implementation of agilent eesof eda touchstone … agilent eesof eda subject

“New Features for Solving HSD Challenges with ADS 2013”

1

New Features for

Solving HSD Challenges with ADS 2013

Implementation ofTouchstone Version 2.0

in ADS 2013.06

Agilent EEsof EDA

Radek Biernacki

June 17/18/20, 2013

Copyright © 2013 Agilent Technologies


Outline

Copyright © 2013 Agilent Technologies 2

Why Touchstone 2.0

ADS Implementation

Touchstone 2.0 Format

Notes on differential ports

Notes on mixed-mode n-port parameters

Some hints for using Touchstone data


Historical Note


S-parameters have been used for many decades to characterize linear

sub-circuits, passive and active devices, interconnects, EM co-simulation,

etc.

Growing interest in S-parameter representation of linear sub-circuits

among the SI/PI engineers.

PI engineers observed improved accuracy when different reference

impedances were used for power than those for signal ports.

The legacy Touchstone format accommodated only the same reference

impedance for all ports.


The Role of the IBIS Open Forum


IBIS Open Forum is a standardization organization that supports I/O

buffer modeling (I/O Buffer Information Specification) with the focus on

signal and power integrity.

http://www.eda-stds.org/ibis/

The IBIS organization took the initiative to standardize on the Agilent’s

Touchstone format.

With Agilent’s permission the official Touchstone File Format Specification

Version 2.0 has been developed, and ratified in 2009.

http://www.eda-stds.org/ibis/touchstone_ver2.0/touchstone_ver2_0.pdf


Notes on Per-Port Reference Impedances


ADS has always allowed different per-port reference impedances

– CITI files

– datasets

This included complex reference impedances, useful for power match

In view of several ways to deal with complex impedances, IBIS decided to

it was sufficient to allow real impedances only.


Version 1.0 Format


The original Touchstone File Format had never been officially

standardized, though it was a de-facto standard.

A few of the original rules have been slightly relaxed with time, including

– three character file name extension as needed for more than 9-port data (e.g., *.s12p)

– reliance on the file name extension

– limited number of data items per line

The IBIS standardization initiative included also the legacy Touchstone

files. They are now referred to as Version 1.0 files. This has effectively put

an end to somewhat uncontrolled attempts to extend the original format

by various vendors.


A Typical Version 1.0 File


! Created Fri Nov 21 11:25:57 2003

# Hz S MA R 50

! freq magS11 angS11 magS21 angS21 magS12 angS12 magS22 angS22

1e+009 0.995383394 167.294765 0.075127918 …

2e+009 0.98389341 153.496417 0.163021787 …

3e+009 0.955822028 137.049238 0.281341042 …

4e+009 0.884013749 115.091936 0.457067209 …

5e+009 0.694146948 81.6998692 0.711192239 …

! 2 Port Noise Data

1e+009 …

3e+009 …

5e+009 …


Example of an Illegal Extension in aLegacy Touchstone File


! Four port data with different per-port reference impedances

# Hz S MA R 50 50 1 1





1e+009 0.995383394 167.294765 0.075127918 …

We have no plans to support such non-standard extensions.

A file like this can be easily converted to a Version 2.0 file.


Touchstone 2.0 Implementationin ADS 2013.06 Release


Import (read)

yes – complete features

all SnP, SnP_Diff and De_Embed components

no – for the DAC component (use SnP directly)

Export (write)

yes – Touchstone 1.0 (as before)

no – Touchstone 2.0 (for now)

SPOutput, Data File Tool, TouchstoneCombiner


Touchstone 2.0 Implementationin ADS 2013.06 Release – cont’d


Familiar SnP components

User does not have to identify the file version or act upon it!


Touchstone 2.0 Implementationin ADS 2013.06 Release – cont’d


All existing features of the SnP components are preserved:

– interpolation techniques

• linear, cubic

• cubic splines

• a few others

– interpolation domain

• real/imaginary

• magnitude/angle

• dB/angle

– extrapolation options

– passivity checking/enforcement

– causality enforcement


Touchstone 2.0 Distinct Features


• different reference impedances allowed for different ports

• mixed-mode n-port parameters

• includes the S, Y or Z matrix types

• format (IBIS style keywords)

• precise rules and specification


Touchstone Version 2.0 vs. Version 1.0Minor Differences


Z, Y, G, H matrices and Noise Resistance are no longer normalized.

Two-port data special order (S11, S21, S12, S22) is not required.

It is allowed to specify either the full matrix or the lower/upper half matrix.


Touchstone 2.0 Version Keyword andOption Line


[Version] 2.0

• the first keyword in the file

• required in Version 2.0 files

• prohibited in Version 1.0 files

The Option line is the same as in legacy files and it determines the units,

data type, data format and the reference impedance, for example

# GHz S MA R 50

• required in all Touchstone files


Touchstone 2.0 Number of Ports and Number of Frequencies Keywords


[Number of Ports] 6



[Number of Frequencies] 501




Handling Different Reference Impedancesin Touchstone 2.0 Files


[Reference] 50 50 0.1 0.1 50 50

• optional in Version 2.0 files


• overrides the reference impedance setting in the Option line

The order of the entries must follow the port ordering (the same as the

row/column ordering in the data matrices).

