1. Electromagnetic Compatibility (EMC)
Definition of EMC: A system is said to be electromagnetically compatible if it
Does not cause interference with other systems
Is not susceptible to emissions from other systems
Does not cause interference with itself
EMC problem may be broken up into three parts shown below.
Interference to the receptor may be prevented by:
Supress the emission at its source (“Nip it in the bud!”)
Make the coupling path as inefficient as possible
Make the receptor less susceptible to the emission
Source
(Emitter)
Transfer
(Coupling Path)
Receptor
(Receiver)

2. Four EMC Sub-problems:

3. Other aspects of EMC

4. Electrical Length of a wire “k” is how long the wire is in terms of wavelengths
k = L / λ (unitless) where L = physical length of wire in meters and λ = wavelength, which is the length of one complete period of the wave at some instant of time as it propagates away from the emitter
λ = v * T = v / f where v = velocity of propagation of an EM wave (m/s) T = period of the wave (time it takes for the emitter to generate one complete period of the wave.) Measured in seconds. f = frequency of the wave = number of complete periods generated by the source per second, f = 1/T. (Measured in Hertz = 1/s).

5. Speed of EM wave in free space (air):
v = 1/sqrt(εOμO) = 3 x 108 m/s
where εO = permittivity of free space
= 1/(36π) x 10-9 F/m
μO = permeability of free space
= 4 π x 10-7 H/m
For a material medium:
v = 1/sqrt(εOεRμOμR) for a medium with relative permeability μR and relative permittivity εR both of which range between 1 and infinity. Thus v is always slower in a material medium compared to free space.

6. For a non-magnetic medium μR = 1.0
Example: Find the electrical length of a 10 cm wire in air at a frequency of 5000 MHz: k = 10*10-2 m / [(3*108 m/s) / 5000*106 1/s)] = wavelengths
In Bakelite: k = 10*10-2 m / [{(3*108 m/s) / sqrt(1*4.74)}/ 5000*106 1/s)] = 3.63 wavelengths

7. Emitter and receptor coupling is most efficient when their dimensions are on the order of a wavelength. As products are made to operate faster and faster, their operating frequencies of products increase. Thus a wavelength becomes smaller and smaller, and even physically small products become efficient receptors and radiators at the frequencies at which they operate. Therefore…. EMC problems are on the rise!

8. Wavelengths at different frequencies in AIR
Note wavelength in meters = v / f = 300 / fMHZ
NOTE: As CPU clock and bus frequencies rise above 3 GHz, very short lengths of interconnecting wires become efficient radiators / receptors.. Increasing EMC problems for the computer engineer!

10. Performance, Pricing and Availability Pentium® 4 Extreme Edition 3
Performance, Pricing and Availability   Pentium® 4 Extreme Edition 3.46GHz, Nov. 1, 2004
Core Speed
Level Two Cache Size
System Bus Speed
1KU Price
Pentium® 4 Extreme Edition
3.46 GHz
2MB level 3
1,066MHZ
$999
Intel® Xeon™ processor
3.2 GHz
1000K
800MHZ
$??
Intel® Pentium® 4 Procesor
2.80 GHz
512K
533MHZ
$508
2.66 GHz
533MHz
$401
2.60 GHz
400 MHz

11. Speeds of PC Components
3.5 GHz Pentium 4 (announced on 28 August 2001)
533 MHz PC system bus
800 MHz DDRAM, RDRAM
1-GHz DSP chip from TI,
6-Gbit/s backplane from PMC-Sierra, LSI Logic, Accelerant, Rambus,
3.46 GHz Pentium 4, August 28, 2001
800 MHz PC system bus
1,066 MHz front-side bus for Pentium 4, November 1, 2004

12. Speeds of Backplane and Networks
10-Gbit/second Ethernet over Category 5e cable demo, March 22, 2004
10-Gbit/, s Backplane design, April 8, 2004
The selector chip operating at 50Gbit/s uses a circuit schematic that takes 1.0V power, standard for 90-nm CMOS chips, Fujitsu, March 23, 2004

13. Wireless Devices
Cordless Phones – 900 MHz, 2.4 GHz (Digital Spread Spectrum)
Walkie Talkie – 467 MHz
Analog Cell Phone, AMPS: Advanced Mobile Phone Service – 800 MHz
CDMA: Code Division Multiple Access – 800 MHz or 1900 MHz
DCS-1800: European 1800 MHz GSM band.
PCS: Personal Communication Services – 1900 MHz
TRI-BAND – GSM phone at 900 MHz, 1800 MHz, and 1900 MHz.
GSM: Global System for Mobile communications.
Most wireless LANs currently use the 2.4 to 2.48 GHz band.
ISM: Industrial Scientific and Medical Unlicensed Frequency Bands - Operates at 900 MHz and 2.4 GHz.
MMDS: Multi-channel Multi-point Distribution Service, a fixed wireless service for data, voice and video which operates in the 2.5 GHz band in North America and in the 3.5 GHz bandwidth internationally.
The Bluetooth system is operating in the 2.4 GHz ISM band.
IEEE – 2.4GHz; g – 5GHz

