A multiband reconfigurable all-digital transmitter (ADT) employing a sturdy multistage noise-shaping (SMASH) delta-sigma modulation (DSM) is proposed in this article. TheN-stage SMASH DSM is presented digitally using unit signal transfer functions across cascaded stages, which supports arbitrary-stage extension for multiband transmission. Each stage is associated with a specific passband. By activating different stage numbers and adjusting only two parameters per stage, the numbers and frequencies of passbands are reconfigured simply and independently. Consequently, computational resources are significantly reduced, which is especially beneficial for four or more bands. Furthermore, the DSM outputs are directly extracted from individual stages to simplify the ADT architecture while the high efficiencies of subsequent power amplifiers (PAs) are maintained. By using the SMASH DSM, an ADT with multiband reconfigurable characteristics is proposed. With a resource-performance tradeoff, an ADT prototype based on a 2–2 SMASH DSM is implemented on a field programmable gate array (FPGA), which uses only 256 DSP48 slices. The transmissions are switched between single-band and dual-band configurations with carrier frequencies (CFs) independently tunable over 0–3.2 GHz. Measured adjacent channel leakage ratios (ACLRs) for 10- and 20-MHz dual-band signals are below −45 and −39.5 dBc, respectively, with error vector magnitudes (EVMs) below 1.6%. These results verify the agile multiband reconfiguration and excellent performance of the proposed SMASH DSM-based ADT.

This paper presents an optimization method of wideband filtering power amplifier (PA) with high efficiency. In order to achieve the expected high efficiency in the wide passband and reduce design difficulty, a high-performance area-based impedance target for computer-aided automatic optimization is proposed, which avoids the unexpected efficiency degradation caused by the conventional impedance target. In the meanwhile, the out-of-band optimization target described by impedance is also proposed to obtain bandpass filtering characteristic. The in-band and out-of-band optimization targets are utilized to design the output matching network to realize fundamental and harmonic impedance matching precisely, as well as the filtering response. For demonstration, a filtering PA operating in 3.3-3.8 GHz is implemented and measured. The measured small-signal$S$-parameter exhibits flat gain in passband and good bandpass filtering response. The measured power-added efficiency (PAE) is larger than 62% within the entire working band and the highest PAE is 71.7%.

In this paper, dual-mode oval dielectric resonator (DR) is proposed as common resonator to realize all four kinds of balanced and unbalanced duplexers. The conventional topology is replaced with the novel one of sharing input and output dual-mode resonators at the same time for miniaturization. By adjusting the aspect ratio and height of the oval DR, the two modes are separated properly to form two channels of duplexers. After locating probes delicately according to the orthogonality of dual-mode fields, the channel transmission and isolation are ensured simultaneously under sharing output DR. Moreover, both dual-mode unbalanced and balanced operations are studied to extend the topology to all four kinds of duplexers. For verification, balanced-to-unbalanced (B-U) and balanced-to-balanced (B-B) duplexers are both fabricated and tested. Low insertion losses better than 0.59 dB are achieved in both two designs. High isolations lower than -36 dB and -50 dB and common-mode rejections lower than -44 dB and -52 dB are observed in the B-U and B-B duplexers, respectively. The exhibited high performance with reduced resonators demonstrates the potentials of the proposed duplexers in miniaturized FDD communication systems for connecting balanced/unbalanced transceivers with balanced/unbalanced antennas.