In this letter, a quintuple‐mode bandpass filter for a UWB system with improved performance is presented. The presented filter is implemented with asymmetric parallel‐coupled lines loaded open stub and short stub connected at the symmetrical plane of the filter to increase its frequency selectivity. Five resonant frequencies within the UWB band and two transmission zeros at the lower and upper passband/stopband edges are observed. A filter prototype is fabricated for verification and the experimental data are corresponding well with the simulated results. The proposed filter achieves a bandwidth that can exactly cover the whole UWB frequency band. Moreover, this filter has a compact size (0.645 λ _g × 0.318 λ _g ) and low insertion loss.

In this letter, an improved balanced Colpitts voltage-controlled oscillator (VCO) with a collector-emitter cross-coupled capacitors is presented. The proposed Colpitts structure can introduce a more robust oscillation startup condition. The noise-shifting technique is used to enhance the loaded quality factor of the tank, which improves the phase noise in turn. In addition, three-bit switches composed of enhancement-mode high-electron mobility transistors (E-HEMTs) are utilized to expand the tuning range and reconfigurability of the proposed VCO. In proof of the concept, a VCO prototype is fabricated in a GaAs BiHEMT [enhancement- and depletion-mode high-electron mobility transistor (E/D-PHEMT)] process. The measured results demonstrate the best phase noise of -139.46 dBc/Hz at 1-MHz offset. To the best of our knowledge, this is the lowest phase noise among the reported ones fabricated on-chip with a similar frequency band, and it achieves a wide tuning frequency bandwidth of 21% (2.65-3.27 GHz) with peak figure of merit (FoM) of -192.26 dB and FOMT of -198.8 dB.

In this letter, to simultaneously realize frequency coarse tuning and electromagnetic (EM) interference suppression, a novel 8-shaped-inductor-based triple-coil transformer structure is presented for CMOS 60-GHz voltage-controlled oscillator (VCO). Based on the proposed novel triple-coil transformer, the proposed VCO can achieve 2-bit frequency coarse tuning without using the switched capacitor banks; in addition, due to the unique EM characteristics of the 8-shaped inductor, the proposed VCO can also achieve EM interference suppression simultaneously. The proposed VCO is implemented in a 40-nm CMOS process, and the measurement results exhibit a wide tuning range of 13.28%, from 52.97 to 60.51 GHz, with a phase noise from $-$ 96.3 to $-$ 103.6 dBc/Hz at 10-MHz offset over the entire frequency tuning range, leading to a figure of merit (FoM) of $-$ 168.6 dBc/Hz. This VCO consumes a 9-mA current from the 1-V power supply and occupies small areas of 0.264 mm $^{2}$ .

A GaAs Colpitts voltage controlled oscillator with low phase noise is presented in this letter. Firstly, the gm-boosting technique realized by an inductor located at the emitter of heterojunction bipolar transistor is applied to relax the oscillation start-up requirements and speed up the oscillation. Moreover, a Collector-Emitter cross-coupling capacitor is adopted to improve the loaded quality factor and oscillation amplitude of the tank by reducing the transformer ratio, which improves the phase noise in turn. Finally, in proof of the concept, a voltage controlled oscillator prototype is fabricated and designed in 2-μm GaAs HBT process. The measured results demonstrate a phase noise of -137.44dBc/Hz at 1MHz offset with figure of merit of -192dBc/Hz and a tuning frequency bandwidth from 3.25 to 3.4GHz. Compared with the conventional Colpitts voltage controlled oscillator, the phase noise of the proposed voltage controlled oscillator with gm-boosting and Collector-Emitter cross-coupling techniques has improved 6.67 dB.

In this brief, a novel design method for on-chip bandpass filter (BPF) is proposed, analyzed and validated. By inserting a highpass filter (HPF) into the lowpass filter (LPF), a BPF with wide stopband can be realized without increasing the die size. The introduction of source-load coupling technique and series inductor in a $\pi $ –type LPF can generate three transmission zeros (TZs), which extends the upper stopband considerably. To improve the selectivity, the source-loading coupling technique is also used in the HPF design. Moreover, a stacked MIM capacitor working at its self-resonant frequency is used to replace the series LC resonator in the BPF to further reduce the size and decrease its sensitivity to process deviation. An amplifier is also designed to validate integration. Finally, a prototype was fabricated in a 2- $\mu $ m GaAs HBT process to verify our methodology. The filtering amplifier achieves a 3-dB fractional bandwidth of 78.9% (2.3-5.3GHz). The upper stopband with rejection level of 34 dB reaches to 68GHz (>17.8f0). To the best of our knowledge, this is almost the widest harmonic rejection achieved with such a small size ( $600\times 500~\mu $ m2). The designed BPF could be well used in a high-density integrated system on chip like satellite and 5G communication, etc.