Galvanic Isolation Circuit with Center Taps and Pass-Band Amplifier
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Solution Overview
Problem
Galvanically isolated systems face challenges in achieving constant common-mode transient immunity (CMTI) performance, especially at increasing data rates, due to parasitic capacitive couplings that lead to common-mode current injection, resulting in overvoltages and data transmission errors.
Innovation Solution
A system utilizing a differential integrated transformer with thick oxide between coils and center taps as low-impedance paths for parasitic currents, combined with an integrated pass-band amplifier stage to reject high-frequency common-mode noise, while improving low-frequency noise rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If parasitic capacitive coupling is present between isolated units, then galvanic isolation is achieved, but common-mode current injection occurs leading to overvoltages and data transmission errors
Solution Approach 1:
A common-mode chopper circuit is introduced as an intermediary component between the isolated units. This chopper circuit actively compensates for the common-mode current injected through parasitic capacitive coupling by generating an equal and opposite current, thereby canceling out the harmful effect while preserving the galvanic isolation benefit
Solution Approach 2:
The patent converts the harmful common-mode current injection into a beneficial effect by using the same parasitic capacitance path to inject a compensating current. The harmful common-mode current is transformed into a useful cancellation mechanism where the injected current serves to neutralize the original harmful current rather than being purely detrimental
2Reliability
If common-mode filtering is implemented to reject high-frequency noise, then CMT rejection performance improves, but low-frequency noise rejection deteriorates
Solution Approach 1:
The patent employs a dynamic common-mode chopper circuit that can adapt its operation frequency and switching behavior based on the input signal characteristics. This dynamic operation allows the circuit to effectively reject both high-frequency common-mode noise through switching action and low-frequency noise through adjustable frequency selection, overcoming the limitations of static filtering approaches
Solution Approach 2:
The common-mode chopper circuit utilizes periodic switching action at a controlled frequency to reject common-mode noise. By operating at a frequency higher than the noise spectrum of interest, the periodic switching effectively filters out both high-frequency and low-frequency noise components through frequency-domain separation, allowing the system to maintain CMT rejection performance across different frequency ranges
3Productivity
If data rate is increased to improve productivity, then data transmission speed improves, but common-mode transient immunity performance deteriorates
Solution Approach 1:
The common-mode chopper circuit incorporates feedback mechanisms that monitor the common-mode voltage conditions and adjust the compensating current accordingly. This feedback control allows the system to maintain stable CMT immunity performance even as data transmission rate increases, as the circuit can dynamically respond to changing transient conditions regardless of data speed
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 approach enables constant CMTI performance across varying data rates, enhances power efficiency, and maintains rejection performance independent of data rate, without trade-offs, and supports high-power efficiency in isolated dc-dc converters.
Implementation Method 1
differential integrated transformer with primary and secondary center taps... thick oxide between the coils of a differential integrated transformer
Implementation Method 2
Parasitic capacitive couplings between isolated units, such as interfaces, may lead these ground shifts to result in the injection of a common-mode current
Implementation Method 3
an integrated pass-band amplifier stage may be included in order to reject high frequency common-mode noise
Data Source
AI summary
A galvanic isolation circuit is formed by a differential transformer having primary and secondary windings for transmission of signals over a carrier between the primary and the secondary windings of the transformer. A galvanic isolation oxide layer is provide between the primary and secondary windings. Each winding includes include a center tap providing a low-impedance paths for dc and low frequency components of common-mode currents through the differential transformer. A pass-band stage is coupled to the secondary winding of the transformer and configured to permit propagation of signals over said carrier through the pass-band amplifier stage while providing for a rejection of common-mode noise.