The number of entries must equal the number of ports.

Complex reference impedances are not allowed.


Network Data in Touchstone Files


The actual n-port data is similar for both versions, but the

[Network Data]

• keyword is required in Version 2.0 files


There are no limitations regarding the number of data items in a single

line.


Some Other Keywords inTouchstone 2.0 Files


[Two-Port Data Order] 12_21

• required in Version 2.0 files for 2-port data, otherwise prohibited

• the order is pre-defined as 21_12 in Version 1.0 files

[Matrix Format] Lower

• optional in Version 2.0 files for specifying Full, Lower, or Upper

• the order is pre-defined as 21_12 in Version 1.0 files

[Number of Noise Frequencies] 151

[Noise Data]

[End]


Example of Version 2.0 File


[Version] 2.0

# Hz S MA R 50

[Number of Ports] 2

[Two-Port Data Order] 12_21 ! Required for 2-port data; otherwise

prohibited

[Number of Frequencies] 5

[Reference] 50 50 ! Optional if the same reference

impedance is used

[Matrix Format] Full ! Optional – Full is the default

[Network Data]


1e+009 0.995383394 167.294765 0.075127918

[Number of Noise Frequencies] 3

[Noise Data]

1e+009 …

[End]


Extensions in Version 2.0 Files


[Version] 2.0

# Hz S MA R 50

...

[Reference] 50 1

[Matrix Format] Lower !or Upper

[Mixed-Mode Order] D2,3 S5 C2,3 C4,1 D4,1

[Begin Information]

Any useful information for the user, but no action by EDA platforms

[End Information]

[End]


Notes on Differential Circuit Ports


Vdiff

P2+

I2V2

-

I2

V1

I1

P1+

Icommon

P1-

+

I1

P2-

one differential port consists of two “normal” single-ended ports.

The “-” node is common for the two single-ended ports.

Therefore, differential ports are 3-terminal objects; however, as we prefer to have just one (common) reference terminal for all the ports they may be perceived as 2-terminal objects – beware!

The mixed mode currents and voltages are linear combinations of the respective single-ended currents and voltages.

In Touchstone 2.0 it is required that the reference impedances for the two ports that form one differential port are identical.


Mixed-Mode Quantities


common mode voltage

differential mode voltage

common mode current

differential mode current

common mode incident wave

differential mode incident wave

common mode reflected wave

differential mode reflected wave

��,� � �� /2

��,� � ��

��,� � ��

��,� � �� /2

��,� � ��,� � ��,��,�/�2 ��,�)

��,� � ��,� � ��,��,�/�2 ��,�)

��,� � ��,� ��,��,�/�2 ��,�)

��,� � ��,� ��,��,�/�2 ��,�)


Mixed-Mode n-port Parameters inTouchstone Version 2.0 Files


Whether the file contains single-ended or mixed-mode n-port data (under

the [Network Data] keyword) is determined by the presence of the

following keyword.


• optional in Version 2.0 files; indicates that the mixed-mode data rather than the single-ended data is given


• the order of the entries follows the row/column ordering in the data matrices

• indices correspond to single-ended port ordering, consistent with the port ordering in the SnP symbol in the UI

• D indicates a “differential” quantity, C indicates a “common mode” quantity and S indicates the single-ended quantity for ports that are not a part of any differential port


Interpretation of [Mixed-Mode Order]




Hints – Using Datasets


Parsing may be time consuming – for large number of ports create and

use datasets.

– binary files using ADS internal data structure

– faster to read

– no need for interpretation

– easily viewable in Data Display

Simply run S-Parameter simulation.


Hints – Verify Data Quality


View S-Parameter simulation results in Data Display.

Bad data may significantly affect the simulation results!


Hints – Impact of Bad Data


Example of what incorrect DC extrapolation may lead to.


Hints – Eliminate Unused Ports


Two techniques.

1.

– load unused ports

– run S-Parameter simulation on a subset of original ports

– subsequently use an n-port with fewer ports

– pay attention to the frequency plan and coverage

2.

– use the following unique ADS feature


Hints – Large SnP Reduction


OPTIONS

Options

Options1

MaxWarnings=10

GiveAllWarnings=yes

I_AbsTol=

I_RelTol=

V_AbsTol=

V_RelTol=

Tnom=25

Temp=25


Summary


• ADS has always allowed the use of different per-port reference

impedances for S-parameter data, yet the Touchstone files required

the same value for all ports.

• Touchstone Version 2.0 relaxes those limitations and unambiguously

defines the allowable format.

• Touchstone 2.0 provides the means to handle mixed-mode n-port data.

• In ADS 2013.06 the new format is adapted in a completely transparent

fashion. The user can use the new files exactly the same way the old

files were used.

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