Design and modeling of a micromachined high-Q tunable capacitor with large tuning range and a vertical planar spiral inductor

In wireless communication systems, passive elements including tunable capacitors and inductors often need high quality factor (Q-factor). In this paper, we present the design and modeling of a novel high Q-factor tunable capacitor with large tuning range and a high Q-factor vertical planar spiral inductor implemented in microelectromechanical system (MEMS) technology. Different from conventional two-parallel-plate tunable capacitors, the novel tunable capacitor consists of one suspended top plate and two fixed bottom plates. One of the two fixed plates and the top plate form a variable capacitor, while the other fixed plate and the top plate are used to provide electrostatic actuation for capacitance tuning. For the fabricated prototype tunable capacitors, a maximum controllable tuning range of 69.8% has been achieved, exceeding the theoretical tuning range limit (50%) of conventional two-parallel-plate tunable capacitors. This tunable capacitor also exhibits a very low return loss of less than 0.6 dB in the frequency range from 45 MHz to 10 GHz. The high Q-factor planar coil inductor is first fabricated on a silicon substrate and then assembled to the vertical position by using a novel three-dimensional microstructure assembly technique called plastic deformation magnetic assembly (PDMA). Inductors of different dimensions are fabricated and tested. The S-parameters of the inductors before and after PDMA are measured and compared, demonstrating superior performance due to reduced substrate loss and parasitics. The new vertical planar spiral inductor also has the advantage of occupying much smaller silicon areas than the conventional planar spiral inductors.     

Monolithic tunable active inductor with independent Q control

A 1.1-GHz fully integrated GaAs MESFET active inductor is presented in this paper. Both the inductance and loss resistance are tunable with the inductance independent of series loss tuning. The measured loss resistance is tunable over a -10- to +15-Ω range with a corresponding change in inductance of less than 10% at 100 MHz and less than 4% for frequencies above 500 MHz. The inductance is tunable from 65 to 90 nH. Considerably larger bandwidths can be achieved depending on the fabrication technology employed and the intended application of the circuit     

基于SiGe HBT 的射频有源电感的设计

基于回转器原理,提出利用两个SiGe异质结晶体管,通过采用不同组态构成四种射频有源电感,其中包括两种正电感和两种负电感,并对它们的性能进行了比较.结果表明,共射组态与共集组态构成的有源电感的性能最优异,并就此做了详细讨论.在带宽为1～15.8 GHz的范围内,其电感值可以达到1 nH以上,电感的品质因数最大值达到75.4.通过调节晶体管的偏置电压,有源电感的电感峰值在1.268 nH-1.914 nH范围内变化.电感值的可调谐性对增强电路设计的可复用性及灵活性具有现实意义.     

MEMS-Based Tunable LC Bandstop Filter With an Ultra-Wide Continuous Tuning Range

This letter presents a new microelectromechanical system-based tunable LC filter that utilizes a tunable capacitor and a tunable inductor in a single device. An electrically floating metal plate is located between the tunable capacitor and the tunable inductor. As the floating metal plate is thermally moved and used commonly for both the capacitor and inductor, the device provides an ultra-wide continuous frequency tuning range by a simultaneous increase or decrease of the capacitance and inductance. The fabricated tunable LC filter showed a continuous frequency tuning ratio in excess of 127% in a range of 8.8 GHz to more than 20 GHz.      

Voltage Regulator Optimization Using Multiwinding Coupled Inductors and Extended Duty Ratio Mechanisms

This paper examines design optimization of voltage regulators (VRs) for microprocessor applications. Optimality of competing VR topologies, such as conventional (Conv) buck, coupled inductor, and extended duty ratio converters, is examined using efficiency norms and a new cost-per-watt metric to compare the amount of output capacitance (which is strongly correlated to the VR cost) to the efficiency. Coupled inductors provide a higher steady-state inductance than transient inductance. Lower transient inductance allows for smaller output capacitance. However, lower output capacitance requires a higher switching frequency and thus yields greater switching losses and lower efficiency. Extended duty ratio mechanisms reduce the switching voltage, and hence, reduce switching losses and increase efficiency. Experimental data are provided that the coupled inductor extended duty ratio converter has the same average efficiency, has higher light-load efficiency, and uses one-third of the output capacitance as the Conv multiphase buck converter. Hence, the combination of multiwinding coupled inductors and extended duty ratio mechanisms is shown to be the optimal VR configuration. The optimality concepts contributed in this paper resolve the ambiguity between VR cost and efficiency, and are essential for selecting the best solution among several competing VR designs.      

