The data carrier normally solely of a microchip and a coil. The code carrier is totally passive, i.e. it has no internal energy source..
The antenna consists of a coil and an electronic circuit to generate the antenna field and detect the field influence respectively the field radiated by the data carrier.
The reading unit evaluates the signals from the data carrier received by the antenna and modulates the radiated field of the antenna to communicate with the data carrier. In addition the reading unit communicates with the host system via a standard interface.