Negative Group Delay Circuit Research Articles

A Design of Reconfigurable Negative Group Delay Circuit Without External Resonators

In this letter, we present the novel design and implementation of a microstirp line reconfigurable negative group delay circuit (NGDC) using a branch-line. Theoretical analysis shows that reconfigurable characteristics in the proposed circuit can be obtained by properly choosing the characteristic impedances of the branch-line and tuning only the termination resistance. Therefore, the proposed reconfigurable NGDC does not require any extra resonators. For experimental validation, the proposed circuit was designed and fabricated for a wideband code division multiple access downlink frequency operating at a center frequency ( ${f_0}$ ) of 2.14 GHz. Measurement results show the group delays variation of $ - 2~\hbox{ns}$ to $ - 10~\hbox{ns}$ with signal attenuation variation of $ - 25~\hbox{dB}$ to $ - 36.6~\hbox{dB}$ at ${f_0}$ . For enhancement of the negative group delay bandwidth, two NGDCs operating at slightly different center frequencies are cascaded and measured.

Miniaturized Dual-Band Negative Group Delay Circuit Using Dual-Plane Defected Structures

In this letter, a design for a dual-band negative group delay circuit (NGDC) using dual-plane U-shaped defected structures is presented. The center frequency and group delay (GD) time of each band are separately controlled by a defected microstrip structure (DMS) and a defected ground structure (DGS) with resistors connected across the DMS and DGS slots. To verify the design concept, the NGDC is designed, fabricated, and compared with the circuit simulation. To get a wideband bandwidth, two NGDCs with different center frequencies are connected in a cascade design. From the measurements, the GD times of -4.54 ±0.6 ns and -4.20 ±0.5 ns are obtained at 3.46-3.58 GHz and 5.10-5.20 GHz, respectively.

Microstrip Line Negative Group Delay Filters for Microwave Circuits

This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of -7.3 ns with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.

Distributed Transmission Line Negative Group Delay Circuit With Improved Signal Attenuation

In this letter, a novel design and implementation of a distributed negative group delay circuit (NGDC) with reduced signal attenuation is demonstrated. By inserting an additional transmission line Z2 into the conventional NGDC, the proposed NGDC provides further design parameters in order to obtain the required differential-phase group delay (GD) time and help to reduce the signal attenuation. As a result, the number of gain compensating amplifiers can be reduced, which can contribute to the efficiency enhancement as well as the stable operation when integrated into the RF system. Both theory and experiment are provided to validate the proposed structure. From the experiment, for the same GD time of -7.9 ns, the signal attenuation of the proposed circuit is 16.5 dB, an improvement signal attenuation of the conventional circuit of 19.2 dB.

A Dual-Purpose Reconfigurable Negative Group Delay Circuit Based on Distributed Amplifiers

In this letter, a novel reconfigurable negative group delay distributed amplifier (NGD-DA) circuit is proposed. This NGD-DA offers a new method to realize negative group delay. By properly choosing the gain coefficient of each tap for the DA, we can synthesize the negative group delay at the reverse port of the DA in the frequency band of interest, while maintaining a flat gain at the forward port; this results in a dual-purpose DA. Moreover, the proposed NGD-DA is reconfigurable; the phase response at the reverse port can be simply controlled by adjusting the tap gain coefficients, and therefore the bandwidth as well as the amount of negative group delay can be manipulated. The proposed active NGD circuit is validated through theoretical explanation and experimental results.

Distributed NGD active circuit for RF-microwave communication

This paper is aimed to the investigation on innovative distributed negative group delay (DNGD) circuits for RF communication. Thanks to the analogy between the lumped and distributed circuits, NGD circuit topologies were identified. By using the S-parameter theory, analysis and synthesis methods of these topologies are proposed. The DNGD circuits developed are mainly comprised of a transistor combined with a series resistance ended by a stub. Then, synthesis relations enabling to determine the NGD circuit parameters from the desired NGD and gain values are established. As application, an active phase shifter (PS) operating independently with the frequency based on the cascade of PGD and NGD devices was synthesized. First, an NGD PS with transmission phase of (135±5)° around 2.56GHz over the bandwidth of about 1.02GHz was obtained. Then, a two-stage DNGD PS exhibiting 90° with ±10° flatness from 4.1GHz to 6.8GHz was designed. The DNGD circuit presented can be used in various telecommunication areas notably for correcting RF/numerical signal delays in the RF-microwave analogue-digital devices.

