Oscilloscope Fundamentals - Oct 2013

06/2009 | Fundamentals of DSOs | 1

Modern Digital Oscilloscopes – Understanding the Fundamentals

James Allman

Oscilloscope BDM

October 2013 UBC


Agenda – Modern Digital Oscilloscopes

l Introduction l Motivation to measure in the time domain

l From analog to digital – the evolution of the scope

l Different scopes for different applications

l The Function Blocks of a Digital Oscilloscope l Vertical System

l Sampling & Acquisition

l Horizontal System

l Trigger System

l Waveform Analysis l Statistics and math functions

l Probes l The different probe types

l Principal of passive, active, current probes

l Probe calibration

l Summary


Time Domain and Its Relation to Frequency Domain

Two sine signals

overlay Time

Domain

Frequency

Domain

Discrete components

of the combined signal


Modern Digital Oscilloscopes






l Horizontal System

l Trigger System




l Probe calibration

l Summary


R&S Measurement Equipment that already Measures Time Domain Signals

Power Meter NRP Audio Analyzer UPV

Pulse profile analysis Up to 250 kHz an audio analyser

can be used for waveform analysis

Signal Analyzer FSx

Time domain power measurement

on a radar signal – baseband analysis


All of the presented measurement equipment is capable of

doing some measurements in the time domain…

but…

this is not their main purpose!!!

R&S Measurement Equipment that already Measures Time Domain Signals


Motivation to Measure in the Time Domain

An oscilloscope is a window…

…into the electronic world

Power signals Baseband TV signals Digital signals


Measurement Equipment that can Measure Time Domain Signals For this we need an…








l Horizontal System

l Trigger System




l Probe calibration

l Summary


1899: Jonathan Zenneck – adds a second

deflection structure, allowing two-

dimensional viewing

1931: Vladimir K. Zworykin – reliable

production, high-vacuum CRT with a

thermionic emitter allows the General Radio

Oscilloscope to be built.

From Analog to Digital – The Evolution of the Scope

The General Radio Oscilloscope (1931), with sweep circuit (right).

1897: Karl Ferdinand Braun, a

German inventor & physicist builds

the first cathode ray tube

oscilloscope


1985: Walter Lecroy – introduces the

first Digital Storage Oscilloscope

1997: Hewlett-Packard – introduces

the first Mixed Signal Oscilloscope


The General Radio Oscilloscope (1931), with sweep circuit (right).

1946: Howard Vollum sees scopes

in Germany. With Jack Murdock

they invent the triggered-sweep

oscilloscope, the Tektronix 511.


From Analog to Digital – The Analog Scope

Principal Block Diagram of an Analog Real Time Oscilloscope (ART)


From Analog to Digital – The Analog Scope

l Real time signal display -> tube technology

l Consist of vertical and horizontal deflection system with deflection plates

l Voltage applied to these deflection plates causes a glowing dot to move

l An electronic beam hitting phosphor inside the cathode ray tube (CRT) creates a glowing trace

Short comings of analog oscilloscopes

l Requires a CRT display, no color graded display

l Measurement bandwidth is limited to several hundred MHz

l No advanced trigger functionality available, no pre-trigger capability

l Limited storage capabilities and limited data processing



1980

Computers

LSI (Large Scale Integration)

Digital data

Mixed signal environments

Faster microprocessor clock rates

System integration

Quality assurance

Signal data

High-frequency effects

Documentation

Market Drivers

Customer Challenges

1950

Military

Vacuum tube technology

Emerging solid state technology

Broadcast video

Device characterization

Signal edges and waveshapes

Digital Analog Scope Technology



l The Vertical System allows adjustment of the analog voltage, and conditions

the signal for the analog-to-digital converter (ADC)

l The probe interface allows selectable impedances, powers and reads active

probes



l The ADC in the acquisition system samples the signal at discrete points in

time converts the signal's voltage at these points to digital values called

sample points

l The sample points from the ADC are stored in memory as waveform points;

these waveform points make up one waveform record



l The trigger system monitors the analog conditioned input to the ADC and evaluates it

to determine when to trigger the Horizontal System, or when to trigger the Acquistion

System‘s storage of acquired data for the Display System (depending on the design)

l The Horizontal System's sample clock determines how often the ADC takes a sample;

the rate at which the clock "ticks" is called the sample rate and is measured in

samples per second


Different Scopes for Different Applications

Handheld (Basic capability, field portable)

General Purpose Scopes (Device power up, Debugging, Embedded design, Research)

High Performance Scopes (Fast Serial busses, data interfaces, compliance testing)

Extreme Performance

(Optical, Very High Speed Digital)








l Horizontal System

l Trigger System




l Probe calibration

l Summary


The Function Blocks of a Digital Oscilloscope The Vertical System

Acquisition

Processing

Memory

Post-

Processing

Display

Trigger

System Horizontal

System

Att. Amp

Amp

Vertical System

ADC


Vertical System Overview

l The controls of the Vertical System are used to scale and position the

input waveform vertically.

l The Vertical System controls Bandwidth to the Acquisition System of

the scope.

