A LUT-based LNA Nonlinear Distortion Compensation Scheme in Direct-Sampling Receivers

The paper analyzes the non-linear distortion effects of the Low Noise Amplifier (LNA) in the radio frequency direct-sampling receiver (DRF). A novel look-up table (LUT)-based linearization scheme was proposed. In this scheme, the LNA nonlinearity is estimated by a specialized training-circuit. During the training process, an internally-generated signal with different power levels ranging from the LNA linear region to the saturated region is fed to the training circuit. An LMS algorithm is used to invert the LNA nonlinear coefficients. The estimated coefficients and the corresponding power level of the input signals are stored in a LUT, accessed during the receiving mode, to remove the distortion. The effectiveness of the proposed method is evaluated by a Matlab simulation with four QPSK channels. The simulation results show that the proposed solution significantly enhances the amplification linearity. The Adjacent Channel Power Ratio (ACPR) increases by 40dB, accordingly the spectra of distorted components reduce close to the receiver's background noise level.