An improved homodyne receiver architecture for wireless communications

The optimal architecture for a modern receiver is required for mobile wireless communication. The superheterodyne architecture dominated the first century of the radio communication. However, a number of high quality filters at radio and intermediate frequency required by the architecture prevent a high level integration. A direct-conversion, homodyne, receiver is a natural and simple solution for next generation wireless communications.; However, one disadvantage of homodyne architecture is self-mixing. We propose a novel solution to prevent the local oscillation (LO) signal from downconversion to the desired baseband. The harmonic mixer utilizes two LO signals 90° out of phase at half of the desired frequency to downconvert the desired signal. With very low conversion gain at the LO frequency and high gain at the desired frequency, LO self-mixing is drastically decreased.; 2nd-order distortion is another disadvantage of the homodyne architecture. 2nd-order distortion will convert interference to the baseband. Due to the low signal power, a very high gain in the baseband processing and a very high 2nd-order nonlinearity is required to keep the interference from corrupting the desired signal. An analysis of the 2nd-order nonlinearity of a double-balanced mixer is presented. A novel way to cancel the 2nd-order nonlinearity by tuning bias voltage of the mixer is demonstrated; the second order input-referred intercept point (IIP2) is improved by about 30dB.; Low power, low noise, high linearity amplifiers are required in many modern wireless communication circuits. To achieve high linearity, degeneration is commonly used. However, degeneration lowers the gain and often increases the noise figure (NF) of an amplifier. In order to obtain a high linearity without the sacrifice of gain and noise figure, a third-order nonlinearity cancellation technique is proposed. By terminating the emitter and the base with proper impedance, the third-order nonlinearity input-referred intercept point (IIP3) is drastically increased with little impact on gain and noise figure. A test chip is designed and tested, IIP3 of the mixer is improved by 10dB compared with a similar mixer without 3rd-order nonlinearity cancellation.