Scale Position

DC Offset Bandwidth

Input Coupling


Bandwidth Definition

l Bandwidth is THE single-most

crucial parameter used for the

oscilloscope selection:

Ensure the scope has enough

bandwidth (& risetime) for the

application!

l Oscilloscope bandwidth is

specified at -3dB (-29.3%)

Frequency

Att

en

uati

on

0dB

-3dB

fBW

Bandwidth x Risetime = 0.35 (for analog response)

e.g. 100 MHz Bandwidth = 3.5 nsec Risetime

0 dB 6 div at 50 kHz

- 3 dB 4.2 div at bandwidth


Harmonic Sine Waves in Rectangular Signals

Animation


Bandwidth – Requirements of the Test Signal

l Required scope bandwidth depends

on test signals frequency components

l e.g. digital “square” waveform is composed

of odd sine wave harmonics

Frequency

Am

plitu

de

fFundamental f3rd harm. f5th harm.

Rule of thumb:

BWScope = 3 … 5x fmax of Test Signal


Bandwidth – Amplitude Measurement Accuracy

Frequency / Scope BW

Am

pli

tud

e M

ea

su

rem

en

t A

cc

ura

cy

100%

70%

75%

80%

85%

90%

95%

-3 dB

0.1 0.2 0.3 0.4 0.5 0.6 0.8 1.0

3.0% 1.0% ~30.0%

Measurement Error

dB3707.0log20

DUT

measure

U

Ulog20

Amplitude

Error

Amplitude

Accuracy

Attenuation

dB

1 % 99 % -0.09 dB

3 % 97 % -0.26dB

5% 95% -0.45dB

10% 90 % -0.9 dB

Attenuation [dB]:


Bandwidth – Application Mapping

l Data rates of typical I/O interfaces

Interface Data Rate Clock

Frequency

Oscilloscope Bandwidth

Requirement Oscilloscope

Classes 3rd harmonic 5th harmonic

I2C 3.4 Mbps 1.7 MHz 5.1 MHz 8.5 MHz Value

LAN 1G 125 Mbps 62.5 MHz 187.5 MHz 312.5 MHz Lower mid-range

USB 2.0 480 Mbps 240 MHz 720 MHz 1200 MHz Mid-range

DDR II 800 Mbps 400 MHz 1.2 GHz 2.0 GHz

SATA I 1.5 Gbps 750 MHz 2.25 GHz 3.75 GHz Upper Mid-range

PCIe 1.0 2.5 Gbps 1.25 GHz 3.75 GHz 6.25 GHz High-end entry

PCIe 2.0 5.0 Gbps 2.5 GHz 7.5 GHz 12.5 GHz High-end

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http://de.wikipedia.org/wiki/Bild:Usb-svg.svg

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Bandwidth – Analog Rise Time Accuracy

l Measured rise time depends on intrinsic rise time of the scope

l Example:

l maximum 3% error for 2ns rise time

l limit of measured rise time: 2.06 ns

<=0.5 ns intrinsic rise time (~700 MHz Bandwidth)

trise_measure2 = trise_intrinsic

2 + trise_signal2

BW * trise_10-90 = 0.35

trise_10-90 = 0.35 / BW

BW = 0.35 / trise_10-90


Bandwidth – Technology Mapping

Logic

Family

Typical

Signal

Rise

Time

Calculated

Signal

Bandwidth

Oscilloscope Band-

width Requirement

TTL 2 ns 175 MHz 525 - 875 MHz

CMOS 1.5 ns 230 MHz 690 - 1150 MHz

LVDS 400 ps 875 MHz 2625 - 4375 MHz

ECL 100 ps 3.5 GHz 10.5 - 17.5 GHz

l Digital technologies have characteristic rise times

Bandwidth Instrument Rise Time pS

500 MHz 700 600 MHz 590

1 GHz 350 2 GHz 175

2.5 GHz 140 3 GHz 117

3.5 GHz 100 4 GHz 87 6 GHz 58

8 GHz 44 12 GHz 30

16 GHz 22 20 GHz 18

25 GHz 14 30 GHz 12

35 GHz 10


The Function Blocks of a Digital Oscilloscope Analog-to-Digital Converter

ADC Acquisition

Processing

Display

Trigger

System Horizontal

System

Att. Amp

Amp

Vertical System

Memory

Post-

Processing


Analog-to-Digital Converter (ADC)

l The Analog-To-Digital converter is one of the critical components of an

oscilloscope

l Most Oscilloscopes use 8-bit ADCs

l ADC for a scope is not available “off the shelf”

l Technology is highly sensitive

l Sample rate: Clock rate of ADC – typically 5 times higher than oscilloscope

bandwidth


Analog-to-Digital Converter (ADC) Sampling

l Samples are equally spaced in time

l Sample Rate measured in Samples/Second (Sa/s, kSa/s, MSa/s, GSa/s)

Taking samples of an input signal at specific points in

time.

Samples

Hold Time Needed for Digitizing

Sample Interval TI

Interpolated Waveform


Analog-to-Digital Converter What Happens To The Samples in a DSO

Memory Storage

1 0 1 1 1 0 0 1

1

0

1

1

1

0

0 1

1

1

1

1

0

1

0 1

0

0

1

1

0

1

1 0

. . . . .

