Flat Group Delay Research Articles

5GHz CMOS All-Pass Filter-Based True Time Delay Cell

Analog CMOS time-delay cells realized by passive components, e.g., lumped LC delay lines, are inefficient in terms of area for multi-GHz frequencies. All-pass filters considered as active circuits can, therefore, be the best candidates to approximate time delays. This paper proposes a broadband first-order voltage-mode all-pass filter as a true-time-delay cell. The proposed true-time-delay cell is capable of tuning delay, demonstrating its potential capability to be used in different systems, e.g., RF beam-formers. The proposed filter achieves a flat group delay of over 60 ps with a pole/zero pair located at 5 GHz. This proposed circuit consumes only 10 mW power from a 1.8-V supply. To demonstrate the performance of the proposed all-pass filter, simulation results are conducted by using Virtuoso Cadence in a standard TSMC 180-nm CMOS process.

A Simple Design of Fractional Delay FIR Filter Based on Binomial Series Expansion Theory

Fractional delay filters modeling non-integer delays are digital filters that ideally have flat group delays. This paper proposes a simple design method of fractional delay FIR filter based on binomial series expansion theory. First, the design technique is based on the binomial series expansion method which is applied to a discrete fractional system to obtain a closed form FIR digital filter which approximates the digital fractional delay operator z−m $$ (m \in \Re^{ + } ) $$ . Then, the principal differentiation is used to design fractional delay FIR filter with a broader group delay bandwidth. Finally, numerical examples of fractional delay FIR filter design show that the proposed approach yields better performance compared to the existing techniques.

A Highly Efficient Ultrawideband Traveling-Wave Amplifier in InP DHBT Technology

This letter presents a 1 to >110-GHz ultrawideband traveling-wave amplifier (TWA) based on 500-nm transferred-substrate InP double-heterojunction bipolar transistor technology. The HBT cells are realized with inductive peaking at the output and match the phase delay between individual stages. The collector bias is slightly below the value for the maximum current gain. This allows a frequency-invariant high-output power characteristic with a flat group delay. The amplifier exhibits a gain of 13 dB with a measured bandwidth of 1–110 GHz and a uniform 10-dBm 1-dB compression output power with an associated maximum PAE of 8% at 110 GHz. To the best of our knowledge, this is the highest PAE and the maximum flat output power reported for such a TWA covering frequencies up to 170 GHz. The amplifier consumes only 129 mW, which is among the lowest dc power dissipations reported for the given gain–bandwidth product. Moreover, the group delay is flat across the band, which makes the TWA very useful in high-speed optical communication systems.

A 24-GHz Source-Degenerated Tunable Delay Shifter With Negative Group Delay Compensation

A true time delay shifter is fabricated in TSMC 65-nm CMOS low power technology for 24-GHz vehicle radar application. Its mechanism of source degenerated negative group delay compensation is proposed for flat group delay generation and tuning in a medium-wide 1.3-GHz instantaneous bandwidth, with simultaneously a reduced S21 of −6 ~ −9 dB (measured S21 excluding simulated extra insertion loss of packaging modeling and printed circuit board traces) compared to typical switched-line delay shifters. For 10-ps relative delay range, the variation is about 1–2 ps (max to 6 ps). For 17-ps range, the variation becomes 8–13 ps due to measurement issues. It consumes 16.3 mW at 1.2-V supply and 0.11-mm2 chip area. This topology is demonstrated to be a suitable and potential choice of delay shifter for medium-wideband time array system.

Compact microstrip lowpass filter with ultrasharp response using a square-loaded modified T-shaped resonator

A miniaturized lowpass filter (LPF) with ultrasharp response, good figure of merit (FOM), and simple structure is proposed. The designed structure is fabricated and measured with a 2.9 GHz cut-off frequency. The proposed LPF consists of high impedance lines that are loaded by three similar resonators and two uniform suppressing cells. The filter size is only 0.08~$\times $~0.23~$\lambda $g, which indicates small circuit size. The proposed design exhibits good features, such as an ultrasharp roll-off rate of about 1609 dB/GHz and a good FOM of 162,820. The insertion loss of the proposed LPF is less than 0.14 dB in the passband. With these excellent obtained specifications and flat group delay, this structure can be used in wireless antennae.