Neutralization of LC- and RC-Disturbances with Left-Handed and NGD Effects

This paper focus is on the neutralization technique of the unwanted physical disturbances in the radio frequencies (RF) and digital electronic structures. Most of parasitic effects induced in these systems can be modeled by RC- and LC- passive networks. For canceling these disturbing effects, we can proceed with the transfer function neutralization in the considered operating frequency bands. This neutralization concept is developed by using first, a left-handed (LH) and negative group delay (NGD) circuits inspired from metamaterials. The fundamental theoretical approach illustrating the RC- and LC-effects transfer function neutralization is described. Synthesis relations enabling to determine the elements of the LH and NGD circuit correctors in function of the perturbation parameters are established. Numerical and experimental demonstrators are presented to validate the technique proposed. This later is particularly useful for the improvement of the analogue and digital signal integrity degraded by electromagnetic interferences.

Synthesis of RF Circuits with Negative Time Delay by Using LNA

A demonstration of the negative time-delay by using active circuit topologies with negative group delay (NGD) is described in this paper. This negative time delay is realized with two different topologies operating in base band and modulated frequencies. The first NGD topology is composed of an RL-network in feedback with an RF/microwave amplifier. Knowing the characteristics of the amplifier, a synthesis method of this circuit in function of the desired NGD values and the expected time advance is established. The feasibility of this extraordinary physical effect is illustrated with frequency- and time-domain analyses. It is shown in this paper that by considering an arbitrary waveform signal, output in advance of about 7 ns is observed compared to the corresponding input. It is stated that such an effect is not in contradiction with the causality. The other NGD topology is comprised of a microwave amplifier associated with an RLC-series resonant. The theoretical approach illustrating the functioning of this NGD circuit is established by considering the amplifier S-parameters. Then, synthesis relations enabling to choose the NGD device parameters according to the desired NGD and gain values are also established. To demonstrate the relevance of the theoretic concept, a microwave device exhibiting NGD function of about -1.5 ns at around 1.19 GHz was designed and analyzed. The NGD device investigated in this paper presents advantages on its faculty to exhibit positive transmission gain, the implementation of the bias network and matching in the considered NGD frequency band.

Methodology of elementary negative group delay active topologies identification

This work introduces a fundamental methodology enabling to identify the elementary negative group delay (NGD) topologies using transistors. These circuits are particularly beneficial compared to the other existing NGD topologies, with its flexibility to operate in ultra wideband (UWB), to compensate losses and potentially integrable. The basic families of NGD topologies obtained from the association of passive and active four-port networks are presented. The NGD existence condition is given. Based on this condition, the simplest NGD active cells are identified. After the analysis of passive networks formed by R, L and C components, first-order transfer functions of innovative elementary NGD cells are established. Then, similar to the classical circuits as the filters and amplifiers, synthesis relations for the design of integrable NGD topology with no self-element are introduced. To illustrate the relevance of the theoretic concept, a proof of concept was proposed. Finally, discussions on the applications of NGD circuits are offered in the conclusion.

Similitude between the NGD function and filter gain behaviours

ABSTRACTThis paper deals with the similitude between the behaviours of linear filter gain and negative group delay (NGD) function. The transposition method of low‐pass/high‐pass, low‐pass/band‐pass and low‐pass/band‐stop NGD circuits is established. To the best of the author knowledge, it acts as the first paper devoted on the NGD function generalized theory. The introduced transform relationships simplify the synthesis of any NGD circuits from simple elementary low‐pass NGD topologies. Families of innovative NGD topologies are identified. To verify the relevance of the concept proposed, frequency‐ and time‐domain analysis results from realistic proofs of concept demonstrating the feasibility of developed NGD transforms were performed. Thanks to the NGD phenomenon, the possibility of the ultra‐wideband pulse signals propagating in time‐advance is verified. Finally, potential applications of NGD circuits are discussed. Copyright © 2013 John Wiley & Sons, Ltd.

