Transceiver Output Stage Switching Against Power Line Noise
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Solution Overview
Problem
Existing transceiver circuits for vehicle networks fail to effectively suppress noise interference and control voltage fluctuations, especially when mounted near alternators that generate ripple voltage, leading to erroneous operation of output transistors.
Innovation Solution
A transceiver circuit design featuring an output transistor with an emitter-collector path between a communication line and ground, a trapezoidal wave signal circuit, and a control circuit that includes a current mirror circuit to drive the transistor based on transmission signal levels, ensuring the transistor turns off during high signal levels and preventing noise-induced operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output transistor is always biased to remain active, then signal transmission is maintained, but noise from power lines causes erroneous operation
Solution Approach 1:
The output transistor's operating state is dynamically changed based on signal level. During high signal levels (transmission), the transistor is turned off to prevent noise interference. During low signal levels (reception), the transistor is turned on to maintain signal transmission capability. This dynamic state change resolves the contradiction between maintaining transmission reliability and preventing noise-induced errors.
Solution Approach 2:
The control circuit preliminarily turns off the output transistor before noise can cause erroneous operation. By detecting high signal levels and proactively disabling the transistor, the system prevents potential noise interference from affecting the output stage during transmission periods.
2Object-affected harmful factors
If the output transistor is turned off during high signal levels, then noise interference is suppressed, but signal transmission capability is reduced
Solution Approach 1:
The system dynamically switches the output transistor between on and off states based on the signal level. During high signal levels, the transistor is off to suppress noise. During low signal levels, the transistor is on to enable signal transmission. This temporal separation of functions resolves the contradiction between noise suppression and transmission capability.
Solution Approach 2:
The output transistor operates in periodic cycles of being on and off, synchronized with the signal transmission/reception phases. This periodic switching allows the system to alternately prioritize noise suppression during transmission and signal capability during reception, resolving the inherent contradiction.
3Device complexity
If a common communication line is used for both transmitting and receiving, then circuit complexity is reduced, but noise from power lines affects both functions
Solution Approach 1:
The output transistor's state is dynamically controlled based on whether the system is in transmission or reception mode. During transmission (high signal level), the transistor is turned off to prevent power line noise from affecting the communication line. During reception (low signal level), the transistor is turned on to enable signal reception. This dynamic control protects the common communication line from noise while maintaining its dual functionality.
Solution Approach 2:
The control circuit applies preliminary anti-action by turning off the output transistor before power line noise can couple into the communication line during transmission. This preventive measure blocks the noise path while allowing the common communication line to serve both transmission and reception functions.
Data Source
AI summary
A noise free transceiver circuit includes a communication line, a power source line, a ground line, an output transistor having output terminals connected between the communication line and the ground line for outputting a communication signal to the communication line, a first circuit for applying a trapezoidal signal to the input terminal of the output transistor to turn on in synchronism with a transmission signal and a second circuit for turning off the output transistor when the level of the transmission signal is high. The output transistor is turned off when the communication signal is outputted. Therefore, noises of the power line are shut out of the output transistor.