Capacitive Isolated Link Using Frequency Mixing for High CMTI
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Solution Overview
Problem
Existing capacitive Galvanically Isolated Communication Links (GICLs) face challenges in achieving effective common mode transient immunity (CMTI) due to susceptibility to high-amplitude and high-slew-rate common mode transients, which can lead to false triggers and degraded system performance.
Innovation Solution
The proposed solution involves a frequency multiplier based capacitive GICL system that includes a first and second modulator to generate periodic signals with specific frequencies, an isolated differential channel with isolation capacitors, a mixer to produce a mixer output signal, a bandpass filter to filter out unwanted frequency components, and a detector to extract the data signal from the envelope of the filtered signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitive GICL is used for isolated communication, then galvanic isolation is achieved, but common mode transient immunity is degraded due to susceptibility to high-amplitude and high-slew-rate transients
Solution Approach 1:
The patent employs periodic carrier waves at different frequencies (first carrier wave and second carrier wave) for modulation. The modulated signals are transmitted through the isolated channel, and the periodic nature of these carrier waves enables the receiver to distinguish between legitimate modulated signals and transient noise through frequency-based detection, thereby improving common mode transient immunity.
Solution Approach 2:
The patent changes the frequency parameter by using two different carrier wave frequencies (f1 and f2) for the two modulated signals. This frequency differentiation allows the receiver to separate and identify valid data signals from common mode transients through frequency-selective detection, enhancing immunity against high-amplitude and high-slew-rate transients.
2Reliability
If isolation capacitors are used in the capacitive GICL, then galvanic isolation is achieved, but mismatched capacitors degrade system performance
Solution Approach 1:
By using periodic carrier waves with distinct frequencies and modulating them differently, the system creates unique temporal patterns for each signal path. Even if isolation capacitors are mismatched, the frequency-based modulation and detection scheme allows the receiver to identify and compensate for capacitor mismatches, reducing their impact on system performance.
Solution Approach 2:
The patent introduces asymmetry by using different frequencies (f1 ≠ f2) for the two carrier waves. This asymmetric frequency approach, combined with the differential modulation scheme, creates an unbalanced signal structure that is less sensitive to capacitor mismatch, as the receiver can differentiate between intentional asymmetric modulation and unintentional asymmetric effects from mismatched capacitors.
3Reliability
If frequency multiplication is implemented, then common mode transient rejection is improved, but device complexity increases due to additional modulators, mixers, and filters
Solution Approach 1:
The use of periodic carrier waves at different frequencies enables frequency-division multiplexing, where two independent modulated signals share the same communication channel. This approach improves transient rejection through frequency discrimination while managing complexity by efficiently utilizing the periodic nature of the carriers for signal separation at the receiver.
Solution Approach 2:
The mixer component performs multiple functions: it combines the two received modulated signals, generates sum and difference frequency components, and enables frequency conversion. This multi-functionality reduces the need for separate dedicated components for each processing step, thereby managing overall device complexity while achieving improved common mode transient rejection.
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 significantly improves the rejection of common mode transients and allows for easier implementation by mitigating the effects of mismatched isolation capacitors, thereby enhancing the system's ability to accurately detect and transmit data signals.
Implementation Method 1
a mixer configured to mix signals received from the first line and the second line of the differential channel and to produce a mixer output signal
Implementation Method 2
a bandpass filter connected to the mixer configured to filter the mixer output signal
Implementation Method 3
an envelope detector configured to detect an envelope of the filtered mixer output signal
Implementation Method 4
an isolated differential channel including isolation capacitors with a first line connected to the first modulator and a second line connected to the second modulator
Data Source
AI summary
A communication system, including: a first modulator configured to modulate a first periodic signal with a first frequency based upon an input signal; a second modulator configured to modulate a second periodic signal with a second frequency based upon the input signal; an isolated differential channel including isolation capacitors with a first line connected to the first modulator and a second line connected to the second modulator; a mixer configured to mix signals received from the first line and the second line of the differential channel and to produce a mixer output signal; a bandpass filter connected to the mixer configured to filter the mixer output signal; an envelope detector configured to detect an envelope of the filtered mixer output signal; and a detector configured to detect a data signal in the envelope of the filtered mixer output signal and to produce an output signal.