15. The Digital Hub as Gateway (IEEE Spectrum July 2002)
Digital hub is a term cointed by Steve Jobs of Apple Computer. The hub should handle all video, audio, and image files and games. It could play the files, record them, edit them, transfer them from hard disk, broadcast or satellite TV, and Internet.
It could also handle wireless intercom, home security, and home monitoring, etc.

16. The Core of A Home Entertainment Hub (IEEE Spectrum July 2002)
At the core of a digital hub is a computer with communications capabilities. The computer should have high speed computation and communications capability. It should also have rich connectivity and intelligence to understand different peripherals such as TV, VCR, DVD, cable and satellite receivers, home antenna, etc.
The problem here is not about individual hardware components but their connection and software to manage everything.
It is true to say that the home is a computer just like a car is a computer.

17. Building Safer Cars

18. Building Safer Cars

19. One subset of a modern vehicle’s network
Expanding Autopmotive Electronic Sysmtes, IEEE Computer, Jan. 2002

20. One property of electron flow is that the electrons don’t stack up anywhere. They don’t just flow
into the receiver and pile up in a bit bucket. The intense electric fields generated by each electron
prevent that from happening. Whatever current goes out must come back, and the path for
returning signal current is equally as important as the path for outbound signal current.
On the schematic, however, the paths for returning signal currents are not even shown.
Many digital engineers therefore assume that the return paths are irrelevant. After all, both
drivers and receivers are specified as voltage-mode devices, so why worry about the current?
This great misconception is reinforced by manufacturers of oscilloscopes and logic analyzers
who primarily market voltage-mode probes. If we had good current-sensing probes with a
pinpoint proximity sensor small enough to see the current flowing on an individual BGA ball, the
flow of current would suddenly become a "reality" for many engineers rather than a merely
theoretical concept.
A misunderstanding of the need for a good return-current path results in two very common
system flaws:
High-speed buses that flow across slots and gaps in digital ground planes, thereby picking up
inordinate amounts of crosstalk, and
Connectors with inadequate numbers of ground pins.

21. I attribute the lack of understanding of magnetic fields to our educational system, with
its disproportionate focus on electric field behavior.
This belief is a relic of the tube era, which was characterized by very high-impedance
circuits. For example, the plate circuit of a tube might have an impedance of 100,000
ohms, much higher than the impedance of free space (377 ohms). Such a circuit
involves HUGE voltages and tiny currents. Therefore, near-field energy surrounding a
tube exists predominantly in the electric field mode, and most crosstalk problems
involve electric-field, or capacitive, coupling.
Today's high-speed digital systems use low-impedance circuits, near fifty ohms, much
lower than the impedance of free space. These circuits use tiny voltages, but HUGE
currents. Therefore, the near-field energy surrounding a digital circuit exists mostly in
the magnetic-field mode, not electric. Most crosstalk, ground bounce, and interference
problems in high-speed digital systems involve loops of current, magnetic fields, and
inductance.
In world of EMC, it is common knowledge that the near-field energy surrounding a
digital board is mostly magnetic. Digital people don't know about that. Digital folks
waste inordinate amounts of time trying to construct electric-field shielding for their
circuits when what they need is magnetic-field shielding.

22. On a typical product datasheet the input voltage sensitivity is rated in units of absolute
volts. It is not clearly stated that the gate responds only to the difference between the
voltages on its input pin and its designated reference pin. Nor are we clear about which is
the designated reference pin. (For TTL it's usually the most negative power rail; for ECL it's
the most positive, but this rule doesn’t always work.)
This ambiguity in the designation of the signal reference leads many engineers to think that
a gate can sense "absolute zero" volts, as if it had a magic wire leading out of the chip to
the center of the earth that could pick up a "true" ground reference potential. As a
consequence, they fail to comprehend the difficulties that arise when the reference voltages
at two points in a system are unequal.
No vendor wants to admit that all their chips are susceptible to ground shifts, so we can't
expect them to talk about it on their data sheets. On the other hand, we all need to
remember that large ground shifts between chips are likely to cause malfunctions.
Most digital designers have spent little time thinking about the existence of different ground
potentials in their systems, or the mechanisms that create ground shifts.
So, if our engineers are lacking key bits of knowledge, what do we do? Nobody can change
our educational structure overnight.