PC Electronics for your PC/pcelectronics.bin/Elec_95/EMC (Filter Simulation)/MANUAL.TXT

Text File | 1996-06-03 | 16KB | 386 lines

'EMCFiltr' EMC Filter simulation Software written by C. Bateman.

see 'about the software section' or
'E-Mail' [e-mail]

Installation.
-------------
Due to the restrictions imposed by Font sizes etc. two versions
of this software are available, optimised for either VGA 640*480
screen or SVGA 800*600 screen, each in a separate directory on
the disc.

While both versions will install and run on either Windows
screen resolution, some on screen features will be incorrectly
displayed. The SVGA version is also suitable for higher screen
resolutions but the presentation will not be optimal.

If you have purchased the 'Demo' disc then all files required
have been included and are uncompressed.

If you have downloaded the 'Demo' then for economy of download,
If VBRUN300.DLL is not already in your Windows/system directory,
this file must downloaded separately and copied to Windows/system
BEFORE commencing with the 'EMCFiltr' installation.

To minimize download times, since the VBRUN300.DLL file is quite
large, most ftp sites request this be excluded from the download
and if not already on your harddisc, it be obtained separately.
It is readily available from most MS Windows archives.

The current version of VBRUN300.DLL used to write this software
was 3.00.0538  12/5/93   extracted size 398,416 bytes.
This version or newer is required.

Before commencing with a VGA installation, if this software has
been downloaded, it is necessary to copy certain files from the
SVGA directory into the VGA directory:-

    DDEML.DL_
    SETUP.EXE
    SETUPKIT.DL_
    VER.DL_


To reduce download times, since these files are common to both
SVGA and VGA installations, only one set is included. If you have
the normal distribution disc, they have already been duplicated
so no action is needed.

To install follow the usual Windows practise of File Run
'A:\SVGA\SETUP'  or  File Run 'A:\VGA\SETUP'  as appropriate.

When installation is complete the program body 'EMCFiltr.exe'
will have been installed in the directory named EMCFiltr and
Setup1.exe in Windows. If not already present, three files
needed to run a compiled Visual Basic program will have been
added to your Windows/System directory.

    VBRUN300.DLL
    DDEML.DLL
    VER.DLL

You need take no action, the file Setup.exe checks for their
existence and actions accordingly (see setup.lst on the disc).

This install makes no alterations to your existing 'Ini' files
or autoexec.bat or config.sys hence can be easily uninstalled by
simply deleting the program group while running Windows, then
deleting the program its directory and Setup1.exe.

The three files in Windows/System are standard Microsoft files
required by many other programs and can be left in place should
you uninstall the main software..

    VBRUN300.DLL
    DDEML.DLL
    VER.DLL

Having completed the installation, double 'click' on the
EMCFiltr Icon to launch the program.

The full program provides analysis of nine pre-set Filter
configurations. The Demo version is restricted to analysis only
of the Two-Tee style, however all other screens are still
available and can be actioned for value change etc., but will
not proceed to the analysis stage.


Familiarisation.
----------------
The quickest way to check program operation is to repeatedly
push Enter which will cycle the program through each default
screen in turn, to demonstrate program action.

Having ascertained the program is functioning at all four
screens, try choosing a filter style - say Two-Tee, and run the
default values, its not a very good Filter.

Try setting silly component values e.g. 0.0 etc. To avoid
'divide by zero' errors the program automatically applies a safe
minimum value. This minimum for the Demo has been increased, the
full program however works down to extremely small values.



Let us now try redesigning this Two-Tee Filter to a target
specification.

Lets assume as a target, good transfer of audio to 12 kHz, with
interference rejection better than 40 dB at 40 kHz and better
than 70 dB at 100 kHz and above.

Exit the program then re-run to restore the original defaults.

Run the default Two-Tee values, its an awful Filter in every
respect.- Terrible Return Loss - Inadequate Pass Band
Transmission and poor EMC attenuation.

1) Try halving the capacitors to 0.5 uF        Looks better
2) Make all inductors 100 uH.            Better again.
3) Increase inductors to 500, 1000 , 500 uH     Very much better
                     but Return Loss still poor.
4) Reduce two outboard inductors to 300 uH    Not quite there.
5) Try reduced capacitance say 0.33 uF.        Almost to spec.
6) Try 330 uH, 920 uH, 330 uH            Looks good.
7) Make DC resistances attainable.
    Try 0.5 ohm, 1.0 ohm, 0.5 ohms        Still good.
8) Reduce inductor Self Capacitances to 2.5 pF    Specification
                        surpassed.

