Wide Frequency Tuning Range Research Articles

A CMOS Self-Contained Quadrature Signal Generator for SoC Impedance Spectroscopy.

This paper presents a low-power fully integrated quadrature signal generator for system-on-chip (SoC) impedance spectroscopy applications. It has been designed in a 0.18 μm-1.8 V CMOS technology as a self-contained oscillator, without the need for an external reference clock. The frequency can be digitally tuned from 10 to 345 kHz with 12-bit accuracy and a relative mean error below 1.7%, thus supporting a wide range of impedance sensing applications. The proposal is experimentally validated in two impedance spectrometry examples, achieving good magnitude and phase recovery results compared to the results obtained using a commercial LCR-meter. Besides the wide frequency tuning range, the proposed programmable oscillator features a total power consumption lower than 0.77 mW and an active area of 0.129 mm2, thus constituting a highly suitable choice as stimulation module for instrument-on-a-chip devices.

Reconfigurable RF Multiband Filter With Widely Tunable Passbands Based on Cascaded Optical Interferometric Filters

Despite the increasing importance and critical needs, reconfigurable radio frequency (RF) multiband filters are currently underdeveloped even both RF electronics and photonics technologies are being explored. Although RF multiband filters with large numbers of simultaneous passbands and wide frequency tuning range are extremely desired, achieving such functionality is extremely challenging. In this paper, a photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach–Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.

A Wide-Tuning-Range Low-Phase-Noise mm-Wave CMOS VCO With Switchable Transformer-Based Tank

In this letter, we present a millimeter-wave (mm-wave) complementary metal-oxide semiconductor (CMOS) voltage-controlled oscillator (VCO) that has a wide frequency tuning range (TR) and low phase noise (PN). The proposed architecture benefits from a switchable transformer-based LC -tank which significantly improves the TR without compromising the PN performance. The proposed 3-D transformer consists of three mutually coupled, switched spiral coils. The secondary and tertiary spiral coils are switched in or out of the circuit and depending on the switch states, the proposed VCO achieves four overlapping frequency sub-bands and a wide overall TR. To lower the loading effect of the switches, we present a design guideline which is based on the mutual coupling between the auxiliary coils. As a proof-of-concept, a mm-wave VCO is implemented in a 65-nm CMOS process. Based on the measurement results, the VCO achieves an average PN of −111.9 dBc/Hz at 10 MHz offset over the entire frequency TR, and a TR of ~18%, from 50.1 to 59.8 GHz, resulting in a figure-of-merit (FOM) incorporating the TR (FOMT) of −184 dBc/Hz. The VCO core consumes 6.2 mW from a 1-V supply and excluding the pads occupies a compact silicon area of 0.06 mm2.

Wide tuning range low phase noise VCO for V‐band application

In this study, millimetre wave (MMW) voltage controlled oscillator (VCO) is designed using 130 nm complementary metal–oxide–semiconductor single poly eight metals (1P8M) technology. Under 0.8 V supply, VCO can be tuned from 46 to 61.2 GHz, i.e. 28% frequency tuning range (FTR) is achieved. For the highest oscillation frequency, phase noise at 10 MHz offset frequency is −117.3 dBc/Hz, while the power dissipation is 9.39 mW. The FTR is improved by adopting multiband scheme using transformer tuned technique. Improvement in phase noise is done with a P-type metal–oxide–semiconductor as a variable capacitor for fine tuning of each band. Single N-type metal–oxide–semiconductor switch is placed on secondary side of transformer which makes the transformer tunable. Figure of merit of the proposed circuit is −183.3 dBc/Hz. Proposed VCO provides wide FTR and acceptable low phase noise for V-band application.

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters.

Here, we demonstrate the advantages of the laser Doppler vibrometer (LDV) over conventional techniques (the network analyzer), as well as the techniques to create an application-based microelectromechanical systems (MEMS) filter and how to use it efficiently (i.e., tuning the tuning-capability and avoiding both failure and stiction). LDV enables crucial measurements that are impossible with the network analyzer, such as higher mode detection (highly sensitive biosensor application) and resonance measurement for very small devices (fast prototyping). Accordingly, LDV was used to characterize the frequency tuning range and resonance frequency at different modes of the MEMS filters built for this study. This wide range frequency tuning mechanism is based simply on Joule heating from the embedded heaters and relatively high thermal stress with respect to the temperature of a fixed-fixed beam. However, we demonstrate that another limitation of this method is the resulting high thermal stress, which can burn the devices. Further improvement was achieved and shown for the first time in this study, such that the tuning capability was increased by 32% through an increase in the applied DC bias voltage (25 V to 35 V) between the two adjacent beams. This important finding eliminates the need for the extra Joule heating at the wider frequency tuning range. Another possible failure is through stiction and requirement of structure optimization: We propose a simple and easy technique of low frequency square wave signal application that can successfully separate the beams and eliminates the need for the more sophisticated and complicated methods given in the literature. The above findings necessitate a design methodology, and so we also provide an application-based design.

