Back to Basics: eSIMs in Vehicles

Posted under Back to Basics, Educational, Tech Explained on September 7th, 2025 by

Most of you who have used an EV or any connected vehicle already know it talks to the cloud. In our cars and scooters, the internet usually comes from an embedded eSIM inside a telematics box. A tiny chip that is usually soldered. Let’s discuss that today.

This is not a personal SIM like your phone. In India, it is an M2M(Machine to Machine) eSIM managed by the manufacturer or its M2M service provider. They buy data in bulk and bundle it in your plan. Technically, no separate Jio/Airtel bill you pay monthly. Your app works because the eSIM authenticates with a telecom profile that the backend pushes over the air.

Who controls those profiles? Not you. The OEM or its M2M provider does. They talk to two GSMA defined servers. One prepares operator profiles. Another installs and activates them on the eSIM. The big 2025 change launched by Govt is the interop. If an OEM asks, its server must integrate with any Indian operator’s profile server within three months. If needed, the OEM can move control of your eSIM to a different server within six months. That gives OEMs leverage.

What does this mean in practice? Owners benefit from fewer long lock ins. If coverage is weak in a region, the OEM has a formal path to add a new operator profile at scale. If an eSIM platform underperforms, the OEM can migrate. You still cannot pop in your own SIM. That is by design. It keeps security and KYC consistent with machine tracking and logs. If your connected pack lapses, you usually keep local features like Bluetooth. Just the cloud features die. I really hope Govt comes up with some data privacy standards for this communication. Because currently you don’t know what data from your vehicle is sent back to OEM servers with data traceable back to you.

BTW: The SIM inside many connected vehicles in India does not use the usual 10 digit format, they follow a dedicated 13 digit numbering scheme for traceability and scale. Pretty neat for something you never see while using your vehicle.

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Back to Basics: Sample/Track and Hold Amplifiers

Posted under Back to Basics, Educational, Tech Explained, Technology on August 31st, 2025 by

Last week we went into details of ADC and how source impedance can effect timing. Now there will be cases where you are looking to sample two independent signals, say bio-med signals, on 2 separate analog channels on an MCU with a single ADC.

With a time-multiplexed SAR ADC, the internal sampling capacitor first charges from channel A. The mux flips to channel B. If the source is not low impedance or acquisition time is short, some charge from A rides into B. You see a ghost voltage of the previous channel. One fix is to wait after each switch so it settles. That reduces ghosting, but it creates timing skew between channels. Meaning it’s non-time synchronised.

Track and hold Amplifier

Sometimes this skew is not acceptable. In bio-med you might want ECG and PPG at the same instant. This is where sample or track-and-hold stages help. You place a T/H per channel and drive all holds with one edge. In track the output follows the input. On hold the switch opens, a small capacitor freezes the value, and a buffer drives the ADC. The ADC then converts sequentially, but the samples come from the same instant.

There are few parameters to keep in mind while selecting one, Aperture delay and Jitter set the exact instant you grab the signal. Lower jitter means cleaner SNR and less channel-to-channel timing error. Droop is how the held voltage slowly sags because of leakage. Too much droop changes readings. Hold step is the small jump when the switch opens due to charge injection. Big steps look like offsets or spikes. I usually aim for low jitter, low droop, and small hold step, so both channels look clean and truly simultaneous.

So next time when you want absolutely 2 signals at the same time look into sample and hold Amplifiers. TI and Analog devices have a few in their portfolio.

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