Wideband active mixer with high gain and high linearity

Abstract

An active mixer is presented with improved conversion gain and linearity over a wide range of frequency. The mixer is combined with a low noise amplifier which not only provides braodband input matching but also cancels out noise at the output. The LNA has two stages, input matching stage and noise cancellation stage. The former provides matching for a wide range of frequency and the latter cancels out the noise of the former stage at the output. A PMOS is used to cancel out the non-linear effects of the noise cancellation stage of the LNA thereby improving the linearity of the system. The non-linear effects of input matching stage is canceled by the noise cancellation stage itself. A current bleeding circuit is used to fulfill the large current requirement of the noise cancellation stage and helps in further improvement of the gain. Gilbert cell topology is used which has differential output thereby providing better immunity from noise and fluctuations. The circuit provides a conversion gain of 20 to 24 dB, noise figure of 8 to 13 dB and a linearity of 17.5 dBm for a frequency range of 1 to 6.5 GHz.