Sampling Digitizing

(Sample & Hold) (Convert to

Number) (Sequence

Store)

1 0 1 1 1 0 0 1

Scope Screen


Analog to Digital Converter - Resolution l Vertical quantization defined by input voltage and number of bits

l Example: Input voltage = 5 V, 8-bit ADC => 19.5 mV / bit

l Zooming is a mathematical magnification

l Samples are interpolated

l Resolution is NOT changed at ADC level

Example: Zoom


Input Range

l Input range and position directly affects the resolution of the waveform

amplitude

l The 10 vertical scales correspond to the full ADC input range

Signal amplitude:

0.5 V

Scale/div = 50 mV/div Scale/div = 100 mV/div

Best ADC resolution

8 bit => 0.2 mV / bit

reduced ADC resolution

8 bit => 0.4 mV / bit


Data Decimation & Waveform Arithmetics

l Differentiated analysis with up to 3 simultaneous waveforms per

channel

1 Channel

Original

Waveform

Envelope

Waveform

Hi-Res

Waveform


Input Range – Overdrive Recovery

l Poor overdrive recovery will not allow vertical selection of part of the

waveform to provide higher digitizer resolution on part of the waveform.

100 mV/div

20 mV/div








l Horizontal System

l Trigger System




l Probe calibration

l Summary


Vertical System

ADC Acquisition

Processing

Display

Trigger

System Horizontal

System

Att. Amp

Amp

Sampling Methods & Acquisition Modes

Memory

Post-

Processing


Aliasing – Too Slow sampling

l Nyquist Rule is violated:

l Sampling rate is smaller than 2x highest signal frequency

l Signal is not sampled fast enough -> aliasing

l False reconstructed (alias) waveform is displayed !!!

Example

-Input: 1 GHz sine wave

-Sample rate: 750 MSa/s

-Alias: 250 MHz

Actual Input Signal

Alias Displayed


Sampling Methods – Sample Rate Effects A 10 kHz Sine Wave Signal (no interpolation)

Nyquist/ Shannon

The sampling rate

must be:

iS ff 2Sf

Sf : sampling frequency

if : frequency of the

input signal

Input Signal: 10kHz Sine Wave

Sampling Rate: 200kHz



Sampling Rate: 12.5kHz


Sampling Methods: Interpolation between points

>10 samples

Real-time Sampling •over-sampling following Nyquist rule

Interpolation

linear sine (sin(x)/x)

>2 samples; improves interpretation of the samples

Dots

I Dots - no interpolation

ILinear - interpolation computes record

points between actual acquired samples

by using a straight line fit.

I Sin(x)/x - interpolation computes record

points using a curve fit between the actual

values acquired.


Low Noise Front End

l Noise floor directly affects the sensitivity of the

oscilloscope

l Noise floor is determined by the noise characteristics of the

components in the signal path of the front end

l Variable Gain Amplifier (VGA)

l ADC

l Front end Layout and shielding

* Specified Performance. Typically lower

ADCs

Front end

& Amplifiers Input channels

Channel-to-Channel Isolation

> 60dB!

Benefit of lower noise:

- Better Test Margin


Single Core ADC


Single Core ADC

l Effective Number of Bits (ENOB): A Number for Signal Fidelity

l Higher ENOB => lower quantization error and higher SNR

Better accuracy

Effective

Bits (N)

Quantization

Levels

Least Significant

Bit ∆V

4 16 62.5 mV

5 32 31.3 mV

6 64 15.6 mV

7 128 7.8 mV

8 256 3.9 mV

Offset Error Gain Error Nonlinearity Error Aperture Uncertainty

And Random Noise

+ + +

± ½ LDB Error

Quantatized

Digital

Level

Sample

Points

Analog Waveforms

<

Ideal ADC vertical 8bits =

256 Quantatizing levels

8 bits Effective

Number of Bits !

Ideal RTO

Others


Multiple ADC Problems

l Conventional ADC-Design:

l Multiple ADCs used in parallel

to increase sampling rate

l Errors in the phase delay and

mismatch of the ADCs result

in signal distortion

Interleaving distortions

In Time Domain

Phase Errors

Spurious

Frequency

Interleaving

Artifact

Signal

Interleaving distortions

In Frequency Domain


4 GHz Multiple ADC Spurious Products


Single Core ADC vs. Multiple ADCs

400MHz Sine Wave. 5mV/div

Non-Interleave

Interleave Distortion


ADCs Vertical Bits Resolution l Input range and position directly affects the resolution of

the waveform amplitude

l Scaling the signal to less than full scale increases the

quantization step size and decreases accuracy.

Scale/div = 50 mV/div Scale/div = 100 mV/div

Best ADC resolution

8 bit => 2 mV / bit

(Best measurement result!)

Reduced ADC resolution

8 bit => 4 mV / bit

(Equivalent to 7 bits resolution)

8 bit

8 bit

Multi-Grid Display

Benefit of Multigrid Display:

- Better Accuracy


Input Sensitivity

l Do you expect your scope to perform with its Full

Bandwidth Specification at all time?

BNC Input

Channel

Amplifiers Position Input Coupling

ADC

Offset

Vertical Input

Sensitive Range

Use with x10

Active Probe

R&S RTO102x

50 Ω 1M Ω

>= 10 mV/div >=100 mV/div Full BW 500MHz

5 mV/div … 9.9

mV/div

50 mV/div … 99.9

mV/div

Full BW 500MHz

2 mV/div … 4.99

mV/div

20 mV/div … 49.8

mV/div

Full BW 500MHz

1 mV/div … 1.99

mV/div

10 mV/div … 19.9

mV/div

Full BW 500MHz

True Accuracy => no BW limitation!

