Low Gain Variation Research Articles

A high‐linearity LC‐VCO with combined MOS varactors and bulk‐biased PMOS varactors for gain variation compensation

AbstractA high‐linearity LC‐voltage‐controlled oscillator (LC‐VCO) with combined metal‐oxide semiconductor varactors and bulk‐biased P‐channel metal‐oxide semiconductor varactors in parallel is proposed to reduce the VCO‐gain (KVCO) variation and extend the linear range of the control voltage. Fabricated in a 180‐nm complementary metal‐oxide semiconductor process, the proposed topology achieves a low gain variation of less than 6.3% and a tuning range of ~28% operating from 2.31 to 3.06 GHz, corresponding to a linear control voltage range from 0.6 to 1.4 V. The phase noise is measured to be −115.3 dBc/Hz at 1 MHz offset at 3.06 GHz and the figure of merit (FoM) is −181.2 dBc/Hz. The oscillator occupies an area of 0.93 × 0.54 mm and consumes 1.8 mW from mixed 1.2/1.8 V supply voltage.

A Low-Phase-Noise RF Up/Down-Converter for Cost-Effective 5G Millimeter-Wave Test Solutions

The increasing demand for millimeter-wave (mmWave) frequencies with wider signal bandwidths, such as 5G NR, requires large investments on test equipment. This work presents a 5G mmWave up/down-converter with a 40 GHz LO, fabricated in custom PCBs with off-the-shelf components. The mmWave converter has broad IF and RF bandwidths of 1∼5 GHz and 21∼45 GHz, and the built-in LO generates 20∼29.5 GHz and 33.5∼40 GHz of output. To achieve high linearity of the converter simultaneously, the LO must produce low-phase-noise and be capable of high harmonics/spur rejection, and design techniques related to these features are demonstrated. Additionally, a reconfigurable IF amplifier for bi-directional conversion is included and demonstrates low gain variation to maintain the linearity of the wideband modulation signals. The final designed converter is tested with 5G OFDM 64-QAM 100 MHz 1-CC (4-CC) signals and shows RF/IF output power of -3/8 dBm with a linear range of 35 (30)/38 (33) dB at an EVM of25 dB.

A 100- to- 10-kHz 5.4- to- 216- μW Power-Efficient Readout Circuit Employing Closed-Loop Dynamic Amplifier for MEMS Capacitive Accelerometer

Micro-electromechanical systems (MEMS) capacitive accelerometer for the Internet of Things (IoT) applications is required to operate at various sampling frequencies while keeping high power efficiency. To meet this requirement, dynamic amplifiers are used in the readout circuit of the accelerometer. However, the dynamic amplifier’s open-loop gain is low and varies with the sampling frequency of the readout circuit. This significantly deteriorates the gain accuracy of the readout circuit. In this article, the dynamic-amplifier-specific oversampling successive approximation (DA-OSA) readout technique is proposed to overcome this gain variation problem and make the dynamic amplifier applicable to the readout circuit. The DA-OSA-based readout circuit is fabricated in a commercial 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> m 1.8-V CMOS process and tested with the MEMS accelerometer sensing element. The measurement results show that, with the sampling frequency varying from 10 kHz to 1 MHz, the proposed readout circuit achieves a variable signal bandwidth from 100 Hz to 10 kHz, a variable power consumption from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.4$</tex-math> </inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{216}\mu \mathrm{W}$</tex-math> </inline-formula> , and a low gain variation of 1.2%.

Dual polarization and mutual coupling improvement of UWB MIMO antenna with cross shape decoupling structure

A simple, compact MIMO antenna that operates in the UWB frequency band is presented in this paper. The proposed antenna consists of four elements where the shape of the radiators derived from series modifications of a conventional rectangular patch antenna. Radiators are placed orthogonally to each other to achieve the dual polarization operation and cross shape Defected Ground Structure (DGS) is inserted in the ground plane to improve decoupling between the antenna elements. The designed model was fabricated on FR-4 substrate with dimensions of 48 × 44 × 1.6 mm3 and measurements were performed to validate the simulated results. The fractional bandwidth reaches 112% from 3.1 GHz to 11 GHz with reflection coefficient less than -10 dB and mutual coupling between antenna elements is less than -20 dB. The antenna has a stable radiation pattern, and low gain variation. In addition, the time domain characteristics and diversity performance indicators were evaluated and compared with the standard values. The miniaturized dimensioning of the antenna along with the good performance metrics indicates that the proposed antenna can be used in various UWB applications such as portable handheld devices.

