Frequency Tuning Circuit Research Articles

Scalable, low-power and high-performance active-RC complex band-pass/low-pass filter with automatic frequency tuning applied to the Internet of Things

This article introduces a comprehensive 3rd Chebyshev active-RC complex band-pass/low-pass filter with an automatic cut-off frequency tuning circuit. The designed filter achieves 2 dB step gain control within the range of −6 dB–24 dB and 4 different bandwidth modes including low-pass modes and complex band-pass modes. A compact fully-differential (FD) amplifier with feedforward compensation and reverse pole splitting technique is used to meet the stringent filter's performance. The novel amplifier achieves an open loop gain of 62 dB and a maximum unity-gain bandwidth (UGB) of 732 MHz with VDD = 0.9 V and 0.32 mW of power dissipation. Using the proposed amplifier, the filter achieves the lowest power consumption reported in the literature for active-RC implementations and 30 % power reduction over similar active-RC filters. By employing an optimized solution for dynamic allocation of inter-stage gain, the filter achieves a maximum in-band-IIP3 of +25.7 dBm and an improvement of 2 dB. Also, an automatic frequency tuning scheme is used to eliminate the effect of process variation. The filter is fabricated in 22 nm CMOS process occupying 0.44 mm × 0.44 mm area and consuming 1.8 mW and 1.2 mW from 0.9 V supply voltage in Wi-Fi and BLE modes, respectively. The maximum figure of merit (FoM) is 142.6 dB/J. The RC tuning circuit has a precision of 1.5 % and covers a range of 20 %.

Autonomous Resonant Frequency Tuner for a 6.78MHz Inductive Coupling Wireless Power Transfer System to Stably Maximize Repeater Current

Recently, the resonant inductive coupling wireless power transfer (RIC-WPT) technique is being widely used to charge small IoT devices dispersed in a wide area, e. g., an office desk and warehouse rack. In this application, the repeater is utilized to expand the chargeable area without an additional AC power source. The repeater comprises a LC resonator commonly with a high-quality factor to induce large current in the repeater coil. However, this causes the problem that the repeater performance is highly susceptible to the variation in its resonant frequency due to the manufacturing tolerance of coil inductance and resonant capacitance as well as the variation of the magnetic coupling between the transmitter and repeater coils. To solve this problem, a previous study has proposed a concept of the autonomous resonant frequency tuning circuit to stably maximize repeater coil current, although this study implemented a part of this control system as a practical circuit. This paper aims to develop a complete autonomous resonant frequency tuning circuit that implements the aforementioned concept. The proposed circuit adjusts the resonant frequencies of the transmitter and repeater by utilizing the Automatic Tuning Assist Circuits. These frequencies are optimized using the infrared wireless signal communication from the transmitter to the repeater. Along with the operating principle of the proposed circuit, this study presents detailed circuit design as well as the experimental results, which verified the stable autonomous maximization of the repeater coil current against the variation in the resonant frequency of the repeater resonator.

A 120 MHz fast automatic tuning CMOS active-RC lowpass filter

In this paper, a fast automatic cutoff frequency calibrating, CMOS lowpass filter with linear-in-dB tunable gain and constant in-band group delay is presented. The automatic frequency tuning (AFT) circuit can successfully tune the cutoff frequency to 120 MHz with less than 4.7% error. In-band group delay variation is handled using a capacitor process variation detection circuit (CPVD), and the overall tuning time is less than 700 ns. The design is done using STM PD-SOI 130 nm CMOS process, and the supply voltage is 1.2 V with a total power consumption of 21.7 mW. The overall filter provides a programmable linear-in-dB gain of 0.5 dB to 17.6 dB range with a cutoff tuning range of 80 to 180 MHz. The in-band group delay variation is below 500 ps with an adjacent channel ratio (ACR) of 85 dB. The spurious free dynamic range (SFDR) is over 66.6 dBc. The active area of the filter with tuning is 0.171 mm2.

