Unit V - Product Debugging and Testing

Dr. Anagha Parag Khedkar
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Contents
 Steps of Debugging, Techniques for troubleshooting,
characterization
 Electromechanical components, passive components,
active components
 active devices, operational amplifier, Analog-Digital
Conversion
 Digital Components, Inspection and test of
components
 Simulation, Prototyping and testing.
 Integration, validation and verification. EMI & EMC
issues.
Electronic Product Design Unit V as per BE E & TC
SPPU syllabus by Dr. Anagha P. Khedkar 2

Debugging, Testing, Troubleshooting
 These tasks are performed at different times during
product's lifetime.
 debugging-done during early phases, testing-done
before delivery of product, troubleshooting-done
afterwards
 debugging- used to identify the cause of problems
occured in design & implementation.
 testing- it assumes that design is correct, identifies
problems occured during manufacturing.
 troubleshooting- design is correct & product worked at
one time. It identifies which hardware components have
failed.

Introduction to Debugging &
Testing
 Debugging: tracking & finding faults & correcting
undesirable system behavior
 Debugging is used to focus search for solution
 Testing: It involves variety of operations that verify
operation within specified environment.
 Hardware Testing: involves inspection, analysis of
destructive & nondestructive parts, static & dynamic
evaluation
 For reliability, planning for testing early is imp.

5 Steps to debugging
 Observe & characterize
 Brainstorm
 Hypothesize
 Test
 Repeat steps 1 thr 4 until problem is solved.

5 Steps to debugging
 Start by collecting observations & characterizing the
problem.
 Brainstorm all possible causes for problems & list them
 Build hypothesis (A hypothesis is a testable statement
about the relationship between two or more variables or a
proposed explanation for some observed phenomenon. )
 Design experiments that test hypothesis
 Repeat steps till working hypothesis is found.

Checklist for debugging
1. Visually inspect ckt.for
missing components, broken wires, traces, bent pins,
leads, damage etc.
2. Check continuity
3. Check power connections
4. Check equipment status
5. Verify schematic
6. Verify software
7. Take a break
8. Get another perspective

Troubleshooting
 Troubleshooting is the process of identifying and
fixing problems.
 Computer troubleshooting may
involve hardware or software and can sometimes
involve both at the same time.
 The basic process of troubleshooting is to check the
most general possible problems first, and then
gradually check for more specific problems.
 This provides a logical approach to problem solving
and can apply to multiple types of products.

Techniques for troubleshooting
 To collect necessary observations, we need proper
diagnostic equipments like power supply, DMM, function
generator, logic analyzer, ICE, CRO, supply of components,
soldering iron.
 CRO-High bandwidth, DMM- high accuracy, CRO probe
i/p capacitance – loading, soldering iron heating aspects,
good stock of precision components
 CRO probes can introduce disturbances in CUT thr load
capacitances, ground lead problems, cables
 CRO probe is an integral part of ckt under test. Its i/p
resistance & capacitance load a ckt & can affect operation
of CUT

ICE: In Circuit Emulator
 A circuit for emulating target system remains
independent of a particular targeted system and
processor
 Emulator or ICE provides great flexibility
and ease for developing various
 applications on a single system in place of
testing that multiple targeted systems.

ICE
 Interface COM port of a computer
 Emulates target MCU IOs
 ICE socket connects MCU externally Interface COM
port of a computer
 Uses computer developed object files and hex files for
the MCU
 Uses debugger at the computer developed files for the
MCU application

 Adjust the probe compensation
 This is done by turning screw that adjusts variable
capacitor.
 Build FET buffer into probe to provide very high input
impedance.
 Ground lead on probe (becomes inductive)can cause
problems of signal ringing at high frequencies. To avoid
this, keep ground leads as short as possible.
 Cabling can significantly alter signals in probed ckts.
Capacitance loading, inductive loops & improper
termination will degrade rise time of signal pulses.

Probe compensation

FET buffer into probe

1. General tips for power
2. Tips for analog ckts
3. Tips for digital ckts
4. Tips for S/w

General tips for power

Tips for analog ckts
 Keep leads short
 Use right oscilloscope
 Layout ckt & grounds properly
 Choose proper location of resistors to reduce noise
from stray capacitances
 Compensate the oscilloscope probe
 Use FET i/p probe for high impedance ckts
 Avoid long settling times

Tips for digital ckts
 Use proper triggers to catch glitches on CRO & logic
analyzer
 s/w in target system can aid debugging h/w
 Use built in tests to test h/w. Built in tests to check
memory chips.
 Use simple looping routines to check I/O ports.
 Partition ckts – s/w & h/w modules. It isolates
problems & makes debugging easy.

