CAN Receiver Front-End Circuit for EMI Immunity and Common-Mode Rejection
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Solution Overview
Problem
Conventional CAN receiver designs lack sufficient immunity against Electromagnetic Interference (EMI) and have limited common-mode rejection, leading to errors in data reading and reduced data rates to mitigate these issues, which in turn increase latency and reduce the number of devices that can be handled on a CAN bus.
Innovation Solution
A CAN receiver architecture featuring a voltage divider network coupled with a front-end amplifier that divides and amplifies input signals to manage a wide common-mode voltage range, providing improved EMI immunity and faster operation by using a resistor divider network and a differential amplifier to reject common-mode signals and maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CAN receiver designs use standard signal amplification without voltage division, then the circuit structure remains simple, but EMI immunity is insufficient and data sampling time must be increased to avoid errors
Solution Approach 1:
The signal processing function is segmented into two distinct stages: voltage division (attenuation) and amplification. The voltage divider network divides the high-voltage differential signal by a predetermined factor N, and the front-end amplifier amplifies the divided signal by a factor substantially equal to 1/N. This segmentation allows the receiver to handle wide common-mode voltage ranges while maintaining signal integrity and improving EMI immunity without excessive complexity.
Solution Approach 2:
The voltage divider network acts as an intermediary element between the high-voltage CAN bus and the low-voltage receiver circuitry. By introducing this intermediate attenuation stage, the receiver can operate with improved common-mode rejection and EMI immunity while protecting subsequent circuit stages from high voltage stress.
2Reliability
If data sampling time is increased to avoid EMI errors, then EMI immunity improves, but latency increases and device handling capacity is reduced
Solution Approach 1:
The voltage division and amplification are performed preliminarily on the incoming differential signal before it reaches the data sampling stage. By pre-processing the signal with improved common-mode rejection, the signal quality is enhanced in advance, allowing for faster and more reliable data sampling without requiring extended sampling times, thus maintaining high device handling capacity while improving EMI immunity.
3Adaptability or versatility
If the receiver operates over a wide input common mode range of -20V to 20V, then adaptability to harsh environments improves, but the circuit becomes more susceptible to EMI interference
Solution Approach 1:
The voltage divider network and front-end amplifier are designed with specific local characteristics optimized for wide common-mode voltage ranges. The voltage division ratio and amplification gain are configured to maintain signal integrity across the -20V to 20V common-mode range, while the differential amplifier topology provides inherent common-mode rejection. This localized optimization allows the receiver to adapt to harsh environments with wide common-mode ranges while maintaining EMI immunity through improved common-mode rejection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed architecture achieves better EMI immunity and faster operation with improved common-mode rejection, reducing glitches and maintaining signal integrity under high EMI conditions, with a 14 dB improvement in EMI immunity and a 25 ns propagation delay, enhancing the CAN transceiver's performance.
Implementation Method 1
a voltage divider coupleable to a controller area network bus for dividing a signal on the bus by a predetermined factor N to generate an input signal
Implementation Method 2
A front end amplifier amplifies the input signal by a predetermined factor substantially equal to 1/N
Implementation Method 3
A front end amplifier amplifies the input signal by a predetermined factor substantially equal to 1/N
Data Source
AI summary
A CAN receiver architecture design that provides better immunity against EMI interference than conventional designs is disclosed herein. This CAN receiver includes a voltage divider network connected to a front-end amplifier for dividing down the input signal from a two wire line by a predetermined amount and amplifying the signal by the same predetermined amount. The front-end amplifier generates the common-mode voltage of the input signal for a reference generator that determines the logic level of the incoming signal and subtracts a bandgap voltage reference from the common-mode voltage. A comparator compares the difference between the output of the front-end amplifier and the resultant signal generated by the reference generator to generate an output signal for the receiver. This CAN receiver architecture is faster than conventional designs and possesses an improved common-mode rejection, while operating over a wide input common mode range.