A Low Gain Variation LC-VCO With Mutual Inductive Tuning for K VCO Linearity Compensation

A high-linearity LC-voltage-controlled oscillator (LC-VCO) with a mutual coupled inductive tuning technique is proposed to reduce VCO-gain ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{\mathrm {vco}}$ </tex-math></inline-formula> ) variation induced by varactors in finite linear region. The oscillator is fabricated in a standard 180-nm CMOS process occupying 0.88 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.9$ </tex-math></inline-formula> mm and consuming 3.6 mW from mixed 0.9/1.8 V supply voltage. With the variable effective inductance of the resonant tank, the proposed topology achieves a low gain variation of less than 6.1%, possessing a linear-tuning control voltage range from 0.5 to 1.8 V and operating from 3.40 to 4.04 GHz. The phase noise is measured to be −108.59 dBc/Hz at 1 MHz offset with a carrier frequency of 4.04 GHz, and the figure of merit (FoM) is −173.8 dBc/Hz.

A Full Ka-Band CMOS Amplifier Using Inductive Neutralization with a Flat Gain of 13 ± 0.2 dB

This paper presents a CMOS wideband amplifier operating in the full Ka-band, with a low gain variation. An inductive neutralization is applied to the amplifier to compensate for the gain roll-off in the high-frequency region. Neutralization inductance is carefully determined considering the tradeoff between stability and gain. To achieve a low gain variation over the full Ka-band, the amplifier employs the frequency staggering technique in which impedance matching for three gain stages is performed at different frequencies of 26, 34, and 42 GHz. The experimental results show that a peak gain of 13.2 dB is achieved at 39.2 GHz. The 3 dB bandwidth is from 23.5 to 41.7 GHz, which fully covers the Ka-band. Especially, the gain ripple of the amplifier is only 13 ± 0.2 dB over a wide bandwidth from 26.2 to 40.2 GHz. The input and output return loss values are better than −10 dB from 26.3 to 40.1 GHz and from 25.3 to 50 GHz, respectively. The DC power consumption is 18.6 mW.

A Single-Transistor Amplifier With Back-Gate Feedback in 22-nm FD-SOI

Fully-depleted silicon-on-insulator (FD-SOI) technology provides an additional degree of circuit design freedom due to its fourth terminal, the back-gate. In this letter, we present a single-transistor common-source amplifier exploiting the FD-SOI back-gate as a feedback injection point. This negative back-gate feedback improves linearity and reduces device-to-device gain variation without increasing noise or power and with no added components. A prototype amplifier, implemented in 22-nm FD-SOI, operates from weak to moderate inversion and achieves 5&#x2013;10&#x00D7; lower gain variation and 6&#x2013;20-dB higher VIP3 compared to a reference two-transistor amplifier with a diode-connected load.

Investigation and optimization of EYDFA + Raman + EYDFA hybrid optical amplifier for SD-WDM systems in C+L band

In this paper, we present a novel erbium–ytterbium doped fiber amplifier (EYDFA) + Raman + EYDFA hybrid optical amplifier (HOA) for a super-dense wavelength division multiplexing (SD-WDM) system application. The performance of the 100-channel system has been investigated for an overall data rate and channel spacing of 100[Formula: see text]Gb/s and 0.4[Formula: see text]nm, respectively, over a wavelength span of 1550–1589.9[Formula: see text]nm. HOA has been optimized for Raman length, EYDFA lengths, pump powers and Er[Formula: see text] concentrations to achieve high average gain and low gain variation ratio of 40.41[Formula: see text]dB and 0.40[Formula: see text]respectively. The optimized configuration of the proposed HOA has been compared with EYDFA + Raman and Raman + EYDFA HOA configurations. The achieved high and flat gain with an acceptable output optical signal to noise ratio (OSNR) in case of EYDFA + Raman + EYDFA HOA; makes it an optimum choice for SD-WDM systems.

A 27–31 ​GHz 6-bit phase shifter with low phase error/gain variation in 65 ​nm CMOS

This paper presents a Ka-band 6-bit phase shifter with low phase error, low gain variation and 27–31 ​GHz bandwidth implemented in 65 ​nm CMOS. The phase shifter consists of a reflective-type phase shifter (RTPS) and a 0°/180° switcher. Benefiting from the addition of the switcher and the optimization of RTPS circuits, higher Q of the reflective load is obtained to improve the phase shifting performance. Measured results of the proposed phase shifter show 5.625° (6-bit) phase resolution, 1.64° in-band RMS phase error, 7.6 ​dB gain and 0.59 ​dB in-band RMS gain variation across the 4 ​GHz bandwidth, which are outstanding compared with the state-of-the-art works. The chip has 0.56 ​mm2 area and 24 ​mW power consumption.

