An Improved Doherty Amplifier Using Cascaded Digital Predistortion and Digital Gate Voltage Enhancement

Green Communications: Digital Predistortion for Wideband RF Power Amplifiers

“…nonlinear PA output and the original signal is small, otherwise, the coefficient adaptation may diverge [31]. Another optimized dual-loop model parameter scheme was also proposed for enhancing the single-loop parameter extraction performance at a cost of slightly increasing the complexity [92].…”

“…For high-power, wideband applications such as UMTS and LTE, those PAs do still suffer from nonlinear distortion, so we still need some kind of linearization. In the second trick, for a given PA operating near saturation, the linearity can be improved by signal processing techniques, PA linearization [11], using techniques such as a) feedback distortion compensation [12], [13], [14], [15], [16], using closed-loop regulators to reduce the nonlinear distortion, b) feedforward distortion compensation [17], [18], [19], [20], [21], which utilizes an additional error amplifier in the forward loop to compensate for the nonlinear distortion introduced by the main PA, and c) predistortion linearization [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], which uses a stand-alone module to pre-distort the input signal to the PA, improving the linearity at PA output. Due to its high flexibility and excellent linearization performance, digital predistortion (DPD) has become one of the most preferred choice for linearizing RF PAs, and tends to be an fundamental component in current and next-generation wireless communication systems.…”

Dual-loop Model Extraction for Digital Predistortion of Wideband RF Power Amplifiers

“…Compared to the combined structure in [4], this dual-loop model extraction does not increase much of the implementation complexity or cost since we still use the same DPD model and the same LS algorithm in (2) and (5). The only difference is that we change the reference signal from the DPD output to the original input, which is already available in the real system.…”

“…However, this approach only works well if the residual distortion is small, otherwise the coefficient adaptation may diverge. In [4], a combined structure was proposed for enhancing the linearization performance for Doherty PAs. This cascade structure solves several problems when using the model inverse or the model reference structure separately.…”

High-performance digital predistortion test platform development for wideband RF power amplifiers

“…To tackle the nonlinear distortion introduced by the PAs, besides the traditional back-off approach, several solutions have been proposed, such as feedback compensation techniques [1][2][3], which use a close-loop regulator to reduce the nonlinear distortion, and predistortion techniques [4][5][6], which use a pre-distorted cascaded system to linearize nonlinear PAs. Because of its flexibility and excellent linearization performance, digital predistortion (DPD) has become one of the most preferred choices, and it also tends to be one of the essential units in wireless transmitters for the next generation wireless communication systems.…”