The above few steps give a good indication of the affect on
Return Loss and Insertion Loss of various component changes.
Dependant on the transmission requirements further fine-tuning
may be needed to improve the Group Delay response.

The default capacitors in the Demo version are X7R Ceramic
Surface Mount chips, these typically have 0.5 to 0.8 nH of Self
Inductance, depending on their physical size. Other styles have
differing Self Inductances, with wire leads the inductance will
be much higher, for the so called 'Discoidal' types the
inductance will be almost zero.

The default inductors in the Demo version assume use of medium u
ferrite toroids, these provide usable inductance value with
little Self Capacitance, although this capacitance is influenced
by winding techniques, hence a value must be input.

Since the d.c resistance of inductors depends on wire gauge and
winding methods, it cannot be pre-determined and is a required
input. The software calculates the frequency dependant AC loss
resistance which is then added by frequency to the d.c.
resistance value.

The full program allows the Capacitor and Inductor base
material to be chosen for each simulation, since this determines
the Frequency Dependant variables needed for realistic
simulation.

The full software package includes a manual describing Inductor
winding techniques together with typical values to be expected,
also covers capacitor choice in detail.

However mostly this software will be used to simulate an
existing Filter when used with source and load impedances other
than 50 ohms.

Most Filter specifications state the capacitance values used or
alternately the total capacitance for Pi (two capacitors) and
larger Filter styles, and generally will be stated as a Minimum
value, but Inductor information is less common. A telephone call
to the makers Technical Support will often fill in the details.

If not available, all is not lost. Simply 'reverse engineer' the
Filter by inserting the stated capacitances perhaps at +10%,
then guess at an inductance value and analyse the Filter,
compare results with stated claims. Generally after five or six
attempts the Filter will have been reverse engineered with
sufficient accuracy. You can then use these derived values to
analyse the Filter's behaviour with any desired source and load
impedance combination.

Remember their catalogue claims will be chosen such that no
Filter fails insertion loss testing. It is also common practise
to considerably underclaim at the higher frequencies to avoid
test failures, since small construction variances have most
affect as frequency increases.



Significance of Return Loss.
----------------------------

In order to pass low frequencies with little attenuation, the
inductors used must have a low DC Resistance, hence unlike an
attenuator the Filter cannot attenuate EMC by dissipating
energy. Since energy cannot be destroyed the only usable
mechanism is to 'return' (Reflect) the unwanted EMC to its
source. This is exactly the mechanism by which Low Pass EMC
Filters work. Depending on the input impedance of the filter the
wanted signals, which should pass through the Filter, can also
be reflected. Automatically resulting in loss of wanted signal.

The perfectly matched Filter would lose by Reflection less than
1% of the wanted signal, expressed in dB this equates to a
Return Loss signal -40dB lower than the incident wanted signal.
A Return Loss of -26dB equates to a VSWR of 1.1:1 and would be
perfectly acceptable in practise, reflecting 5% of the signal.
Return Losses of -20dB and less are not desirable.

Obviously Return Loss results from the value of source and load
impedances used as well as the Filter's Input impedance, thus
making this an important parameter when designing for EMC
suppression with good transmission of a wanted signal.

With DC Power supplies, Return Loss traditionally has been
ignored, resulting in the oft quoted advice to design for
maximum mismatch between source and Filter. This is extremely
bad practise whenever a wanted signal must be transmitted
through the Filter.



About the Software.
-------------------

Simulators come in three basic forms:-

Those based on measured 'S Parameters' and generally used for
Microwave design only, since the software is expensive.
Measurement of 'S Parameters' for capacitors and inductors is
time consuming, also extremely expensive 'characterised'
jigging is essential, otherwise the measurement is valueless.
While most RF rated semiconductors have 'S Parameter'
information available, this is almost non-existent for
capacitors and inductors, especially those not specifically
intended for RF use.

Lower cost 'Frequency Domain' simulators which calculate node
by node the 'Kirchoff' solutions, are available but these assume
'idealised' capacitor and inductor models. While it is obviously
possible to apply a series loss resistor, since with real
components this resistance is frequency dependant, this would
only be applicable to a restricted range of frequencies.

