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 jitter, often requiring complex modulation and demodulation processes that increase circuit size and introduce integration limitations.
Innovation Solution
A digital isolator design using sawtooth signals transmitted through differential channels with controlled edge transitions, employing sawtooth modulators and threshold comparators to ensure robust data transmission with reduced jitter and delay, eliminating the need for PWM or OOK modulators and FSK demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional isolators using magnetic transformers or capacitive isolators are used, then galvanic isolation is achieved, but the isolators occupy large area and consume excessive power
Solution Approach 1:
The patent replaces conventional magnetic transformer-based isolation mechanisms with a digital signal processing approach using sawtooth modulators and capacitive coupling. This substitution eliminates the need for large magnetic cores and reduces power consumption while maintaining isolation functionality through digital signal regeneration on the isolated side
Solution Approach 2:
The invention changes the operating parameters from analog magnetic transformation to digital signal modulation using sawtooth waves. By modulating digital signals onto sawtooth carriers and using capacitive coupling with controlled impedance networks, the system achieves isolation with significantly reduced power consumption and smaller footprint
2Reliability
If conventional isolators are used, then galvanic isolation is achieved, but they occupy large area
Solution Approach 1:
The patent replaces bulky magnetic transformer structures with planar capacitive isolation elements and digital signal processing circuits. This substitution dramatically reduces the physical area required while maintaining galvanic isolation through capacitive coupling and digital signal regeneration
Solution Approach 2:
The isolated side circuitry is designed to perform multiple functions: it detects the capacitive-coupled digital signals, regenerates them using logic circuits, and simultaneously provides galvanic isolation. This multi-functionality reduces the overall area by eliminating dedicated components for each function
3Reliability
If high-pass filters with large time constant are used for isolation, then isolation performance is improved, but signal transmission delay increases
Solution Approach 1:
The patent uses periodic sawtooth wave modulation to transmit digital signals through the capacitive isolator. This periodic action allows the use of smaller time constants in the high-pass filters while maintaining signal integrity, as the regular waveform structure provides sufficient signal levels for reliable detection and regeneration
Solution Approach 2:
The isolated side circuitry creates accurate copies of the original digital signals by detecting the capacitive-coupled sawtooth-modulated signals and regenerating them using logic circuits. This copying process compensates for signal degradation and allows the use of faster, lower time-constant filters without increasing transmission delay
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 provides reliable digital signal transmission with minimized delay and jitter, enhancing integration capabilities by simplifying the circuit design and reducing the risk of fatal failures due to parasitic signals.
Implementation Method 1
two isolation capacitors C1 and C2 connected in series between a first ground G1 and a second ground G2
Implementation Method 2
A first sawtooth modulator STM1 provides a first sawtooth signal at a node A1 comprising a fast rising edge triggered by a rising edge of a clock signal, followed by a slow falling edge, when D equals 1
Data Source
Figure 1~2
Figure 3a~3b
Figure 4
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 STM1 provides a first sawtooth signal at a node A1 comprising a fast rising edge triggered by a rising edge of a clock signal, followed by a slow falling edge, when D equals 1 and comprises a fast falling edge triggered by a rising edge of the clock signal, followed by a slow rising edge, when D equals 0. A second sawtooth modulator STM2 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.