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Some Electronic Design Problems
Design To pass reliability Tests and avoid hanging
for example
-Type Test: proper function – accuracy – casing
-EMC Test ( Electromagnetic compatibility ):
Work properly in the presence at strong EM field
Reasons of hanging
1- Software Reasons
•Unequal PUSH and POP or CALL and RET
•Improper values in index registers
•Executing improper code
•Stack overflow
•Corruption in Interrupt vector
2- Hardware Reasons
•High ripples in DC supplies
•Spikes at important control signals
•Communication of enable pins to ground
•Ground loops
•Improper shielding
•Improper PCB design
Precaution in Soft ware Design
• Mirrors of key parameters
1- Write: calculating checksum and storing
it in the two mirrors
2-Read: checking checksum while reading
checksum
and overwriting the wrong mirror
checksum
Safety solution
•Hot stand by
•2 out of 2
•2 out of 3
•Voting logic Module ( VLM )
•Diagnostic Module and Fail – Safe technique
Watch dog monitor
Reset
Carry
interface
CPU
PTM
circuit
Prog
Timer
Module
Initial
count
value
Carry
output
Time
•Initializing Timer instructions must be in all
paths of all routines
•Timer may be internal
Init
Init
If your design is based on 2 processors
reset
CPU1
CPU2
Data interchanged
Between them
reset
If one CPU misses data from the 2nd CPU it sends reset to it
PRECAUTIONs IN HARDWARE
DESIGN
* Power Supply filters
1. Large value capacitors
2. Small value capacitors
3. Ferrite beads
4. Transient Voltage Suppressor “TVS”
*Grounding
analog
digital
*Shielding
*Connecting points (where spikes are expected) with
capacitors to the case ( toke care of timing )
power
case
Imperial and Metric
PCB design measurement units are: •
Imperial (inch) –
1 inch is known as 1pitch –
Thou=1/1000 of inch –
1 mil=1 thou=1 –
metric millimeter (mm) –
100 thou (0.1 inch) = 2.54mm
Types of PCBs
Single Layer •
– Lower coast, but old style
– Fits low density better
– Regarded inversely proportional to the number of
jumpers used
– Component placement is very critical, and it is
always preferred to give " minimizing the number of
jumpers” higher priority over aesthetical rule sand
neat
orientation and placement rules.
Double Layers •
– Much easier to route than single layer PCB
– Accommodate higher density design much better
than
Multi-Layer PCBs •
More Expensive and difficult to manufacture, but
essential for dense PCB.
Good practice to dedicate at least one layer for GND
and one for Vcc.
Adds a lot of routing flexibility.
It comes in even number of layers; 4, 6, 8, etc.
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PCB Elements & Layers
Track
Pads
Via
Polygons
Silkscreen
Solder Mask
Other PCB Basics
– Mechanical Layer
– Clearance
– Layer Alignment & Netlists
•
•
•
•
•
•
•
Track
Also called “traces” •
Tracks are •
transmission lines
and can be of
different types;
microstrip, stripline,
co-planar-wg,etc.
Types of Tracks
Microstrip refers to outer trace(s) on a PCB,
which are separated by a dielectric material
and then a solid plane
Advantage: Faster clock and logic signals due
to less capacitive coupling.
Disadvantage: The outer layers can radiate RF
energy
Stripline refers to placement of a circuit plane
between two solid planes either voltage or
ground.
Advantage: provides better noise immunity
for RF emissions.
Disadvantage: slower propagation speeds
Microstrip trace
Stripline trace
PCB Tracks
Track width (structure) depends, in order of importance, on electrical •
requirements, routing space and clearance available, and personal
preference.
Minimum track width/space limits are manufacturer capability •
The closer to the width/space limit, the greater the manufacturing
risks, and the higher the cost.
Tracks can change width “necking down”
may be used to go between IC/components.
Track thickness is usually specified in terms of copper layer weight (oz)
per unit area (ft2) [0.5oz, 1 oz, 2oz, etc.]
– Thickness and width must be chosen to accommodate the current
ratings as well as the thermal ratings (max allowed temp raise) .
•
•
•
•
PCB Pads
A metallic patch on the PCB surface to •
provide connectivity to pins and balls of