The most common circuit simulation software derives from the
'Spice' system detailed in Lawrence Nagel's doctoral thesis.
This was funded and targeted expressly towards the simulation of
Integrated Circuits having amplitude dependant non-linearities,
thus the basis of 'Spice' is modelling in the 'Time' domain and
not 'Frequency' domain. While it is true that 'Spice' offers
'Small Signal  Simulation' by Frequency this does not permit the
use of measured frequency dependant variables.

The 'EMCFiltr' software models Insertion Loss strictly in
accordance with the US Specification MIL-STD-220A, which is
recognised world wide.

Real world capacitors and inductors, when carefully measured,
each comprise three elements, all of which are strongly
frequency dependant.

Capacitors translate to a 'series' combination of capacitance,
inductance and resistance, with capacitance being dominant at
the lower frequencies, i.e. below self resonance.

Inductors similarly equate to a 'parallel' combination of
capacitance and inductance both being in 'series' with
resistance, with inductance being dominant at frequencies below
self resonance.

For both, the resistive part comprises a fixed resistance value
in series with a frequency dependant variable resistance.

For inductors this fixed resistance is the dc resistance of the
winding (DCR), the variable part results from the various
frequency dependant losses which cause the 'Q' value to change
with frequency.

For capacitors the fixed part is the irreducible resistance
measured at high frequency (TSR), largely comprising metallic
connection resistances. The variable resistance derives from AC
dielectric losses, described as tan d, being frequency
dependant. At lower frequencies this can amount to many ohms,
dependant on capacitance value.

Any simulation based on 'ideal' components will differ
significantly from practical measured results of working
Filters. The maximum insertion loss from simulation will far
exceed measured results. At frequencies below Filter resonance
the insertion loss will be overstated while above resonance it
will be understated. These differences can accrue to many dB's
difference.

The EMCFiltr software package is a node by node solution by
frequency of Kirchoff, but considerably enhanced by using true
three component models for each part with the frequency
dependency variations required to simulate real world parts.
This frequency dependency is derived from manufacturers
published characteristics and stored as data in the software.
Hence assuring realistic simulation results.

The 'standard' version software is targeted to Filter users and
provides a choice of base capacitor and inductor materials
commonly used in the production of Filters.

The 'professional' edition is targetted towards those intending
to manufacture Filters, and while based on the standard
version's simulator engine, this version provides the facility
to 'tailor' the frequency dependant material models to your
choice of materials.

The high dielectric constants used with some ceramic capacitors
and their physical size, can result in narrow band resonance
modes, these also can be modelled given the precise physical
descriptions of the parts.

This is incompatible with the objectives of simplest possible
no-learning curve approach of this 'standard' version hence  is
available only in the 'enterprise' edition software currently
under development.

The full version of the software, also any technical support you
might need, is available from:-

C.Bateman Engineering.
'Nimrod'
New Road.
ACLE.
Norfolk.
NR13 3BD.
England.

Tel. [phone]
'E-Mail'
[e-mail]
[e-mail]

Also see Web Page at:-
http://ourworld.compuserve.com/homepages/cyrilb




About the Author.
-----------------

He first trained as an RF Electronics Engineer in the mid '50's
and subsequently became an Electronics applications and design
engineer for one of the then largest capacitor manufacturers. As
an application engineer he was deeply involved with both the
birth of the Hi-Fi and Colour Television industries in England,
and personally designed the first Aluminium Electrolytic
Capacitors optimised for Hi-Fi sound. These were used in the
first volume produced quality amplifier, the original Goodmans
90 and 100 series. Around the time the Apollo program got
underway in America, he also inherited the EMC Filter
Applications tasks.

Subsequently as the use of EMC Filters increased, principally in
Military equipments, he founded 'Mercator', a trading house
tasked to import Components and EMC Filters not available from
UK Manufacture.

Subsequently the volume of EMC Filters increased such that he
was then tasked to setup a UK design / development program to
manufacture these Filters, and gain full European Quality
approvals. For this operation he wrote all the design and
measurement software needed to gain the approvals and for their
production which was 100% Insertion Loss tested and Certified to
1 GHz.

While with Mercator as a result of pressures from customers
engineers, in 1983 wrote his first computer simulation program
designed specifically to select the most appropriate Filters
for differing source and load impedances.

As a result he has had much practical experience of Filter
simulation both with his own programs and commercial simulators,
ranging from various Spice based programs to the most
professional Microwave Design systems, and has been responsible
for characterising RF capacitors using 'S Parameters' up to 3
GHz.

He is now an independent design consultant working principally
with RF topics, EMC Filters and  Capacitors.