Serial Output Circuit Impedance Switching Against Line Noise
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Solution Overview
Problem
The slew rate output circuit is prone to malfunction when subjected to communication line noise, leading to unstable gate voltage and failure to maintain a high output level, resulting in communication errors due to noise interference.
Innovation Solution
A serial communication apparatus with a slew rate control circuit, noise detection circuit, and switching circuit that adjusts impedance to reduce noise amplitude and prevent communication errors, featuring a slew rate control circuit that supplies constant currents, an output circuit that drives a load, and a noise detection circuit that outputs a switching signal to adjust impedance in response to detected noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If slew rate control is applied to suppress EMI noise, then electromagnetic interference is reduced, but the circuit becomes vulnerable to communication line noise causing malfunction
Solution Approach 1:
The patent implements dynamic impedance switching in the slew rate control circuit. The circuit transitions between high-impedance state (during normal operation to suppress EMI) and low-impedance state (when noise is detected to improve noise resistance). This dynamic adaptation resolves the contradiction by changing circuit characteristics based on operating conditions rather than maintaining a fixed state.
Solution Approach 2:
The patent employs a noise detection circuit that monitors the communication line and provides feedback to the slew rate control circuit. When noise exceeding a threshold is detected, the feedback signal triggers impedance switching. This feedback mechanism enables the system to respond to actual noise conditions, maintaining reliability while minimizing EMI during normal operation.
2Reliability
If impedance is reduced to suppress noise impact, then noise resistance improves, but EMI suppression capability deteriorates
Solution Approach 1:
The patent uses dynamic impedance switching to change the circuit's impedance characteristic from high (for EMI suppression) to low (for noise resistance) only when necessary. The impedance remains high during normal operation to suppress EMI, and switches to low only when noise detection circuit triggers, thus resolving the contradiction between EMI suppression and noise resistance.
Solution Approach 2:
The patent implements periodic monitoring of noise levels through the detection circuit, which periodically assesses the communication line quality. Based on this periodic detection, the impedance is switched only when noise thresholds are exceeded, allowing the circuit to maintain EMI suppression capability during normal periods while providing noise resistance when needed.
3Object-generated harmful factors
If constant current is used for slew rate control, then EMI noise is suppressed, but communication errors occur under noise interference
Solution Approach 1:
The patent dynamically changes the current supply mode in the slew rate control circuit. During normal operation, constant current mode is used to suppress harmonic components and EMI. When noise is detected, the circuit switches to a different current supply mode that provides stronger drive capability and noise resistance, thus maintaining communication reliability while minimizing EMI during normal conditions.
Solution Approach 2:
The patent changes the electrical parameters of the slew rate control circuit based on noise conditions. The current magnitude and supply mode are adjusted according to the detected noise level. This parameter change allows the circuit to maintain optimal EMI suppression during normal operation while providing enhanced noise resistance when communication errors would otherwise occur.
Data Source
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AI summary
A serial communication apparatus (100) comprises a slew rate control circuit (1) that has a predetermined impedance, and supplies a constant current from an output according to an input signal (Ti), an output circuit (21) that has a first capacitance (Cgs) charged and discharged by the constant current from the slew rate control circuit (1), and outputs from an output terminal (Tout) a digital signal according to a drive voltage that the first capacitance outputs, a detection circuit (31) that detects noise propagated from the output terminal (Tout), and outputs a switching signal (Vc) according to a detection result, and a switching circuit (4) that switches an impedance of the slew rate control circuit (1) to a value smaller than the predetermined impedance according to the switching signal (Vc).