Abdellatif Bellaouar

Novel analysis of passive mixer output impedance using switched-capacitor techniques

Passive mixers became an essential component of SAW-less receivers. It has been well known that the passive mixer behaves as a switched-capacitor circuit (SC) but to the authors knowledge, there is no reported analysis of the mixer impedance that truly accounts for the SC behavior. In this paper, we present for the first time a closed form of the passive mixer output impedance using SC techniques. We prove that the fundamental lower limit of the mixer impedance is proportional to the well-known switched capacitor resistor 1/(fLOC) different from the previously reported mixer switch ON resistance. We also explain that the equation is useful in estimating output bandwidth in voltage mode mixers and estimating blocker filtering in both voltage mode and current mode passive mixers.

IIP2 requirements in 4G LTE handset receivers

SAW-less receivers have become the state-of-the-art architecture in multiband receivers. These receivers eliminate the SAW filter between the low-noise amplifier (LNA) and the direct-conversion mixer. Large TX leakage signals hit the mixer in full-duplex receivers which imposes challenging mixer linearity requirements. Second order intercept point (IIP2) was intensively studied in 3G receivers. In this paper, we derive the IIP2 specification for LTE receivers and report the simulated and measured correction factors needed to estimate the modulated carrier 2nd order distortion using the conventional 2-tone carrier test.

Estimation of passive mixer output bandwidth using switched-capacitor techniques

Passive mixers have become an essential component of SAW-less receivers. It is well known that the passive mixer behaves as a switched-capacitor circuit (SC) but to the authors knowledge, there is no reported analysis of the mixer impedance that truly accounts for the SC behavior. In this paper, we present for the first time a closed form of the passive mixer output impedance based on SC techniques. We prove that the fundamental lower limit of the mixer impedance is proportional to the well-known switched capacitor resistor 1/ (fLOC) and different from the previously reported mixer switch ON resistance. We also explain that the equation is useful in estimating output bandwidth of passive mixer based front-ends with general LNA load impedance. We finally show that our bandwidth estimation matches measured results of two receiver front-ends.