For the next generation of low-cost, battery operated, wireless IoT products, the design goal is to provide exceptional RF signal range and stability, while also reducing power consumption, in a miniaturized package. As a result, RF chipset and component manufacturers are increasingly fine-tuning and improving their products to do just that.
According to Semtech, LoRa® and LoRaWAN® are already the “de facto technology for Internet of Things (IoT) networks worldwide,” and these technologies will provide long-range connectivity for a variety of IoT applications, including next-generation “smart” medical devices.
To accomplish this PCB effective-area reduction task, chipset manufacturers like Semtech create reference designs — technical blueprints of a system — that third parties can adapt and modify as required for their products’ applications.
The reference design serves as proof of the platform concept and is usually targeted for specific uses. The goal is to fast-track products to market by using Johanson’s front-end solutions, thereby reducing risk in the OEM’s integration project.
“The starting point is the chipset, but the chipset requires specific RF circuitry to connect to the antenna,” explains Manuel Carmona of Johanson Technology, a developer of high-frequency ceramic components, including chip antennas, integrated filters/baluns, High Q capacitors, and EMI chip filters.
For the LoRa® platform, specifically, the ability to integrate all of the RF components into a much smaller, low-profile package would only increase the attractiveness of the chipset for miniaturized, battery-powered IoMT products. Without this option, medical OEM’s would have to design the entire capacitor/inductor scheme and mount many separate components onto the printed circuit board.
“Medical OEMs now have the option to utilize the integrated solution as opposed to the inductor and capacitor discrete solution. Using a Johanson integrated passive device (IPD) makes the final PCB size smaller and simpler,” explains Carmona. “Also, any changes in the geometry of the layout can affect the output performance, battery life and signal range.”
In this case, the RF circuitry required is used to convert the signal from differential to single-ended in a specific impedance ratio using an impedance matching network and a balun. Most chipsets require this type of conversion due to the differential, two pin input/output configuration to connect with the single-ended antenna.
“For many chipsets, the output straight out of the chipset is usually not matched to 50 Ω, which requires one to have an impedance matching network that must be designed in order to avoid loss of power signal, reduced battery life, and decreased signal range,” says Carmona.
To meet the requirements, Johanson Technology collaborated with Semtech to develop an IPD that serves as an impedance-matched-balun-filter.
Manufactured using low-temperature cofired ceramic (LTCC) technology that allows the passive components to be layered three-dimensionally, IPDs deliver the same functionality as 10–40 individual RF components. With this approach, the entire front end between the chipset and the antenna is manufactured in a single, ultra-low-profile package that is less than 40 percent the total size of the same circuit comprised of discrete components.
With this device, which combines an impedance matching network, balun, and a filter, the entire front-end RF circuitry is reduced to a single EIA 0805 (2.0 × 1.25 mm) SMT component. The impedance-matched balun-filter is designed to operate within the license-free 868 MHz RF band used in Europe and the 915 MHz band in Australia and the Americas. The product pairs seamlessly with Semtech’s LoRa ® and LoRa Smart Home™ RF transceivers SX1261, SX1262, and LLCC68.
IPDs deliver another significant benefit: increased reliability. By creating a literal circuit within a small LTCC package, variability and potential points-of-failure are all but eliminated when compared with mounting many discrete components.
According to Carmona, material development is the key to being able to create the entire circuit in such a small package. The product utilizes a novel proprietary ceramic material in an LTCC manufacturing process designed to improve performance to High-Q levels.
The process to manufacture IPDs is similar to the technology already used to create multi-layer SMD component parts such as capacitors and inductors. However, LTCC manufacturing allows the circuits to be embedded in as many as 40 separate layers in a three-dimensional package that is still very low profile. Because IPDs require much less board space, IoT devices with RF circuitry can be designed in much smaller form factors.
“With PCB real estate at a prime, the size and placement of the passive components are critical because as everything gets smaller it becomes increasingly difficult to place more components on the board,” explains Carmona. “Therefore, design engineers are looking to component manufacturers to deliver miniaturized solutions that occupy next to no real board space.”
Beyond size, a smaller PCB can also impact the aesthetics of a product, allowing for slim, low profiles. The elimination of components on a 10:1 or greater basis also reduces the overall weight of devices, even if that savings is measured in tenths of grams.
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