A Subcircuit-Based Model for the Accumulation-Mode MOS Capacitor

The accumulation-mode metal-oxide-semiconductor (MOS) capacitor is commonly employed to implement MOS varactors in frequency-tuning circuits for radio frequency (RF) and analog applications. A subcircuit model for the accumulation-mode MOS (AMOS) capacitor based on the Berkeley Short-channel IGFET Model (BSIM) for the MOS field effect transistor (MOSFET) is presented. The proposed model accurately fits the capacitance-voltage (C-V) characteristics of an AMOS capacitor fabricated in a submicron CMOS process over the full range of operating gate voltages. The model also accounts for the impact of the distributed series resistance on the transient response of the AMOS capacitor. Notably, the gate capacitance and the associated series resistance are modeled as a distributed resistor-capacitor (RC) network to derive a subcircuit-based model with the bias-dependent resistance of the accumulation layer modeled as a voltage-controlled resistor (VCR). The proposed model is evaluated based on SPICE simulation of the intrinsic transient response of the AMOS capacitor using a basic circuit, representing the distributed RC network associated with the MOS device structure. Fine tuning of the effective series resistance in the subcircuit model can be achieved by fitting the measured data characterizing the charge–discharge behavior of the AMOS capacitor to the simulated data characterizing the intrinsic transient response generated by SPICE.

A 0.45-to-1.8 GHz synthesized injection-locked bang-bang phase locked loop with fine frequency tuning circuits

This paper proposes a synthesized injection-locked bang-bang phased-locked loop (SILBBPLL) with high digital controlled oscillator (DCO) frequency resolution. The SILBBPLL is expressed with hardware description language and automatically placed & routed (APR) by using standard digital circuit design flow. As the mismatch issues of the circuits are not considered carefully during the APR design flow, the phase noise performance is severely deteriorated. We adopt pulse injection locking technique to improve the phase noise performance. The DCO frequency resolution is critical for reducing the reference spur in a digital injection-locked PLL. Therefore, we propose novel frequency tuning circuits to increase the DCO frequency resolution so that the reference spurs are reduced. The frequency tuning circuits consist of a standard cell based high-linearity output feedback DAC (OFDAC) and two custom varactors. The OFDAC is used to tune the frequency of the DCO with the custom varactor precisely. The custom varactor is firstly designed, added into the standard cell library, and APR with the standard cells. The SILBBPLL chip with a core area of 0.008 mm2 is implemented in 65 nm CMOS process. When operating at 1.8 GHz, the measured results show that the root-mean-square (RMS) jitter integrated from 10 kHz to 100 MHz is 1.1 ps, and the power consumption is 1.5 mW with a 0.8-V supply. The proposed SILBBPLL achieves a figure-of-merit (FoM) of −237.4 dB and a reference spur of −50.9 dBc.

0.18 mW/pole inverter‐based G m ‐C bandpass filter with automatic frequency tuning

A low-power Gm-C filter with the elliptic prototype targeting wireless application of the IEEE 802.15.4 (ZigBee) standard is presented. A modified inverter-based Gm cell is proposed to increase the current efficiency. Due to the tail current source, this Gm cell also shows better common-mode rejection and power supply rejection performance than traditional operational transconductance amplifier (OTA) structure. The filter is implemented in a 65 nm CMOS process. It achieves a figure of merit of 0.01 fJ with a power consumption of 0.18 mW/pole from a 1.2 V supply voltage. It provides stopband attenuation better than 40 dB, and an in-band IIP3 of 9 dBm. An automatic frequency tuning circuit based on sine-wave PLL method is introduced to compensate for the process variations. The centre frequency and bandwidth can be simultaneously tuned to satisfy the specifications. They are also stable over the process variations with only 2.3% deviation.