True Resolution => no software magnification!

Benefit of dedicated amplifiers:

Ability to analyze weak signal


l Oscilloscopes have significant blind-times!

typical ratio: max. 0.5% active –> 99.5% blind (= 50,000 wfm/s)

Waveform Update Rate - Important Specification!

acquisition

of 1st wfm blind time acquisition

of 2nd wfm

acquisition cycle

for 1 waveform

e.g. 100 ns e.g. 19.9 us

Scope display

is missing the

critical signal

faults!








l Horizontal System

l Trigger System




l Probe calibration

l Summary


Horizontal System

Vertical System

ADC Acquisition

Processing

Display

Trigger

System Horizontal

System

Att. Amp

Amp

Memory

Post-

Processing


Sampling Rate

Record Length

Resolution

Time Scale

Acquisition time

Sample Rate Time

Scale

# of

Div’s

Record

Length

• total # samples

• time/div

• 10 x time/div • time between

2 samples

x x =

e.g. 10 GS/s x 100 ps/div x 10 Div’s = 1000 samples

10 GS/s x 100 s/div x 10 Div’s = 10M samples

Acquisition time

1 / Resolution

Horizontal System Control Parameters

• samples/sec


Horizontal System Memory

l ADC Samples stored in the memory

l Deep memory stores more samples (more to manipulate)

l Longer time periods at high sample rate allow better signal

reproduction & zoom

1 0 1 1 1 0 0 1

Sampling Digitizing

(Sample & Hold) (Convert to

Number)

1 0 1 1 1 0 0 1

1 0 1 1 1 0 0 1

1 1 1 1 0 1 0 1

(Sequence Store)

Scope Screen

Memory Storage

…




l Advantage of Deep Memory l Maintain high sample rate in long time captures

l Allow greater waveform count in segmented memory

l Advantage of High Sample Rate l Signal fidelity increased (more accurate signal reproduction)

l Better resolution between sample points

l Higher probability of capturing high speed glitches or anomalies

l Better Zoom Capability



Acquisition Memory Implementation RTO Unique – History View Mode

l Each waveform

acquisition:

l is being stored in

memory automatically

l Can be played back

anytime!!

l Memory segmentation

controllable by user.








l Horizontal System

l Trigger System




l Probe calibration

l Summary


Channel

Input

Vertical System

ADC Acquisition

Processing

Display

Trigger

System Horizontal

System

Att. Amp

Amp

Memory

Post-

Processing

Trigger System


Trigger System

l Motivation

l Get stable display of repetitive waveforms

In 1946 the triggered oscilloscope was

invented, allowing engineers to display a

repeating waveform in a coherent, stationary

manner on the phosphor screen

l Isolate events & capture signal before and after (Pre-trigger not possible with analog scopes)

l Define condition for acquisition display in digital

oscilloscopes, trigger the acquisition to start in

analog oscilloscopes


Trigger Accuracy

l Key accuracy parameter:

l Minimum detectable glitch (a small signal spike):

– what is the smallest pulse that can be triggered on

– typically [ps] (related to trigger bandwidth)

l Sensitivity:

– minimum voltage amplitude required for valid trigger

– typically [mV or div]

l Jitter:

– timing uncertainty of trigger,

determines smallest measurable signal jitter

– typically [ps rms]

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Unique Digital Trigger System Challenges of Traditional Analog Triggering

l Traditional: Analog trigger

Separate paths for signal and trigger different time-invariant

behavior of hardware components causes measurement errors

which cannot be compensated in real-time

l Comparison of Digital and Analog triggering architecture

Innovative

Digital

Trigger

Traditional


Unique Digital Trigger System Challenges of Analog Triggering

l Separate paths for signal and trigger cause measurement errors

l Analog trigger jitter often corrected by using post processed DSP

techniques slowing down trigger/waveform rates and consuming

computing resources, and transferring jitter to other channels


Unique Digital Trigger System Implementation Benefits l Digital Triggering in Realtime is unique to the RTO:

Real time, no DSP post correction!

l Benefits over Analog Triggering

l Industry leading Trigger Jitter <1ps rms without using DSP

correction

l High trigger sensitivity down to 0.1 div for small signal amplitude

l Adjustable trigger hysteresis for stable trigger

l Flexible trigger filtering (user-defined low pass filter) for noisy

signals

What you can see,

you can trigger on!


l Edge Trigger is the original, most basic and common trigger type

l Triggering is executed once a signal crosses a certain threshold

(and passed the hysteresis)

l Bi-Directional trigger for unknown signal direction, e.g. electric discharge

Trigger Types (I)

rising edge falling edge rising and falling edge


l Auto – Trigger is injected automatically to

ensure there is a regular update rate on

the display. The scope will also trigger

off the trigger circuit.

– Useful for DC voltage measurement

and to assist in instrument setup.

l Normal – Trigger will only come from trigger

circuitry.

– No trigger = No display update

l Free Run – Trigger generated by the scope and

trigger circuit ignored completely.

– No signal synchronization!

