Stopband Rejection Research Articles

A 50–450 MHz Tunable RF Biquad Filter Based on a Wideband Source Follower With > 26 dBm IIP$_{3}$, +12 dBm P$_{1{\rm dB}}$, and 15 dB Noise Figure

This paper reports a source follower-based active RC filter topology for RF front-ends in wideband systems. In the proposed active RC filter, the noise figure and bandwidth are improved through adopting the proposed sub-1 $\Omega$ $Z _{\rm out}$ source follower, which replaces the conventional operational amplifier-based unity gain buffer and through simply changing its location in the filter. Applying the proposed scheme to the conventional Sallen–Key filter also improves the stopband rejection performance. Furthermore, the proposed filter topology ultimately suppresses the DC offset voltage and flicker noise of the unity gain buffer, which is the only active circuit in the filter. The proposed biquad filter is implemented in 0.18 $\mu\hbox{m}$ CMOS and the measurements exhibit $>$ 26 dBm IIP $_{3}$ , +12 dBm input $P _{1{\rm dB}}$ , and ${ 15 dB noise figure over 50–450 MHz of a 6 bit tunable frequency range. The proposed biquad filter consumes 14 mA from a 1.8 V supply and the chip occupies 1000 $\times$ 500 $\mu \hbox{m} ^{2}$ .

High-Power Waveguide Low-Pass Filter With All-Higher-Order Mode Suppression Over a Wide-Band for Ka-Band Satellite Applications

In this letter, the design of a compact high-power waveguide low-pass filter with low insertion loss, all-higher order mode suppression, and stopband rejection up to the third harmonic, intended for Ka-band satellite applications, is presented. The method is based on step-shaped bandstop elements separated by very short (ideally of zero length) waveguide sections easily manufactured by low-cost computer-controlled milling. Matching is achieved by short input/output networks based on stubs whose heights are optimized following classical approaches. The novel filter presents a reduction in insertion loss and a remarkable increase in the high-power handling capability when compared to the classical waffle-iron filter and alternative solutions previously proposed, while the out-of-band frequency behavior remains unaltered.

Filter Design Masks for C37.118.1a-Compliant Frequency-Tracking and Fixed-Filter M-Class Phasor Measurement Units

The new amendment to the phasor measurement unit (PMU) standard C37.118.1a makes several significant changes compared with the standard C37.118.1 (2011). This paper highlights some of the most important changes, with a particular emphasis applied to how those changes relate to the way that an M-class PMU filter needs to be designed. In particular, there is a delicate tradeoff between passband flatness (the bandwidth test) and stopband rejection in the out-of-band (OOB) test. For a PMU algorithm using frequency-tracking and adaptive filters, it is shown that passband flatness can be relaxed to about 2.5 dB, but that the stopband needs to begin up to 14.8% closer to 0 Hz than for a fixed-filter PMU. This is partly due to the exact procedures of the C37.118.1a OOB testing and partly due to the adaptive nature of a frequency-tracking PMU filter section. Both the above lead to modified filter masks being required for frequency-tracking devices compared with the mask required for fixed-filter devices. The M-class PMU with a reporting rate of 25 Hz is the most difficult to design, for reasons given in this paper. The validity of the masks is shown using filter Bode plots and simulated C37.118.1a test results of a fixed-filter and frequency-tracking device, which have been designed to meet the masks defined in this paper.

Efficient UWB filter design technique for integrated passive device implementation

A new approach is proposed to act as an efficient design technique for the implementation of ultra-wideband (UWB) bandpass filters in integrated passive device technology. The proposed design is based on two major original contributions. First, the use of hourglass filter theory which, to the best of authors knowledge, has not been applied yet to such technology. Then, the minimisation of the number of inductors involved in the filter circuit through the zigzag technique. Implemented in 0.18 µm CMOS technology, the designed filter exhibits excellent performances such as two finite tunable transmission zeros, enhanced selectivity, a bandwidth covering the entire UWB spectrum of 3.1–10.6 GHz, a stopband rejection better than 15 dB throughout frequencies below 2.7 GHz and above 11 GHz, a good matching better than 11 dB, a minimum mid-band insertion loss of 1.8 dB and, finally, a sufficiently constant group delay. With these features and only 10 lumped elements, the proposed filter is one of the most promising compact filters for UWB applications.

Quasi-Elliptic Wideband Bandstop Filter Using Stepped-Impedance Coupled Line

A cross-coupled wideband bandstop filter (BSF) with a 5th-order quasi-elliptic response is proposed and investigated in this letter. The BSF is composed of stepped-impedance coupled line connected by an open-circuited shunt stub. An enhanced selectivity and stopband rejection can be achieved as a result of two new transmission zeros, generated from the stepped-impedance coupled line. Based on the derived rigorous correspondence between the BSF and its lumped prototype, design of the proposed BSF can be handled as the same to the lumped network. A BSF example is given with measured stopband attenuation of 34.4 dB over a fractional bandwidth of 113.4%.

