Oscilloscope In General

1
Agenda
Digitizing Oscilloscope Topics

• Oscilloscope In General
• Analog Bandwidth
• Sampling
• Memory Depth
• Display Quality
• Number of Channels
• Triggering Modes
• Ease of Use

2
Analog Scopes

• How do they work?

VERTICAL OUTPUT AMP
3
Analog Scopes

• What are their benefits?
• Easy to use
• Very fast display update of tens of
  thousands/sec
• Display intensity shows signal anomalies
• Inexpensive
• What are their disadvantages?
• Bandwidth limited by display tube.
• No single shot storage of waveform.
• Difficult to obtain a hard copy of the signal,
  needs a camera
• Trigger capabilities very restricted
• On screen measurements and Maths functions are
  very basic
• Cannot get data offline for Analysis ie to a
  personal computer

4
Analog Bandwidth
What does bandwidth mean and why is it
important? All oscilloscopes have a bandwidth
specification and this is specified as the
frequency at which a sinusoidal input signal is
displayed 3dB lower than the peak signal
amplitude. For example in the displayed
oscilloscope above a sine wave of freq X is input
into an oscilloscope of bandwidth X. The blue
trace represents the actual signal amplitude and
the yellow trace the displayed signal amplitude
which is 30 lower
5
Analog Bandwidth
What does a 50MHz signal really look like?
60MHz
Scope
100MHz
Scope
350MHz
Scope
500MHz Scope
6
Overview Frequency versus Time Domain
Amplitude (power)
frequency
time
Time domain Measurements
Frequency Domain Measurements
7
FFT Function
8
Analog Bandwidth
Scope BW Can Affect Your Digitized Signal

• Affects Signal by
• Slowing Rise Time
• Attenuating Amplitude

tr
tr

• Caused by
• Attenuator/Amplifier
• Also Account For Probing Accessories

9
Analog Bandwidth
Active versus Passive Measuring 1ns Signal
Signal Before Probed Signal After Probed Output
of Probe
1165A 600MHz Passive Probe with Alligator Ground
Lead
1156A 1.5GHz Active Probe with 5cm Signal Lead

• Signal Loaded, Now Has 1.9ns Edge
• Probe Output Contains Resonance and Measures
  1.85ns Edge

• Signal Unaffected by Probe, Still has 1ns Edge
• Probe Output Matches Signal and Measures 1ns

10
Probe Compensation

• Equivalent circuit for probe

Oscilloscope
Probe
11
Revue

• Purpose of probe
• Improving loading effect
• Improving low frequency characteristic at AC
  coupling
• Expand maximum input voltage
• Expand measuring voltage range

12
Analog Bandwidth
How Much Bandwidth is Enough?

• Know Your Signals Fastest Rise Time, tr
• Calculate Your Signals Bandwidth, BWsignal
• BWsignal 0.35 / tr
• Use 0.4 as factor in applications gt1.5GHz BW
• Calculate Needed Scope Bandwidth, BWscope
• BWscope 3 BWsignal (for 5.4 error)
• Use different factors for different errors
• Multiplier Error
• 1 41.4
• 3 5.4
• 5 2.0
• 10 0.5

13
Digital Scopes

• How do they work?

bandwidth
Sample rate
Memory depth
14
Sampling
Three Sampling Techniques

• Equivalent Time (Repetitive)
• Real Time (Single-Shot)
• Sequential Sampling (Repetitive)

15
Sampling
Equivalent Time (Repetitive) Technique

• Used ONLY with Repetitive Signals
• Samples From Previous Triggers Maintained
• Multiple Trigger Events Build Up Waveform
• Sample Rate is Not a Major Factor
• Best Resolution Determined by Trigger Hardware

1st Trigger
2nd Trigger
3rd Trigger
16
Sampling
Equivalent Time Build Up of Waveform
Acq 1
Acq 2
Acq 3
Acq 200
17
Sampling
Equivalent Time (Repetitive) Example

• Fastest Rise Time, tr 3ns
• BWsignal 0.35 / tr 0.35 / 3ns 117MHz
• BWscope 3 BWsignal 3 117MHz 350MHz
• For a 5.4 error
• Sample Rate Not a Factor in Equivalent Time

