The RFID (Radio Frequency Identification) can be defined as Automatic identification technology which uses radiofrequency electromagnetic fields to identify objects carrying tags when they come close to a machine reader. In this paper authors designed the analog part using frequency 13.56 MHz in the RFID tag, includes a rectifier, demodulator and modulator. The first part a method of rectifier cascade combines multiple cells to obtain voltage doublers which used source of voltage on other components, the second part we call demodulator. Demodulator uses two stage of comparator that detects bias negative voltage, and the last part modulation used Amplitude Shift Keying (ASK) modulation. In this paper using 0.35μm CMOS technology to design RFID tag. The research goals purpose to design the analog part of the RFID tags are biased to function well as it should.