[SI-LIST] Re: Can I help?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 02 Oct 2013 01:51:36 -0700
Ralph, if someone asks a question that you have and are willing to
provide useful guidance on then answer away. If you know your stuff
then your contributions will be welcomed by the approximately 5000
subscribers. The list does not exist to offer direct product or service
promotions.
Steve.
On 10/1/2013 9:14 PM, Ralph Morrison wrote:
> Hello to the SI list.
>
> I am new to this list but not new to problems of board design. I
> have read many of the discussions submitted to the list and I want to
> help. That is easy to say but not easy to do as I face a barrier
> that I will call "language". With out establishing some rules, I can
> be totally correct and at the same time be totally misunderstood. So
> the problem I face is where to start so I can be effective. Each
> engineer has a vocabulary and a set of mental images that supports his
> or her understanding and I am going to challenge many of them. To
> some of you I will be a thorn in the side and to others perhaps a ray
> of hope. It is not an easy path to take as many assumptions will
> have to be discarded. This is a difficult path to follow as it hits
> everyone in their ego. Letting go of a weak support structure can be
> tough.
>
> Nature solves every electrical problem and never makes a mistake. We
> seek ways to control electricity so we can achieve our goals. If
> Nature's goals are the same as our goals then we can have our way.
> Nature will not budge. To determine Nature's goals we need to define
> electricity as Nature sees it. It is the electric field around a
> group of electrons called a charge and it is the magnetic field
> associated with a moving stream of electrons called a current. It
> takes work to create a field as a force is needed to move charges or
> increase the current. We have learned how to move these fields in our
> circuits. We use the presence of a field to represent logic. We use
> some of these fields to operate components. Under the right
> conditions these fields can leave the confines of conductors and
> radiate at the speed of light. These fields are electricity. These
> fields are what Nature pushes around. To understand Nature we must
> understand these fields. Below 10 MHz we could get away using
> circuit concepts. In todays GHz world, circuit ideas can lead us
> astray. We need to use fields as Nature does not read schematics,
> follow diagrams or read color codes. The trouble is field theory can
> be very complicated and Nature could care less. Avoiding fields
> because of these difficulties is the big problem. There are ways to
> appreciate fields without getting wound up in details. It need not
> be complicated. It takes a change in approach.
>
> In physics once a principle is accepted it must be universally
> accepted. Light from the sun is the flow of electromagnetic field
> energy. There are no wires. This means that fields carry energy.
> There are no exceptions. There are no frequency limitations. This
> means that utility power is carried in fields. The energy from a
> battery flows in a fields. The purpose of conductors is to direct
> where the energy flows. Conductors also act to steer fields away
> from critical areas. Without this viewpoint the true nature of the
> problems in board design will not be explained.
>
> To illustrate the problem consider the word "impedance". It is used
> in electrical engineering to calculate current flow for sine wave
> voltages when reactances are involved. The term is basic to circuit
> theory. When transmission line theory was developed it was a world of
> sine waves. Today with logic signals having picosecond rise times
> the word impedance has survived even when individual sine waves are
> not involved. We obviously need some general way to express
> opposition to current flow but a new term has not evolved.
>
> In transmission line theory we call it characteristic impedance.
> This unit measures the ratio of current to voltage for a step voltage
> applied to a pair of conductors. It is correctly the square root of
> the ratio of inductance to capacitance per unit length. The
> capacitance can store electric field energy and the inductance can
> store magnetic field energy. The characteristic impedance is the
> ratio of a possible E or electric field and the H or magnetic field at
> a given point in space even if no fields are present. It is a
> measure of conductor geometry. But few of us accept this definition.
> By matching impedances (characteristics) we are providing a smooth
> transmission path for fields to follow.
>
> My new book Digital Circuit Boards - Mach 1 GHz published by John
> Wiley takes these field ideas and explains what really happens on a
> circuit board.
>
> I close by giving you food for thought. A baby carriage can go 6
> mph. We need automobiles to go 60 mph. To go 600 mph the technology
> must move to jet aircraft. 6000 mph is the domain of space travel.
> That's a change of three orders of magnitude. Early logic was was
> around 1 MHz. Little by little we have progressed to where todays
> logic is well above 1 GHz. This is also more than a three orders of
> magnitude change in speed and yet we are still trying to design using
> a very similar technology and using the same terminology. There is a
> need for change. Can I help?
>
> Ralph Morrison
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>
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