Breaking down the sensor path

EDN has an excellent article about a recently emerging trend in consumer electronics: The insertion of analog electronics in traditionally digital devices. One example is the accelerometer in Apple's wildly popular iPhone--the accelerometer is an analog device whose signal is first digitized and then amplified and filtered.

You must digitize a sensor's analog signal so that the system can use it, and the signal path goes through amplification, filtering, and digitization stages. Each stage usually involves a component with passives around it to perform properly for an application. Once you digitize the signal, you can pass it to a control system on the microcontroller or massage the data and pass it to a host processor through a communication protocol. The protocol can use the sensor data as necessary.

You should check out the rest of the article because it offers an excellent, detailed run-down of the entire process.