Process Variation Aware Wide Tuning Band Pass Filter for Steep Roll-Off High Rejection

A wide tuning band pass filter (BPF) with steep roll-off high rejection and low noise figure is presented. The design feature of steep roll-off high stopband rejection (>20 dB) and low noise figure (<6 dB) provides a wide tuning frequency span (1–2.04 GHz) to accept desirable signals and reject close interfering signals. The process variation aware design approach demonstrates robustness of the BPF after calibration from process variations, operating in 1.04 GHz tuning frequency span: almost zero deviation on center frequency, an average maximum deviation 1.16 dB on a nominal pass band gain of 55.6 dB, and an average maximum deviation 1.06 MHz on a nominal bandwidth of 12.3 MHz.

A 44 GHz CMOS RFIC Dual-Function Attenuator with Band-Pass-Filter Response

A dual-function attenuator possessing both attenuation and band-pass filtering functions is proposed. The new dual-function band-pass attenuator architecture is derived by replacing the quarter-wavelength transmission line of a conventional attenuator with a 2nd-order admittance-inverter band-pass filter. Design formulas for the dual-function band-pass attenuator are derived. A 3-b CMOS dual-function band-pass step attenuator designed using a 0.18 $\mu{\rm m}$ BiCMOS technology shows measured insertion loss of 4.4–5.9 dB, RMS amplitude error of 0.8–1.4 dB, RMS phase error of 1.9–6.7 $^{\circ}$ over 36–52 GHz, input P1dB higher than 20 dBm at 44 GHz, and band-pass-filtering response with stop-band rejections greater than 18 dB at 24 and 64 GHz.

Compact multilayer self‐packaged filter with surface‐mounted packaging

A new self-packaged bandpass filter by using multilayer print circuit board technology is proposed and investigated. By using a multilayer structure, a lumped step-impedance resonator as well as self-packaging, the designed filter can achieve a much more compact size, low insertion loss and a wide stopband. The implemented filter operated at a centre frequency of 800 MHz with a 3 dB bandwidth of 120 MHz demonstrates stopband rejection better than 25 dB up to 4 GHz. The measured insertion loss including the connector loss in the input and output is 1.48 dB. The size of the filter is only 12 × 8 mm, i.e. 0.059λ g × 0.039λ g.

Ku‐band compact bandpass filter with wide upper stopband using multilayer liquid crystal polymer technology

ABSTRACTAn improved compact bandpass filter (BPF) with ultrawide upper stopband on three‐layer liquid crystal polymer substrate is presented. In this work, a broadside‐coupled H‐shape resonator and open circuited with radial stub are used to realize compact BPF. The first BPF is designed with three broadside‐coupled H‐shape resonators, which are placed on the top layer and middle layer, respectively. To improve the selectivity and reduce the size while not widen the bandwidth, an improved filter based on the first filter is proposed, which adds two open circuited with radial stubs and removing two H‐shape resonators. The measured results show that the second filter has better selectivity and much more compact size of 6 mm × 6 mm (about 0.52λg × 0.52λg) while keeping wide upper stopband and high rejection, comparing with the first filter, which size is 7 mm × 8 mm (about 0.61λg × 0.7λg). © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1121–1125, 2015

Substrate Integrated Waveguide (SIW) With Koch Fractal Electromagnetic Bandgap Structures (KFEBG) for Bandpass Filter Design

High-performance bandpass filters (BPFs) based on substrate integrated waveguide (SIW) and half mode SIW (HMSIW) with Koch fractal electromagnetic bandgap (KFEBG) patterns etched on the waveguide surface are proposed. These BPFs are designed using a new methodology. The BPF responses are improved by applying a chirped and tapered technique to the KFEBG patterns which exhibit a radius-to-period ratio r/a ≥ 0.5. Simulation results and experimental verification are presented. Good values for insertion losses and stopband rejection are achieved.