Trigger Types (I) Trigger Modes

l Beware! – Auto will inject triggers in to a

slow trigger rate, causing an

unstable display


Trigger Types (I) Holdoff

l Holdoff - Forces a delay before the next trigger event.

l Time – User adjusted fixed time

l Events – Skip number of valid trigger events

before triggering

l Random – User limited variable times inserted to

ensure no synchronization of trigger with DUT

l Auto – Delay by a multiplication factor of the

horizontal timebase full scale

l Off – Instrument triggers as fast as possible


Trigger Types (II) – Advanced Glitch

Glitch l typically a narrow pulse, e.g. caused by cross-talk


Trigger Types (II) – Advanced Width

Width l defined pulse width, e.g. observing Inter-Symbol-Interference (ISI)


Trigger Types (II) – Advanced Runt

Runt l Limited amplitude, e.g. meta-stable conditions in digital systems, bus contention


Trigger Types (II) – Advanced Window and Time Out

Window l event that enters / exits a window , e.g. capture bus contentions

Time Out l dead time, e.g. system errors by a lack of

activity such as a system hang or delay


Trigger Types (II) – Advanced Interval

Interval l Period cycle timing, e.g. Pulse Width Modulated systems


Trigger Types (II) – Advanced Slew Rate

Slew Rate (Transition Time) l Slow/Fast edges, e.g. circuit instability / radiation of troublesome energy


Trigger Types (II) – Advanced Setup and Hold (Data to Clock)

Setup & Hold l timing relation between 2 channels, e.g. synchronous data interface to IC


Trigger Types (II) – Advanced State and Pattern

State l Qualify the desired signal’s trigger by

the logical combination of other

channels, e.g. troubleshooting parallel

busses using clock and control lines

Pattern l Trigger on a valid parallel pattern by the

logical combination of any channels

with the capability to include or exclude

the desired channel as a trigger.


Trigger Types (II) – Advanced Serial Pattern (Synchronous Data)

Serial Pattern l Decode and trigger on synchronous serial data patterns, e.g. clocked data interface to IC


Trigger Types (II) – Advanced Analog Television

TV l Trigger analog television signals, e.g. composite video, component high definition video,

display VITS, Teletext


Trigger Types (II) – Advanced A-> B -> Reset

A -> B -> Reset/Timeout l Allow complex triggers with time and/or count periods, plus time or event reset capability to

qualify time dependant events filtered by other events.


Trigger Types (II) – Advanced Trigger Hysteresis (Noise Reject)

Trigger Hysteresis l Usually fixed, more advanced instruments have fixed level choices, or fully adjustable








l Horizontal System

l Trigger System




l Probe calibration

l Summary


Analyzing Waveforms Cursors

• Cursors - Horizonal/Vertical

- Track Waveform

- Couple

- Labels

- Peak Search (FFT only)

- Rhombus

(Like S/A markers for FFT)


Analyzing Waveforms Measurements

• Measurements - Can be gated to control where the measurement is made in the waveform

- Statistics available

- Eye specific

- FFT specific

- Probemeter (with equipped Active probes)

- Pass / Fail tests

- Long term plotting on screen


Analyzing Waveforms Measurement Example – Setup and Hold


Analyzing Waveforms Measurement – Basic Eye/Jitter Measurement


Analyzing Waveforms Measurement – Basic Spectrum Measurement on FFT


Analyzing Waveforms Measurement – Histograms


Analyzing Waveforms Measurement – Measurement Plot, Mask Test, Statistics


Analyzing Waveforms Display


Analyzing Waveforms Display


Analyzing Waveforms Math – “Basic”

• Basic Math - Simple waveform math

- FFT

- Multiple source selection

- Waveform averaging

- Up to four simultaneous

math waveforms

- Vertical controls also

control math like an input

channel

- Scaling can be manually

or automatically controlled


Analyzing Waveforms Math – “Advanced”

• Advanced Math - Advanced waveform math

allows complex equations

- Equation Inputs

-Channels

-Math

-Reference waveforms

-Digital Bus

-Measurements

- Digital filtering is possible

- Selectable units & multipliers


Analyzing Waveforms Math – FFT








l Horizontal System

l Trigger System




l Probe calibration

l Summary

l


Probes

l Intro

l Probing Fundamentals

l probe types overview

l Passive (Voltage) Probes

l 1x type, 10x type, Low-Z type

l R&S RT-ZP10

l compensation

l Probing Limitations

l loading, filtering, resonance, reference ground

l Active (Voltage) Probes

l single-ended

l differential

l R&S RT-ZS20/30

l Current Probes

l Safety Aspects

l Selection Summary


Probes

l Probes become necessary when the electrical signal is not

available at a socket/connector, or a simple cable connection

cannot transport the signal properly due to the characteristics

of the source.

l A probe is more than a cable with a clip-on tip. It is a high-

quality connector, carefully designed not to pick up stray radio

and power line noise.

l Probes are designed to minimize the impact to the behavior of

the circuit you are testing. However, no measurement device

can act as a perfectly invisible observer. The unintentional

interaction of the probe and oscilloscope with the circuit being

tested is called circuit loading.


Probes – introduction

l If every connection to our

DUT‘s was easy…

… nobody would talk about

probing.

l But the real world will look like

this…

… and then probing becomes an

essential part of solving the

problem!


