A low-noise cartesian error feedback architecture

Feedback improves the linearity of the main path; however, this increases the linearity requirement of the feedback path in conventional transmitter Cartesian feedback architecture. To alleviate this issue, the feedback signal should be largely attenuated, which then inevitably degrades the system noise performance. To mitigate the trade-off between noise and linearity, we have invented a new architecture, named error feedback architecture by introducing an external feedforward path to suppress the feedback signal while only feeding back the error information in principle. In this paper, first, the trade-off between noise and linearity in the conventional TX Cartesian feedback loop is described. Then, how the signal cancellation provided by the new architecture can mitigate the inherent noise-linearity trade-off is discussed. The noise and nonlinearity of the feedforward path, which cannot be regulated by the loop, are also analyzed. Finally, WCDMA power class 4 (21dBm) is utilized as one application example for the evaluation of noise and linearity.