Novel Compact Microstrip Stepped-Impedance Resonator Using Computational Approach and Application to Dual-Band Bandpass Filters

This paper discusses a novel multi-stub-loaded stepped-impedance resonator (MSLSIR) with a specific feeding structure. The fundamental and higher order modes of resonant frequencies of the stepped-impedance resonator are key parameters involved in the design of a dual-band bandpass filter (DBPF). However, since resonant frequencies are dependent on each other, the overall structure is not compact. The proposed MSLSIR has the advantage of flexible control over one resonant frequency while the other frequency is fixed. Furthermore, the utilization of isosceles right-angled triangular (IRT) and short-circuited stubs as loaded elements improves size miniaturization of DBPF when a low permittivity substrate is used. The analysis of the IRT stub is based on the coupling impedance formulas derived by integration of the associated Green`s function. As an application, a DBPF is presented, which operates at 3.5 and 5.2 GHz, corresponding to the WiMAX and WLAN applications, respectively. In addition, a good stopband rejection, up to $$3\hbox {f}_{1}$$3f1, is obtained using the defected ground structure technique. An overall good agreement between the calculated, simulated and measured results is observed, thereby confirming the effectiveness of the proposed method.

A Low-Voltage CMOS-Microelectromechanical Systems Thermal-Piezoresistive Resonator With $Q > 10\,000$

We report a thermally driven and piezoresistively sensed CMOS-microelectromechanical systems (MEMS) resonator with quality factor Q >10000 and stopband rejection of 15 dB under CMOS-compatible bias voltage. The bias voltage requirement of this letter is two orders of magnitude lower than that of the previous CMOS-MEMS capacitively transduced resonators. In addition, the combination of the bulkmode resonator design and highQ SiO2/polysilicon structural material leads to resonator Q >10000, a key index for low-phasenoise oscillators and low-insertion-loss filters. The resonator with a center frequency at 5.1 MHz was fabricated using a standard 0.35 μm 2-poly-4-metal CMOS process, featuring low cost, batch production, fast turnaround time, easy prototyping, and MEMS/IC integration. To resolve the feedthrough issue often seen in conventional thermal-piezoresistive resonators: 1) separation of the heater and piezoresistor is first adopted because of the routing flexibility of the structural configuration offered by CMOS back-end-of-line materials and 2) fully differential measurement scheme is then applied to the proposed device, both of which enable a low-feedthrough level with 65-dB improvement as compared with its single-ended counterpart.

DUAL-BAND SUBSTRATE INTEGRATED WAVEGUIDE RESONATOR BASED ON SIERPINSKI CARPET

In this paper, a dual-band Substrate Integrated Waveguide (SIW) resonator with Sierpinski fractal geometry is proposed. The space-filling property of the employed fractal shape allows to reduce the resonator size. The bandwidth, the minimum insertion loss, the maximum return loss and the stop band rejection are considered for evaluating the effect of the fractal geometry on the resonator characteristics. An accurate electromagnetic investigation is made using a full wave finite element method solver (Ansoft HFSS). Simulated and measured results are in good agreement. The second iteration fractal resonator exhibits two simulated bands centered at the frequencies f1 =1 1.57 GHz and f2 =2 5.7 GHz, while the measured frequencies are f1 =1 1.33 GHz, f2 =2 3.67 GHz. The measured bandwidths are BW = 1.15 GHz and BW = 2 GHz and the minimum insertion losses are close to −1.36 dB and −1.97 dB, respectively. The prototypes of the square resonator without, with first and with second iteration fractal geometry are fabricated via standard printed circuit board process (PCB). A Rogers Duroid 5880 substrate with thickness t =0 .381 mm is employed.

COMPACT MICROSTRIP NARROW BANDPASS FILTER WITH GOOD SELECTIVITY AND WIDE STOPBAND REJECTION FOR KU-BAND APPLICATIONS

A new microstrip narrow bandpass filter with good selectivity and wide stopband rejection for Ku-band application is proposed in this letter. The characteristic of the triple-mode stub-loaded resonator has been investigated. The resonance frequencies of the degenerate modes can be adjusted easily to satisfy the bandwidth of the narrow bandpass filter. Two parallel-coupling feed structures with cross-coupling have been used to generate two transmission zeros at the lower and upper stopband, which can improve the filter selectivity. To validate the design theory, a new microstrip Ku-band narrow bandpass filter has been designed, fabricated, and measured. Simulated and experimental results are provided with good agreement.

Compact lowpass filter with wide stopband using stepped impedance hairpin units

A novel microstrip lowpass filter (LPF) with a wide stopband is presented. The basic resonator is composed of two stepped impedance hairpin units with one embedded in another, which can obtain two more transmission zeros and extend a wide stopband. Based on the proposed resonator, a demonstration LPF of compact size, sharp transition and wide stopband has been designed, fabricated and measured. The proposed filter exhibits a small size of 0.081λg × 0.113λg, where λg is the waveguide length at the cutoff frequency of 1.6 GHz. Results show good agreement with simulations and the 20 dB rejection stopband can be extended to more than 15 GHz.

