Gain and noise enhancement mixer technique for 2.4 & 5.x GHz application

Abstract

In a direct-conversion receiver, flicker noise degrades signal-to-noise ratio and total noise figure, which results in the degradation of receiver sensitivity. In narrowband RF system, bandwidth utilization is a critical issue and it can be maximized by using a reduced flicker-noise receiver system because we can utilize more channels around the dc area. In a multicarrier modulation system like orthogonal frequency division multiplexing, spectral efficiency can also be improved by using a reduced flickernoise receiver system. CMOS transistors suffer from high intrinsic flicker noise, which is inversely proportional to the device area. Therefore, minimum length of the device increases flicker noise. In general, passive CMOS mixers are considered as the appropriate choice for direct-conversion receivers because they do not contribute to flicker noise. However, due to conversion loss, a higher gain of a low-noise amplifier is required to minimize baseband noise contribution. In order to decrease flicker noise in CMOS active mixers, the bias current of the local oscillator switches should be small enough to lower the height of noise pulses. The static current bleeding technique was proposed to reduce the bias current of the LO switches. However, the impedance of the LO switches as seen from the RF stage is increased as we reduce the bias current of the LO switches. In addition, RF leakage current flows into the bleeding circuit, which decreases conversion gain and also allows more RF current to be shunted by tail capacitance at the node between the LO switches and RF transconductance stage. The tail capacitance should be minimized to decrease the indirectly translated flicker noise. To minimize the tail capacitance, a smaller device size is appropriate for the LO switches, which increases the intrinsic flicker noise. In this thesis, a novel switching mixer with gain and noise enhancement technique is demonstrated. By reducing the time interval where switching...