18
Sampling
Real Time (Single Shot) Technique

• Used with either Repetitive or Single-Shot
  Signals
• All Samples Are Taken From a Single Trigger
• Samples from Previous Triggers are Erased
• Sample Rate May Limit Scopes Overall Bandwidth
• Best Resolution Depends Directly on Sample Rate

Each
Trigger
Identical
19
Sampling
Real Time (Single Shot) Example

• Fastest Rise Time, tr 3ns
• BWsignal 0.35 / tr 0.35 / 3ns 117MHz
• BWscope 3 BWsignal 3 117MHz 350MHz
• For a 5.4 error
• SRscope 4 BWscope 1.4GSa/s
• With sin(x)/x Interpolation, Use a Factor of 4
• Without sin(x)/x Interpolation, Use a Factor of 10

20
Sampling
No Major Benefit of SR gt 4 BW
21
Sampling
Example No Major Benefit of SR gt 4 BW
Input Signal 1ns Pulse With 200ps Rise Time
BW500MHz, SR2GSa/s
BW2.25GHz, ET Sampling
BW500MHz, SR5GSa/s
22
Sampling
Sequential Sampling Technique

• Used ONLY with Repetitive Signals
• One Sample is taken for each Trigger
• Multiple Trigger Events Build Up Waveform
• Used in High Speed Applications with BW gt10GHz
• No Pre-Trigger Information

23
Memory
Purpose of Memory In Digitizing Scopes

• Every Sample Must be Stored in Memory
• Deeper Memory Stores More Samples
• Longer Periods of Time Captured Also Means More
  Samples to Store if Sample Rate is to be
  Maintained

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16
43
122
176
232
231
229
228
Scope Memory
24
Memory
Purpose of Deep Memory

• Maintain High Sample Rate When Capturing Longer
  Periods of Time
• Higher Sample Rate
• More Accurate Reproduction of Signal
• Better Resolution Between Points
• Better Chance of Catching Glitches or Anomalies

25
Memory
Purpose of Deep Memory (cont.)

• Capturing Longer Periods of Time
• Still be Able to Zoom In and See All the Details
• Deep Memory Especially Important In
• Mixed Analog and Digital Applications
• Serial Communication Applications

26
Memory
Sample Rate versus Time/Division Setting
2G
1G
100M
10kpts
8Mpts
100kpts
Sample Rate (Sa/s)
10M
PCI Packet
10BaseT
CDMA
Video
PID Ctrl
1M
100K
1s/div
1us/div
10us/div
1ms/div
100ns/div
10ms/div
100us/div
100ms/div
27
Memory
Bluetooth Example Time Period 100ms
Scope at 50MSa/s and 5Mpts

• 80 Repeating Bluetooth Transmit Packet Captured
  Over 0.1 Second
• Zoom-in on Incorrectly Truncated Packet at 400us
  to View Complete Signal Details

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28
Memory
Bluetooth Example Time Period 100ms
Scope at 100kSa/s and 10kpts

• Same Repeating Bluetooth Transmit Packet Captured
  Over 0.1 Second
• Zoom-in on Same Incorrectly Truncated Packet at
  400us to See That The Signal Was Under-Sampled

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29
TV Signal Agilent 6000 series memory 1Mb
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TV Signal Digital Scope memory 10Kb
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Memory
How Much Memory is Enough?

• Determine Required Resolution Between Samples, Tr
• 1 / Tr lt Scope Sample Rate (Real Time Mode)
• Determine Required Period of Time to Capture, Tp
• Calculate Required Memory Depth
• Memory Depth Tp / Tr

32
Memory
Memory Depth Example

• Required Resolution Between Samples, Tr 500ps
• Required Period of Time to Capture, Tp 2ms
• Memory Depth Tp / Tr 2ms / 500ps 4Mpts

33
Memory
Example Tp 2ms with scope at
2GSa/s and 4Mpts
34
Memory
Example Tp 2ms with scope at
4MSa/s and 8kpts
35
Memory
Possible Negative Implications of
Deep Memory

• Slower Display Update Rate
• Slower User-Input Response Time
• Increased Dead-Time Between Acquisitions
• Missed Glitches and Anomalies during Dead-Time

36
Memory
Solving the Dead-Time Problem in
Deep Memory Oscilloscopes

• Custom ASIC Hardware Built Into Acquisition
  System
• Agilents MegaZoom Technology
• MegaZoom is a Memory Management Tool
• Ping-Pong Acquisition Memory
• Intelligent Selection of Display Points
• No Special ModesAlways On and Always Fast

Result is a fast display update rate with minimal
dead-time between acquisitions and no processing
bottlenecks.
37
Display Quality
What is the Importance of the Display?
The display is the window between the human eye
and the sampled waveform.