components.
Pad sizes, shapes and dimensions will •
depend not only upon the component (surface
mount or through hole) you are using, but
also the manufacturing process used to
assemble the board, among other things.
For components that have a pin numbering, •
pin 1 is usually of a different shape
(rectangular) to identify it.
PCB Pads
pad/hole ratio: This is the ratio of the pad •
size to the hole size.
Recommended pad shapes
resistors, capacitors and diodes
•
round pad
IC’s
•
oval pad
Most surface mount components
•
rectangular
Pin 1 of the chip should be a different pad •
shape (rectangular), and with the same
dimensions as the other pins.
Vias
A plated through hole (PTH) in (PCB) that is used to •
provide electrical connection between a trace on one
layer to a trace on another layer.
it is generally a small hole and pad diameter. •
Using a via to connect two layers is called stitching. •
there are 3 types of via •
1-throug hole (standard)
2-blind
3-buried
Types Of Vias
Polygons
Is an area that is filled with copper •
It can be solid copper (preferred) or •
crisscrossed traces (old fashion)
Frequently used in ground and power •
planes.
Usually laid out after laying out all traces. •
Silkscreen
This layer takes its name from the printing •
process it uses.
A layer at the top, and at the bottom if •
needed, of the PCB that contains
components outlines, designators, names,
..,free text.
It is preferred and more professional to •
use single font size and one text
orientation on the silkscreen.
Alignment accuracy of the silkscreen is •
Solder Mask
Is a thin polymer coating that surrounds pads
to prevent solder from bridging between pins.
Essential for surface mount and fine pitch
devices.
Typically covers everything except VIAs and
pads.
It affect the characteristic impedance of
microstrip TLs.
Can be either “silkscreen” or “photo
imageable”. The later provides better
resolution and alignment, hence is preferred.
Solder mask can be used to cover VIAs (to
•
•
•
•
•
•
Other PCB Basics
Mechanical Layer •
– The mechanical layer (which may go under other names depending on the
package) is
used to provide an outline for the PCB, and other manufacturing instructions. It is not
part of the actual PCB design, but is very useful to tell the PCB manufacturer how to
assemble the board.
– There are no hard and fast rules for this layer, use it however you like, just make
sure
you tell your PCB manufacturer.
Keepout •
– The keepout layer generally defines areas on the PCB that the designer don’t want
auto or manually routed.
– It can include clearance areas around mounting hole pads or high voltage
components
for instance.
Clearance •
– Is the copper-free distance for components, traces or pads
– Violating the electrical clearance may results in “Hairline” shorts or etching
problems
– High voltage PCB clearance may be in hundreds of mils
Other PCB Basics
Layer Alignment •
– During the PCBs manufacturing, there is alignment tolerances on the artwork film
for
each layer. This includes track, plane, solder mask, and drilling. If the design don’t
allow
for this tolerance, the design can end up in big trouble.
Netlist •
– Is a list of connections (“nets”) which correspond to schematic. It also contains the
list
of components, component designators, component footprints and other information
related to the schematic.
– The netlist file can be generated by schematic package and this process is called
“schematic capture”. •
– PCB package can import this netlist file and do many things. It can automatically
load
all the required components onto blank board. It can also assign a “net” name to
each of
component pins.
– With nets assigned to PCB components, it is now possible to Auto Route, do
Design
Making Layout
PCB Design Cycle
Before layout •
Components management. –
Schematic. –
During layout •
Placement. –
Routing. –
Checking. –
After layout •
Extract output files. –
Signal integrity for high speed. –
Fabrication/Assembly/Soldering. –
Components management
Choose Components. •
Collect it’s Datasheets. •
Some tools need to create components in •
its library
Symbol. –
Padstack. –
