Digital Isolator Demodulator Circuit for Low-Delay Signal Detection
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Solution Overview
Problem
Conventional isolation channels experience substantial propagation delay and asymmetric propagation delay during demodulation of signals, which affects the reliability and efficiency of communication across isolation barriers, particularly in applications with large voltage differences and transient conditions.
Innovation Solution
A receiver signal path that includes a high pass filter to center differential signals around a common mode voltage, followed by a demodulator with a differential stage and an extremum selector circuit to remove the carrier signal and generate a logic signal based on a predetermined threshold, thereby reducing propagation delay and duty-cycle distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional demodulator techniques are used, then the demodulation function is achieved, but substantial propagation delay and asymmetric propagation delay occur
Solution Approach 1:
The patent implements dynamic signal routing using switch elements that can rapidly transition between different signal paths based on the received signal state. The differential stage dynamically selects between direct signal paths and demodulated signal paths, enabling the system to adapt to different signal conditions and minimize propagation delay while maintaining reliable demodulation functionality.
Solution Approach 2:
The demodulator is divided into separate functional stages: a differential stage for initial signal processing and an extremum selector circuit for final demodulation. This segmentation allows each stage to be optimized independently, with the differential stage handling high-speed signal differentiation and the extremum selector performing threshold-based logic generation, thereby reducing overall propagation delay.
2Reliability
If conventional demodulator techniques are used, then the demodulation function is achieved, but asymmetric propagation delay occurs
Solution Approach 1:
The patent employs asymmetric signal path design where the differential stage uses unequal weighting for positive and negative signal components. By applying different gain factors to the differential inputs and using asymmetric threshold comparison in the extremum selector, the circuit compensates for inherent asymmetries in the isolation channel, thereby reducing duty-cycle distortion while maintaining signal integrity.
Solution Approach 2:
The extremum selector circuit incorporates feedback mechanisms that monitor the output signal characteristics and adjust the threshold levels dynamically. This feedback allows the system to compensate for asymmetric propagation delays by adjusting the decision thresholds based on observed signal behavior, thereby improving duty-cycle accuracy without compromising signal integrity.
3Measurement precision
If a complex demodulator design is used to improve demodulation accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the essential demodulation function into a dedicated extremum selector circuit that operates independently from the main signal path. By separating the demodulation logic from the amplification and filtering functions, the design achieves high demodulation accuracy through specialized circuitry while keeping the overall device complexity manageable through functional modularity.
Solution Approach 2:
The patent replaces complex mechanical or analog demodulation mechanisms with a streamlined electronic differential stage followed by a digital-like extremum selector. This substitution uses simple voltage comparison and switching operations instead of complex analog modulation/demodulation circuits, achieving high precision with reduced component count and lower overall circuit complexity.
Data Source
AI summary
A receiver signal path includes a high pass filter that centers a received differential pair of signals around a common mode voltage to generate a centered received differential pair of signals. The receiver signal path includes a demodulator that removes a carrier signal from the centered received differential pair of signals to generate a demodulated signal and generates a logic signal based on the demodulated signal and a predetermined threshold signal. The demodulator includes a differential stage including an extremum selector circuit that generates the demodulated signal based on the centered received differential pair of signals. The demodulated signal corresponds to a mean level of the rectified version of the centered received differential pair of signals. The differential stage includes a second circuit that provides the reference signal based on the predetermined threshold signal. The logic signal is based on a comparison of the demodulated signal to the reference signal.