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Book Sections Year : 2010

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

Blaise Elysée Guy Ravelo
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André Pérennec
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Marc Le Roy
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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.


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hal-00492503 , version 1 (16-06-2010)


  • HAL Id : hal-00492503 , version 1


Blaise Elysée Guy Ravelo, André Pérennec, Marc Le Roy. A New Technique of Interconnect Effects Equalization by using Negative Group Delay Active Circuits. Zhongfeng Wang. VLSI, In-Tech (www.intechweb.org), pp.409-434, 2010, 978-953-307-049-0. ⟨hal-00492503⟩
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