This paper presents a low-power and fast start-up crystal oscillator (XO) operating at 48 MHz. To reduce the start-up time (Ts) required to oscillate the crystal (XTAL) resonator, the XO uses a combination of two different techniques. A dynamic negative resistance boosting (DNRB) technique is utilized to efficiently control the duration of the boosted gm and total power consumption. In order to further improve the start-up speed, a novel technique to set the initial condition is used to increase the initial motional current amplitude. The proposed XO achieves a start-up time of 7.6 μ s while it is powered by a 0.85 V power supply and consumes 107 μ W of steady-state power and 1.9 nJ of start-up energy. The proposed techniques are implemented using CMOS transistors in 130 nm BiCMOS technology occupying an active area of 0.004 mm2.