Crossing Boundaries with SIM Cards in IoT Devices
Pulse
Octopart Staff
Sep 9, 2020

When I pick up my phone, a SIM card is probably the last thing I think about. Most people outside the telecom industry probably don’t know much about these pieces of plastic. In the simplest sense, a SIM card helps a telecom carrier identify your phone once your phone passes in range of a cell tower. These cards are important as they provide devices with a unique identity, which can then be linked back to your mobile phone plan and your billing account. IoT engineers care more about the former, while telecoms (unsurprisingly) care more about the latter.

There are already some components you’ll need to add if you want your next IoT product to have cellular capabilities. Using a SIM card for IoT devices to gain access to cellular networks provides some advantages over cellular-capable devices without SIM cards. There are some other components you’ll need in order to access data from a SIM card for use with local carriers. Take a look at our short list of the essential components you’ll need if you want to use a SIM card in your next IoT product.

UICCs and SIM Cards for Carrier-Agnostic IoT Devices

To understand the context behind this discussion, one should note the current class of subscriber identity module (SIM) cards is known in the industry as universal integrated circuit cards (UICC). The related universal SIM (uSIM) is a logical module for accessing  Everyone I’ve talked to in the industry uses SIM, uSIM, and UICC almost interchangeably, but I’ll try to provide sufficient distinction here.

In the recent past, your SIM card was used to tie your handset exclusively to a specific mobile network operator (MNO, like Verizon), or a mobile virtual network operator (MVNO, basically a sub-network on a larger carrier). You could swap your SIM card into a new phone with ease (such as with AT&T phones), and your subscriber information would be linked to the new phone. It’s a pretty simple concept, but it was a pain if you ever wanted to change up subscriber/carrier information for a particular handset. You needed to swap out a SIM card in the device for one that was linked to your new carrier, or you had to hope your handset supported remote provisioning.

Recent advances changed this dynamic: UICCs as mentioned above and virtual SIM. UICCs are as close as you can get to carrier-agnostic SIM cards. Key credentials required to access multiple carriers are written onto a standard SIM card. In a UICC, access is chosen at the software or firmware level, and access is validated at the carrier level. In virtual SIM, there is no physical SIM card; everything is stored and controlled on the cloud. This has led to the creation of cloud-based MVNOs.

Nano SIM cards are ideal for IoT products that require cellular services.

Despite the availability of newer MVNO services, they haven’t seemed to have caught on in the IoT space because these cloud-based MVNOs are basically reselling telecom access. Developers can go straight to the primary carrier and get mobile access for a discount.

Going the old-fashioned route and sticking with a physical SIM card provides a few benefits for IoT ecosystem developers:

  • Easily swap cards between devices. You don’t need to go through an application layer or directly contact your virtual SIM provider to move service between devices. Simply pull the SIM from one device and place it into another.

  • Greater support for physical UICCs. Currently, there is still greater support for physical SIM cards in terms of network coverage.

  • 5G compatible. If you’re going to operate on a 5G network, UICCs are forward compatible.

  • Backup for embedded SIM. Some wireless modems have an embedded SIM inside the module (called eSIM, or SIM-on-chip by some component manufacturers). You can expand your connectivity options with an analog switch (see below) for interfacing with an additional SIM.

The primary drawbacks of using a discrete SIM card and other components are larger board space and lack of remote provisioning from providers.

Component Options for SIM Cards in IoT Devices

If you want to work with a SIM card in your next IoT device, there are a number of components you’ll need to interface with the card and pull data from it as needed. Here are some options for your next IoT product.

Semtech, ECLAMP2465T

With industrial IoT concepts and designs increasing in popularity, the ECLAMP2465T EMI line filter from Semtech is a recommended component for ESD/EMI protection on clock, I/O, reset, and power lines for SIM cards. This component provides ESD protection meeting IEC 61000-4-2 Level 4 standards up to ±18 kV (air) and ±10 kV (direct contact). This IC includes an additional TVS diode on the VCC bus for additional ESD protection.

ECLAMP2465T EMI line filter schematic with termination resistors. From the ECLAMP2465T datasheet.

ON Semiconductor, FSA2567MPX

The FSA2567MPX from ON Semiconductor is a low-power analog switch for interfacing with two SIM cards in a single system. Dual SIM card systems give you flexibility to switch between multiple sets of credentials. This component was first released around the same time as the first smartphones, but it is still a recommended analog switch for interfacing with general-purpose I/Os in the device’s baseband processor. This IC provides low input capacitance on data lines (10 pF) with low power consumption (1 μA max) and at least 160 MHz bandwidth (-3 dB).

The FSA2567MPX provides low crosstalk with high gain up to ~100 MHz bandwidth. From the FSA2567MPX datasheet.

Infineon, SLM 97 Series

IoT products need to be secure, and the SLM 97 series of security modules from Infineon provides a range of industrial-grade solutions. Applications for these components include eCall, industrial IoT, V2X, smart infrastructure, and related areas. These modules communicate via standard interfaces (I2C, SPI, ISO 7816, GPIO, SWP) with AES 128/256 encryption.

Infineon provides a portfolio of solutions for embedded system security aimed at IoT products.

Other Components for IoT Products with SIM Cards

Mobile IoT products will need a number of other components for communicating on cellular networks and other protocols beyond SIM cards. Cellular modems include the interfaces you need to communicate with a card, but other components include:

No matter what type of IoT product you want to design, you can find the SIM cards for IoT devices and other components with the advanced search and filtration features in Octopart. When you use Octopart, you’ll have a complete solution for sourcing and supply chain management. Take a look at our integrated circuits page to start searching for the components you need.

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