Package. –
Parts. –
Schematic
Accurate and complete schematic is a •
must before you start the layout
Full pin names and pin connectivity is •
absolutely useful.
May include notes on the drawing may be •
helpful.
Schematic
Forward & Back Annotation
Forward Annotation
is when you make changes to your PCB •
layout via the schematic editor. IT takes
schematic netlist and component designators,
and import them into PCB design, and make
relevant changes.
Some packages will also automatically •
remove old
PCB tracks that are no longer connected.
Back Annotation
is when changing one of the component •
designators
(eg.“C1” to “C2”) on PCB then automatically
During Layout
Placement
Routing
Component Placing
An old saying is that PCB design is 90% placement •
and 10% routing.
Placing components to a grid “snap grid” makes the •
PCB
Neat, symmetrical, aesthetic and makes future editing
and
modification easier and faster. And it helps interconnects
to
be organized.
Good practice start up with coarse grid and •
progressively
refine it as your design need. Refinement should be
made in
Component Placing
PCB Routing – General Rules
Routing is the process of laying down tracks to connect •
components on your
board. An electrical connection between two or more pads is
known as a “net”.
– Keep nets as short as possible.
– Tracks should only, unless needed, have angles of 45 degrees.
nice rounded track corners, are harder and slower to •
place and have no real advantage. •
– “Snake” your tracks around the board, don’t just go “point to
point”. [It is an ugly and not very space efficient ]
– Always take your track to the center of the pad, “not just
touch”.
Proper use of a snap grid and electrical grid will avoid problems
here.
– Use a single track, not multiple tracks tacked together end to
end
(hard to debug and edit).
– Often you’ll have to extend a track a bit. It’s best to delete the
old one and place a new one.
PCB Routing – General Rules
– One track between pads is preferred. On large and very dense
designs two tracks between pads is considered. Three tracks
between pads is possible but not a common practice and have
risks
(clearance and X-talk)
– For high currents, use multiple VIAs when going between
layers.
– “If your power and ground tracks are deemed to be critical,
then
lay them down first. Also, make your power tracks as BIG as
possible.
– Keep power and ground tracks running in close proximity to
each
other, don’t send them in opposite directions around the board.
This
lowers the loop inductance of your power system, and allows for
effective bypassing.
PCB Routing – General Rules
An electrical connection between two or more •
pads is known as a “net”.
If you are laying out a non-plated through double •
sided
board, then there are some additional things to watch
out as
you will need to solder a link through the board on
both the
top and bottom layer.
– Do not place VIAs under components. Once the
component is soldered in place you won’t be able to
access the joint to solder a feed through. The solder
joint for the feed through can also interfere with the
Auto Routing
Auto routing is the process of •
getting the PCB software to route
the tracks for you.
PCB Routing – Examples
SCADA Systems
Sub-master
Station
MODEM
ISDN or Leased Line or GSM or RF
DP
MODEM
MODEM
DP
MODEM
DRL
Distribution
Point (DP)
Fault Indicators
AMR
RTU
RTU
Urban
Distribution
Rring
Metering Systems
Zones
Meters
Transformers
Ethernet
Control Center
Ethernet
Compounds
Buildings
Business
SMS
PLC
Commercials
@
Public Lighting Intelligent
Monitoring Systems
IMPORT
EXPORT
GSM
/GPRS
NETWOR
K
RTU
Ethernet
Power Lines
Overcurrent Digital Protection Relay
• Protection and Control
–
–
–
–
Instantaneous overcurrent
Delay time overcurrent, definite type.
Inrush blocking
Breaker failure protection
• Monitoring and Metering
–
–
–
–
–
Breaker health
Metering true RMS and fundamental
Event record
Waveform recording
Self-test diagnostics
Power Quality Monitoring
Distributed Power Quality Monitors (PQi)
Centralised
information
Power
Distribution
Network
Events and
waveforms of
disturbances
PQ
history
PQ2
PQ1
PQn
Power Transmission Network
