A cell-based 5-MHz on-chip clock generator for smart sensing applications is presented. By exploiting relative reference modeling, our proposed design can dynamically track both voltage and temperature variations after four-point chip calibrations. The proposed on-chip clock generator is fabricated using a 90-nm CMOS process, the frequency stability is 160 ppm/$^{\circ}$C and 72 ppm/mV over 0 $^{\circ}$C to 75 $^{\circ}$C and 0.9 V to 1.1 V, and the settling time of the proposed on-chip clock generator is 5.12 $\mu$s. The proposed on-chip clock generator was implemented with standard cells that can greatly reduce the design complexity and design time for on-chip oscillators.