Broadband Isolation Coupler Using Split-Frequency Transformer Paths
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Solution Overview
Problem
Current signal coupling methods using isolating transformers and optocouplers face limitations in bandwidth, suffer from offset errors, and result in low signal-to-noise ratios, with modulation requiring frequencies double that of the highest signal component, wasting transformer bandwidth and being sensitive to production tolerances and time delays.
Innovation Solution
The solution involves splitting the input signal into high and low frequency parts, using separate isolating transformers for each, modulating the low frequency part with a rectangle or sinusoidal signal at a frequency lower than the transformer bandwidth, and employing a sample-hold device and low pass filters to compensate for time delays and improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire input signal is modulated with a rectangle signal at double the highest frequency component and transformed through a single transformer, then galvanic separation is achieved, but a large percentage of the transformer bandwidth is wasted and production tolerance significantly affects accuracy and signal-to-noise ratio
Solution Approach 1:
The input signal is divided into high frequency partial signal and low frequency partial signal using a frequency splitter. The high frequency partial signal is transformed directly through a first isolating transformer, while the low frequency partial signal is modulated with a rectangle signal and transformed through a second isolating transformer. This segmentation allows each transformer to operate within its optimal bandwidth range, improving both signal-to-noise ratio and bandwidth utilization.
2Manufacturing precision
If modulation frequency is chosen significantly higher than the low pass filter cut-off frequency to filter modulation products, then filtering is effective, but small time delays affect the transformation factor negatively and increase system ripple
Solution Approach 1:
A sample-hold device is introduced to capture and hold the instantaneous value of the modulated low frequency partial signal at the optimal sampling moment. This preliminary action freezes the signal at its peak value, compensating for time delays introduced by filtering and transformation. The held signal is then combined with the high frequency partial signal, ensuring accurate transformation factor and minimal ripple.
3Productivity
If a high frequency partial signal is transformed through an isolating transformer with high absolute and relative bandwidth, then bandwidth is maximized, but the low frequency partial signal requires modulation at frequencies that waste transformer bandwidth
Solution Approach 1:
The signal spectrum is segmented into high frequency and low frequency components. The high frequency partial signal (above the low pass filter cut-off frequency) is transformed directly without modulation, utilizing the full bandwidth capability of the first isolating transformer. The low frequency partial signal (below the cut-off frequency) is modulated to a higher frequency range suitable for transformation by the second isolating transformer. This segmentation ensures optimal bandwidth utilization for each transformer.
Solution Approach 2:
The frequency parameter of the low frequency partial signal is changed through modulation with a rectangle signal. This frequency transformation shifts the low frequency components to a range that can be efficiently transformed by the second isolating transformer, preventing bandwidth waste while maintaining signal integrity.
4Manufacturing precision
If synchronous demodulation is performed to compensate for time delays, then transformation factor accuracy is improved, but the system complexity increases and production tolerances still affect performance
Solution Approach 1:
The sample-hold device performs the compensation function in advance, capturing the signal at the optimal moment before time delays and filtering effects degrade the transformation factor. This preliminary sampling and holding action simplifies the overall system architecture compared to complex synchronous demodulation circuits, while achieving the same goal of maintaining accurate transformation factors despite production tolerances and time delays.
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 allows for high bandwidth and high signal-to-noise ratio coupling while reducing the impact of time delays and production tolerances, achieving efficient signal transformation with minimal phase errors and ripple in the frequency transmission function.
Implementation Method 1
transforming a signal derived from the high frequency partial signal with the help of a first isolating transformer
Implementation Method 2
modulating the low frequency partial signal with a modulation signal with at least double the frequency of the highest frequency component of the partial low frequency signal
Implementation Method 3
transforming a signal derived from the modulated low frequency partial signal with the help of a second isolating transformer
Implementation Method 4
The second low pass filter is set up for compensating an envelope delay of the filtered transformed low frequency partial signal
Data Source
AI summary
An isolation coupler comprises a frequency splitter (36) for splitting an input signal (1) into a low frequency partial signal (2) and a high frequency partial signal (4) and a first isolating transformer (33) for transforming a signal derived from the high frequency partial signal (4) in a transformed high frequency partial signal (5). Moreover it comprises a modulator (21) for modulating the low frequency partial signal (2) with a modulation signal (6) resulting in a modulated low frequency partial signal (7) and a second isolating transformer (34) for transforming a signal derived from the modulated low frequency partial signal (7) in a transformed low frequency partial signal (8).