Digitally Enhanced Alternate Path Linearization of RF Receivers
The design of radio-frequency (RF) receivers is fundamentally constrained by the scarcity of gain at the high frequencies at which these circuits must operate. As feedback, a staple design technique at lower frequencies, is difficult to implement at RF due to its bandlimiting nature, signals entering the receiver are exposed to the full brunt of the active-gain device nonidealities. This situation often leads to the presence of self-generated interference, in which signals, desired or otherwise, interact with circuit block nonidealities in such a way that error terms arise and corrupt the signal intended for reception. This interference is sometimes so severe that even increasing the circuit area and power dissipation arbitrarily to reduce the nonidealities is insufficient, and costly off-chip components are required for the receiver to meet specifications.
Often, this self-generated interference manifests itself as distortion products due to block nonlinearities, but can also arise due to I/Q mismatch, interstage coupling, or various other mechanisms. Unfortunately, it can also be said that these problems worsen in general as CMOS processes continue to scale. As supply voltages drop, less headroom is available to apply large overdrive bias voltages to devices in critical RF circuit blocks, worsening ...