• Analog Scope Displays
• Represent Waveforms That Can Be Trusted
• Show Bright Spots Where Anomalies Exist
• Yield Infinite Levels of Intensity Grading
• Traditional Digitizing Scope Displays
• Appeared Grainy
• Offered Very Little or No Intensity Grading

38
Display Quality
Agilents High-Definition Display

• 256-Levels of Intensity Grading
• Pixels Hit More Often Appear Brighter Than Others
• Allows 3rd Dimensional View Into Signal
• Fast Display Update
• Utilizes the MegaZoom Custom ASIC
• Minimal Dead-Time Between Acquisitions
• Twice the Horizontal Resolution

Results in a display system that you can trust,
just like an analog scope display.
39
Display Quality
Agilents High-Definition Display
40
Number of Channels
How Many Channels Are Enough?

• Simple Debug May Require Only 2 Channels
• More Complex Debug Requires 4 or More Channels
• Many Designs Have Both Analog and Digital Content
• Real-World Analog Input and Output Signals
• Complex Digital Signals for Processing
• Interfacing Done With
• ADCs, DACs, MCUs, DSPs, etc.

41
Number of Channels
Mixed Analog/Digital Design Example
Parallel Comm.
I2C Comm.
Microcontroller
Serial I/O
PWM Output
Analog Inputs
42
Number of Channels
Viewing and Triggering on gt4 Channels

• Agilent Mixed-Signal Oscilloscopes (MSO)
• 2 Analog Channels
• 16 Digital Channels
• All Timed Aligned
• Up to 500MHz 2GSa/s for High-Speed Apps.
• Correlates Fast Digital and Slow Analog Using
  MegaZoom Deep Memory

43
Number of Channels
Viewing and Triggering on gt4 Channels

• Agilent Mixed-Signal Oscilloscopes (MSO)
• 2 or 4 Analog Channels
• Plus 16 Digital Channels
• All Channels On Same Timebase for Cross
  Triggering and Viewing
• Various Models Fit Low to High-Speed Applications
• Correlates Fast Digital and Slow Analog Using
  MegaZoom Deep Memory

• May be the Only Logic Analyzer Youll Ever Need
• Bridges the Gap Between a Traditional Scope and a
  Logic Analyzer

44
Triggering Modes
What Triggering Capabilities Are Needed?

• Edge Triggering
• Signal Integrity Triggering
• Pulse Width
• Setup and Hold
• Transition
• Parallel Logic Triggering
• Pattern/State
• Sequence

• Serial Triggering
• SPI
• I2C
• CAN
• USB

45
Triggering Modes
Signal Integrity Triggering

• Pulse Width
• Find a Pulse Too Narrow, Too Wide, or Within a
  Range
• Setup and Hold
• Find a Pulse Without Proper Setup and/or Hold
  Times
• Transition
• Find Edge Too Fast or Too Slow

46
Triggering Modes
Parallel TriggeringPowerful in MSO Models

• Pattern/State
• Find a Specific Parallel Logic Pattern
• Sequence
• Find Consecutive Parallel Logic Patterns

47
Triggering Modes
Serial TriggeringPowerful in MSO Models

• SPI
• Serial Peripheral Interface
• MCU/DSP Comm.

• I2C
• Inter-Integrated Circuit
• MCU/DSP Comm.

48
Triggering Modes
Serial TriggeringPowerful in MSO Models

• CAN
• Controller Area Network
• High Reliability Automotive Systems Industrial
  Systems
• LIN
• Local Interconnect Network
• General Purpose Automotive Systems
• USB
• Universal Serial Bus
• PC Peripheral Connectivity

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Inter-Integrated Circuit (I2C)
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Inter-Integrated Circuit (I2C)
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Inter-Integrated Circuit (I2C)
52
Serial Peripheral Interface(SPI)
53
Serial Peripheral Interface(SPI)
54
Controller Area Network (CAN)
55
Controller Area Network (CAN)
56
Universal Serial Bus (USB)
57
Universal Serial Bus (USB)