A wide tuning range Gm-C complex filter with master-slave automatic frequency tuning based switched-capacitor

A wide tunable Gm-C complex filter with programmable operational transconductance amplifier (OTA) is presented in this paper. With automatic tuning of the master-slave stage, the filter's time constant C∕Gm is set to a fixed value. Programmable OTA prevails wider tunable range. To achieve high linearity, an optimized differential OTA structure based on second-generation current conveyors (CCIIs) is employed for achieving wider tuning range in the complex filter. And the linearity of the filter suffers less from the master frequency tuning circuit because of no modification in the inner V-I conversion core during the tuning course. Benefited from the virtual ground created by the amplifier in switched-capacitor circuit, higher tuning accuracy is obtained. The prototype of the filter was fabricated in SMIC 0.18-μm CMOS process. Measurement results show that the tunable center frequency ranges from 147 kHz to 1.95 MHz and the tunable bandwidth ranges from 94 kHz to 1.96 MHz. Meanwhile, the filter achieves an in-band IIP3 above 18.2 dBm.

A low power wide tuning range baseband filter for multistandard transceivers**Project supported by the Scientific Research Plan Projects of Hebei Education Department (No. Q2012019).

This paper presents the design and implementation of a low power wide tuning range baseband filter with an accurate on-chip tuning circuit for reconfigurable multistandard wireless transceivers. The realized low pass filter (LPF) is a six-order Butterworth type by cascading three stage active-Gm-RC biquadratic cells. A modified linearization technique is used to improve the filter linearity performance at low power consumption. A new process-independent transconductor matching circuit and a new frequency tuning circuit with frequency compensation are proposed to achieve a high precision filter frequency response. The proposed LPF is realized in a 130 nm standard CMOS technology. The measured results show that the LPF exhibits a high bandwidth programmability from 0.1 to 25 MHz with a tuning frequency error less than 2.68% over the wide tuning range. The power consumption is scalable, ranging from 0.52 to 5.25 mA, from a 1.2 V power supply while achieving a 26.3 dBm in-band IIP3.

Resonant frequency tuning of an industrial vibration energy harvester

This paper presents preliminary results of tuning the resonant frequency of two industrial vibration energy harvesters. The VEH-450 from Ferro Solutions and the PMG17-50 from Perpetuum were tested using discrete reactive electrical loads. The former could be tuned to +0.5 Hz and -2 Hz from its natural resonant frequency of 50.5 Hz at 0.1g. The latter, however, has a broadband output power spectrum that spans ±10 Hz and its output voltage saturates at 7 Vrms, thereby rendering it un-tunable using the method presented here. A comparison of output power between a tuned VEH-450 and an un-tuned PMG17-50, normalised by harvester weight, shows that the former outperforms the latter only at a tuned frequency of 49.8 Hz. A discussion of a resonant frequency tuning circuit that can be fitted to an existing harvester without making modifications to the harvester is presented.

1-V 365-$\mu{\rm W}$ 2.5-MHz Channel Selection Filter for 3G Wireless Receiver in 55-nm CMOS

This paper presents a novel 1-V 2.5-MHz continuous-time filter for 3G wireless application, fabricated using a standard 55-nm CMOS process. The four-pole filter topology includes a single pole-tracking Operational Amplifier (OPAMP) structure to achieve low in-band noise levels, high out-of-band linearity, and reduced power consumption. An automatic frequency tuning circuit is developed to compensate for process and environmental variations. The proposed filter achieves inband noise of 18-μV rms and out-of-band IIP3 of 33 dBm within 365 μW. The out-of-band spurious-free dynamic range is measured at 76.7 dB, resulting in a figure-of-merit of 1.24 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> fJ.

Design of Low Voltage Low Power LPF for WSN Node

A fourth-order low-pass continuous-time filter for a WSN transmitter is presented. The active RC filter was chosen for the high linearity, designed by using the leapfrog topology imitates the passive filter. The operation amplifier (op-amp) adopted by the filter is feed-forward operation amplifier, which could get the GBW as large as possible under the low power consumption. The cut-off frequency deviation due to the process corner, aging and temperature deviation is adjusted by an automatic frequency tuning circuit. The filter in a 0.18μm RF CMOS technology consumes 1mW from a 1V power supply. The measured results of the chip show that the bandwidth is about 1.5MHz. The voltage gain of filter is about-4.5dB with the buffer, the ripple in the pass-band is lower than 0.5 dB, and the channel rejection ratio is larger than 30dB at 4MHz.