Novel Spurious Suppression Approach for SIR Dual-band Bandpass Filter Design

Abstract A new design approach for a stepped impedance resonator (SIR) dual-band bandpass filter (BPF) with high multi-spurious suppression is proposed in this paper. The external coupling property of an SIR at multi-order resonant frequencies is fully studied. Different input impedances at desired frequencies are achieved by optimizing the unequal impedance transformer. The new solution shows the freedom in the choice of tapping point. The external quality values of multi-order harmonics vary with the shift of the tapping position. Wide upper stop-band rejection is realized by mismatching Qe at the unwanted harmonic frequencies, while keeping the Qe suitable for operating dual band to obtain good in-band performance. A traditional dual-band BPF and a novel practical BPF operated at 2.45/5.25 GHz are designed and fabricated to demonstrate the above idea. Good simulated and measured results are presented.

Analysis and Design of a High-Order Discrete-Time Passive IIR Low-Pass Filter

In this paper, we propose a discrete-time IIR low-pass filter that achieves a high-order of filtering through a charge-sharing rotation. Its sampling rate is then multiplied through pipelining. The first stage of the filter can operate in either a voltage-sampling or charge-sampling mode. It uses switches, capacitors and a simple gm-cell, rather than opamps, thus being compatible with digital nanoscale technology. In the voltage-sampling mode, the gm-cell is bypassed so the filter is fully passive. A 7th-order filter prototype operating at 800 MS/s sampling rate is implemented in TSMC 65 nm CMOS. Bandwidth of this filter is programmable between 400 kHz to 30 MHz with 100 dB maximum stop-band rejection. Its IIP3 is +21 dBm and the averaged spot noise is 4.57 nV/$surd$ Hz. It consumes 2 mW at 1.2 V and occupies 0.42 mm 2.

An independently tunable dual-band bandpass filter using open-loop resonators

Based on open-loop resonators (OLRs), an independently tunable dual-band (ITDB) bandpass filter (BPF) is presented in this paper. The top layer of the proposed ITDB-BPF is composed of transmission feed lines and OLRs in a stepped-impedance resonator (SIR) structure. The bottom layer is constructed by OLRs in an asymmetrical SIR with a defect-grounded structure. To obtain the required frequencies and bandwidths, the sizes of resonators and feed lines are realized by defining the coupling coefficients and the external quality factors. As to the proposed ITDB-BPF, the first center frequency is set to be 2.45 GHz for Wireless Local Area Network systems. The second center frequency is selected to be 3.5 GHz for a Worldwide Interoperability for Microwave Access systems. The measurement results show that the insertion losses are 2.9 and 2.6 dB for 2.4 and 3.5 GHz, respectively. The minimum return losses are 14.5 dB for 2.4 GHz and 22.8 dB for 3.5 GHz. The stopband rejections of the lower band from dc to 1.84 GHz and the upper bands from 4.34 to 6 GHz are both greater than 30 dB. The center frequencies of the two passbands can be tuned independently by adjusting different resonators which makes the design of dual-band BPF more flexible than conventional ones.

Comment on sharp‐rejection and ultra‐wide bandstop filter with five transmission zeros frequencies

In this letter, explicit transmission zero conditions, for the ultra-wide bandstop filter (BSF) with five transmission zeros, are derived using even-odd mode, analysis. The BSF topology is obtained by folding the two connecting transmission lines in a conventional optimum BSF to compose a stub-loaded coupled-line section and using λ g/2 end open-stubs. A necessary and sufficient condition is explored for the crucial coupled-line section to produce three transmission zeros. Further, it is shown that the same five zeros BSF stopband bandwidth and rejection level performance is obtained with compact three zeros BSF (without λ g/2 open-stubs) with improved passband flatness and return loss.

A Method for Attenuating the Spurious Responses of Aluminum Nitride Micromechanical Filters

We present a method for attenuating the spurious responses in aluminum nitride micromechanical filters and demonstrate the technique in a 4-pole self-coupled filter operating at 494 MHz. In the standard implementation of a 4-pole self-coupled filter, each filter pole is realized using physically identical resonators. The spur mitigation approach reported here realizes the four poles of the filter using two different physical implementations of the resonator. Both resonators are designed to have identical responses at the desired resonant frequency of 494 MHz, while many of the spurious responses of the two resonators appear at nonidentical frequencies and do not add constructively at the filter output. Using the reported method, the measured attenuation of the largest filter spur is increased by 47.5 dB when compared with a 4-pole filter realized using identical resonators (standard approach) to form each filter pole. The filter realized using the reported spur attenuation approach has >59.6 dBc of stopband and spurious response rejection over nearly a 2-GHz frequency span.