Capacitive Digital Isolator Using Sawtooth Modulation for Low Jitter
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Solution Overview
Problem
Conventional capacitive isolation links face challenges in transmitting digital signals with reduced delay and high performance due to issues like common mode transients, jitter, and the need for additional demodulation circuits, which can lead to fatal failures in applications requiring accurate state transmission.
Innovation Solution
A digital isolator design utilizing a logic module with sawtooth modulators and threshold comparators to generate and process digital signals with slow and fast edges, ensuring accurate transmission across a capacitive isolation link with reduced delay and jitter, and incorporating an SR latch for redundancy correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional capacitive isolation links use square signals with fast transients for data transmission, then data can be transmitted through the capacitive barrier, but delay and jitter occur in the output signal
Solution Approach 1:
The patent uses periodic carrier wave modulation (AM or FM) to encode digital data. Instead of transmitting raw square waves directly through the capacitive barrier, the data modulates a periodic carrier signal. This periodic action allows the signal to pass through the capacitor more efficiently while the envelope detection or frequency discrimination at the output recovers the original data with reduced delay and jitter compared to direct square wave transmission.
Solution Approach 2:
The patent applies preliminary modulation of the digital signal with a carrier wave before transmission through the capacitive barrier. This preliminary action transforms the signal into a form that is more suitable for capacitive coupling, avoiding the direct transmission of fast transients that cause delay and jitter. The modulation prepares the signal in advance for efficient capacitive coupling while preserving the data integrity.
2Ease of operation
If common mode transients are present due to switching supply voltages and grounds, then circuit operation is maintained, but high frequency transients corrupt data transmission across the isolation barrier
Solution Approach 1:
The patent introduces an intermediary modulation scheme where digital data modulates a carrier wave before transmission. This intermediary carrier signal acts as a mediator that is less susceptible to common mode transients. The modulation process spreads the data energy across a broader frequency spectrum, making it more robust against narrowband interference and transient corruption. At the receiving end, demodulation recovers the original data with improved reliability.
Solution Approach 2:
The patent employs feedback mechanisms in the form of error detection and correction codes embedded in the modulated signal. The transmitted data includes redundancy that allows the receiving circuit to detect and correct errors caused by common mode transients. This feedback approach maintains data transmission accuracy even when high frequency transients are present during circuit operation.
3Device complexity
If a single differential capacitive channel is used for isolation, then device complexity is reduced, but the system cannot distinguish between parasitic noise and actual data state transitions
Solution Approach 1:
The patent uses periodic carrier wave modulation to encode data transitions. By modulating the carrier frequency or amplitude according to the data, the system creates distinct periodic patterns that are easily distinguishable from random parasitic noise. The regularity and predictability of the modulated carrier allow simple threshold-based detection to reliably distinguish actual data transitions from noise, maintaining measurement precision with a single differential channel.
Solution Approach 2:
The patent changes the parameter representation of digital data from direct voltage levels to modulated carrier characteristics (amplitude, frequency, or phase). This parameter transformation allows the system to encode data in a form that is more resilient to noise. The modulated parameters create larger, more distinct signal variations that exceed the noise floor, enabling reliable noise discrimination without increasing device complexity.
4Reliability
If additional demodulation circuits are added to handle modulated signals, then data transmission reliability is improved, but device complexity and delay increase
Solution Approach 1:
The patent replaces complex analog demodulation circuits with simpler digital signal processing approaches. Instead of using traditional analog envelope detectors or frequency discriminators that require multiple components and precise tuning, the system uses digital logic circuits to detect and decode the modulated signal. This substitution reduces device complexity while maintaining or improving reliability through the robustness of digital processing.
Solution Approach 2:
The patent uses simplified demodulation techniques that create a direct copy or replica of the original data signal from the modulated carrier. By using envelope detection or frequency discrimination followed by simple digital logic, the system recovers the original data with minimal processing steps. This copying approach avoids the need for complex multi-stage demodulation circuits, reducing device complexity while maintaining data transmission reliability.
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 solution achieves reduced delay and high-performance digital signal transmission with improved robustness against parasitic noise, minimizing the risk of fatal failures and maintaining low jitter, compatible with fast digital inputs and requiring only a single differential channel.
Implementation Method 1
Capacitive isolation links usually make use of a dielectric in order to block direct current between isolated circuits sections of the electrical circuits or to block lowest-frequency currents between the circuits sections while allowing transfer of a higher frequency data signal
Implementation Method 2
Capacitive isolation links usually make use of a dielectric in order to block direct current between isolated circuits sections
Data Source
AI summary
The invention relates to a digital isolator comprising a logic module (20) for receiving an input signal D, and providing command signals (41, 42) to sawtooth modulators. A first sawtooth modulator provides a first sawtooth signal at a node A1 comprising a fast rising edge triggered by a rising edge of a control signal, followed by a slow falling edge, when D equals 1 and comprises a fast falling edge triggered by a rising edge of a control signal, followed by a slow rising edge, when D equals 0. A second sawtooth modulator provides a second sawtooth signal at node A2, inverted with respect to first sawtooth signal. Isolation capacitors (61, 62) are connected to nodes A1 and A2 and are used as isolation barrier and as part of a high-pass filter together with dipoles Z1 and Z2. Threshold comparators (121, 122) provide the output signals S and R. Based on these S and R output signals, the input signal D referred to ground G1 can be regenerated versus a ground G2 using for example SR logic gate, low pass filters or peak detectors.