Wide digitally tunable lowpass filter for biomedical and wireless applications

A fully differential Gm-C lowpass filter for wireless and biomedical applications is introduced in this Letter. The proposed filter is based on a highly linear CMOS digital programmable operational transconductance amplifier (DPOTA).The filter consists of a parallel connection of three fourth-order Butterworth sections. Each section is optimised for a specific band of frequencies which can be tuned digitally. Switching between the different sections is achieved by controlling the corresponding DPOTAs' transconductance values, hence, this filter design eliminates the need for switches. Simulation results for a 90 nm CMOS technology are given. The third-order harmonic distortion (HD3) of the DPOTA remains below −60 dB up to 0.5 V differential input voltage at 1.2 V supply voltage. The proposed filter exhibits a wide cutoff frequency tuning range, from 100 Hz to 12 MHz, thus it covers many biomedical and wireless communication standards.

High-Efficiency, Broadband Converter From A Rectangular Waveguide TE10Mode to A Circular Waveguide TM01Mode for Overmoded Device Measurement

To accurately measure the performance of overmoded devices used in high-power microwave systems, a novel structure that effectively converts the TE10 mode in a rectangular waveguide to a high-purity TM01 mode in a circular waveguide is proposed. The circular TM01 mode is excited by a hybrid rectangular E-T waveguide structure, which uses a circular waveguide as the E element. Convex slots loaded at the rectangular waveguide, axially symmetric about the cylindrical waveguide, are introduced to suppress the competing lower order TE11 mode. A tuning stub loaded at the rectangular short wall is used to increase the frequency tuning range. The scattering matrix technique was used to study the mode converter along with the microwave network analysis method using some generalizations of the input port reflection and conversion efficiency, which were verified by the numerical full-wave simulation. Based on the theoretical analysis, an X-band TM01 mode generator is designed and measured. Low-power tests show that, when the length of the tuner increases from 5.7 to 11.7 mm, a wide frequency tuning range of ~500 MHz is obtained with a conversion efficiency of ~99%. Measured results and the theoretical analysis are in good agreement.

A Low-Profile Frequency Reconfigurable Grid-Slotted Patch Antenna

This paper presents a novel low-profile high gain frequency reconfigurable patch antenna with unidirectional radiation pattern by using a grid-slotted patch with tunable varactors loading. The antenna consists of two stacked substrates and three metal layers. A grid-slotted patch with two tunable varactors is placed on the top layer, a microstrip line is placed in the middle of two substrates, and the ground plane is on the bottom layer. A single dc voltage applied on two varactors is used to control the working frequencies of the proposed antenna. By altering the bias voltage, the working frequency of the proposed antenna can be continuously changed within a wide range from 2.45 to 3.55 GHz. The antenna maintains broadside radiation and stable radiation pattern in all the operating modes. The measured antenna gain of the proposed antenna rises from 4.25 to 8.49 dBi with the working frequency increases from 2.45 to 3.55 GHz. Compared to other frequency-reconfigurable antennas available in the literature, the proposed antenna has advantages of a wide frequency tuning range over a bandwidth of 1.45:1, high frequency selectivity, low profile (0.016 free-space wavelength at 2.45 GHz), high gain, stable unidirectional pattern, simple structure, and low cost. These advantages make it a promising candidate for cognitive radio and future wireless communication systems.

Quasi‐lumped dual‐mode reconfigurable eight‐way FPD

A quasi-lumped dual-mode reconfigurable eight-way filtering power divider (FPD) is presented. Two operating modes are one eight-way tunable FPD and one all stopband filter (ASF) with high suppression. The measured eight-way FPD can be tuned from 1.0 to 2.15 GHz, corresponding to the frequency tuning range (FTR) of 73%. The ASF is obtained by misaligning resonant frequencies of LC resonators and weakening their coupling. The proposed dual-mode FPD has the advantage of wide FTR, compact size, high isolation, ultra-wide isolation BW, and high suppression.

