Abstarct: To achieve goals such as power consumption reduction, the possibility of low-level integration and the ability to use implantable sensors in the body, use of LC oscillators because of high power consumption and crystalline ones due to the impossibility of integration are not appropriate options. For this reason, in this thesis, a ring oscillator including five inverters with transistors in the sub-threshold region has been investigated. Since the output frequency of this oscillator in the sub-threshold region increases with increasing temperature and has a temperature coefficient of 2430 ppm¬/¬˚C, it requires temperature compensation. This high temperature coefficient can affect the performance of overall system, so it does need to utilize a compensation technique. In this thesis two CTAT current references have been simulated in 0.18um CMOS technology to reduce output frequency changes versus temperature. A method of generating a negative temperature coefficient is to apply the baxse-emitter voltage of a bipolar transistor on a resistor and another method of producing it is to use the negative temperature coefficient of the threshold voltage of the PMOS transistor. In the proposed circuit, the obtained CTAT current from both methods along with a constant temperature coefficient of a temperature independent current reference supplied the ring oscillator. The temperature coefficient of output frequency of the proposed oscillator in the structure utilized by the baxse-emitter voltage is about 117 ppm/¬˚C for 0¬˚C to 100¬˚C and the total power consumption is 13.3¬µW. The temperature coefficient of output frequency of the proposed oscillator in the structure utilized by the threshold voltage is about 131.7 ppm/˚C for 0¬˚C to 100˚C and the total power consumption is 33 µW.