Solving a combined economic emission dispatch problem using adaptive wind driven optimization

A miniaturized lowpass filter (LPF) with ultrasharp response, good figure of merit (FOM), and simple structure is proposed. The designed structure is fabricated and measured with a 2.9 GHz cut-off frequency. The proposed LPF consists of high impedance lines that are loaded by three similar resonators and two uniform suppressing cells. The filter size is only 0.08~$\times $~0.23~$\lambda $g, which indicates small circuit size. The proposed design exhibits good features, such as an ultrasharp roll-off rate of about 1609 dB/GHz and a good FOM of 162,820. The insertion loss of the proposed LPF is less than 0.14 dB in the passband. With these excellent obtained specifications and flat group delay, this structure can be used in wireless antennae.

A new approach for the design of fractional delay by an FIR filter

Fractional delay filters modeling non-integer delays are digital filters which ideally have flat group delays. In this letter, a new, simple, accurate and efficient FIR filter design to implement the digital ideal fractional delay is presented. The design technique is based on the MacLaurin series expansion formula which is applied to a given function to obtain a closed form FIR digital filter approximation of the digital ideal fractional delay operator z−α. The obtained FIR filter approximation formula of the digital ideal fractional delay operator z−α is similar to the well known Grünwald-Letnikov FIR digital filter approximation formula of the ideal analog fractional differentiator sα. Some examples have been presented to illustrate the performance and the effectiveness of this new design method. Some comparisons results show that the proposed design yields better performances than the existing designs in the literature.

Maximally Flat Group Delay of Bessel Polynomials

In this note, we report a simple proof that Bessel polynomials satisfy maximally flat group delay requirement for low-pass filters.

Switched‐bandwidth SAW‐based bandpass filters with flat group delay

Tunable surface-acoustic-wave-(SAW)-based bandpass filters (BPFs) with flat in-band group delay (Tg) and variable passband bandwidth (BW) are reported. They are based on N hybrid acoustic-wavelumped-element-resonator (AWLR) modules shaped by one lumpedelement resonator and K RF-switched SAW resonators that are arranged in a Gaussian-type source-to-load impedance-inverter network. Fractional bandwidth (FBW) tuning is achieved by reconfiguring the number of SAW resonators within the AWLR modules. Major advantages of the proposed filter concept when compared to conventional SAW BPFs are as follows: (i) they do not depend on the electromechanical coupling coefficient (k t 2 ) of the SAW resonators - FBW>k t 2 can be realised -, (ii) they do not require lossy elements or SAW resonators with different frequencies, and (iii) they can be tuned. For experimental-validation purposes, a 433.9 MHz two-pole/fourtransmission-zero prototype was built and measured. It exhibited flatin-band-T g passbands with discretely-tunable BW between 0.18 and 0.45 MHz (i.e. 2.5:1 tuning ratio).

A 32 Gb/s, 201 mW, MZM/EAM Cascode Push–Pull CML Driver in 65 nm CMOS

This brief presents a 32 Gb/s driver for a Mach–Zehnder modulator (MZM) and an electro-absorption modulator (EAM). A push–pull current-mode logic driver is chosen to achieve a better power efficiency and a large voltage swing. A double cascode with thin oxide transistors is employed to mitigate the over-voltage stress associated with a large output voltage swing. At the same time, shunt-peaking inductors are incorporated in a compact way to extend the bandwidth and to have a flat group delay. The proposed driver has been fabricated using 65 nm CMOS technology with an active area of 0.086 mm2. The electrical measurement result shows that the driver exhibits a differential output swing of 4 ${\text V}_{\text {pp}}$ at 10 Gb/s. The measured extinction ratios of the driver using the MZM and EAM are 4.53 dB and 4.17 dB, respectively, at 32 Gb/s. The power consumption is 201 mW at 32 Gb/s, which corresponds to an energy efficiency of 6.28 mW/Gb/s.