A CMOS Gm—C complex filter with a reconfigurable center and cutoff frequencies in low-IF WiMAX receivers

This paper presents a reconfigurable fifth-order complex Gm—C filter for different data rates in low-IF WiMAX applications. The design procedure and linearized measures to realize the complex filter are described. In order to achieve the reconfigurability of bandwidth window, the center frequency and the cutoff frequency filter are adjusted simultaneously by changing capacitor values while keeping transconductors unchanged. Also, the filter integrates an on-chip automatic frequency tuning circuit based on a PLL. Experimental results show that it has an IRR of 32 dB, a THD of −43 dB, and an input-referred noise of 21 μVrms. The chip is fabricated in 0.13 μm CMOS process, occupies 0.7 × 1 mm2, and consumes 4.8 mA current from a 1.2 V power supply.

Compact SC frequency tuning circuit for continuous-time Gm–C filters

A novel automatic frequency tuning circuit for continuous-time filters is presented. Based on the switched-capacitor technique, the circuit offers an advantage in terms of simplicity resulting from the use of only two matched current sources, an operational amplifier with relaxed specifications and a transconductor that is a replica of the filter transconductors. Despite the simplicity of the scheme, the accuracy of the system is less than 1 % of frequency error. The circuit has been designed in a 0.5 μm CMOS technology with a 3.3 V power supply and simulation results confirm the suitability of the proposed approach.

A 1.8-V, 5-mA reconfigurable analog baseband circuit for low-IF multi-mode multi-band receivers

A 1.8-V, 5-mA reconfigurable analog baseband circuit for low-intermediate frequency multi-mode multi-band receivers is presented. It consists of four fixed-gain amplifiers, four programmable gain amplifiers, a complex band-pass filter (CBPF) with reconfigurable bandwidth and a received signal strength indicator (RSSI). CBPF is implemented as the third-order Bessel active resistor–capacitor structure to provide the image rejection with flat group delay, and one on-chip automatic frequency tuning circuit is utilised to set the accurate frequency characteristics and overcome the effects of the process and temperature variations. The reconfigurable analog baseband circuit has been implemented in 0.18 µm complementary-symmetry metal–oxide–semiconductor. The measured results show that the presented circuit could provide 34 dB variable gain, 2 MHz/1 MHz/0.5 MHz reconfigurable bandwidth and accurate RSSI indicator. The analog baseband circuit is powered with a 1.8-V supply and totally draws a current of 5 mA.

A baseband LPF for GSM, TD-SCDMA and WCDMA multi-mode transmitters

This paper describes a low-pass reconfigurable baseband filter for GSM, TD-SCDMA and WCDMA multi-mode transmitters. To comply with 3GPP emission mask and limit TX leakage at the RX band, the out-of-band noise performance is optimized. Due to the distortion caused by the subthreshold leakage current of the switches used in capacitor array, a capacitor bypass technique is proposed to improve the filter's linearity. An automatic frequency tuning circuit is adopted to compensate the cut-off frequency variation. Simulation results show that the filter achieves an in-band input-referred third-order intercept point (IIP3) of 47 dBm at 1.2-V power supply and the out-of-band noise can meet TX SAW-less requirement for WCDMA & TD-SCDMA. The baseband filter incorporates −40 to 0 dB programmable gain control that is accurately variable in 0.5 dB steps. The filter's cut-off frequency can be reconfigured for GSM/TD-SCDMA/WCDMA multi-mode transmitter. The implemented baseband filter draws 3.6 mA from a 1.2-V supply in a 0.13 μm CMOS process.

