Process tolerant highly linear mixer output stage with feedforward linearity improvement method for a high-IF converter

摘要

A highly linear output stage for passive mixers in mixer-first front-ends is presented. Passive nature and mixer-first can provide high linearity for a transmit chain front-end and the linearity is generally limited by the mixer output stage and the succeeding stages. The output amplifier design presented in this paper utilizes feedforward cancellation using an auxiliary transistor to cancel the Inter-Modulation Distortion (IMD3) products to improve the linearity. With the addition of this feedforward technique a linearity improvement of 8 dB can be obtained by optimum biasing. In order to reduce the dependence of linearity under process variations, constant-gm biasing scheme is used and bias points are selected such a way that the resulting variation from process is still within the specification. The third order intermodulation point (IIP3) of such a linearized stage is 22dBm for a frequency of 500 MHz. The total current consumption and gain are 4mA and 10 dBV respectively. The design is performed in CMOS130 technology with 3.3V power supply.