Next Topic

l Intro





l R&S RT-ZP10

l compensation




l single-ended

l differential

l R&S RT-ZS20/30

l Current Probes

l Safety Aspects

l Selection Summary


l Task:

l Bring the signal to be measured to the scope

l The Challenge:

l The oscilloscope itself can only display voltages in a rather limited range (typ. 1mV…5V)

l The probe should not load (and thus alter) the signal to be measured

l The connection may introduce or suppress signal components (hum, noise, filter)

l The Solution depends on the quantity to measure with respect to

l Signal type

– Voltage (single-ended or differential), current, power, pressure, optical, etc.

l Signal amplitude

– a few mVolts to 10 Volts are easy to handle. Smaller or much larger signals require specialized equipment

l Signal frequency

– Higher frequencies require advanced equipment and/or techniques in order to get correct results

l Source characteristic

– The source impedance is a decisive factor when choosing the suitable connection.

Probing Fundamentals


l The ideal connection properties:

l Easy to establish

– Reliable, safe (to circuit and user) contacts

l No degradation or distortion of the transferred signal

– Linear phase behavior

– Zero attenuation

– Infinite bandwidth

– High noise immunity

l No loading of the signal source

– No energy taken from circuit

Probing Fundamentals


Probing Fundamentals – real connection

l Frequently Encountered:

l Signal is not easy to reach

l Source impedance can vary

widely

l Setup is sensitive to noise

and will be frequency

dependent

l Probe hookup has severe

bandwidth limitations

l Differences in signal

propagation delay create

slight timing offsets (skew)

between multiple

measurement channels


Different Types of Probes – voltage probes

Low Impedance


Next Topic

l Intro





l R&S RT-ZP10

l compensation




l single-ended

l differential

l R&S RT-ZS20/30

l Current Probes

l Safety Aspects

l Selection Summary


Passive Voltage Probes

l No active components so no need for external power

l Low cost

l Robust

l Wide input voltage range


Passive Voltage Probes Special Types

l High voltage passive probes:

l High resistance for measuring high voltages

l Usually has a selectable divider ratio

l Limits: Reduced bandwidth

l Low impedance passive probes:

l Minimal capacitive loading that will impact the timing behavior

l Higher bandwidth at constant impedance

l Limits: Relatively heavy resistive loading that may impact the source

l High Impedance Passive Cable Divider

l 10:1 probe with BNC connector instead of probe tip

l Mechanically robust and reliable


Passive Probe – High Impedance 1X

l 1:1 passive High-Z probe (uses 1 Meg Ohm scope input impedance)

l Advantages:

– Sensitivity (no attenuation)

– Inexpensive

– Mechanically rugged


Passive Probe – High Impedance 10x

l 10:1 passive High-Z probe (uses 1 Meg Ohm scope input impedance)

l Advantages:

– Wide dynamic range

– Mechanically and electrically rugged

– Increased input R and low input C as compared to a 1x probe


Passive Probes – R&S RT(M)-ZP10

l One probe per channel included

l Optimized bandwidth if connected

to RTO/RTM

l Attenuation factor detectable by

instrument through read-out pin

l Specs:

l 500 MHz (-3dB) system BW

l 1:10 attenuation

l Input C 9.5 pF typ.

l Input R 10 Meg Ohm

l Input voltage 300 V rms max


Passive Probes Accessories


Rcable

CCable

Probe

RScope CScope

Oscilloscope

RHFcomp Rp

Cp

Compensate your Passive Probe before Use

Under Compensated Signal

Over Compensated Signal

Properly Compensated Signal

This maintains probe attenuation ratio and flatness over the rated bandwidth


Detailed Passive Voltage Probe Adjustment

Rp

Cp

Rcable RHFcomp

RScope CScope CCable

Probe Oscilloscope

LOW FREQUENCY (e.g.

1kHz) ADJUST of RC

resonators by trimming

the probe capacitance Cp

HIGH FREQUENCY

(e.g. 1MHz) ADJUST of

electrical cable length to

used frequency by

trimming the probe

resistance RHFcable

p

pRCprobeCf

CfZ2

1~,

ScopeScopepp

RCCRCR

11~

!

Scope

p

p

Scope

R

R

C

C !


Passive Probe – Transmission Line 10x

l 10:1 passive probe (uses the 50 Ω scope input impedance)

l Alternative terms: “Low Impedance Probe”, “Low-Z Probe”, “Low Capacitance Probe”,

“Transmission Line Probe”, “Z0-Probe”, “Resistive / Passive Divider Probe”

l Probe impedance variation over frequency is low

l Not BW limited by high impedance 1M Ω input of the scope

l The load on the source is high due to the low nominal impedance of 500 Ω

Probe

50 Ohms

Oscilloscope DUT

Rsource

450 Ohms

0.1 pF

Cable

50 Ohms

Lground lead


Passive Probe – typical parameters

l High impedance 1x:

l Bandwidth 10 - 5 MHz, input 1 MOhm, capacitance 80-100 pF

l High impedance 10x:

l Bandwidth 100 - 600 MHz, input 10 MOhm, capacitance 7-15 pF

l High impedance – high voltage 100x/1000x:

l Bandwidth 25 - 400 MHz, input 50…100 MOhm, capacitance 3-7.5 pF

l Low impedance 10x:

l Bandwidth 1.5 - 9 GHz (!), input 500 ohms, capacitance 0.15-1.5 pF ,

max. voltage 12-25 volts


High Voltage passive probes

l High Voltage passive probes

l Large physical dimensions on very high

voltage

l Low bandwidth

l Safety considerations as rated by category

( CAT II, III, IV...)