Arbitrary Prescribed Wideband Flat Group Delay Circuits Using Coupled Lines

This paper presents the analytical design of transmission-type arbitrary prescribed wideband flat group delay (GD) circuits (type-I and type-II) using $\lambda $ /4 coupled lines. The GD circuit type-I consists of two sections of coupled lines, whereas the GD circuit type-II consists of $\lambda $ /4 transmission lines (TLs) at input and output, in addition to coupled lines. The additional $\lambda $ /4 TLs at input–output ports in GD circuit type-II provide more freedom to obtain larger GD, as compared to type-I, without fabrication difficulties. The analytical analysis shows that the wideband flat GD response can be obtained by selecting the appropriate even- and odd-mode impedances of coupled lines and the characteristic impedance of TLs. To obtain the arbitrary prescribed wideband flat GD response, the closed-form analytical design equations are provided. For experimental validation of the proposed structures, prototypes of GD circuits (type-I and type-II) are designed and fabricated at the center frequency of 2 GHz. The measurement results agree well with the simulation and theoretical predicted results.

Multi-band reconfigurable microwave filter using dual concentric resonators

This article presents the design and testing of a novel frequency reconfigurable microwave filter. The filter structure is composed of an all stop resonator coupled with C- and E-shaped parasitic resonators. PIN diodes are located at suitable positions to achieve multi-band reconfiguration from 1.2 to 3.2 GHz making the filter suitable for multiple wireless communication systems. The frequency and bandwidth of the filter are governed by the length of the resonators and coupling between the resonators and the transmission line, respectively. A sharp rejection of −30 dB is observed between the passbands. The proposed filter offers 56% size reduction with flat group delay performance. The prototype filter is fabricated and the simulation results are validated using experimental measurements. The measurement results show good agreement with the simulation results.

Leaf‐shaped CPW‐fed UWB antenna with triple notch bands for ground penetrating radar applications

AbstractA compact (38.31 mm × 34.52 mm × 0.8 mm) leaf shaped CPW fed ultra‐wideband antenna is proposed. The antenna gives wide impedance bandwidth from 2.58 GHz to 11.62 GHz with sharp triple notch bands (3.28 GHz–3.82 GHz, 5.12 GHz–5.4 GHz, and 5.7 GHz–6 GHz) to eliminate interference from co‐existing IEEE 802.16 WiMAX (3.3 GHz–3.8 GHz), IEEE 802.11y (3.65 GHz–3.69 GHz), IEEE 802.11a WLAN (5.15 GHz–5.35 GHz and 5.725 GHz–5.825 GHz), and IEEE 802.11p DSRC (5.85 GHz–5.925 GHz) bands. The antenna provides minimal gain variation (2–5 dBi), flat group delay response and non‐varying transfer function with high average efficiency of 88% in the pass band. Significant drop in gain and efficiency, nonlinearity in transfer function, and high variation in group delay are observed at notch bands. Antenna VSWR, and efficiency are measured in close proximity of sand, wood, and glass. Satisfactory results ensure its ability to work as Ground penetrating radar antenna.

Compact Lowpass Filter with Ultra-High Figure-of-Merit and Flat Group Delay

ABSTRACTThis paper presents a microstrip lowpass filter with compact size, and ultra-wide stopband. The structure consists of a modified hairpin resonator loaded with tapered cells and the circular patches as the suppressing cell. The proposed lowpass filter has −3 dB cut-off frequency at 1.64 GHz. It also has suitable performances such as: ultra-sharp transition-band of 0.09 GHz that is from −3 to −20 dB, an extended stopband bandwidth from 1.73 to 21 GHz with the attenuation level more than −20 dB, low insertion-loss, flat group delay in the passband, and simple structure. The proposed lowpass filter is simulated and fabricated and there is good agreement between the simulation and measurement results.

A Wideband Variable Gain LNA With High OIP3 for 5G Using 40-nm Bulk CMOS

This letter presents a CMOS wideband variable gain LNA for 28-GHz 5G integrated phased-array transceivers preserving high third-order intercept point (OIP3) at all gain settings. The prototype LNA has three stages providing digitally controlled gain optimized for higher IIP3 at lower gain. The stages are coupled together using double-tuned transformers for maximum group delay flatness. Fabricated in a 40-nm CMOS process, it achieves 18–26 dB gain at 1-dB gain step with 12–14.5 dBm OIP3 and 3.3–4.3 dB noise figure, while consuming 21.5–31.4 mW across 26–33 GHz frequency range. The root-mean-square error of the gain steps is less than 0.38 dB.

