CAN Wake-Up Receiver Circuit for Common-Mode Pulse Accuracy
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Solution Overview
Problem
Existing wake-up receivers in CAN transceivers experience significant pulse width distortion due to variations in bus common mode voltage and fail to perform reliably under high stress voltages, such as those encountered in Direct Power Injection testing, making it difficult to detect wake-up patterns within the narrow specification window required for fast bus arbitration and good noise immunity.
Innovation Solution
The proposed receiver circuitry includes a gain stage with offset generation circuits referenced to the common mode voltage, combined with high-bandwidth common-gate and auxiliary gain stages, and a pulse filter with optimized time constants to minimize pulse width distortion and quiescent current, enabling reliable detection of wake-up pulses under varying common mode voltages and stress conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wake-up receiver circuits are used, then the circuit can detect wake-up signals, but significant pulse width distortion occurs due to variations in bus common mode voltage
Solution Approach 1:
The patent changes the operating parameters of the wake-up receiver by introducing common mode voltage compensation circuitry that dynamically adjusts the receiver's reference voltage to match the varying bus common mode voltage. This parameter adjustment eliminates pulse width distortion caused by common mode voltage variations, maintaining accurate wake-up signal detection across different operating conditions.
Solution Approach 2:
The patent introduces an intermediary common mode voltage sensing and compensation circuit between the bus and the wake-up receiver core. This intermediary circuit senses the bus common mode voltage and generates compensating signals that cancel out the distortion effects, allowing the receiver to accurately detect wake-up patterns without being directly affected by common mode voltage variations.
2Speed
If the wake-up receiver operates with high bandwidth to detect fast wake-up patterns, then detection speed improves, but the circuit becomes more susceptible to noise and stress voltages
Solution Approach 1:
The patent applies local quality by implementing differential signaling specifically in the wake-up receiver input stage, where the highest noise immunity is needed. The differential configuration is localized to the critical signal path while other parts of the circuit use single-ended signaling, providing targeted noise rejection exactly where fast edge detection occurs without unnecessarily complicating the entire circuit.
Solution Approach 2:
The patent implements beforehand cushioning by including clamping diodes and voltage limiting circuitry at the receiver input that activate before stress voltages can damage the circuit. These protective elements are pre-positioned to clamp excessive voltages during Direct Power Injection events, cushioning the sensitive high-bandwidth circuitry from damage while allowing normal fast signal detection.
3Use of energy by moving object
If the wake-up receiver uses low power consumption during standby mode, then energy efficiency improves, but the detection sensitivity may be reduced
Solution Approach 1:
The patent implements periodic action by using a duty-cycled operation mode where the full-power high-sensitivity receiver circuit is activated only during brief intervals when wake-up signals are expected or detected. Between these active intervals, the receiver operates in a low-power standby mode with reduced functionality, achieving low average power consumption while maintaining the ability to detect wake-up patterns when needed.
Solution Approach 2:
The patent applies self-service by implementing an automatic gain control and threshold adjustment mechanism that adapts the receiver's sensitivity based on the detected signal conditions. The circuit automatically adjusts its operating parameters to maintain optimal detection sensitivity across varying signal strengths while consuming minimal power, eliminating the need for external power management intervention.
Data Source
AI summary
A controller area network (CAN) transceiver including a transmitter, a receiver, a wake-up receiver including an attenuator, a gain stage, a comparator, a pulse filter, and wake-up monitor logic. The gain stage includes an offset generation circuit, a common-gate amplifier, and first and second resistors. The first and second resistors are coupled between outputs of the attenuator to develop a common mode voltage. The offset generation circuit is referenced to the common mode voltage. The pulse filter can include start/stop logic, a transistor, a third resistor and a first capacitor coupled to one input of a second comparator, and a fourth resistor and a second capacitor coupled to another input of the second comparator.