In this article, the architectural choices and design of a fully integrated integer-N frequency synthesizer operating in the 902–928 MHz Industrial, Scientific and Medical (ISM) band is presented. This frequency synthesizer, optimized for ultra-low power operation, is being integrated in the transceiver of an implantable wireless sensing microsystem (IWSM), which is dedicated to in vivo monitoring of biological parameters such as temperature, pressure, pH, oxygen, and nitric oxide concentrations. This phase-locked loop-based synthesizer includes a 1.830 GHz LC voltage-controlled oscillator (VCO) using a 10 nH on chip inductor. Varactors are implemented using P+ in N-well diodes for their linearity and high quality factor. The transistors of the VCO are operated in moderate inversion, and their bias point was chosen using the g _m/I _d design methodology. The output of the VCO, operating at twice the ISM frequency band, is divided by 2 to generate differential, quadrature versions of the carrier. Power minimization of the programmable divider was achieved by designing the latches and flip-flops using appropriate circuit techniques such as True Single Phase Clocking (TSPC) and first-type Dynamic Single Transistor Clocking (DSTC1) depending on their operating frequency. The power consumption of the proposed synthesizer is 580 μW under 1 V; almost an order of magnitude lower compared to that of recent synthesizer designs having a similar architecture.