A Novel Electrically Tunable RF Inductor With Ultra-Low Power Consumption

In this study, we propose for the first time an electrically and continuously tunable RF inductor using grounded metal oxide semiconductor (MOS) transistor as a control device. By adjusting the output resistance of the grounded MOSFET, the ground-return current can lead to a significant variation in series inductance. This proposed inductor structure was implemented in a standard CMOS process and characterized up to 30 GHz, which demonstrates maximum inductance variations of 32% and 58% at 5.8 and 18 GHz, respectively. The dc power consumption of the proposed design is kept within 50 muW over the entire tuning range.     

一种采用LC谐振电路的高频差分有源电感

提出了一种采用LC并联谐振电路的新型差分有源电感,实现了宽的工作频带、高的Q值、较大的电感值和可调谐功能.采用无源电感和MOS晶体管可变电容构成LC谐振电路,减小了等效串联电阻和等效并联电容,在增大电感值、Q值的同时,扩大了工作频带.仿真结果表明,在2～7.6 GHz频率范围内,该新型差分有源电感的电感值大于26 nH...     

A 25–75-MHz RF MEMS Tunable Filter

This paper presents a state-of-the-art discrete RF microelectromechanical systems (MEMS) tunable filter designed for 25-75-MHz operation. This paper also presents an enhanced model of the RF MEMS switch, which is used for accurate prediction of the tunable filter response. The two-pole lumped-element filter is based on digital capacitor banks with on-chip metal-contact RF MEMS switches and lumped inductors, and results in a tuning range of 3:1 with fine frequency resolution, and a return loss better than 13 dB for the entire tuning range. The relative bandwidth of the filter is 4 plusmn 1% over the tuning range and the insertion loss is 3-5 dB, limited mostly by the inductor Q and the switch loss. The IIP₃ measurements prove that tunable filters with metal-contact series RF MEMS switches show extremely linear behavior (IIP₃ > 68 dBm).     

Wide tunable CMOS active inductor

A tunable CMOS active inductor is presented. The circuit uses a crosscoupled pair of transistors providing positive feedback for enhanced quality factor. The circuit is biased with a controllable current source varying the feedback and tuning the inductor. The proposed inductor is designed and simulated in a 90 nm digital CMOS process. It shows a wide-frequency range inductive impedance and a very high resonance frequency. By cascading two inductors, a wideband filter/ amplifier is designed to characterise the inductor performance.     

Design of multilevel pyramidically wound symmetric inductor for CMOS RFIC’s

This paper presents the design of a multilevel pyramidically wound symmetric (MPS) inductor structure. Being multilevel, the MPS inductor achieves high inductance to area ratio and hence occupies smaller silicon area. The symmetric inductor is realized by winding the metal trace of the spiral coil down and up in a pyramidal manner exploiting the multilevel VLSI interconnects technology. Closed form expressions are also developed to estimate the self resonating frequency (f _res ) of the MPS inductor and results are compared to two layer conventional symmetric and asymmetric stack. The estimation is also validated with full wave electromagnetic simulation. The performance of various MPS inductors of different metal width, metal offsets and outer diameter is demonstrated. For an inductance of 8 nH, the MPS inductor reduces the area by 65–95% over conventional planar symmetric inductors and 71–94% over its equivalent pair of asymmetric planar inductors. The performance is also compared to other symmetric inductors reported in literature. With MPS inductor, the cost and size of RF IC’s will be reduced significantly.     