Network
topology and
parameters
communication
network
Control
center
(incidents)
...
APQ
1i
APQ
2
APQ
n
Distributed
PQM
Interface
PQi
R
Net
PQi
DB
Hist
Net.i
model
APQi
Measuring Instruments – Digital Multimeters
ELC-N100 Lecture 4
Measuring Instruments – Digital Multimeters
Digital multimeters (DMMs) are used to measure voltage, current, and
resistance and to indicate measured value on a digital display rather
than using a moving pointer as analog meters.
ELC-N100 Lecture 4
Measuring Instruments – Digital Multimeters
Digital multimeters (DMMs) are used to measure voltage, current, and
resistance and to indicate measured value on a digital display rather
than using a moving pointer as analog meters.
Compared to analog multimeters, DMMs provide higher accuracy at
lower cost. In addition, digital processing allows providing additional
functions such as automatic range selection, test of semiconductor
devices, ...etc.
ELC-N100 Lecture 4
Measuring Instruments – Digital Multimeters
Digital multimeters (DMMs) are used to measure voltage, current, and
resistance and to indicate measured value on a digital display rather
than using a moving pointer as analog meters.
Compared to analog multimeters, DMMs provide higher accuracy at
lower cost. In addition, digital processing allows providing additional
functions such as automatic range selection, test of semiconductor
devices, ...etc.
DMM basically measures DC voltage. Any other measured quantity
need to be converted first to a corresponding DC voltage.
ELC-N100 Lecture 4
Block diagram of a DMM
ELC-N100 Lecture 4
A/D converter works for a fixed range of voltages. Larger voltages
must be attenuated, and smaller voltages must be amplified.
Electronic circuits provide a very high input impedance.
ELC-N100 Lecture 4
A/D converter works for a fixed range of voltages. Larger voltages
must be attenuated, and smaller voltages must be amplified.
Electronic circuits provide a very high input impedance.
ELC-N100 Lecture 4
To measure current, it is passed in a precision resistor and the voltage
across the resistor is measured.
ELC-N100 Lecture 4
To measure current, it is passed in a precision resistor and the voltage
across the resistor is measured.
ELC-N100 Lecture 4
To measure resistance, a constant current is passed through the
unknown resistor, then the voltage across it is measured.
ELC-N100 Lecture 4
To measure resistance, a constant current is passed through the
unknown resistor, then the voltage across it is measured.
ELC-N100 Lecture 4
Analog-to-Digital Converter (ADC)
The ADC will accept an input analog voltage and produce a binary
output code that represents the magnitude of the voltage.
ELC-N100 Lecture 4
Analog-to-Digital Converter (ADC)
The ADC will accept an input analog voltage and produce a binary
output code that represents the magnitude of the voltage.
We consider first the Digital-to-Analog Converter (DAC) which
performs the inverse function, since a DAC is used inside the ADC.
ELC-N100 Lecture 4
Analog-to-Digital Converter (ADC)
The ADC will accept an input analog voltage and produce a binary
output code that represents the magnitude of the voltage.
We consider first the Digital-to-Analog Converter (DAC) which
performs the inverse function, since a DAC is used inside the ADC.
Digital-to-Analog Converter (DAC)
DAC circuits receives an n-bit binary input and produces an output
voltage whose magnitude is proportional to the input value.
ELC-N100 Lecture 4
Analog-to-Digital Converter (ADC)
The ADC will accept an input analog voltage and produce a binary
output code that represents the magnitude of the voltage.
We consider first the Digital-to-Analog Converter (DAC) which
performs the inverse function, since a DAC is used inside the ADC.
Digital-to-Analog Converter (DAC)
DAC circuits receives an n-bit binary input and produces an output
voltage whose magnitude is proportional to the input value.
Thus, it produces 0V if all bits are zero, and produces a maximum
value if all bits are 1. Any other binary input produces a fraction of
the maximum output.
ELC-N100 Lecture 4
then
,b
,b
,
,b
,b
Thus if input bits are b
n

