CAN Receiver Comparator Topology for Low Skew and RF Immunity
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Solution Overview
Problem
Faster CAN bus receivers face challenges in reducing duty cycle distortion and complying with RF immunity requirements, as existing designs with multiple pre-amplification and level shifting stages result in substantial propagation delay and signal skew.
Innovation Solution
A CAN bus receiver circuit with a pre-amplifier stage and a comparator that eliminates the need for additional pre-amplification and level shifting stages, utilizing a folded cascode input and push-pull output configuration to reduce propagation delay and improve RF immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple pre-amplification and level shifting stages are used, then signal amplification and level conversion are improved, but propagation delay and signal skew increase
Solution Approach 1:
The patent combines multiple pre-amplification stages into a single differential amplifier stage that directly couples the CANH and CANL signals. This merging eliminates the need for separate voltage level shifting stages, thereby reducing the total number of amplification stages from multiple to one, which directly reduces propagation delay while maintaining signal amplification capability.
Solution Approach 2:
The patent extracts and eliminates the intermediate voltage level shifting stages from the signal path. By removing these redundant stages that only added delay without contributing to signal amplification, the design achieves faster response time while maintaining the necessary signal level conversion through the differential amplifier's inherent capability.
2Power
If multiple pre-amplification stages are used, then signal amplification is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple discrete amplification and level-shifting functions into a single integrated differential amplifier stage. This consolidation reduces the circuit from multiple separate stages to one unified stage, simplifying the overall device architecture while maintaining the necessary signal amplification and level conversion functions.
Solution Approach 2:
The differential amplifier stage is designed to perform multiple functions simultaneously: it amplifies the voltage difference between CANH and CANL signals, converts voltage levels, and provides differential-to-single-ended conversion. This multi-functionality eliminates the need for separate dedicated stages for each function, reducing device complexity.
3Difficulty of detecting and measuring
If additional pre-amplification and level shifting stages are added, then signal processing capability is improved, but RF immunity deteriorates
Solution Approach 1:
The patent removes intermediate amplification and level-shifting stages from the signal path, eliminating potential sources of RF interference and susceptibility. By reducing the number of active stages, the design minimizes the opportunities for RF coupling and interference, thereby improving RF immunity while retaining essential signal processing through the direct differential amplification.
Data Source
AI summary
A circuit (e.g., implemented as part of a controller area network (CAN) bus receiver includes a pre-amplifier stage having first and second outputs. The circuit also includes a comparator having first and second inputs. The first input is coupled to the first output of the pre-amplifier stage, and the second input is coupled to the second output of the pre-amplifier stage. The comparator includes an input differential transistor pair, a second pair of transistors coupled to the input differential transistor pair in a cascode configuration, and a push-pull output stage coupled to the second pair of transistors.