This paper discusses an 8MHz square wave oscillator used for a clock signal of the digital core of a mixed signal integrated circuit (IC). The frequency is determined by a bias current that charges a capacitor until it triggers a comparator with a voltage reference as the second input. A low drop out (LDO) voltage regulator is used to supply the oscillator so that variations in the battery voltage do not affect the oscillator. The circuits have been designed and taped out and the measured results are closed to the SPICE simulated values. The oscillator has very low power consumption of 165 μW which is very attractive for a general handheld device that is operated off of a battery.