A Process-Independent and Highly Linear DCO for Crowded Heterogeneous IoT Devices in 65-nm CMOS

The Internet of Things (IoT) devices are manufactured under different fabrication quality standards, considering the wide variety of vendors. As a result, global process variations in the IoT system-on-chip (SoC) are an enormous concern that can affect reliability of the device. Among the components in a typical SoC, oscillator is the most susceptible element to process variations. This paper proposes a feedback-assisted digitally controlled oscillator (DCO). The DCO has 512 operating modes, for wide-range frequency tuning from 0.6 to 3.1 GHz. By adding a dynamic feedback to inner current-controlled oscillator using a frequency-to-current converter, the DCO remains linear and invariant to the process for entire 2.5-GHz frequency band. Thanks to pseudodifferential cross-coupled structure used in each stage, this paper achieves a 2.3 ps deterministic jitter at 1.87-GHz output frequency. Furthermore, Monte Carlo analysis is performed at 1.87-GHz frequency; indicate that standard deviation from the mean is 2.47% that verifies reliability of this design. Power consumption varies from 0.86 to 3.68 mW at 1.2 V supply voltage, corresponding to the code word. The DCO is implemented in 65-nm standard CMOS process.

A Simple Frequency-Agile Bandpass Filter With Predefined Bandwidth and Stopband Using Synchronously Tuned Dual-Mode Resonator

This letter proposes a novel and simple synchronously tuned dual-mode resonator (STDR) to achieve a frequency-agile bandpass filter (FA-BPF) with predefined bandwidth (BW) location, BW variation, and stopband characteristics. This solution overcomes the difficulty with predefining the BW of previous tunable filter designs. The proposed STDR is controlled by two varactors and a single bias. The two resonant frequencies’ separation of the resonator can be adjusted by changing the varactor loading position and the shorted stub length. Meanwhile, the transmission zero location can be predefined by specifying the corresponding dimensions. Based on the predefined STDR, the FA-BPF can be achieved easily. An FA-BPF with a constant BW is realized to demonstrate such a unique feature. The measurement results of the FA-BPF verify the theory, and also exhibit high selectivity, wide frequency tuning range, and simple design/ control procedure.

A Compact Trans-Directional Coupler With Wide Frequency Tuning Range and Superior Performance

In this paper, a compact coupled-line trans-directional (TRD) coupler with wide continuous frequency tuning range and superior performance is presented. The proposed tunable TRD coupler is composed of three coupled lines, two shunt stubs, and three types of varactors. By providing suitable reverse bias voltages on these varactors, the operating frequency of the proposed TRD coupler can flexibly be adjusted as desired. Moreover, better impedance match and port isolation are maintained at all tuning center frequencies. A theoretical analysis using the even–odd mode theory is presented to clarify the influence of the design parameters on the minimum and maximum operating frequencies. It is exhibited that the proposed TRD coupler has approximately 150% frequency tuning range in ideal conditions. Due to the manufacturing limitation, a microstrip TRD coupler with a tunable frequency of 1.0–2.5 GHz (85.7%) is designed and fabricated. The measured results show that the proposed TRD coupler can be tuned from 1.0 to 2.5 GHz with more than 27 dB return loss and more than 35 dB isolation in the entire tuning range, agreeing well with the simulation results.

Electrically varactor‐tuned bandpass filter with constant bandwidth and self‐adaptive transmission zeros

This paper presents a wideband frequency-agile bandpass filter (BPF) with constant absolute bandwidth (ABW) and two self-adaptive transmission zeros (TZs) at lower and higher stopbands. A frequency-dependent source-to-load (S-L) coupling is incorporated in this design so that two symmetrical TZs close to the tunable passband are self-adaptive and the separations between the passband center frequency and two TZs can almost keep the same for achieving continuous high selectivity in the frequency-tuning process. A lumped capacitor C1 and a varactor diode are loaded to the two open ends of the half-wavelength resonator. With the aid of the employed C1, the desired external quality factor can be obtained in a wide frequency-tuning range. Meanwhile, properly choosing the specific coupling region can make the coupling coefficient close to the desired one. As a result, the constant ABW can be obtained as the passband frequency changes. For demonstration, the proposed BPF is designed and fabricated. The simulated and measured results are presented. The results exhibit the tuning range from 430 MHz to 720 MHz with 3-dB constant ABW of around 75 MHz and the insertion loss of 1.34–2.92 dB, and the distance from TZs to center frequency is nearly constant at 150 MHz.

