Embedded Bandpass Filter Galvanic Isolator for High-Frequency Radar
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Solution Overview
Problem
Existing intrinsic safety circuits using known capacitors and zener diodes introduce attenuation and distortion in non-contact radar systems operating at frequencies above 10 GHz, making them unsuitable for reliable RF signal transmission, and require large physical areas for capacitors, which is impractical.
Innovation Solution
A printed circuit board (PCB)-based embedded bandpass filter with gaps in a microstrip line provides distributed capacitance and impedance, forming a bandpass filter that isolates and filters out frequencies outside the carrier frequency range, used as a galvanic isolator between the RF output of the transceiver circuit and the antenna in tank gauging systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If known capacitors and zener diodes are used for intrinsic safety circuits, then galvanic isolation and safety protection are achieved, but the RF signal experiences attenuation and distortion at frequencies above 10 GHz
Solution Approach 1:
The patent changes the electrical parameters of the isolation circuit by using a bandpass filter design that is specifically tuned to pass RF signals above 10 GHz with minimal attenuation. The filter's frequency response is optimized to maintain signal integrity while providing galvanic isolation, resolving the contradiction between safety protection and signal quality.
Solution Approach 2:
The patent replaces the traditional discrete component approach (capacitors and zener diodes) with an integrated bandpass filter structure implemented on a PCB. This substitution creates a more suitable electrical pathway for high-frequency RF signals while maintaining the galvanic isolation function, thereby preserving signal integrity.
2Reliability
If known capacitors are used to provide capacitance for intrinsic safety, then safety isolation is achieved, but the physical area required becomes too large to be practical
Solution Approach 1:
The patent merges the capacitance function with the bandpass filter structure. The distributed capacitance is provided by the gaps in the microstrip line that form part of the filter's resonant structure. This integration eliminates the need for separate discrete capacitors, significantly reducing the physical area while maintaining both safety isolation and RF signal transmission capabilities.
Solution Approach 2:
The patent changes the capacitance implementation from discrete component values to distributed capacitance through the microstrip line gaps. This parameter change allows the capacitance to be provided by the geometric dimensions of the filter structure itself, reducing the overall area requirement while achieving the same electrical function.
3Reliability
If zener diodes are used for voltage limiting in intrinsic safety barriers, then open circuit voltage is limited to safe levels, but the equivalent junction capacitance acts as a low pass filter at carrier frequencies
Solution Approach 1:
The patent extracts the voltage limiting function from the zener diode and implements it through the bandpass filter's frequency-selective characteristics. The filter naturally attenuates frequencies outside its passband, including low-frequency noise and transients, while allowing the high-frequency RF carrier to pass through with minimal distortion, thereby removing the low-pass filtering effect that zener diodes introduce.
Solution Approach 2:
The patent changes the voltage protection mechanism from zener breakdown voltage clamping to frequency-based signal filtering. The bandpass filter's passband is centered on the RF carrier frequency, allowing rapid signal switching and modulation to pass through unchanged while blocking lower frequency disturbances, thus preserving signal speed and integrity.
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 effectively passes RF signals at the carrier frequency while blocking other frequencies, ensuring reliable and safe RF signal transmission in hazardous environments, reducing size and maintaining signal integrity, and providing effective galvanic isolation for explosion-proof and intrinsic safety requirements.
Implementation Method 1
gaps in an embedded microstrip line to provide a distributed capacitance that together with the microstrip line impedance provides a BP filter
Implementation Method 2
Disclosed filters are placed between the RF output of the transceiver circuit and the process connector that is connected to the antenna in the tank. Disclosed BP filters thus pass RF signals only at or near the carrier frequency, and isolate or filter out all other frequencies that lie outside the passband of the BP filter.
Implementation Method 3
Galvanic isolation isolates functional sections of electrical systems to prevent direct current flow by breaking the direct current path. Energy or information is instead exchanged between the galvanically isolated sections by non-direct connections, such as capacitive, inductive (transformers), electromagnetic waves, optical, acoustical or mechanical arrangements.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A galvanic isolator (100) includes a multi-layer printed circuit board (PCB) (105) including a dielectric material (108) having a top side (108a) and a bottom side (108b). An RF transmission line (125) is embedded within the PCB including a plurality of conductor traces (125a, 125b, 125c) spaced apart from one another to include a plurality of gaps (G1 and G2) in a path of the RF transmission line to provide an inline distributed capacitor that together with an impedance of the RF transmission line (125) forms a bandpass (BP) filter. A top metal layer (120) is on the top side and a bottom metal layer (110) on the bottom side connected to one another by a plurality of metal filled vias (115) on respective sides of the RF transmission line. The top metal layer (120) and bottom metal layer (110) each also include at least one gap.