A Wide Tuning-Range CMOS VCO With a Differential Tunable Active Inductor

By utilizing a differential tunable active inductor for the LC-tank, a wide tuning-range CMOS voltage-controlled oscillator (VCO) is presented. In the proposed circuit topology, the coarse frequency tuning is achieved by the tunable active inductor, while the fine tuning is controlled by the varactor. Using a 0.18-$muhbox m$CMOS process, a prototype VCO is implemented for demonstration. The fabricated circuit provides an output frequency from 500 MHz to 3.0 GHz, resulting in a tuning range of 143% at radio frequencies. The measured phase noise is from$-$101 to$-$118 dBc/Hz at a 1-MHz offset within the entire frequency range. Due to the absence of the spiral inductors, the fully integrated VCO occupies an active area of$hbox 150times hbox 300 muhbox m^2$.     

Surface micromachined solenoid on-Si and on-glass inductors for RFapplications

RF performance of surface micromachined solenoid on-chip inductors fabricated on a standard silicon substrate (10 Ω·cm) has been investigated and the results are compared with the same inductors on glass. The solenoid inductor on Si with a 15-μm thick insulating layer achieves peak quality (Q-) factor of 16.7 at 2.4 GHz with inductance of 2.67 nH. This peak Q-factor is about two-thirds of that of the same inductor fabricated on glass. The highest performance has been obtained from the narrowest-pitched on-glass inductor, which shows inductance of 2.3 nH, peak Q-factor of 25.1 at 8.4 GHz, and spatial inductance density of 30 nH/mm². Both on-Si and on-glass inductors have been modeled by lumped circuits, and the geometrical dependence of the inductance and Q-factor have been investigated as well     

Flip-Chip-Assembled Air-Suspended Inductors

This paper discusses high-performance planar suspended inductors for hybrid integration with microwave circuits. The inductors are fabricated using a silicon surface micromachining foundry process and assembled using flip-chip bonding. The silicon substrate is removed, leaving a metal inductor suspended 60 mum above the microwave substrate, thus reducing the parasitic capacitance and loss. Various rectangular, octagonal, and circular inductor geometries with one to five windings are designed with inductance values between 0.65 and 16 nH to demonstrate the flexibility of this technique. Measured self-resonant frequencies are between 5 and 34.8 GHz, with quality factors from 45 to 100. Equivalent circuits extracted from measurement for each inductor type show good agreement with measured impedance and full-wave simulations over frequency. The dc current handling limit is 200 mA     

Flip chip assembled MEMS inductors

High performance suspended MEMS inductors produced using a flip chip assembly approach are described. An inductor structure is fabricated on a carrier and then flip chip assembled onto a substrate to form a suspended inductor for RF-IC applications with significant improvement in Q-factor and frequency of operation over the conventional IC inductors. A spiral MEMS inductor has been successfully produced on a silicon substrate with an air gap of 26 /spl mu/m between the inductor structure and the substrate. The inductance of the device was measured to be /spl sim/2 nH and a maximum Q-factor of 19 at /spl sim/2.5 GHz was obtained after pad/connector de-embedding.     

A low power tunable inductor based on active capacitor with negative resistance

A method to provide a low power tunable inductor is presented in which the inductance and its equivalent series resistance can be independently tuned. This equivalent series resistance can be also set to negative or zero value that is corresponding to inductor with ideal quality factor. In this method, a varactor is placed in parallel with a passive inductor and then, an active capacitor is placed in series with them. To this end, a low power Tunable Active Capacitor (TAC) is proposed which is capable of generating tunable capacitor and large negative resistance to compensate the loss of tunable inductor circuit. Also, the power consumption is low because of using a diode-connected transistor. A prototype of the proposed circuit is designed and simulated at 4 GHz. The electromagnetic simulation results show the inductance tuning range of 0.48–2.3nH with zero or even negative equivalent series resistance is obtained while the power dissipation is less than 3 mW. Moreover, noise analysis shows that higher inductance translates to lower noise while there is a weak correlation between noise and quality factor of the obtained inductances.     

