A 4 GHz, 100 kb/s FM-UWB transceiver for short-range communications in a body area network is presented. Two receivers and a transmitter use the same RF port with a fully-integrated matching network. The first receiver provides multi-user communication capability with up to 4 sub-carrier channels and a sensitivity of -68 dBm while consuming 550 mu W. The second receiver provides a low-power mode reducing the consumption to 267 mu W for a single channel with -57 dBm sensitivity. The two receivers provide good robustness against narrowband interferers and can tolerate a reference clock frequency offset of up to 8000 ppm eliminating the need for a quartz reference. The transmitter consumes 575 mu W while transmitting at an output power of -11.4 dBm. The transceiver was integrated in a 65 nm standard CMOS technology.