1. Purpose and scope
A sensor is only as good as the specification it was designed to. Motion sensors, pressure sensors, microphones, humidity, gas and temperature sensors, and image and light sensors each turn a physical quantity into a number that a customer's system will trust. The purpose of this stage is to write down exactly what that number must mean: its range, resolution and noise, its bandwidth or output data rate, its accuracy after calibration, its stability over temperature, time and stress, and the conditions under which each of these holds.
The stage is just as much about the environment as about the electrical specification. A pressure sensor in a wearable sees sweat and water, a microphone sees dust and sound pressure spikes, an inertial sensor in a vehicle sees shock, vibration and a wide temperature range for many years. The environmental and mission profile records these conditions so the transducer, the package and the qualification plan can be built around them. The stage also lists the standards the sensor must meet: its host interface, such as I2C, MIPI I3C or SPI, its qualification grade, and environmental, materials and export rules.
In scope: the application use case list, the sensor requirements specification, the environmental and mission profile, a first system error budget, the compliance and interface standards list, the first process capability summary and a sensor business case good enough to fund definition. Out of scope: choosing the transduction principle and structure, which belongs to Transducer & Process Co-design, and committing the full development investment, which happens at the Sensor development commit.
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