Tips for S/w
 Use modular designs
 Do good documentation
 Use proper tools
 Some h/w tools also can help like LED, ICE, CRO
 LED can glow to indicate whether program is toggling
a signal or not. E.g Serial communication programs
send data on TxD & receive on RxD. LEDs on TxD &
RxD to check data/pulses

Characterization
 First step in debugging is to characterize components
 Test components and ckts in a variety of environments to
evaluate their performance & their margins
 Do simulation of components to understand
characteristics of components. But testing of components
is necessary
 Tests of components characterize parameter tolerances &
variations & provide for calibration of their functions. Tests
in different thermal environment.
 E.g. power consumption of Ics, conversion accuracy of ADC
vary with temp., also other parameters.

Electromechanical components
 These include connectors, Fuses, switches, keyboards.
 Connectors- metal contacts- consider its electrical,
mechanical, chemical properties
 Resistance of contacts & current carrying capacity
change with wear, dust & force
 Rate of corrosion in contacts
 Specify this in the design & perform environmental
testing to verify reliability

 Fuse- metallic conductor with specifies cross section &
resistance that melts when current density exceeds limit
 Types of fuses- for various situations-normal blow/class F,
slow blow/type T
 Consider fuse opening time duration, rated current
capacity
 For use in international products, understand differences
in fuse, protection methods, current capacity & size
 Fuse standards specify length & diameter in mm
 Tests for fuses: measure statistical variation in time to open
ckt for high currents of 10 times rating, next 2 times rating,
test that terminals of blown fuse sustain high voltage
without arcing.

 Switches: ergonomics, basics, parameters.
 Switch properties- low contact resistance, low force to
maintain contact, no corrosion, durability, low cost,
durability.
 Contacts-NO/NC
 Current capacity rating-AC/DC application
 Arcing across contacts
 Contact bouncing
 Precious metal contacts-cost

Passive components
 R,L, C- each has its characteristic properties, based on
manufacturing processes & materials used for each type of
component.
 Use of resistors in ckt-current limiting, pull up, pull down,
impedance matching, voltage division, bias set, gain
control etc.
 Resistance varies- manufacturing tolerances, temp.,
humidity, voltage stresses.
 Tolerances:20%, 10%, 5%, 1%
 At high frequencies, lead inductance & internal
capacitance –significant- changing impedance
 Resistance contribute thermal noise
 If resistors to be used at high temp., you will have to derate
amount of power that they dissipate.

Passive components- resistors
 Types-carbon composition, carbon film, metal film,
thick film, thin film, wire wound, thin film
 Characteristics: max. resistance, max. voltage, temp.
coefficient of resistance, accuracy, shelf life, stability
 Wire wound- high precision, high power ratings(upto
2KW), excellent TCR(as low as 1 ppm/degree c)
 Thin film-best TCR <1

Passive components-capacitors
 Capacitor- function-to store charge
 Types:block dc, pass ac, filter, couple, tune,
decouple/bypass, compensate, isolate, suppress noise
 Capacitor’s impedance varies with frequency.
 Capacitor- leakage resistance, lead inductance, lead
resistance
 Use high Q capacitor with low ESR, ESL
 Capacitor: breakdown voltage, memory effect-dielectric
absorption(reduce discharge capabilities)
 Capacitor-failures: open ckt, short ckt, leakage failure,
arcing between plates may occur
 Causes: excessive voltage, current, temp. , sudden charging
& dischargingElectronic Product Design Unit V as per BE E & TC

Passive components: inductor
 Role of inductor- significant in power supplies & high
voltage generators
 Inductance – depends on no. of turns, current,
permeability
 Nonlinear devices with hysteresis, saturation, eddy
current.
 Most of time-inductors- custom produced for
application.

Active Devices
 These either amplify or control greater power with lesser
power.
 Mechanical relay, solid state relay, semiconductors- diode,
transistors, optoisolators
 Relay: nonlinear switched device
 Power required to pull in armature is greater than power
required to hold armature closed.
 So switching relay with larger current & holding it with
lower current, power dissipation in relay can be reduced.
 Max power dissipation is limited by overheating within coil.