基于SOI衬底的射频电感优化设计

比较了SOIRF电感与体硅电感的性能 ,并根据模拟结果分析了电感中空面积 ,电感形状结构 ,金属宽度、间距对SOI电感品质因数Q、自谐振频率、电感量L的影响 ,最后提出了一种基于SOI衬底RF电感的优化设计原则 .以往射频集成电感性能的比较并不固定电感值 ,而文中全部参数的变化都是在电感值相同的情况下进行比较     

Small-Resistance and High-Quality-Factor Magnetic Integrated Inductors on PCB

We have designed and fabricated both single-coil and parallel-coil magnetic integrated inductors with extremely small resistances and high quality factors on an 8-in-round printed circuit board (PCB) substrate for microprocessor power delivery applications. The dc resistances of these inductors are less than 12 ${hbox{m}} Omega $. Soft magnetic material CoFeHfO was successfully integrated into the inductor fabrication to increase the inductance. The quality factors are more than 80 in a frequency range of 1.5–2 GHz for air-core inductors and more than 23 in a range of 200–300 MHz for magnetic inductors. The net inductance improvement of the magnetic inductor over air-core inductor is about 12%, which could be further enhanced with a thicker magnetic core, according to our theoretic calculation and HFSS simulation. We also characterized the permeability spectra of CoFeHfO material on the PCB substrate, simulated the high-frequency performance of the magnetic integrated inductor by HFSS, and, for the first time, reached a good agreement with the experimental data. The experimental and simulation results of the magnetic inductors as compared to those of the air-core inductors point out the future direction to further optimize magnetic integrated inductors.      

A 0.13-μ m CMOS Phase Shifter Using Tunable Positive/Negative Refractive Index Transmission Lines

This letter presents a tunable positive/negative refractive index transmission line (TL) phase shifter utilizing active circuits. It comprises a microstrip TL loaded with series varactors and a shunt monolithic microwave integrated circuit (MMIC) to synthesize a tunable inductor. This implementation increases the phase tuning range and maintains the input and output matching of the phase shifter across the entire phase tuning range, while eliminating the need for bulky passive inductors. The phase shifter is capable of providing both positive and negative phase shifts. The MMIC tunable inductors are fabricated in a 0.13-mum CMOS process and operate from a 1.5-V supply. The phase shifter achieves a phase of -40deg to +34deg at 2.5GHz from a single stage with less than -19dB return loss, and better than 1.1-dB insertion loss at 2.5 GHz. The phase shifter has a 1-GHz bandwidth over which the return loss remains better than 12.1dB     

Reduction of Inductive Crosstalk Using Quadrupole Inductors

Interference due to inductor crosstalk is a growing concern in modern RFICs where inductors are placed in close proximity. A quadrupole inductor is explored as a method to reduce inductive crosstalk. A quadrupole inductor and standard inductor are compared with respect to inductance, quality factor, and area. Then, physics-based calculations are corroborated with simulation and measurement to predict crosstalk reduction as a function of position. Measurements verify up to a 31 dB reduction in crosstalk. Finally, phase noise measurements of voltage-controlled oscillators show that the quadrupole inductor can be used in circuits without negatively impacting performance.      

MMIC用NiFe-SiO_x磁性金属颗粒膜电感研究

在蓝宝石基的氮化镓衬底上采用射频磁控溅射结合剥离的方法制作了NiFe-SiOx磁性金属颗粒膜,利用PECVD淀积绝缘层,制备出"SiN绝缘层/NiFe-SiOx薄膜/SiN绝缘层/金属线圈"结构的平面电感。测试表明,对于单圈电感,与无磁膜结构相对比在1 GHz时电感量有30%的提升,且对Q值影响不大;对于多圈电感,电感量与电感结构密切相关,当磁膜同时存在于线圈下和线圈之间时对电感量提升最大,但截止频率较低;而磁膜在电感线圈正下方的结构对电感量提升较前一种磁膜电感低,但截止频率较前一种磁膜电感高。