A four element, planar, compact UWB MIMO antenna with WLAN band rejection capabilities

AbstractA planar, compact UWB MIMO antenna with four elements that accomplish band rejection from 4.91 to 6.41 GHz is presented. Rejection is accomplished using an L‐C stub connected to the ground plane. The length of the stub is changed to reject the band starting from 2.5 GHz to above 8.8 GHz. The perpendicular placement of the elements enables polarization diversity and attains high isolation. Elements 3 and 4 are 180° mirrored transforms of elements 1 and 2 on the opposite corners of the substrate. The antenna measures 50 × 50 mm2 only with all four elements placed. The simulated results are validated by measurements of a fabricated prototype. The design attains the targeted specifications over the entire bandwidth of 2 to 12 GHz with a reflection coefficient better than −10 dB (except the rejected band), isolation more than 17 dB, low envelope correlation, low gain variation and strong rejection of the signals in the WLAN band. The small size and reduced complexity to obtain WLAN rejection makes the proposed design very useful for diversity applications and portable handheld devices with MIMO antennas as designed by panorama antenna.

A low‐profile wideband dual‐polarized antenna with gain enhancement, low gain variations, and low cross polarization for 5G indoor communications

A low-profile wideband dual-polarized antenna with high gain, low gain variations, and low cross-polarization for the fifth generation (5G) indoor distribution system is proposed. By using circular-thread vase-shaped structure, a low profile of 0.23λ0 (λ0 is the free-space wavelength at the starting frequency) as well as low gain variation feature can be achieved by the vertically polarized (VP) radiating element. An eight-way power divider network is employed to feed the horizontally polarized (HP) dipoles so that wideband performance is obtained. Here, eight pairs of arc-shaped parasitic strips are used to broaden the bandwidth, and eight pairs of director elements are introduced to enhance the gain and reduce the gain variations. In addition, the protruded stubs that are extended from the circular ground plane will help to reduce the cross polarization in the VP direction. Measured results show that a bandwidth of 46.5% (3.3-5.3 GHz) (S11 < −10 dB) with a gain of 0.85 ± 0.35 dBi, and another bandwidth of 85.0% (2.5-6.2 GHz) with a gain of 4.75 ± 1.75 dBi can be realized in the HP and VP directions, respectively. Furthermore, high isolation (>27 dB) and low cross polarization (<−24 dB) can also be attained. Therefore, the proposed antenna is a good candidate for 5G indoor distributed system.

Production and properties of a charging-up “Free” THGEM with DLC coating

THGEM detectors usually exhibit time-evolution of gain, caused by avalanche charges accumulating on the open insulator surfaces (charging-up effect). Coating resistive layer on the insulator surfaces may help to release the charges to overcome the charging-up effect. Diamond-like carbon (DLC), as a class of amorphous carbon material, can be used as a resistive layer. In this study, thin DLC layers with stable and controllable resistivity were coated on a series of THGEMs by magnetron sputtering technique. A batch of single THGEM detectors was fabricated with these DLC-THGEM films. The gas gain of DLC coated THGEMs (DLC-THGEM) have been tested in detail and compared with normal THGEM. DLC-THGEM with suitable resistivity show very low gain variation versus time and literally no charging-up effect. However, a DLC-THGEM detector shows a gain decrease with increasing irradiation rate. A qualitative theoretical model was built to understand the gain decrease. And the simulation results fit the experimental results well.

Ultra-Compact Reconfigurable Band Reject UWB MIMO Antenna with Four Radiators

A compact reconfigurable UWB MIMO antenna with four radiators that accomplish on-demand band rejection from 4.9 to 6.3 GHz is presented. An LC stub is connected to the ground plane by activating the PIN diode for each radiator. Two radiators are placed perpendicular to each other to exploit the polarization diversity on a compact 25 × 50 mm 2 FR4 laminate. Two additional radiators are then fixed obliquely on the same laminate (without increasing size) in angular configuration at ±45 ∘ perpendicular to the first two planar radiators still exploiting polarization diversity. The design is validated by prototyping and comparing the results with the simulated ones. On demand band rejection through the use of PIN diodes, wide impedance matching (2–12 GHz), high isolation amongst the radiators, compactness achieved by angular placement of the radiators, low gain variation over the entire bandwidth, band rejection control achieved by adjusting the gap between stub and ground plane, and low TARC values makes the proposed design very suitable for commercial handheld devices (i.e., Huawei E5785 and Netgear 815S housings). The proposed configuration of the UWB MIMO radiators has been investigated first time as per authors’ knowledge.

