Digital Isolation Circuit for Common-Mode Transient Immunity

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Solution Overview

Problem

Existing isolation circuits, such as optocouplers, face issues with temperature instability, performance degradation, low common-mode rejection ratio due to parasitic capacitance, and limitations in speed and power efficiency, making them inadequate for modern applications.

Innovation Solution

A digital isolation device is introduced, featuring a pair of buffers that store incoming signals at a first voltage level, a common-mode circuit to reduce common-mode transient voltage, and a latch circuit to store intermediate signals, along with a crossover circuit and PMOS or BJT transistors configured in a crossover configuration to enhance signal transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If optocoupler is used for signal isolation, then signal transmission is achieved, but temperature stability deteriorates due to electrical property variations of light-emitting diode

Engineering Contradiction:

Improvesignal isolation reliabilityVSAvoidtemperature stability

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent replaces the optical system (light-emitting diode and photosensitive receiver) with an electrical system using isolation capacitors and coupling circuits. This substitution eliminates the temperature-sensitive light-emitting diode while maintaining signal isolation functionality through electrical capacitance-based isolation, thereby improving temperature stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the isolation mechanism from optical parameters (light emission and detection) to electrical parameters (capacitance and voltage coupling). By using isolation capacitors with stable electrical characteristics across temperature ranges, the system achieves better temperature stability while maintaining isolation performance.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If optocoupler is used for signal isolation, then signal transmission is achieved, but common-mode rejection ratio deteriorates due to parasitic capacitance

Engineering Contradiction:

Improvesignal isolation performanceVSAvoidcommon-mode rejection ratio

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent extracts and eliminates the parasitic capacitance issue by removing the light-emitting diode and its associated parasitic capacitance. The new design uses isolated capacitors that can be precisely controlled and minimized, thereby improving common-mode rejection ratio while maintaining signal isolation.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary coupling circuit with controlled isolation capacitors between the input and output sides. This intermediary structure provides a well-defined capacitance path that reduces unwanted parasitic effects and improves common-mode rejection compared to the direct optical coupling in traditional optocouplers.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If optocoupler is used for signal isolation, then signal transmission is achieved, but transmission speed deteriorates

Engineering Contradiction:

Improvesignal isolation capabilityVSAvoidsignal transmission speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces the optical transmission mechanism with direct electrical coupling through isolation capacitors. This substitution removes the limitations of light emission and detection speeds, enabling faster signal transmission while maintaining isolation functionality through the capacitive coupling path.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If optocoupler is used for signal isolation, then signal transmission is achieved, but power consumption increases

Engineering Contradiction:

Improvesignal isolation functionVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the power-intensive light-emitting diode with passive isolation capacitors and low-power coupling circuits. This substitution eliminates the continuous power requirement for light generation while maintaining signal isolation through capacitive coupling, thereby reducing overall power consumption.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12028028B2Isolation circuit systems and methods thereof

Publication Date: 2024.07.02 2PAI SEMICON (SHANGHAI) CO LTD

AI summary

A digital isolator device which includes a first input buffer configured to receive a first differential signal from a transmitter and to provide a second differential signal, the first differential signal being characterized by a first magnitude, the second differential signal being characterized by a second magnitude, the first magnitude being greater than the second magnitude. The device also includes a second input buffer configured to receive a third differential signal from the transmitter and to provide a fourth differential signal, the second input buffer being coupled to the second ground terminal. The device also includes a common-mode circuit coupled to the second differential signal and the fourth differential signal, the common-mode circuit being configured to reduce a common-mode transient voltage, the common-mode transient voltage being associated with a voltage differential between the first ground terminal and the second ground terminal.