As CMOS technology scales down, digital supply voltage and digital power consumption goes down. However due to dynamic range limitations, power supply and power consumption of the RF front-ends and analog sections do not scale in the same fashion. In fact, in scaled systems, the RF section of a wireless transceiver consumes more energy than the digital part. For better understanding of the design trade offs, we first develop an accurate and comprehensive energy model for the analog front-end of wireless transceivers. Next, we evaluate a single user point-to-point wireless data communication system and a multi-user CDMA based system with respect to RF front end energy consumption and communication quality. We demonstrate the effect of occupied signal bandwidth, peak-to-average ratio (PAR), symbol rate, constellation size, and pulseshaping roll-off factor on single user system, and the effect of number of users and multiple access interference (MAI) on CDMA based multi-user system. For a given quality specification, we show how the energy consumption can be reduced by adjusting one or more of these parameters.