Three-Conductor Capacitive Isolation Signaling With Lower EMI
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Solution Overview
Problem
Existing galvanic isolation techniques, such as differential signaling, face challenges with signal propagation delays, power consumption, and pulse width distortion, particularly in communication between circuits operating in separate voltage domains.
Innovation Solution
A three-conductor interface is used for data communication between galvanically isolated circuits, where one signal is maintained at a set voltage, and the other two signals alternate between high and low voltages according to a carrier frequency, with the third signal being out of phase, allowing for decoding without direct comparison and reducing electromagnetic emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential signaling is used for galvanic isolation, then data can be transmitted between isolated voltage domains, but signal propagation delays and pulse width distortion increase
Solution Approach 1:
The patent segments the signaling approach by using three separate conductors instead of traditional differential pairs, with each conductor carrying a distinct signal (two alternating at carrier frequency, one DC). This segmentation allows independent optimization of each signal path, reducing propagation delays and pulse width distortion while maintaining galvanic isolation capability.
Solution Approach 2:
The patent employs periodic alternating signals at a defined carrier frequency on two of the three conductors. This periodic action enables synchronized signal transmission that reduces timing skew and propagation delays compared to asynchronous differential signaling, while the DC conductor provides a stable reference level.
2Reliability
If differential signaling with direct comparison is used, then data transmission is achieved, but power consumption increases
Solution Approach 1:
The patent implements self-service by having the receiver autonomously reference the three incoming signals to each other without requiring external voltage references or complex differential comparison circuits. The receiver decodes data by comparing signal arrangements relative to each other, eliminating the need for power-hungry external reference voltages and high-speed differential amplifiers.
Solution Approach 2:
The patent changes the signaling parameters from traditional differential voltage swings to a three-conductor scheme with two AC signals at carrier frequency and one DC signal. This parameter change allows the receiver to use simpler, lower-power comparison circuits that reference signals to each other rather than requiring high-power differential amplifiers with external voltage references.
3Reliability
If traditional galvanic isolation techniques are used, then voltage domain isolation is achieved, but electromagnetic emissions increase
Solution Approach 1:
The patent achieves equipotentiality by maintaining a DC voltage level on one conductor that serves as a stable reference, while the other two conductors alternate at the same carrier frequency. This creates a balanced electromagnetic environment where the alternating signals are out of phase, causing their electromagnetic emissions to cancel each other out, reducing overall EMI while maintaining galvanic isolation.
Solution Approach 2:
The patent converts the potential harm of electromagnetic emissions from alternating signals into a benefit by deliberately making two signals out of phase with each other. The harmful electromagnetic emissions from these two conductors cancel each other out through destructive interference, transforming what would be EMI pollution into an advantage that reduces overall electromagnetic radiation while maintaining effective data transmission.
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
This method enables efficient data transmission across isolated voltage domains with reduced power consumption and minimized pulse width distortion, suitable for low-power CMOS-based applications and applications with large voltage differences.
Implementation Method 1
One type of galvanic isolation technique involves the use of differential signaling and capacitive coupling
Data Source
Figure 1~1C
Figure 2~2C
Figure 3
AI summary
In one embodiment, a method of communicating data values over a three conductor interface is provided. Different data values are transmitted by generating and transmitting three respective signals to a receiver using three conductors. The first signal is maintained as a set voltage level. The second signal is alternated between a high voltage and a low voltage according to a carrier frequency. The third signal is alternated between the high and low voltages and is out of phased with the second signal. To transmit a first data value, the first signal is generated on a first conductor, the second signal is generated on a second conductor, and the third signal is generated on a third conductor. To transmit a second data value, the second signal is generated on the first conductor, the first signal is generated on the second conductor, and the third signal is generated on the third conductor.