A 0.015-mm<inline-formula> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> Inductorless 32-GHz Clock Generator With Wide Frequency-Tuning Range in 28-nm CMOS Technology

This brief illustrates the design of an inductorless high-speed clock generator. Compared to inductance-capacitance ( $LC$ ) oscillators, ring oscillators are used in order to achieve a wide frequency-tuning range with a small chip area. By employing a cascaded phase-locked loop (PLL) architecture, the phase noise of the oscillator can be effectively suppressed. The first PLL is implemented with high-voltage devices under 1.8-V supply to provide a clean reference for the second PLL. The second PLL consists of only low-voltage devices, with a supply voltage of 0.9 V for high-speed operation. Following the second PLL, a clock doubler multiplies the PLL output clock by a factor of 2, which avoids power-consuming high-frequency clock dividers. In order to minimize any mismatch effects, special layout techniques are employed for the second voltage-controlled oscillator and the clock doubler. The prototype chip was fabricated in 28-nm complementary metal oxide semiconductor (CMOS) technology, and it occupies an active area of only 0.015 mm2. The proposed PLL achieves a maximum output frequency of 32 GHz and consumes a total power of 30 mW, exhibiting a power efficiency of 0.9 mW/GHz.

A band-selective low-noise amplifier using an improved tunable active inductor for 3–5 GHz UWB receivers

We propose a three stage 3–5GHz band-selective ultra-wideband low noise amplifier (LNA). A capacitor cross-coupled gm-boosting broadband input stage is adopted for input matching and high gain, and also improves the noise figure (NF) and reduces current consumption. The noise performance of the LNA is improved significantly using a noise cancelation stage. A band-selective stage using a proposed tunable active inductor controls input and output matching simultaneously using one output stage tuning circuit. The key aspect of the proposed active inductor is reduced interference, noise, and complexity problems encountered with conventional wide input-tunable output and input tuning architectures. We use a variable capacitor to further improve noise performance, the quality factor, and inductance of the active inductor and to provide a wide frequency tuning range. The simulation results show gains of 12.7, 13.3, and 13.3dB, and NF values of 3.2, 3.4, and 3.7dB at the 3.432, 3.960, and 4.488GHz frequency bands, respectively. The proposed band-selective LNA consumes 8.4mW from a 1.8-V power supply.

Series Resonator Mode Switching for Area-Efficient Octave Tuning-Range CMOS $LC$ Oscillators

Integrated oscillators with octave frequency tuning range (FTR) are desirable for wireless transceivers supporting multiple frequency bands. In this paper, we describe a wide-FTR CMOS voltage-controlled oscillator (VCO) based on a novel area-efficient series resonator mode-switching scheme that preserves resonator quality factor $Q$ across the entire octave tuning range. This allows the CMOS VCO to simultaneously achieving wide FTR, area efficiency, and low phase noise, demonstrating state-of-the-art figure of merit (FoM) for > 10-GHz octave-tuning range VCOs. We also analyze the relationship between $Q$ and FTR across common resonator band-switching schemes, quantifying performance limits and highlighting the benefits of using mode-switching for wide-FTR VCOs. The proposed approach is demonstrated through a 6.4–14-GHz (74.6% FTR) VCO implemented in 65-nm CMOS that achieves 186–188-dB VCO FoM, demonstrating good FoM across the entire FTR. The scalability of this approach toward achieving even larger FTR is also demonstrated by a triple-mode 2.2–8.7-GHz (119% FTR) CMOS VCO. Area efficiency of the proposed mode-switching scheme is demonstrated by the state-of-the-art 197-dB FoM area achieved by the 14-GHz VCO.

Tunable Bandpass Filter Using a Switched Tunable Diplexer Technique

In this paper, a new technique using two p-i-n diodes to switch between two channels of a tunable diplexer with constant return loss is proposed to design a tunable bandpass filter (BPF) with wide frequency tuning range (FTR). The used third-order tunable diplexer with two independently tuned channels consists of one common varactor-tuned lumped-element dual-resonance resonator and two varactor-tuned LC resonators. The ports of its two channels are connected by a single-pole double-throw switch, so that one port of the tunable BPF is constituted. And its common port serves as the other port of the tunable BPF. In the switched tunable diplexer design, its direct current (dc) bias voltages are also appropriately selected to improve the in-band and out-of-band performances of the tunable BPF. As examples, a third-order tunable diplexer with constant return loss of 15 dB is first designed. The measured results show that the 3 dB cutoff frequency of its lower channel can be tuned from 0.5 to 1.02 GHz, while the 3 dB cutoff frequency of its upper channel can be tuned from 1.01 to 1.78 GHz. Then, a tunable BPF is designed, and its 3 dB cutoff frequency covers from 0.485 to 1.82 GHz. The proposed tunable BPF exhibits good return loss, wide FTR, and compact size.