Active devices: mechanical relay
 Characterize relay coils by their resistance &
inductance.
 Resistance sets I2R dissipation, inductance determines
spike suppression
 Operational life of relay can be specified by no. of
open/closed cycles of armature & contacts can
complete without failure.
 Test & specify relay for shock & vibration.
 High voltage test for relay
 Wear & tear of relay contacts

Active devices: semiconductors
 Test & qualify each component
 Maintain alternative source for each component
 Common problems with devices- leakage current,
reverse current, safe operating areas, thermal effects,
ESD & parameter variations.
 Do not exceed voltage, temp. & current ratings
 Curve tracer helps to identify good or bad
components.
 Transistors-gain vary, switching speed , current gain &
frequency response

Active devices:MOSFET
 MOSFET: high impedance, low noise, no thermal
runaway
 Consider parameters: Id Vs Vds, noise, gate
capacitance
 Allow margins of tolerance on parameters while
designing in ckt
 Failures: defects in silicon die, thermal & current stress
betn wire bond & die
 Electrical & temp. testing – reveals defects in die

Op-amps
 Op-amps-amplifiers, filters, oscillators, control
systems
 Passive components around opamp cause most
problems
 Don’t rely on characteristics not guaranteed by
manufacturer.
 Virtual ground at i/p - at high frequencies, these
inputs have significant error voltage to drive output

Op-amp characteristics
 Test ckts for imp. Parameters of opamp
 Offset voltage
 Loop gain
 CMRR
 Slew rate
 o/p noise
 PSRR

Test ckts for imp. Parameters of
opamp

Test ckts for imp. Parameters of op-
amp

amp

ADC
 No single test can completely characterize ADC/DAC
 Tests are specific as per application
 Some apps need ADC’s good transient response, some
need linearity, high resolution
 Verify performance & accuracy of converters at desired
conversion speed.
 Converters are subjected to errors from sources viz.
architecture, quantization, fabrication & ckt layout

ADC: equipment to evaluate
converters

ADC: equipment to evaluate
converters
 It should have proper amplifier bandwidth, settling
time, filtering to remove harmonics & broadband
noise, low jitter clock, clean power supply with
decoupling & controlled temp.

ADC: Basic definitions
 Ideal transfer function for ADC: graph of binary code
Vs Analog input
 In transfer function, single binary value represents a
range of analog values in quantization band around its
code center point.
 Analog values not exactly at the center have associated
amount of quantization error
 Resolution of ADC defines its capability to represent
analog values. The no. of bits in o/p sets resolution

ADC: Errors
 Quantization error: range of analog values around the code
center point.
 Differential nonlinearity: Differences in quantization band
between each digital code. It can vary between -1 LSB & >
+1LSB .
 Integral nonlinearity: deviation from linear transfer
function
 Missing codes
 Aperture jitter
 I/p noise
 Settling error(DAC): time for o/p to reach final analog
output value

ADC 0808 specifications
 Easy interface to all microprocessors
 Operates ratiometrically or with 5 V DC or analog span
 adjusted voltage reference
 No zero or full-scale adjust required
 8-channel multiplexer with address logic
 0V to 5V input range with single 5V power supply
 Outputs meet TTL voltage level specifications
 Resolution 8 Bits
 Non-linearity +/-1/2LSB
 Single Supply 5 V DC
 Low Power 15 mW
 Conversion Time 100 µs

DAC
 Resolution in no. of bits
 Settling time: It is one of the important dynamic parameter. It
represents the time it takes for the output to settle within a specified
band ± (1/2) LSB of its final value
 Accuracy
 Quantization error
 Linearity
 Monotonicity: A Digital to Analog converter is said to be monotonic if
the analog output increases for an increase in the digital input.
 Conversion Time:
 It is the time taken for the D/A converter to produce the analog output
for the given binary input signal. It depends on the response time of
switches and the output of the Amplifier.
 Stability:
The ability of a DAC to produce a stable output all the time is called as
Stability.

DAC
 DAC availability: current o/p or voltage o/p
 Test for linearity: Compare o/ps from production DAC
with o/p of a precise converter as a reference(higher
resolution).
 While testing for settling time, avoid overdriving the
differencing ckt.
 Glitches occur during transitions of the digital input
signals
 So choose either low-glitch DAC or deglitched DAC

Digital Components
 These deal with more than high & low logic levels.
 Digital components face 4 problems particularly at high
frequencies- ground bounce, phase jitter, metastability,
transmission line concerns
 Ground bounce: also called simulteneous switching noise
can cause unswitched o/ps to exceed threshold of driven
gate forcing unwanted logic transition.
 Factors contributing to ground bounce are signal rise time,
load capacitance, no. of simultaneous switched o/ps.
 Avoid ground bounce by using good layout that reduces
inductive loop

Important Questions
 Explain tecniques for Troubleshooting.
 Define Debugging process and explain steps of
debugging.
 Differentiate between active and passive components.
 Explain Analog-Digital in detail.
 What are the different steps in debugging? Differentiate
troubleshooting from debugging.
 Compare different types of ADCs with respect to
resolution, power consumption, multiple inputs and
nonlinearity.

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Text Book Reference
 Kim Fowler, Electronic Instrument Design Oxford
university press.

Unit V - Product Debugging and Testing

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