Performance Improvement of a Down-Conversion Active Mixer Using Negative Admittance

Abstract

This paper presents a down-conversion active mixer with improved performance for direct conversion receivers in wireless local area networks. The effect of negative admittance on the Gilbert cell mixer performance is investigated in terms of flicker noise, conversion gain, and linearity. The proposed negative admittance is implemented using a modified negative capacitance connected in parallel to a negative resistance, which exhibits a high degree of freedom to achieve high negative capacitance along with low negative resistance. The proposed mixer is designed and simulated using TSMC 0.18 µm CMOS technology in Cadence Spectre-RF at the input frequency of 2.4 GHz and intermediate frequency of 10 MHz. Post-layout simulation results show using the negative admittance can improve the flicker noise more than 16.7 dB at the frequency of 1 kHz. The proposed mixer exhibits a conversion gain of 19.3 dB and a flicker noise corner frequency of 5 kHz. The double-side band noise figure is 7.57 dB at the output frequency of 10 MHz, and the third-order intermodulation intercept point (IIP3) is − 7.5 dBm. The power dissipation is 13.6 mW from the power supply of 1.8 V. Moreover, the linearity of the proposed mixer can be enhanced by choosing the proper values for transconductance of switching quad and negative resistance so that it achieves the IIP3 of + 7.9 dBm with the conversion gain of 7.6 dB.