1
n

2
n

3
1
0
ELC-N100 Lecture 4
then
,b
,b
,
,b
,b
Thus if input bits are b
n

1
n

2
n

3
1
0



1

2

3

n
V

V
b
2

b
2

b
2



b
2
oR
n

1
n

2
n

3
0
where VR is a reference voltage that determines the maximum output
voltage.
ELC-N100 Lecture 4
then
,b
,b
,
,b
,b
Thus if input bits are b
n

1
n

2
n

3
1
0



1

2

3

n
V

V
b
2

b
2

b
2



b
2
oR
n

1
n

2
n

3
0
where VR is a reference voltage that determines the maximum output
voltage.
DAC circuit produces this output using a multiple input amplifier with
different gain for each input and an addition circuit.
ELC-N100 Lecture 4
then
,b
,b
,
,b
,b
Thus if input bits are b
n

1
n

2
n

3
1
0

Vo  2VR bn 1 21  bn 2 22  bn3 23    b0 2 n

where VR is a reference voltage that determines the maximum output
voltage.
DAC circuit produces this output using a multiple input amplifier with
different gain for each input and an addition circuit.
ADC takes an input voltage Vin and produces output bits such that:

Vin  2VR bn 1 2 1  bn 2 2 2  bn3 2 3    b0 2  n
ELC-N100 Lecture 4

DAC
Vout
R
R
R
 k (V0
 V1
 V2
....)
R0
R1
R2
 B0  2 B1  B2 .2 2  B3 .23  ...  Bn 1.2 n 1
4 R 2  2 R1  R0
R
V ref
R0
B0
-
B1
R1
+
V out
R
R-2R Ladder Network
R
V ref
-
B n-1
2R
+
R
2R
B n-2
V out
R
2R
B0
R
2R
V

V
out
V
2
ref
 V
ref
n 1

ref
(B
V
.B
n 1
n 1 .2

n 1
V
ref
2
 B
.B
n  2
n  2
.n
 .....
n  2
 ....  B
0
fs
V
2 *signal,
* For bipolar
use a summer
add vfs/2fscircuit to add
For bipolar
signal, circuit
use a to
summer
2
)
Counter type ADC
ELC-N100 Lecture 4
Successive Approximation ADC
ELC-N100 Lecture 4
Vn
Sample and Hold
END
V out
R on
R of
Tc
Vin
V out
Ts
C
Start
End
4 RON c  T5  TC
-
V in
+
+
C
V out
R off
R leak
R in
OFF  C (RLeak // Rin // ROFF )
 CR / 3
Vf
Vs
R /2
 Vs

R /2  R
3
Vs
0.98 Vs
Vf
tc
0.98Vs  V f  (Vs  V f )e
 t c / o ff
 c  ........
Other Digital Instruments: Frequency Meters
ELC-N100 Lecture 7
Other Digital Instruments: Frequency Meters
Digital instruments can be used to measure signal frequency
and period, as well as other parameters such as pulse
widths, rise times, …etc
ELC-N100 Lecture 7
Other Digital Instruments: Frequency Meters
Digital instruments can be used to measure signal frequency
and period, as well as other parameters such as pulse
widths, rise times, …etc
If a pulse waveform is applied to a digital counter for exactly
one second, the counter output indicates the frequency of the
waveform.
ELC-N100 Lecture 7
Other Digital Instruments: Frequency Meters
Digital instruments can be used to measure signal frequency
and period, as well as other parameters such as pulse
widths, rise times, …etc
If a pulse waveform is applied to a digital counter for exactly
one second, the counter output indicates the frequency of the
waveform.
Frequency meter uses an accurate crystal controlled clock
source (time base) to generate counting time period
accurately.
ELC-N100 Lecture 7
ELC-N100 Lecture 7
The counter reading is latched to the display at the end of the
counting period. The counting may be repeated periodically.
ELC-N100 Lecture 7
The counter reading is latched to the display at the end of the
counting period. The counting may be repeated periodically.
A triggering circuit is used to convert sinusoidal or other
waveforms to pulse waveforms of the same frequency before
counting.
ELC-N100 Lecture 7
The counter reading is latched to the display at the end of the
counting period. The counting may be repeated periodically.
A triggering circuit is used to convert sinusoidal or other
waveforms to pulse waveforms of the same frequency before
counting.
To measure frequency with good accuracy, other time periods
may need to be used. For example, for high frequency, the 1
sec period may cause the counter to overflow, while for very
low frequencies no count may be obtained.
ELC-N100 Lecture 7
The counter reading is latched to the display at the end of the
counting period. The counting may be repeated periodically.
A triggering circuit is used to convert sinusoidal or other
waveforms to pulse waveforms of the same frequency before
counting.
To measure frequency with good accuracy, other time periods
may need to be used. For example, for high frequency, the 1
sec period may cause the counter to overflow, while for very
low frequencies no count may be obtained.
Typically a number of frequency divider circuits are provided
so that the user can conveniently select a measurement
range.
ELC-N100 Lecture 7
ELC-N100 Lecture 7
If input and time-base connections are interchanged, we can
measure the period of a signal. This may be preferred for
frequencies less than the time-base frequency.
ELC-N100 Lecture 7
If input and time-base connections are interchanged, we can
measure the period of a signal. This may be preferred for
frequencies less than the time-base frequency.
ELC-N100 Lecture 7
Example: A square wave is applied to a digital frequency
meter that uses a 1 MHz clock generator which has its output
divided by decade counters.
Determine the counter
indication when:
a) the input frequency is 5 KHz and six decade counters are
used to generate the measuring period.
b) the input frequency is 2.9 KHz and five decade counters
are used to generate the measuring period.
ELC-N100 Lecture 7