A concurrent dual-band digital predistortion (DPD) system is presented to compensate for the nonlinearity of the radio-frequency power amplifiers (PAs) driven by a concurrent dual-band signal. Recently, a closed-form orthogonal polynomial basis has been introduced showing stability improvement compared with the conventional polynomial. An experimental test bed employing a field-programmable gate array (FPGA) linked to two mixed-signal system boards has also been presented. Based on the FPGA, this paper focuses on the hardware implementation of the new concurrent dual-band orthogonal DPD forward path using time-division multiplexing. Performances are evaluated with an experimental test setup cascading 1-10 W peak PAs and a dual-band signal center frequency spaced by 310 MHz. The lower side band (LSB) and upper side band (USB) are centered at 1890 and at 2200 MHz, respectively. Two signal scenarios are presented combining alternatively 1-carrier wide-band code-division multiple access (WCDMA) and 10-MHz long-term evolution (LTE) signals to a 5-carrier WCDMA signal. Experimental results show that the proposed time-division-multiplexing implementation approach gives similar performance compared with the software implementation with half of the resources. Adjacent channel power ratios (ACPRs) are reduced below 50 dBc and normalized mean-square error (NMSE) close to 40 dB.Index Terms-Concurrent dual-band, digital predistortion (DPD), orthogonal polynomials, power amplifiers (PAs), time-division multiplexing.

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This paper describes the implementation of a sigma-delta ( ) A/D converter within an FPGA, with minimal use of external analog components. The approach takes advantage of existing low-voltage differential signaling (LVDS) I/O pads; this allows the implementation of lowcost ADCs into existent FPGAs, even though such digital devices do not posses analog interfacing capabilities at first. The converter was implemented in an actual FPGA and had its performance evaluated.

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