Tagged biosignal
4 pieces
- · 7 min read
The Physical Ceiling: What No Model Can Recover From Your Sensor
Whatever your sensor and that first little circuit throw away is gone. You cannot get it back later with software. A photo that comes out blurry does not become sharp with editing, and the fancy tools that appear to sharpen it are inventing plausible detail rather than recovering real detail, which is exactly the distinction that matters when the output drives a decision about a person.
- · 8 min read
The Driven Reference Electrode: Your Front End's Hero and Its Hidden Risk
The third electrode is a feedback loop wrapped around a person. It senses the body's common mode and drives against it, which is what turns a hope about electrode symmetry into an actively regulated quantity and gives you rejection figures worth quoting. It is also a deliberately low-impedance connection between your circuit and the body, which makes it a stability problem, a safety-limited path, and the exact node any injected current will come home through.
- · 7 min read
Common Mode Rejection: How a Biosignal Front End Hears a Whisper at a Concert
When you measure off a body you are not measuring your signal. You are measuring your signal plus the person plus the room, all summed at the amplifier, and the thing you want is microvolts while the mains hum coupling into the person can be a thousand times larger. The entire job of the front end is pulling the small thing out from under the large thing, by throwing away everything that appears equally on both inputs.
- · 16 min read
The Return-Path Bug That Kills Your Biosignal Front End
On a closed-loop bio device, the instant you turn the actuator on, the signal can vanish to a flat line, and it is not coupling. The current you inject is a loop that has to come home, and it takes the lowest-impedance path, often the exact electrode protecting your front end. It forces a voltage the amplifier cannot reach, the amplifier rails, and your sensor goes blind. The fix is a decision about where the current returns, not a better part.