Continuously Tunable 0.55–1.9-GHz Bandpass Filter With a Constant Bandwidth Using Switchable Varactor-Tuned Resonators

This paper reports on tunable 2- and 3-pole bandpass filters with a wide frequency tuning range (tuning ratio >3) and a constant bandwidth using switchable varactor-tuned resonators. The wide center frequency tuning range is obtained using p-i-n diodes to switch in and out quarter-wavelength ( $\lambda $ /4) or half-wavelength ( $\lambda $ /2) resonators for low-band or high-band modes, without increasing the tuning capacitance range of the varactors. A combination of electric and magnetic coupling is utilized to realize a near constant absolute bandwidth across the tuning range. A switchable feed line with a fixed matching capacitance is used to realize the external coupling. Two filters are designed and fabricated on a Duroid substrate with $\varepsilon _{r} = 2.2$ and $h =0.787$ mm. For the 2-pole filter, the center frequency is tuned from 550 to 1900 MHz while maintaining a 3-dB bandwidth of 92 ± 6 MHz, insertion loss of 3.2~4.4 dB, and return loss of better than 15 dB. For the 3-pole filter, the center frequency is tuned from 540 to 1800 MHz while maintaining a 3-dB bandwidth of 89 ± 4 MHz, insertion loss of 4~5.4 dB, and return loss of better than 12 dB. For both filter types, the third-order intercept point and 1-dB compression point ( $P_{\mathrm {1~dB}})$ are 11 and 7 dBm, respectively. The rejection level at 200-MHz offset frequency from the passband center frequency is better than 25 and 41 dB for 2- and 3-pole filters, respectively, across the entire tuning range. To the best of our knowledge, this planar bandpass filter exhibits the widest tuning range with a near-constant bandwidth.

Temperature tunable metamaterial absorber at THz frequencies

Dynamic or active control over the resonance frequency of the perfect metamaterial absorbers have attracted considerable attention, and many kinds of frequency tunable absorbers have been proposed. Unfortunately, these designed absorbers have drawbacks of very small frequency tuning range as well as complex unit structure. In this paper, a simple design and large frequency change range of terahertz metamaterial absorber is investigated. The absorber structure consists of only a patterned square metallic patch and an appropriate thickness of the dielectric spacing slab on top of a metallic board. Results show that the frequency tuning range of the metamaterial absorber can be up to 80.4%, which is much greater than that of the existing absorbers (no more than 30%). The continuous shift of the resonance frequency can be explained by the temperature dependent dielectric m. Besides, we also found that the presented design strategy is a genetic method and can apply to other types of structure designs. The simple design and wide frequency tuning range of the absorbers could find potential applications in materials detection, biological sensing, and frequency selective thermal emitters.

THz polariton laser using an intracavity Mg:LiNbO3 crystal with protective Teflon coating.

An enhancement in the performance of a THz polariton laser based on an intracavity magnesium-doped lithium niobate crystal (Mg:LiNbO3) in surface-emitted (SE) configuration is demonstrated resulting from the deposition of a protective Teflon coating on the total internal reflection surface of the crystal. In this cavity geometry the resonating fields undergo total internal reflection (TIR) inside the lithium niobate, and laser damage to that surface can be a limiting factor in performance. The protective layer prevents laser damage to the crystal surface, enabling higher pump power, yielding higher THz output power and wider frequency tuning range. With the unprotected crystal, narrow-band THz output tunable from 1.50 to 2.81 THz was produced, with maximum average output power of 20.1 µW at 1.76 THz for 4 W diode pump power (limited by laser damage to the crystal). With the Teflon coating, no laser damage to the crystal was observed, and the system produced narrow-band THz output tunable from 1.46 to 3.84 THz, with maximum average output power of 56.8 µW at 1.76 THz for 6.5 W diode pump power. This is the highest average output power and the highest diode-to-terahertz conversion efficiency ever reported for an intracavity terahertz polariton laser.