Noise Analysis Simple Introduction

joemool

介于有坛友询问SI阶段的timing window文件使用问题，我特意新开本贴更新一些基本concept和methodology。同时，也请其它几位资深版主斧正。

首先，申明一下本帖的背景。

1. 工具：EDI 12.0
2. 帮助文档：EDI 12.0 User Guide (Beta)
3. 其它文献：(之后添加)

本帖可以随意跟帖，本人不准备占楼！

joemool

Crosstalk is the undesired electromagnetic coupling between signal lines that causes functional failures and delay variation. The effects of crosstalk might slow down or speed up the delay depending on the transition direction of the two coupling nets.

The Encounter™ software supports signal integrity (SI) operations that include crosstalk prevention, analysis, and repair.

Analyzing and repairing crosstalk is part of the signal integrity closure repair loop, which reduces both timing and crosstalk violations starting from the prevention stage to the post-route optimization stage in the design flow.

joemool

Inputs and Outputs for SI Analysis
The following design input files are required in order to repair crosstalk violations:
1 Netlist
2 SDC (timing information)
3 Routed Encounter database or DEF file (placement and routing information)
4 LEF file (physical library)
5 .cdB noise library
6 XILM data
7 Liberty library (.lib)
8 Encounter extended capacitance table file
9 QRC standalone extraction technology file and library (optional)

Note: Before you begin, ensure that your routed design meets all the timing requirements.

When finished, the software produces an Encounter database optimized for crosstalk violations. The following files are generated:
1 Incremental SDF file
2 Incremental transition time file
3 Timing reports with and without incremental delays

joemool

Setting Up Encounter for SI Analysis
There are three main parts of EDI settings:
1 RC Extraction Settings
2 Noise Analysis Settings
3 Static Timing Analysis (STA) Settings

In this section, we are focusing on Noise Analysis.

djbobo

谢谢分享。

djbobo

回复 1# joemool


    谢谢分享讨论。

joemool

Noise Analysis Settings
Noise analysis settings include：

1 loading the input noise model,
The primary input for noise analysis is a cdB library, which contains characterized noise data. In the absence of a cdB file, you can use a Liberty library (.lib) file. However, it is strongly recommended that you use a cdB noise library for SI analysis.


2 configuring the timing windows,
Timing windows are used to filter out signals that are not switching simultaneously. The internal timing engine computes the timing windows and slew rates automatically. Alternatively, you can load the timing window information by using a timing window format (TWF) file.


3 choosing the noise analysis engine,
The Encounter software uses native signal integrity analysis to perform crosstalk analysis. This engine is same as the one used by Encounter Timing System. If you are using Encounter Timing System as the SI signoff tool, the same settings can be applied in Encounter for performing noise analysis by using equivalent CeltIC NDC commands.


4 setting the delta delay threshold,
You can set the delta delay threshold for noise-on-delay analysis using the following command:
setSIMode -deltaDelayThreshold value
By default, the Encounter software uses the same default delta delay threshold value that is used by the internal SI engine, which is 1ps.


5 specifying the virtual attacker mode.

To efficiently model the many small attackers on a victim net, the SI analysis engine replaces them with an imaginary net, called a virtual attacker. The two main characteristics of a virtual attacker are: coupling capacitance, and the voltage source waveform used as a transition on the virtual attacker.

joemool

How to Set SI Mode for Timing Windows?
1 Internally Generated Timing Windows

You can use the following timing window settings based on your requirement:

By default, the Encounter software computes the timing windows and uses that information during noise analysis. The following is the default setting for timing windows:
setSIMode -noiseTwfMode " "
To use a conservative approach for analysis, set the timing windows to infinite switching mode as shown:
setSIMode -noiseTwfMode "-infSW"
To use the timing window files generated by common timing engine (CTE) during SI analysis, specify the following command:
setSIMode -noiseTwfMode "-useCTE"


2 Externally Generated Timing Windows

To use an external timing window format (TWF) file, specify the read_twf command to load the timing window information. The TWF information specified with the read_twf command is passed to the internal SI engine and is honored by the optDesign and timeDesign commands.

Consider the following points when loading an external TWF file using the read_twf command:

The -skiptw parameter is passed to the SI engine if you have specified the setSIMode -noisTwfMode -infSW command.
The read_twf command can be used to read multiple TWF files (for each view) in case of MMMC designs.
For example:
read_twf twfFile1 -view view1
read_twf twfFile2 -view view2
optDesign -postRoute -si
If you have one TWF file for one of the views of an MMMC design, you can load the available TWF file for that view and the software will create the timing window information for all other views internally.
Multiple TWF files can be loaded for the same view. In this case, all the loaded files will be  passed on to the SI analysis engine.
Only one iteration of SI fixing is performed when using the external TWF file, and the flow stops after routing. You will need to regenerate the external TWF files for the modified design (after timing optimization) and then run the timeDesign command to get the updated timing numbers.
For non-MMMC designs, if you are running hold fixing using the -fixHoldIncludeXtalkSetup parameter of the setSIMode command, then:
specify the setup TWF file using the -setup parameter of read_twf
specify the hold TWF file using the -hold parameter of read_twf

joemool

How to Generate Timing Window for Crosstalk Analysis Internally?
write_timing_windows
[-sstorm]
[-pin] Generates a TWF for each pin instead of each net.
[-view viewName ]
[-ssta_sigma_multiplier value ] (Specifies a sigma multiplier between 0 and 3. The value that you specify increases the arrival window by that amount and worst slack value is generated. The transition and impedance values are not impacted.)
[-voltage_threshold {lower_threshold
upper_threshold }] (Specifies voltage threshold values for generating a Timing Window File (TWF). All the slews in the TWF file will be scaled with these values. The lower threshold value must be less than the higher threshold value.)
output_file

Generates a Timing Window File (TWF) used by crosstalk analysis tools such as Celtic NDC or delay calculator tools such as SignalStorm™ . The TWF file mainly contains the earliest and the latest possible arrival times that a signal may arrive on a net or a pin.


Note:

SignalStorm requires a pin-based timing windows file. Using the -sstorm option, the Encounter software writes out pin-based timing windows for SignalStorm.

hit0821201

感谢楼主的无私奉献