CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Application No. PCT/US2018/025403, filed on 30 Mar. 2018, and published as WO 2019/19055 A1 on 3 Oct. 2019, which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure pertains generally, but not by way of limitation, to user communication devices such as phones. More specifically, aspects of the present disclosure pertain to transmit circuitry for processing an input signal. Other aspects of the disclosure relate to feedback control systems for wireless devices.

BACKGROUND

Communication devices may exchange various signals with other devices, such as data signals, control signals or other signals. As an example, a baseband (BB) signal may be up-converted to a radio frequency (RF) range for input to a power amplifier (PA). In some cases, one or more components of an input path may operate on the baseband signal before it is input to the PA. In some cases, the PA and/or component(s) of the input path may cause one or more types of distortion, including in-phase/quadrature (IQ) distortion, memory distortion, and/or other types of distortion. Such distortion may potentially cause issues, such as splatter into frequency bands adjacent to the RF channel, passband ripple, and/or other issues, which may degrade performance of the devices. Accordingly, there is a need for devices and components to reduce and/or control such distortion in these and other scenarios.

To address these distortions, often significant current consumption is required, draining battery life. In sum, a balance between reducing current consumption for increased battery life and maintaining linearity of the signal can be helpful in meeting industry standards. Digital predistortion is used to mitigate the increase of PA current consumption. By appropriate predistortion of the PA input signal, less PA headroom and PA quiescent current can be used, while maintaining sufficient linearity, e.g., meeting adjacent channel leakage ratio (ACLR), transmit spectral mask, and error vector magnitude (EVM) targets. However, increased transmit bandwidth increases the complexity of the pre-distorter because the linearity characteristic of the transmit chain depends on the instantaneous RF frequency and how fast the envelope of modulated RF signal changes. Subsequently, the linearity characteristic depends on the IQ data stream which modulates the RF carrier. The amplitude modulation to amplitude modulation (AMAM) and amplitude modulation to phase modulation (AMPM) response is no longer constant and depends on the sequence of modulation symbols. This can be referred to as a “memory effect” or “memory disturbance,” and can be more pronounced at higher transmit bandwidth. While doing so in different manners, both average power tracking (APT) and envelope tracking (ET) systems produce memory disturbance. Thus, as communication devices intake more complex signals with increased aggregated bandwidth, signal processing techniques can be used to accommodate these signal without performance losses.

