Potentiometric mixer noise analysis under leakage condition

Abstract

This thesis presents a design result of 900MHz RFID and noise analysis of the mixer under leakage condition. The designed mixer is potentiometric mixer including DC offset cancellation circuit and fabricated on $0.18\microm$ CMOS technology. In the thesis, noise performance degradation phenomenon under leakage condition is defined, and the relationship between leakage power and noise is explained. In addition, noise figure of potentiometric mixer is derived. First, brief explanation of the designed mixer is presented, and the measured results are reported with the incensement of noise under leakage condition. Second, noise of switch transistor is analyzed. The output noise of composed of three types of noise: thermal noise, noise from $R_{on}$ modulation, and noise from zero-crossing modulation. The equation of each noise is derived, and gain is also derived. From the derived equations, the phenomenon of noise performance degradation is verified, and noise figure equation is obtained. Finally, the derived equations are compared with simulation result to prove the validity of the equations. From the comparison, thermal noise is quite closed to the simulation result with a maximum error of 1dB, and low frequency noise is also similar with the simulation result with a average error of 3.5dB. The gain is same to the simulation result, and the noise figure curve is also same to the simulation result with a smaller error of 3.8dB. The noise analysis provides understanding of potentiometric mixer noise and some guide lines to reduce mixer noise. In addition, the noise analysis offers a foundation to explain noise of passive mixer and noise performance degradation of multi-carrier system.