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Overview

Quantum Channel Designer analyzes the behavior of multi-gigabit serial links to accurately predict end‑to‑end link Bit Error Rate (BER). Designers enter circuit descriptions graphically and have access to several analysis methods to predict eye closure and BER.  The effects of transmit and receive equalization, channel loss, clock recovery, and crosstalk are modeled in both pre- and post-layout.

High-Speed Channel Design

Traditional serial link methodologies rely on lab measurements to determine mask compliance at the SERDES driver and receiver.  Increasing transmission speeds and line losses attenuate and disperse the signal to the point where measured receiver eyes close. At this point, mask-based design methods fail and accurate modeling becomes essential for successful serial link design.

Predicting BER

The key measure of serial link performance is BER.  Typical designs target less than one error in every 1012-1017 bits transmitted.  In order to predict BER, the behavior of the transmitter, transmit equalization, modulation, encoding, channel, receiver, receive equalization, crosstalk, and clock recovery circuitry must be modeled.  Correctly predicting BER requires analyzing channel behavior over very long bit sequences (>109 or more). Quantum Channel Designer uses a mix of frequency-domain, time-domain and statistical techniques to predict channel behavior.

Channel Modeling

Modeling is the key to any form of simulation.  Quantum Channel Designer models transmitters, receivers and network interconnects at the electrical level to characterize the channel.  SiSoft has developed proprietary modeling techniques to accurately characterize the behavior of transmission lines, vias and connectors operating above 5Gbps.

Device Modeling

Transmitter/receiver equalization and clock recovery are modeled using a combination of signal processing and statistical techniques ideally suited to analysis of very high bit rate systems and long ISI patterns.

Model interoperability is a critical issue with current serial link design tools. In the absence of modeling standards for SERDES devices, semiconductor vendors often supply proprietary simulation tools and models for customer use. System designers have no means of designing and analyzing the behavior of a system with SERDES components from different semiconductor vendors.

Quantum Channel Designer allows semiconductor vendors to model equalization and clock recovery behaviors while still protecting critical IP. This permits model interoperability on a common simulation platform.  SiSoft is co-authoring a modeling standards proposal for SERDES transmitters and receivers though the IBIS-ATM task group.

Graphical Design Capture

Quantum Channel Designer provides a graphical design editor with symbols for transmitters, receivers, transmission lines and parasitic elements.  S‑parameter blocks represent portions of the circuit modeled with 3-D field solvers or extracted from measurement.  Topologies for crosstalk aggressors and coupling sections can be captured to describe how noise couples into the signals of interest.

Users specify the channel encoding scheme and bit rate along with key network parameters to be swept during analysis. Transmitter / receiver configurations (equalization, peaking filter settings, impedances) can be specified, swept, or automatically optimized by the tool.

Network Analysis

Network analysis uses detailed electrical models of the transmitter, receiver and channel interconnect to characterize the channel.  Results can be plotted graphically or output in S-parameter format.  The system’s pulse response can also be plotted, allowing the effects of swept network and model parameters to be compared.

Statistical Analysis

Quantum Channel Designer uses proven techniques to predict channel behavior over billions of bits.  This provides bathtub curves with enough data to accurately reflect the effects of Inter-Symbol Interference (ISI), jitter and crosstalk. Quantum Channel Designer uses information provided by the receiver model to establish the recovered clock’s probability density function (PDF) and determine error distributions.

Outputs from statistical analysis include bathtub curves with and without crosstalk, recovered clock PDF, eye contour plots, statistical eye diagrams, and BER.

The statistical engine’s large capacity is key to accurate error prediction.  Designers must be able to analyze bit sequences long enough to accurately account for ISI effects.   This depends on the specific channel and bit rate, but often requires analysis of many billions of bits.

Semi-Analytical (Time Domain) Analysis

Quantum Channel Designer uses time domain analysis to predict channel behavior for moderate sequences (fewer than 10 million bits).  This allows users to explore the effect of specific stimulus sequences and encoding schemes on channel performance. Time domain analysis models the channel’s behavior and the effect of clock recovery circuitry.

Outputs include time-domain waveforms, eye diagrams, bathtub curves with and without crosstalk, recovered clock PDF, eye contour plots, statistical eye diagrams, and BER.

Incorporating Crosstalk

Crosstalk has become a major factor in serial link design.  As serial links enter mainstream use, they can no longer be physically isolated from other signals.  Crowding against other signals in the design picks up crosstalk with widely varying spectral content.   Quantum Channel Designer leverages SiSoft’s existing Quantum-SI™ simulation infrastructure to model aggressors with arbitrary encoding schemes, edge and data rates.  Crosstalk is characterized and used by the statistical and semi-analytical engines to predict its effect on link BER.

When enough crosstalk noise couples onto a victim, the signal cannot be sampled without errors at any point during the bit time (represented in the figure below by the dotted red line).  This establishes a “floor” for the link’s BER.  Quantum Channel Designer allows designers to explore different design parameters and evaluate their effect on the link’s performance.

Quantum Channel Designer leverages Quantum-SI’s post-route infrastructure to construct post-route PCB electrical models.  Quantum Channel Designer scans routed PCB databases to locate critical coupling regions and then extracts the appropriate victim and aggressor topologies to model the effects of PCB physical layout on link BER.

Consulting Services

SiSoft’s consulting staff has extensive experience in design and analysis of serial links operating at speeds up to 20 Gbps.  We can model your application with Quantum Channel Designer to help ensure your design’s success.
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