Electrically Conformal Antenna Array With Planar Multipole Structure for 2-D Wide Angle Beam Steering

Electrically conformal antenna arrays (ECAA) for 2-dimensional (2-D) beamforming configured by wide beamwidth multipole radiation elements are proposed. Unlike the conventional conformal antenna array with physically curved shape, the proposed arrays are planar structures with wide-angle beam steering. The wide range of beam steering with a low gain variation allows the planar array structure to achieve the electrically conformal phased array patterns. In order to verify the ECAA concept, two different types of ECAA in a 1 × 8 configuration using planar multipole antenna elements were fabricated at 5.8 GHz and compared to the conventional patch array. Each multipole element had half-power-beamwidth (HPBW) wider than 110° at both E- and H-planes with the maximum HPBW of 175°. The first type of ECAA showed a measured peak gain of 10.8 dBi with a measured half power steering angle of 155° while maintaining a side lobe level (SLL) less than -10 dB. Further, the second ECAA showed a measured peak gain of 12.8 dBi with a measured half power steering angle of 144° while keeping the SLL less than -10 dB. These scan angles of the first and second types were extended about 66.7% and 54.8%, respectively from the conventional patch array with the same size. Lastly, two types of 8 × 8 array modules for 2-D beam steering were verified at 5.8 GHz and the first type showed a maximum peak gain of 21.0 dBi. Further, the 2-D half power steering angles in E- and H-planes of the second type were about 145° and 137°, respectively.

Eight-Element Compact UWB-MIMO/Diversity Antenna with WLAN Band Rejection for 3G/4G/5G Communications

An eight element, compact Ultra Wideband-Multiple Input Multiple Output (UWB-MIMO) antenna capable of providing high data rates for future Fifth Generation (5G) terminal equipments along with the provision of necessary bandwidth for Third Generation (3G) and Fourth Generation (4G) communications that accomplishes band rejection from 4.85 to 6.35 GHz by deploying a Inductor Capacitor (LC) stub on the ground plane is presented. The incorporated stub also provides flexibility to reject any selected band as well as bandwidth control. The orthogonal placement of the printed monopoles permits polarization diversity and provides high isolation. In the proposed eight element UWB-MIMO/diversity antenna, monopole pair 3-4 are 180o mirrored transform of monopole pair 1-2 which lie on the opposite corners of a planar 50 x 50 mm2 substrate. Four additional monopoles are then placed perpendicularly to the same board leading to a total size of 50 x 50 x 25 mm3 only. The simulated results are validated by comparing the measurements of a fabricated prototype. It was concluded that the design meets the target specifications over the entire bandwidth of 2 to 12 GHz with a reflection coefficient better than -10 dB (except the rejected band), isolation more than 17 dB, low envelope correlation, low gain variation, stable radiation pattern, and strong rejection of the signals in the Wireless Local Area Network (WLAN) band. Overall, compact and reduced complexity of the proposed eight element architecture, strengthens its practical viability for the diversity applications in future 5G terminal equipments amongst other MIMO antennas designs present in the literature.

Low-Profile Implementation of U-Shaped Power Quasi-Isotropic Antennas for Intra-Vehicle Wireless Communications

Intra-vehicle wireless communication applications, e.g. the wireless sensor network, are in need of antennas with uniformly radiated power for signal transmitting and receiving with their randomly distributed neighboring targets. This demand can be met with power quasi-isotropic antennas with low angular gain variation (GV). In this paper, two types of practical implementation for conventional U-shaped λ/4 resonators, which are supposed to have theoretically ideal (approaching zero) GV but have intrinsically low radiation resistance, have been proposed. One is a dual-layer U-shaped radiator. The extra added layer introduces a resonance that can be utilized for a good impedance matching with a commonly used 50 Ω feeding line. A two-element array model and the two-port network are used to show the working mechanism and design considerations. The other is a U-shaped RFID tag antenna, which can be considered as the miniaturized form of a U-shaped λ/4 resonator. With a structure evolution starting from a simple triple element model, the tag can have a good conjugate impedance matching with the terminated chip. Compared to their respective counterparts, both proposed antennas have the lowest measured GV. Meanwhile, their attracting features such as extremely low profile, small lateral size, light weight, simple configuration and fabrication process, and the possibility of a conformal implementation make them excellent candidates for future intra-vehicle wireless communications.

