Log amps are suited for such applications because of their ability to detect varying signals over a very large dynamic range. A signal's dynamic range is dependent on variables such as its distance from the receiver. In an automotive toll tag application the signal coming from the toll tag in the car very rapidly changes from a small voltage to a high voltage as the car passes through the toll booth. This 1000x variation in voltage combined with the need to measure rapid signal bursts (< 40 ns) requires a log amp with a wide dynamic range and fast response time.
The AD8310 is available in a micro-SOIC package. Evaluation boards and technical support are also available.