Marc Le Roy

Experimental validation of the RC-interconnect effect equalization with negative group delay active circuit in planar hybrid technology

This paper deals with the experimental validation of equalization technique of RC-line degradations based on a negative group delay (NGD) active circuit. The feasibility of this method is illustrated by brief theoretical recalls. Formulas permitting the synthesis of this NGD circuit according to the RC-line parameters are proposed. Then, the analytical predictions are verified by experimental results, which also provide evidence the efficacy of the technique for prototypes in planar hybrid technology. So, for an input square-wave pulse of 25 Msym/s-rate, the rise-time and the propagation delay of the regarded RC-circuit were respectively reduced by 71.4% and 86.4%. As expected, the recovered measured signal shows enhancement of both the raising and trailing edges. Finally, the main benefits provided by this technique compared to the use of repeater are discussed.

Spurious responses suppression of parallel coupled-lines microstrip bandpass filters: Comparison and improvements of planar approaches

This article presents a technique to analyze and optimize Continuously Varying Transmission Lines (CVTLs), used to design microwave band-pass filters in planar technology. For millimeters waves, radiation losses can increase quickly, especially for sharp discontinuities in planar circuits. In this approach, rather than taking account of this effect in a full-wave analysis, we generate structures without discontinuities. Moreover, the line shape is optimized to reduce spurious responses out of the band-pass. For several filters, measurements are compared with simulation results.

Study and Application of Microwave Active Circuits with Negative Group Delay

A simple topology of an NGD active circuit consisting of a FET terminated by a shunt RLC-resonant network and dedicated to the microwave signals was proposed and extensively studied. To our knowledge, in this chapter, the first experimental time-domain demonstration of a circuit able to exhibit simultaneously gain and NGD in microwave domain is proposed. By injecting in the NGD circuit a sufficiently smoothed input short-pulse modulating a sine carrier, one gets an output having an envelop peak in advance compared with the input one. Of course, this phenomenon does not contradict the causality principle. It is also worth emphasizing that the tested circuit respects all required criteria of classical active microwave devices such as gain, matching and stability. As predicted in theory (Ravelo et al., 2007a, 2007b, 2007c and 2008a), for a prototype implemented in planar technology, we have measured in time-domain a pulse peak advance of about -2 ns or 24% of the 1/e-input pulse half-width without attenuation. It is also interesting to note that through this experimentation, the input noise contribution did not destroy the occurrence of time-domain advance induced by the NGD active circuit. Moreover, in this chapter, thanks to the S21-magnitude form, the understudied NGD circuit is able to exhibit a pulse compression phenomenon with a possibility of amplification. Then, it should be worth using the presented NGD active topology to compensate for dispersion effects and especially to reduce the intersymbol interference in certain telecommunication channels. As a potential application of this NGD circuit, a new principle of frequency independent phase shifter is proposed. By cascading a classical transmission line with this NGD circuit, a constant phase value is obtained. The efficiency of this principle was demonstrated by measurement. Indeed, a constant phase value of 90°±5° was obtained within a 76% relative frequency band centred at about 1.5 GHz. The impacts of the PS parameter variations and sensitivity analysis are stated. The main benefits of this NGD active PS concerns its compactness and also the facility to generate very low group delay, and the broad band characteristics. Besides, a two-stage NGD PS was also designed; the simulation results showed a bandwidth enhancement of the constant phase up to 125%. Some fields of applications such as the design of broadband active balun for RF front end architectures are discussed. As ongoing research, design of reconfigurable devices dedicated to telecommunication applications is envisaged. Future investigations will be devoted to the design of NGD devices able to operate at higher frequencies through the use of distributed elements. In this optic, the implementation of MMIC devices based on distributed elements is envisaged.

