1. Lesson 28 Signal Sources
Unit 10 Electronic
Instruments & Measurements
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Lesson 28 Signal Sources
• Backgrounds
• Text tour
• Language in use
– Vocabulary
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• Terminology
– Oscilloscope
– An oscilloscope, previously called an oscillograph and
informally known as a scope or o-scope, CRO (for
cathode-ray oscilloscope) or DSO (for the more modern
digital storage oscilloscope), is a type of electronic test
instrument that allows observation of varying signal
voltages, usually as a two-dimensional plot of one or
more signals as a function of time.
– Other signals (such as sound or vibration) can be
converted to voltages and displayed.
Backgrounds
4. Logic analyzer
A logic analyzer is an electronic instrument that captures
and displays multiple signals from a digital system or
digital circuit.
A logic analyzer may convert the captured data into timing
diagrams, protocol decodes, state machine traces, assembly
language or may correlate assembly with source-level
software.
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5. Troubleshooting
• Troubleshooting is a form of problem solving, often
applied to repair failed products or processes. It is a
logical, systematic search for the source of a problem in
order to solve it and make the product or process
operational again.
• Troubleshooting is needed to identify the symptoms.
Determining the most likely cause is a process of
elimination—eliminating potential causes of a problem.
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6. DMM: Digital Multimeter
• A multimeter or a multitester also known as a VOM (volt-
ohm-milliammeter), is an electronic measuring instrument
that combines several measurement functions in one unit.
A typical multimeter can measure voltage, current and
resistance.
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Text tour
• Outline
– The Complete Measurement System
– What is a Signal Source?
– Types of Digital Signal Sources
– Signal Generation Techniques
– Basic Signal Source Applications
– Signal Source Hardware Architecture: The
Arbitrary Waveform Generator
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The Complete Measurement
System
• An acquisition instrument (use to locate)
– an oscilloscope
– a logic analyser
• A stimulus instrument (use to detect the changes)
– The signal source or signal generator, is the stimulus
source that pairs with an acquisition instrument to
create the two elements of a complete measurement
solution.
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What is a Signal Source?
• A signal source is nothing less than the cornerstone of
almost any instrumentation setup used in hardware design,
debug or evaluation projects.
– It is a key engineering tool.
– It is an essential troubleshooting aid for the technician.
– It is a surrogate for an automotive ignition pulse, a heart
pacemaker or a guided missile’s gyro output.
– Second only to the global DMM, signal sources are perhaps the
most universal class of electronic test instruments.
An ignition system generates a
spark or heats an electrode to a
high temperature to ignite/combust
a fuel-air mixture in spark ignition
internal combustion engines oil-
fired and gas-fired boilers, rocket
engines etc.
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Types of Digital Signal Sources
• AWG: Arbitrary Waveform Generator can produce any
waveform you can imagine. You can use a variety of
methods - from mathematical formula to “drawing” the
waveform - to create the needed output.
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Types of Digital Signal Sources
• AFG: Typically this instrument offers fewer waveform
variations but with excellent stability and fast response to
frequency changes. If the UUT requires the classic “sine
and square” waveforms and the ability to switch almost
instantly between two frequencies, the AFG is the right
tool. An additional virtue is the AFG’s low cost, which
makes it very attractive for applications that do not require
an AWG’s versatility.
* UUT: Unit Under Test
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Types of Digital Signal Sources
• DG (Data/Pattern Generators): This third type of signal
source meets the special stimulus needs of digital devices
that require long, continuous streams of binary data, with
specific information content and timing characteristics.
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Signal Generation Techniques
• Simulation: “Building” an event or sequence of events,
based on a specific waveform definition (often from a
simulator or a library of waveforms)
• Replication: Capturing an existing signal on an
oscilloscope and sending it to the signal source for
reproduction
• Substitution: Creating and/or modifying a defined signal
to substitute for a signal from unavailable circuitry
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Signal Generation Techniques
Figure 10.1 Signal sources can use standard, user-created or captured waveforms,
adding impairments where necessary for special test applications
GPIB =
General
Purpose
Interface
Bus
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Basic Signal Source Applications
Verification
• Analyzing Digital Modulation
Wireless equipment designers developing new transmitter
and receiver hardware must simulate baseband I&Q
signals–with and without impairments/defect–to verify
conformance/standard with emerging and proprietary
wireless standards.
Some high-performance arbitrary waveform generators can
provide the needed low-distortion, high-resolution signals
at rates up to 1 gigabit per second (1 Gbps), with two
independent channels, one for the“I”phase and one for
the“Q”phase.
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Basic Signal Source Applications
characterization
• Testing D/A and A/D Converters
Newly-developed digital-to-analog converters (DAC) and
analog-to-digital converters (ADC) must be exhaustively
tested to determine their limits of linearity, monotonicity,
and distortion. A state-of-the-art AWG can generate
simultaneous, in-phase analog and digital signals to drive
such devices at speeds up to 1 Gbps.
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Basic Signal Source Applications
stress/margin test
• Stressing Communication Receivers
Engineers working with serial data stream architectures
need to stress their devices with impairments, particularly
jitter and timing violations. Advanced signal sources save
the engineer untold hours of calculation by providing
efficient built-in jitter editing and generation tools. These
instruments can shift critical signal edges as little as 0.3 ps.
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Signal Source Hardware Architecture
The Arbitrary Waveform Generator
• Fundamentally, an AWG is a sophisticated “playback”
system that delivers waveforms based on stored digital
data that describes constantly changing voltage levels of
AC signal.
• Digital sampling
• A simplified block diagram of an AWG
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Signal Source Hardware Architecture
The Arbitrary Waveform Generator
Figure 10.2: AWGs use stored digital samples to construct a waveform.
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Signal Source Hardware Architecture
The Arbitrary Waveform Generator
Figure 10.3 AWG block diagram (simplified)
21. AWG Advantages
Memory depth in AWG plays a key role in instrument
flexibility:
More cycles of the desired waveform can be stored –
minimize number of endpoints (last memory location).
More waveform details can be stored – to store edges and
transients of high frequency complex waveforms &
reproduce complex RF waveforms.
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Acquisition in dictionary
• The act of acquiring. e.g. an asset bought or obtained
• Something acquired, especially an addition to an
established category or group.
• The process of locating a satellite, guided missile or
moving target so that its track or orbit can be determined.
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Acquisition in text
• An acquisition instrument – usually an oscilloscope or
logic analyser–is probably the first thing that comes to
mind when you think about making electronic
measurements.
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Acquisition in use
• aircraft target acquisition
• high-speed data acquisition
• language acquisition
• technique acquisition
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Stimulus in dictionary
• Detectable change in the internal or external environment.
• Something causing or regarded as causing a response.
• An agent, an action, or a condition that elicits or
accelerates a physiological or psychological activity or
response.
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Stimulus in text
• The toolset for digital design characterization differs
from its counterpart in analog/mixed signal design, but
both must include stimulus instruments and acquisition
instruments. The signal source, or signal generator, is the
stimulus source that pairs with an acquisition instrument to
create the two elements of a complete measurement
solution.
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Stimulus in use
• under the stimulus of this hope
• Light is a stimulus to growth in plants.
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Ancillary in dictionary
• Subordinate:
• Auxiliary; helping:
• Something, such as a workbook, that is subordinate to
something else, such as a textbook.
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Ancillary in text
• It can be very difficult to design an instrumentation-quality
signal generator, and of course, the time spent designing
ancillary test equipment is a costly distraction from the
project itself.