An FET-based microwave active circuit with dual-band negative group delay

Recent studies proved that certain electronic active circuits are capable to exhibit simultaneously a negative group delay (NGD) and amplification in microwave frequency bands. One of the simplest topologies generating this counterintuitive NGD function effect is formed by a series RLC-network in cascade with a transistor. By using this cell, similar to the classical electronic functions, dual-band NGD microwave devices with loss compensation possibility can be designed. Theoretic demonstrations concerning the theory of the NGD circuit considered are presented. The dual-band NGD concept feasibility is concretely illustrated by an example of EM/circuit co-simulations. So, in frequency domain, dual-band NGD with minimal values of about -1 ns was observed simultaneously within two frequency bands centered at about 1.05 GHz and 2.05 GHz. To highlight the functioning of the hybrid device considered, time-domain analysis showing the RF/microwave signal advancement is performed. As application, the concept investigated can be envisaged for data synchronization in multi-channel wireless communication systems eventually degraded by undesired EMI effects.

Investigation on Microwave Negative Group Delay Circuit

In this article, a fundamental analytical approach and experimental verification of a radio frequency active circuit capable of exhibiting negative group delay at microwave wavelengths are presented. By using the S-parameter theory, basic properties and characteristics of the negative group delay circuit under study are established. To highlight the functionality principle of this innovative circuit, time-domain investigations based on ultra-wide-band pulse signal tests are performed. Then, the mechanism of propagating output signal envelopes in time advance compared to the input is demonstrated. To validate this concept, a prototype of a negative group delay device was designed, fabricated, and tested. Experimental results in good agreement with theory and simulation were obtained. In the frequency domain, a negative group delay of about −2.5 ns with amplification of 2 dB was measured at around 622 MHz. Due to this negative group delay effect, envelope advance of about −1.5 ns was observed by considering a pulse signal with a half-height full-width of 10 ns, which modulates a sine carrier with a frequency of 622 MHz. The negative group delay topology presented is potentially useful for the compensation of radio frequency/microwave signal delays.

Asymptotic Limits of Negative Group Delay in Active Resonator-Based Distributed Circuits

In this paper the asymptotic limits of negative group delay (NGD) phenomena in multi-stage RLC resonator-based circuits are discussed. A NGD-bandwidth-product limit is derived as a function of the number of stages and the out-of-band gain, which is independent of the circuit topology and can include active gain compensation. The limit is verified experimentally at microwave frequencies using a gain-compensated NGD circuit employing a parallel RLC resonator in the feedback path of a high-frequency op-amp. It is shown that, in the asymptotic limit, the NGD-bandwidth-product is proportional to the square root of the number of stages, and also to the square root of the logarithm of the out-of-band gain. The relation between the time-domain transient amplitude and the out-of-band gain is analyzed for finite-duration modulated signals, indicating an exponential increase in transient amplitudes with the square of NGD. Analysis shows that any attempt to increase the NGD of a finite-duration modulating waveform, by cascading more stages, is thwarted by the transients.

Demonstration of negative signal delay with short-duration transient pulse

This paper introduces theoretic and experimental analyses of short-duration pulse propagation through a negative group delay (NGD) circuit. The basic analysis method of this electronic circuit operating in baseband and microwave frequencies is investigated. Then, its electrical fundamental characteristics vis-a-vis transient signals are developed. To validate the theoretic concept, planar hybrid devices with one- and two-stage NGD cells were designed, simulated, fabricated and tested. Transient analyses with ultra-wide band (UWB) pulse signals with different widths are realized. Then, experimental results in good agreement with the theoretical predictions were observed. Consequently, group delay going down under −2.5 ns is evidenced in baseband frequency up to 63 MHz with one-stage NGD cell. In time-domain, a Gaussian pulse in advance of about t 0 = −1.5 ns or 20% of its half-height time-width was measured. This corresponds to a negative group velocity of about v g = L / t 0 = −0.13 c ( L is the physical length of the tested device and c is light speed in the vacuum). More significant NGD value over 100-MHz bandwidth is stated with two-stage NGD cells. This results in a Gaussian pulse peak advance of about −5 ns (raising a group velocity of about v g = −0.12 c ) or 31% of its half-height time-width. Finally, some potential applications based on the NGD function are discussed.