A Simple On-Chip Automatic Tuning Circuit for Continuous-Time Filter

A simple on-chip automatic frequency tuning circuit is proposed. The tuning circuit is modified from voltage-controlled filter (VCF) frequency tuning circuit. We utilize an operational transconductance amplifier and a capacitor to from a single-time constant (STC) circuit which can produce a controllable delay time clock to tune the frequency of the filter. It can efficiently reduce the deviations in the 3 dB bandwidth from the variations of PVT (Process, Voltage and Temperature). The design of the STC circuit is simpler than VCF and it has less chip area. The chip has been implanted using TCMC 0.35 μm CMOS technology and the power consumption is less than 9.05 mW.

An eighth order channel selection filter for low-IF and zero-IF DVB tuner applications

An eighth order active-RC filter for low-IF and zero-IF DVB tuner applications is presented, which is implemented in Butterworth biquad structure. An automatic frequency tuning circuit is introduced to compensate the cut-off frequency variation using a 6-bit switched-capacitor array. Switched-resistor arrays are adopted to cover different cut-off frequencies in low-IF and zero-IF modes. Measurement results show that precise cut-off frequencies at 2.5, 3, 3.5 and 4 MHz in zero-IF mode, 5, 6, 7 and 8 MHz in low-IF mode can be achieved, 60 dB frequency attenuation can be obtained at 20 MHz, and the in-band group delay agrees well with the simulation. Two-tone testing shows the in-band IM3 achieves –52 dB and the out-band IM3 achieves –55 dB with –11 dBm input power. This proposed filter circuit, fabricated in a SMIC 0.18 μm CMOS process, consumes 4 mA current with 1.8 V power supply.

Electrically small antenna with frequency tuning circuit for wideband applications

This study proposes the concept of frequency tuning for an electrically small antenna to be used in wideband applications in low frequencies. An electrically small antenna has too narrow bandwidth to be utilized for wideband systems. However, in such mobile TV services that the band is composed of each sub channel in VHF band, the narrow bandwidth can be appropriately utilized with wideband frequency tuning. That is, each service channel is covered by the narrow resonant band of a small sized radiator and the entire service band is satisfied by moving its frequency. To prove the idea of this study, a small helical antenna with the size of less than λ/10 is chosen as a sample and the T-DMB service, a kind of the mobile TV services allocated to 200-MHz band, is selected for testing. With the designed tuning circuit constituted of lumped elements and a varactor, a low impedance of the small radiator is matched to about 50 Ω and the wide bandwidth is satisfied by moving its narrow resonant frequency. The validity of the proposed antenna is also proved by the receiving measured result. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 244–247, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23049

Verilog-A Modeling of Ferroelectric High-K Capacitors for Tunable Circuit Applications

Ferroelectric capacitors have shown very good prospect for use in circuits where voltage dependent tuning is required. We are studying high-K capacitors made from Ba1 - xCaxTi1 - yZryO3 (BCTZ) to fully characterize their tunable and high frequency behavior. A model for capacitance-voltage, current-voltage, and impedance-frequency relations is presented. The model can be used for simulation of high frequency tuning circuits.

Sliding backshorts for planar circuits

The Superconductor-Insulator-Superconductor (SIS) tunnel junction is an extremely sensitive heterodyne detector at millimeter and submillimeter wavelengths. The large inherent capacitance associated with this device results in a substantial impedance mismatch with typical antennas and, therefore, requires a tuning circuit for optimum results. At frequencies where waveguide dimensions are realizable, impedance matching can be accomplished by embedding the detector in a waveguide circuit with adjustable waveguide backshorts. At higher frequencies, where waveguide dimensions become prohibitively small, a planar transmission line embedding circuit provides a reasonable alternative. Typically, such planar circuits offer no post-fabrication adjustability, resulting in demanding materials and design requirements. An adjustable planar embedding circuit based on coplanar transmission lines with movable noncontacting shorting elements has been developed. The shorting elements each consist of a thin metallic plate with an optimized arrangement of rectangular holes, placed along the insulated metallic transmission line to provide a periodic variation of the line impedance. A scadel (1–5 GHz) has shown that a large reflection coefficient, |s11|≥−0.5 dB, can be achieved with these sliding elements. A low frequency tuning circuit incorporating these shorting elements has been tested to demonstrate practical tuning ranges.