l Not as popular with less products

containing CRT based displays


Safety Aspects – Measurement Category l CAT I – Measurements on circuits not

directly connected to a mains supply

l CATII – Measurements on circuits

directly connected to the low voltage

building installation (non-stationary

equipment in labs, offices,

households)

l CAT III – Measurements directly on

the building installation

(distribution and breaker boards, wall

outlets, stationary equipment)

l CAT IV – Measurements at the

source of the installation

(electricity meters, primary over-

current protection)

IEC/EN 61010-1 Overvoltage Protection

Category, Phase to Earth

Transient Test

Voltage CAT II 600 V

4000V CAT III 300 V CAT III 600 V

6000V CAT IV 300 V

CAT II 1000V 8000V

CAT IV 600V


l Bandwidth: 400 MHz

l Max input voltage: 1kV RMS, 4 kV Peak

l Attenuation factor

RT-Z10 100:1

RT-ZH11 1000:1

l Read-out pin RTO / RTM automatically detect attenuation factor

l Basically the same as the RT-ZP10 but with higher attenuation and

longer cable (also needs probe compensation adjustment on first use)

High voltage passive probes R&S High voltage probe example

RT-ZH10 / RT-ZH11


Active Probes


Active Probes - Different Manufacturers

l Scopes from different vendors have different probe-sockets

at the scope interface

l Consequence: active probing solutions will only work with

the respective vendor‘s oscilloscope

l However: numerous probes are created by third-party

manufacturers who adapt their products to different base

units. These probes often come with a standard BNC plug,

possibly a read-out pin, and a power source like a battery,

USB-cable, or external AC adaptor.


Active Probes

l Single-ended or differential versions available

l Requires operation power from instrument

l Proprietary interface to instrument

l Accessory interface for use with RF instruments

Example single-ended probe schematic:


Probe Schematic R&S Single-ended Active Probe

RF

Am

p

Pre

c

DC

Am

p

24 bit

AD-Conv

Divider Amplifiers Hybrid Cable Probe Box

Control

RF Signal

Micro Button

&

ProbeMeter

µC π

Laser

Trimming

Tip Scope input


R&S Single-ended Active Probe Micro-electronics and Mechanics


l Advantage:

l low loading on signal source

l adjustable DC offset at probe tip allows high resolution on small AC

signals which are superimposed on DC levels

l automatically recognized by base unit – no adjustment needed

l Disadvantage:

l integrated buffer amplifier works only on limited voltage range

l the probe impedance is still strongly dependent on the signal frequency

l the DC impedance is lower than with a 10x passive probe

Active Probes


Active Probes – Differential l Why measure in differential mode?

l There are signals that are by principle referenced against each other, not against

ground, e.g. signal lines like twisted-pair or LVDS

l In general: voltages which are not referenced to ground

l across a resistor or other electronic component

l generated by an inductive pick-up or secondary side of a transformer

l OR: if the signal ground is noisy or subject to crosstalk

l A major parameter is the Common Mode Rejection Ratio (CMRR):

l CMRR is degraded:

– over signal frequency

– by any mismatch between the probes or instrument inputs

– by differences in the source impedance


Active Probes – Differential

l A differential signal can be

displayed through a two-

channel setup as in figure a.

l A setup according to figure b

is superior with respect to

l symmetry (same amplification,

cable length, ... on both paths)

l Common Mode Rejection Ratio

l immunity to interference/noise

l only one scope channel used

l Bandwidth


Why Differential?

l Most high speed signaling systems use differential transmission. (better noise immunity)

l Logic “swing” voltage levels are getting lower as speeds get

faster. (fast rise times & higher voltages consume power)

l Thus, noise amplitudes are increasing as a percentage of logic

voltage swing.

l Noise superimposed on the transition edges add jitter in single

ended signaling.

l With differential, the threshold detection is based on crossing

point of both lines – not fixed voltage as in single ended. (common

mode noise removed)


Differential Probing Reduces Noise

l In single ended systems, noise superimposed on the edge adds time

uncertainty to the exact threshold crossing point.

l In differential, the noise injected in both lines is almost identical in

amplitude and phase. It does not alter the crossover point –

lowering jitter.

+ =

VTH

+ -

+

-


Dynamic Ranges

l Differential Mode Range (DMR)

l Maximum voltage instantaneous between + and - inputs.

l Verify on scope.

l Common Mode Range (CMR)

l Maximum voltage between either input and ground.

l Normally not seen.

l Verify by grounding one input at a time (use of diff. probe as active

single-ended probe)

Differential Mode Range

Maximum voltage

between inputs

Common Mode Range

Maximum voltage from

either input to ground


Operating Voltage Window

l If the operating voltage window of the probe is exceeded,

unwanted signal clipping may happen.

l RT-ZD probes offer high operating voltage window of +/- 5V.

l An additional offset range of +/- 5V is available.

Operating voltage window Differential offset compensation voltage


Differential Terminology

dc

inincinindout

AA

VVAVVAV

2

l Differential Mode - the voltage difference between the + and - input as

referenced to ground.

l Processed by the amplifier

l Common Mode - the voltage common in amplitude and phase on both

inputs.

l Ignored by the amplifier

VCM

inV

inV

+

-

Vd

Vc


V pk-pk versus Vpk

l Differential Mode Range (DMR) = maximum instantaneous

voltage which can appear between inputs.

l Maximum voltage between + and - inputs.

l Generally symmetrical with polarity (but not always)

l Peak to peak voltage is 2 times this value

l Example: ±1V can handle 2 Vpk-pk signal – max voltage between

inputs = 1 V. This does not mean the amplifier has a 2 V range!

