This paper develops simple system-level energy models for different kinds of transmitter implementations. Different communication protocols such as ASK, OOK, FSK, PSK are considered to evaluate the energy cost of both the architecture of the system as well as the electronic circuitry. These models are developed for the systems operating in the Medical Implant Communications Service frequency band. These models are useful for the optimisation of system and circuit parameters and provided some guidelines to choose the right modulation and circuit implementation for energy limited wireless transmitters.