Digital and analog IM3 product compensation circuits for an RF receiver

摘要

Third-order intermodulation products (IM3) are attenuated in RF receivers by providing a typical main signal path and a parallel auxiliary signal path in which the IM3 products are accentuated, and the output from the main signal path is adaptively filtered to attenuate the IM3 products. In one embodiment, a multirate filter bank (MRFB) with asymmetric analysis and synthesis sections is used to detect and isolate the IM3 products. In another embodiment an analog nonlinear term generator is placed at the front of the auxiliary signal path. The analog nonlinear term generator takes advantage of the nonlinearities of a differential MOSFET circuit and a multiplier to extract the IM3 products in the RF input signal. The outputs of the main signal path and the auxiliary signal path are inputs to a complex least mean squares filter to attenuate the IM3 products in the resulting signal.

主权项

1. A RF section of a receiver for receiving quadrature modulated RF signals comprising:
a) a first RF circuit configured to receive a RF signal received at a first RF signal input terminal, configured to down convert and digitize said received RF signal and configured to provide a first set of digitized down-converted I and Q signals at a first set of output terminals; b) a second RF circuit configured to receive said RF signal, said second RF circuit comprising an analog nonlinear term generator, said analog nonlinear term generator configured to provide third order intermodulation interference (IM3) products of said RF signal while attenuating the portions of said RF signal which are not IM3 products, said second RF circuit configured to provide a second set of digitized down-converted I and Q signals at a second set of output terminals, said second RF circuit comprising a first pair of differential MOSFETs in said analog nonlinear term generator, said first pair of differential MOSFETs having a first single ended output, said first single ended output coupled to a first gate of a second pair of differential MOSFETs, which in turn are coupled to a multiplier cell having two outputs coupled to said second set of output terminals; and c) an adaptive filter configured to receive said I and Q signals from said first RF circuit as I and Q signals containing interfering IM3 products, and configured to receive said I and Q signals from the second RF circuit containing compensatory IM3 products of unknown magnitude and phase with respect to said I and Q signals from said first RF section, said adaptive filter configured to provide I and Q signals with attenuated IM3 products compared to said I and Q signals at said first set of output terminals.