output EN is changed from "0" to "1" and kept as "1" about us, and then restored to "0 ". Another double-mode controllable three-state Buffer 2) controls the logical "pass" and "break" through the control end EN. When the EN = "1, VP = H, VM = L, and when EN = "0", the output VP and VM are in high-resistance state.

2.2 convert the USB signal into a circuit diagram for Optical Fiber Transmission

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Circuit Diagram for converting USB signals into Optical Fiber Transmission convenience. Assume that the USB is in full speed status of 12 Mb). At this time, D + is connected to + 5 V power supply through a resistor of about KB. Normally, the USB signal is in the Idle status. At this time, D + is "1" high, about 3 to 5 V), and D-is the logic "0" low, about 0 to 1.4 V ). IC1 is "or. IC2, IC4, IC5, and IC6 are controllable three-state buffers. Among them, IC2 and IC4 are turned on when the control signal EN is "0", while IC5 and IC6 are turned on when the control signal EN is "1. Because IC2 and IC4 are in the high-impedance status when EN is "1 ",

The uplink resistance R1 is added at the output end of IC2 and the uplink resistance R2 is added at the output end of ic4. IC3, IC10, and IC11 are comparator. IC7 is a monostable Trigger Circuit Triggered by the VP of the input signal. The output EN is "0" at ordinary times ". When the input end of IC7 has a descent edge, its output end will have a "1" State lasting about 1000us and then return to "0 ". The IC7 Output Signal EN controls the "receive/Send" Status of D + and D-by controlling IC2, IC4, IC5, and ic6. Because EN is usually "0", so usually allowed to receive D + and D-IC2, IC4 conduction ), the IC5 and IC6 output to D + and D-are prohibited as high-impedance states ).

3. Signal Processing Method

In normal Idle status, D + is logical "1" and D-is logical "0". Therefore, the output of IC1 and IC2 is "1 ", the output of IC3 and IC4 is "1", and the output laser intensity is "dark ". When the laser intensity is "dark", the output of the laser receiver of the other side circuit after going through the circuit's IC9 is VP = "1", VM = "0 ". Once the USB starts to transmit data, the logic status of the d + and D-signals changes. The signal status of full-speed USB changes from D + to 0 and from 0 to 1 ". The USB Signal Status of the host computer changes first. At this time, the output of IC1 and IC2 is still "1", and the output of IC3 and IC4 is changed to "0 ". The laser emitting diode will change from "dark" to "fully bright ". The "completely bright" laser is transmitted to the laser receiving tube of the other side circuit through the optical fiber. The VP of the opposite circuit changes from "1" to "0", and the VM changes from "0" to "1 ". The VP of the Peer circuit changes from "1" to "0", that is, this VP generates a descent edge, which triggers the IC7 of the Peer circuit, change the output EN of IC7 from "0" to "1" and keep "1" about us and then return to "0 "). The VM of the opposite circuit changes from "0" to "1", so that the USB signal of the other circuit is changed from prohibited sending EN = "0") to prohibited receiving EN = "1 "). In this case, the VP and VM of the opposite circuit can pass the circuit D + and D-to the other circuit through the circuit IC5 and IC6 -, in this way, the USB signal of the upper computer is transmitted to the D + and D-lines of the lower computer through optical fiber in us. In this 1000us, three D + and D-states can be transmitted over optical fiber: ①, D + is "1", and D-is "0" represents the idle status and Data "1 ") ② If D + is "0" and D-is "1", the data is "0 ") ③ if D + is "0" and D-is "0", it indicates the end mark of data transmission ). These three states can indicate that all States of the USB signal D + are "1" and D-is "1" is disabled ). Within about us, the upper computer transmits a USB data frame to the lower computer, and waits for the lower computer to return a response signal. After 1000us, the output EN of IC7 of the lower computer is restored to "0". At this time, the USB data status of the lower computer changes first. The procedure of transmitting USB data from the lower computer to the upper computer is exactly the same as that of transmitting USB data from the upper computer to the lower computer described above.

4. Experiment and Application

After the system is designed, the USB signal can be reproduced at the remote end based on the timing requirements of the circuit. This circuit can be used for various USB peripherals without changing the original driver. Some USB peripherals do not have an effective extension scheme, such as USB mouse, so this circuit can be successfully implemented.

Currently, the remote optical fiber transmission scheme of images usually requires special hardware interfaces and special image processing software. After using the circuit of this scheme, you only need to extend the general USB camera.