Reflection-Type Topologies With Arbitrary Wideband Flat Group Delays Using Coupled Lines

This paper presents the analytical design techniques of several reflection-type group delay (GD) circuits (types-I-III) with arbitrarily prescribed wideband flat GD responses using $\lambda $ /4-coupled lines. The type-I GD circuit consists of the $\lambda $ /4 transmission lines and an open-circuited coupled line with a short-circuited load, whereas type-II consists of a short-circuited coupled line with an open-circuited load. For a compact circuit size, the type-III circuit is realized by a parallel combination of the open-circuited and short-circuited coupled lines. To obtain the arbitrarily prescribed response of wideband flat GD, closed-form analytical design equations are provided. An analytical analysis shows that the wideband flat GD response can be obtained by controlling the appropriate even- and odd-mode impedances of the coupled lines. For an experimental validation of the proposed structures, prototypes of the three GD circuits were designed and fabricated at the center frequency of 2.5 GHz. To realize a higher GD response over a wideband bandwidth, a number of reflection-type GD circuit units are cascaded and measured. The measurement results agree soundly with the simulation and theoretical prediction results.

Trisection Microstrip Delay Line Filter With Mixed Cross-Coupling

It has been discovered that a trisection bandpass filter with mixed cross-coupling K 13 has flat group delay if the condition K 13 = 0 is satisfied, which occurs when magnetic Km and electric |K e | components of the coupling are equal. It has been proven that the group delay of the filter increases as the values K m = |K e | increase. The microstrip construction of the trisection delay line filter is proposed. The analysis of this construction has been carried out, which allows controlling the values Km = |Ke| at the zero of cross-coupling. The results of the measurements and the simulation are presented.

Use of Phase Delay Analysis for Evaluating Wideband Circuits: An Alternative to Group Delay Analysis

A phase delay analysis is proposed against pursuing a flat group delay response for the design of wideband circuits. While it is believed that a large group delay variation introduces a large data-dependent jitter, this brief reconsiders the effectiveness of the group delay analysis in the evaluation of wideband circuits. Because of its own differentiating nature, the group delay provides a good insight on the delay variation at a vicinity of a certain frequency. However, for certain kind of wideband circuits, the group delay analysis cannot provide a sufficient insight since much of useful information is lost or distorted during the differentiating operation. In this brief, the effectiveness of the phase delay analysis is investigated and comparison with a traditional group delay analysis is presented with a theoretical approach and through a few circuit examples.

Compact microstrip low pass filter with flat group-delay using triangle-shaped resonators

In this paper, a compact microstrip lowpass filter (LPF) using triangle-shaped resonators is presented. The designed LPF includes three symmetric triangle-shaped resonators to provide a suitable passband and sharp response. A suppressing unit composed of several suppressing cells is designed to obtain a wide rejection band and low insertion loss in the passband. The fabricated LPF has been measured and indicts that it has −3 dB cut off frequency at 5.15 GHz. The rejection band has been expended from 5.51 GHz to 43.2 GHz with maximally flat return loss in this region nearby to 0 dB. Also, simulation and experimental results show that the proposed filter has a very flat group delay in the passband, which is the minimum value in comparison with the published works since 2017.

Synthesis of Reflection-Type Coupled Line All-Pass Circuit With Arbitrary Prescribed Wideband Flat Group Delay

In this letter, the analytical design method of a reflection-type coupled line all-pass circuit with arbitrary predefined wideband flat group delay (GD) is presented. The proposed circuit consists of 90° hybrid and coupled lines with a short-circuited load. The proposed structure is simple and does not require any iterative process to obtain optimum circuit parameters. Theoretical and experimental results are provided for validation of the proposed structure. The prototype circuits were fabricated at a center frequency of 2.5 GHz with 2 and 4 ns flat GD responses. The measurement results agreed well with the simulation and theoretical predicted results.