This paper reports the design, fabrication, and validation of a novel integrated interface circuit for ultra-low voltage step up converter in 0.18 mu m CMOS technology. The circuit does not use off-chip components. Fully integrated centre-tap differential inductors are introduced in the proposed LC oscillator design to achieve 38% area reduction compared to the use of four separate inductors. The efficiency of the system is hence enhanced through the elimination of clock buffer circuits traditionally utilized to drive the step-up converter. The experimental results prove that the system can self-start, and step 0.25 V up to 1.7 V to supply a 46 mu W load with 15.5% efficiency. The minimum validated input voltage is 0.15 V, which is boosted up to 1.2 V under open circuit conditions.