A Radio Frequency(RF) transmitter circuit is designed for wireless Electro-Encephalo-Graph(EEG) system. The transmitter is manufactured in 0.18 μm Complementary Metal Oxide Semiconductor(CMOS) process and it consists of two parts, Phase-Lock Loop(PLL) and Power Amplifier(PA). A novel 16/17 prescaler is proposed in PLL, which improves the circuit speed. The range of frequency is expanded in result of combining digital tuning with analog tuning. As is measured, the output has a wide range of frequency from 2 225 MHz to 2 580 MHz. The lock-time is about 49 μs. The output power of the transmitter can achieve -3.14 dBm by using the class E PA. The transmitter utilizes On-Off Keying(OOK) with a max data rate of 5 Mbps.