Dual-Band Negative Group Delay Circuit Using λ/4 Composite Right/Left-Handed Short Stubs

In this paper, a novel design for a dual-band negative group delay circuit (NGDC) is proposed. Composite right/left-handed (CRLH) <TEX>${\lambda}/4$</TEX> short stubs are employed as a dual-band resonator. A CRLH <TEX>${\lambda}/4$</TEX> short stub is composed of a typical transmission line element as the right-handed component and a high-pass lumped element section as the left-handed component. It is possible to simultaneously obtain open impedances at two separate frequencies by the combination of distinctive phase responses of the right/left-handed components. Negative group delay (NGD) can be obtained at two frequencies by using dual-band characteristics of the CRLH stub. In order to achieve a bandwidth extension, the proposed structure consists of a two-stage dual-band NGDC with different center frequencies connected in a cascade. According to the experiment performed, with wide-band code division multiple access (WCDMA) and worldwide interoperability for microwave access (WiMAX), NGDs of <TEX>$-3.0{\pm}0.4$</TEX> ns and <TEX>$-3.1{\pm}0.5$</TEX> ns are obtained at 2.12~2.16 GHz and 3.46~3.54 GHz, respectively.

Baseband NGD circuit with RF amplifier

This presented report deals with the synthesis of baseband negative group delay (NGD) RF circuits. A theoretical approach based on the S-parameter analysis is presented. The NGD circuit synthesis formulae according to the desired gain value, NGD level and bandwidth are established. To validate the theoretical approach, a two-stage NGD device employing LNAs was investigated. Baseband NGD with minimal value below −1 ns with 400 MHz frequency bandwidth was found. The synthesised circuit presents a gain higher than 5 dB. To highlight the functionality of the NGD effect, time-domain analysis was performed. The NGD circuit allows the reduction of signal pure delays caused by telecom devices and is useful for the correction of interleaved symbols in RF/digital numerical systems.

Bilateral Gain-Compensated Negative Group Delay Circuit

We present a symmetric reciprocal (bilateral) gain-compensated negative group delay circuit, operating at 310 MHz and exhibiting a group delay of -0.5 ns. The circuit allows the conditionally stable gain-compensated propagation in both directions. The analytically predicted results are validated with frequency domain measurements, and stability is examined. Application of the circuit to a bilateral, gain-compensated constant phase shifter design is demonstrated.

UWB Active Balun Design with Small Group Delay Variation and Improved Return Loss

Different from distributed baluns, active baluns have group delay variations in the lower bands related to inherent internal capacitances and resistance in transistors. A negative group delay (NGD) circuit is employed as a compensator of group delay variation for an ultra-wideband (UWB) active balun. First, three-cell NGD circuit is inserted into a simple active balun circuit for realizing both group delay compensation and return loss improvement. The simulated results show a group delay variation of 4.8ps and an input return loss of above 11.5dB in the UWB band (3.1-10.6GHz). Then, a pair of one-cell NGD circuits is added to reduce the remaining group delay variation (3.4ps in simulation). The circuit with the NGD circuits was fabricated on an InGaP/GaAs HBT MMIC substrate. The measured results achieved a group delay variation of 7.7ps, a gain variation of 0.5dB, an input return loss of greater than 10dB, and an output return loss of larger than 8.1dB in the UWB band.

A Novel Design for a Dual-Band Negative Group Delay Circuit

In this letter, a novel design for a dual-band negative group delay circuit (NGDC) is proposed. Based on the topology of a single-band reflection type NGDC, composite right/left handed λ/4 short stubs are employed to obtain a negative group delay (NGD) at two separate frequency bands simultaneously. In order to achieve a bandwidth extension, the proposed structure consists of a two-stage dual-band NGDC with different center frequencies connected in a cascade. According to the measurements performed for wide-band code division multiple access and worldwide interoperability for microwave access, an NGD of -3.0 ± 0.4 ns and -3.1 ± 0.5 ns are obtained at 2.12-2.16 GHz and 3.46-3.54 GHz, respectively.

Temporally Advanced Signal Detection: A Review of the Technology and Potential Applications

In recent years, a physical phenomenon referred to as Negative Group Delay (NGD) or superluminal wave propagation has been implemented in electronic circuitry and shown to temporally advance the detection of analog signals. Specifically, the output of such a circuit precedes the complete detection of its input as the group (and therefore time) delay through the circuit is negative. In this article we describe the background and theory behind this phenomenon, discuss its implementation in electronics and demonstrate a specific biomedical signal application (the human ECG). We discuss some key NGD circuit design considerations/configurations and potential applications in which this technology could offset or eliminate entirely, closed-loop control system delays.