CAN Transmitter Fast Control Loop via Replica Circuit
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Solution Overview
Problem
Existing CAN transmitters face challenges in achieving fast and accurate control of CANL signals, particularly in maintaining signal levels and matching CANL and CANH currents amidst electromagnetic interference and varying electromagnetic environments, which affects bus reliability and data transmission speed.
Innovation Solution
A CAN transmitter design incorporating an output stage circuit, a replica circuit, and a control amplifier that actively controls the CANL output signal, using a lateral double-diffused NMOS transistor and freewheeling diodes, with a control amplifier configured to maintain the replica signal at a desired level and bias transistors during dominant and recessive states, and employing active feed-forward to stabilize the control loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional CAN transmitter control is used, then device complexity is reduced, but signal control speed and accuracy deteriorate
Solution Approach 1:
The control circuit is segmented into separate control amplifiers for CANH and CANL signals, with the CANL control amplifier being selectively enabled. This allows independent optimization of control speed for CANL while maintaining simpler control for CANH, resolving the contradiction between control speed and overall system complexity.
Solution Approach 2:
The patent implements dynamic control where the CANL control amplifier is selectively enabled or disabled based on operational requirements. During states requiring fast control (dominant or recessive transitions), the amplifier is enabled; during idle periods, it is disabled. This dynamic approach achieves fast signal control speed only when needed, reducing average power consumption and effective complexity.
2Loss of time
If fast control loop is implemented, then signal rise and fall times improve, but power consumption increases
Solution Approach 1:
The CANL control amplifier operates periodically rather than continuously, being enabled only during state transitions (dominant to recessive or vice versa) and disabled during steady states. This periodic operation achieves fast signal transitions when required while minimizing power consumption during idle periods, directly resolving the contradiction between transition speed and power usage.
Solution Approach 2:
The control amplifier is enabled in advance of state transitions to prepare the output stage for rapid response. By anticipating transition requirements and pre-enabling the amplifier, the system achieves fast rise and fall times without requiring the amplifier to remain continuously active, thereby reducing overall power consumption while maintaining fast transition capability.
3Use of energy by moving object
If selective CANL control is used, then power consumption is reduced, but control accuracy during transitions may worsen
Solution Approach 1:
The control amplifier incorporates feedback mechanisms that actively monitor the output signal levels and adjust the control voltage accordingly. This feedback ensures accurate signal level control during transitions even when the amplifier is selectively enabled, preventing degradation of control accuracy while maintaining power savings from selective operation.
Solution Approach 2:
The control amplifier is enabled in advance of state transitions to ensure it is fully operational and stabilized before the actual transition occurs. This preliminary enabling allows the amplifier to establish accurate control parameters before the transition begins, ensuring high control accuracy during the critical transition period while still limiting overall power consumption by not keeping the amplifier continuously active.
Data Source
AI summary
A controller area network (CAN) transmitter includes an output stage circuit, a replica circuit of the output stage circuit configured to produce a replica signal, and a control amplifier configured to control a CANL output signal of the CAN transmitter in order to maintain the replica signal at a desired level.