A 5-15GHz Switchless Broadband Monolithic Integrated Bidirectional Amplifier

Based on SiGe HBT technology, two broadband monolithic integrated bidirectional amplifiers (BDA) with different operating voltages (1.8V/3.3V) are designed. By adjusting the bias voltage, the transceiver and receiver of the amplifier are switched. At the same time, a temperature compensation bias circuit is added to reduce the high and low temperature gain variation of the amplifier. It is suitable for multi-function transceiver chip or T/R module. The simulation results show that the gain of 1.8V broadband monolithic integrated bidirectional amplifier can reach 9dB in 5-15GHz operating band, the reflection coefficient of input and output ports is less than - 13dB and - 17dB respectively, the output power of 1dB compression point is + 5.5dBm, the working current is 12.2mA, the gain of 3.3V bidirectional amplifier can reach + 10.5dB, and the reflection coefficient of input and output ports is less than -12dB and -13dB. The output power of 1dB compression point is + 10dBm, and the working current is 20.3mA. The core area of the chip is 0.45 × 0.45mm2.

Wideband Dual-Polarized Omnidirectional Antenna Array for Base-Station Applications

A compact wideband dual-polarized omnidirectional antenna array for base-station applications is proposed. It consists of ten antenna units. To generate ±45° dual-polarized ominidirectional radiation with low gain variation for each unit, three close-in crossed-dipole elements are uniformly arranged in a regular triangle shape and excited by two 1-to-3 power dividers with equal magnitude and phase, acting as a dual-polarized loop antenna. To obtain wide impedance bandwidth for each unit, the dipole element and power divider are designed to operate in a wide and well-matched band. Moreover, the unit features steady structure, easy fabrication, and high scalability, which makes it convenient to form an antenna array. To achieve a high gain for base-station applications, a ten-unit antenna array is designed, fabricated, and measured. A wide impedance bandwidth of 52.3% (1.62–2.77 GHz) for standing-wave ratio (SWR) < 1.5 and a high port-to-port isolation of 26 dB are realized. It also features a high gain of 10.3 ± 0.9 dBi and a small gain variation of less than 2.5 dB in the horizontal plane. Additionally, the sidelobe suppression of 18 dB and null filling below the main vertical beam are obtained by the designed feeding networks. These results make the proposed design attractive in base-station applications.

Broadband Horizontally Polarized Omnidirectional Antenna Array for Base-Station Applications

This communication presents a broadband horizontally polarized (HP) omnidirectional antenna array with low gain variation for base-station applications. It consists of six omnidirectional antenna units. In order to generate HP omnidirectional radiation patterns for each unit, three wideband planar dipoles are employed as basic elements and they are connected by a wideband three-way power divider with equal magnitude and phase, conducting as a loop antenna. Based on such a configuration, the antenna unit obtains an HP omnidirectional pattern as well as a wide bandwidth of 48.2% (VSWR < 1.5 within 1.67–2.73 GHz). However, the gain variation is more than 2.5 dB, which is relatively large. To reduce the gain variation, a novel approach is proposed by dividing the six antenna units into three unit pairs. Each unit pair consists of two antenna units which are complementary in radiation pattern. Using this method, the number of basic elements in each antenna unit is not increased, but the simulated gain variation is effectively reduced to about 1.24 dB.

Optical Fiber Amplifiers: Optimization and PerformanceEvaluation

This work demonstrates the simulation of two different types of optical fiber amplifiers (OFA) utilizing OptiSystem–10, namely, 3 m length of erbium doped fiber amplifier (EDFA) and 7 km length of Raman fiber amplifier (RFA). The counter-pumped architecture is adopted for both proposed optical amplifiers. The optimum pump power (OPP) for each amplifier determines in which the longest 3–dB flat gain bandwidth (3–dB BW), reasonable average gain level (Gav), proper average noise figure (NFav) and lower gain variation (Gvar) were achieved. The EDFA shows best performance at conventional band (C–band) within the pump power of 30 mW.While the better performance is observed at long band (L–band) within the pump power of 600 mW for the RFA.