A New Technique of Interconnect Effects Equalization by Using Negative Group Delay Active Circuits

A novel and innovative technique of interconnect effect equalization in electronic systems was developed through theoretical studies and experimentally validated. It relies on the use of active circuits able to simultaneously generate gain and negative group delay in baseband over broad bandwidth. The properties of these circuits were used to propose a new compensation approach consisting in an equalization of both the positive group delay and attenuation induced by interconnects by an equivalent negative group delay and gain. The theory on commonly used circuits to model interconnect effects were briefly recalled. Then, a circuit composed of a first-order interconnect model (i.e. an RC-circuit) cascaded with an NGD cell was theoretically studied in order to determine the conditions required to compensate for both the degraded propagation delay and the attenuation and to express the synthesis relations to be used in the determination of the values of the NGD cell components. This NGD cell simply consists in a FET fedback by an RL series network. Then, for this first modelling of interconnect line, a proof-of-concept circuit implemented in hybrid planar technology was fabricated to demonstrate the efficiency of this technique. The experimental results in frequency- and time-domains were in very good agreement with simulations and validated the compensation technique in the case of an input signal with a 25 Mbit/s data rate. Indeed, the reductions of the rise time and the 50% propagation delay were 71 and 86%, respectively. In many VLSI systems and particularly in long wires and/or for high data rates or clocks, the inductive spurious effects can no longer be neglected. So, a more elaborated system composed of an RLC interconnect model compensated with NGD cells was also studied analytically in order to check for the validity and efficacy of the equalization technique and to determine the synthesis relations to be used in further applications. To validate the approach, a first series of simulations was run with an RLC lumped model for an input signal at 1 Gbits/s-rate; then , the model used in the second set of simulations was an RLC distributed line for an input signal at a rate of 200 Mbit/s. These simulations under realistic conditions confirmed the compensation approach with reduction of the propagation delay of the same order as previously. Moreover, as observed with the RC-model, the front and trailing edges both showed great enhancements indicative of a good recovery of the signal integrity. Finally, to be able to compensate for interconnect effects in VLSI systems, the proposed circuits must be compatible with a VLSI integration process. This requirement drove us to propose improvements of the proposed topology in order to cope with inductance integration and manufacturing prerequisites. So, a topology with no inductance, but with the same behaviour and performances as previously was proposed. A theoretical study provided evidence of its ability to exhibit a negative group delay in baseband together with gain. Then, time-domain simulations of a two-stage NGD device excited by a 1 Gbits/s-rate input signal were run to validate the expected compensation approach and check for the signal recovery. The implementation of this equalization technique in the case of a VLSI integration process is expected to allow compensation for spurious effects such as delay and attenuation introduced by long inter-chip interconnects in SiP and SoC equipments or by long wires and buses. A preliminary step would be the design and implementation of such a circuit in MMIC technology and especially by using distributed elements. At this stage, even if experimentally the NGD cells were not particularly sensitive to noise contribution, it would be worth comparing this approach and repeater insertion under rough conditions, i.e. long wires with a significant attenuation, in order to gain key information on their respective behaviour under conditions of significant noise. As identified in ITRS roadmap, the power consumption is now one of the major constraints in chip design and has been identified as one of the top three overall challenges over the last 5 years. Faced to these constraints, further investigations are needed to accurately evaluate the consumption of the presented NGD active circuits.

Small-size and low-cost wideband 800 MHz delay line tunable from 1.3 ns to 1.67 µs for automotive radar sensor

A small-size and low-cost wideband delay line tunable over a 1250:1 delay range is presented in this paper. The delay line should take place afterward in an automotive radar target simulator. The initial specifications require merging different technologies to simulate the desired distances from 0.2 m to 250 m with a high resolution and a large frequency band better than 800 MHz. Three technologies are highlighted, SAW filters, optical fibers and LTCC components, to generate delays between 1.3 ns and 1.67 µs. Prototypes were realized, tested and characterized for each technology. Moreover, a hybridization of these technologies is proposed together, with the whole delay line simulations.

Spurious responses suppression of parallel coupled-lines microstrip bandpass filters: Comparison and improvements of planar approaches: Research Articles

This paper presents recent advances in the areas of modeling, design, and fabrication of microwave filters for space applications. A fast and accurate hybrid analysis method, combining boundary integral resonant mode expansion (BI-RME) and integral equation (IE) techniques, is described. Several filters used in satellite payloads have been successfully designed, manufactured, and measured.