Differential Mode Range

Maximum voltage

between inputs

+ 1 V

0 V

- 1 V


Common Mode Rejection

l Common Mode Rejection is the ability of the differential amplifier to eliminate the common mode voltage from the output.

l Real world differential amplifiers do not remove all of the common mode signal.

l The measure of how effective the differential amplifier is in removing common mode is Common Mode Rejection Ratio (CMRR).

c

d

dc

inincinindout

A

ACMRR

AA

VVAVVAV

2


Why do we care about CMRR?

l Common mode feedtrough sums with the VDM (signal of

interest) into the output of the differential amplifier,

becoming indistinguishable from the true signal.

l Essentially, lower CMRR equates to greater noise.

l Example above for a CMRR or 20 dB (10:1)

+5V

+4V

45.0sin tVout


What is Quasi-Differential?

l Quasi-differential acquisition is a method of acquiring a differential signal without a differential probe.

l Uses two single ended probes and scope channels to acquire the + and – sides of the signal.

l A math waveform of A-B is used to generate the differential waveform.

l Commonly used with direct cabled fixtures (e.g. SMA connectors on target or fixture) and when active differential probes with sufficient bandwidth are not available.


Quasi-differential limitations

l Quasi-differential has many problems in other

applications, but can work for high speed

digital systems.

l Possible issues:

l Consumes 2 channels for each signal.

l Difficult or impossible to trigger when CM component is

large relative to DM.

– Most scopes cannot trigger on math waveform.

l Requires very good channel matching.


Probing Limitations – overview

l Loading l Resistive (mainly relevant for DC measurements)

l Capacitive (relevant for AC measurements)

l Resonance effects l Mostly due to ground lead effects

l Filtering l Due to the system (probe + scope) bandwidth, higher frequencies tend to

be attenuated (bandwidth limitation)

l Stability of (reference) ground l Single-ended probes need an invariable signal ground

l If not available, use differential probes


Probing Limitations – resistive loading

l Example: Voltmeter Loading Effect

Loading Effect

Current Flows

The example demonstrates a substantial error of -34% introduced by resistive loading.

If a scope with 1 MΩ input and a 10:1 probe was used, the error could be

reduced to a value under 10%.


Probing Limitations – capacitive loading

l The input capacitance

(combined probe and scope

contribution) will introduce an

capacitance in parallel to Rin.

l As a result, rise time is slowed Rsource


Probing Limitations – inductive loading

l The ground lead (or any

additional lead between probe

tip and signal source) will

introduce an inductance.

l This inductance, in

combination with Cin , forms a

resonator with a ‚ringing‘

frequency

l As a result, the step response

is distorted with overshoot and

long settling times.

Rsource


Probe Loading

l All probes will add a load to the test circuit, which will

change the characteristics of the waveform.

l Severe loading can alter the operation of the circuit.

l The input impedance of all probes becomes lower as the

frequency increases.

Probe loading vs. frequency


Probe Loading Input Capacitance vs. Impedance

l Our customers are asking:

“What is the input C?”

l For frequency components over 1 GHz, this is

the wrong question. They should ask:

“What is the input impedance over frequency”

l Input resistance:

l Determines the loading of the DUT at DC and very low frequencies (< 100 kHz).

l Note that a low input resistance can also disturb measurements of high-frequency signals as it influences the DC operating point of active components.

l Input Capacitance:

l Causes the input impedance to decrease in the medium-frequency range (100 kHz to 1.0 GHz).

l Note: Affects the settling time of the input voltage in the case of fast transients

impedance dominated by

capacitance resistance inductance


Probe Loading Input Resonance l The input capacitance of

the probe, acting on the

inductance of the input tip

or leads, forms a series

resonate circuit.

l At resonance, the ZIN drops

very low.

l If the resonance is in the

passband, serious

waveform distortion can

result.

Frequency

Input

Impedance

W

DC 4 GHz

0

avoid

resonance

area


Probing Limitations – ground lead effects (1)

l Examples for ground lead connections:


Probe Loading Performance Impact of Probe Accessories l The connection accessories impacts the signal fidelity

Typical Characteristic:

Conn. Inductance: ~4 nH ~8 nH ~20 nH ~60 nH

Rise Time: 110 ps 120 ps 500 ps >ns

Bandwidth: 3.2 GHz 3.0 GHz 1 GHz <500 MHz

Solder-in pins Browser Flex-adapter 4cm Micro-clips + 6cm leads

Browser

Pins

Leads

Flex

adapter



l ground lead effect:

step response of different ground connections:


Probing Limitations – ground lead effects

l Passive probe with

l 150mm (blue) ground lead

l 15 mm spring hook (magenta)

l Active probe with

l 15 mm ground lead (black)


Frequency Response vs. Step Response

l The Frequency Response filter characteristic determines

the Step Response in the time domain

l Key parameter of Step Response:

l rise time

l overshoot

l ringing

Overshoot

Rise time



l Ground lead effect: different probe types

Probe type Passive 10x

Active High

Impedance

Passive Low-Z

10x

Input Capacitance Cin 14 pF 0.9 pF 0.25 pF

Resonance frequency with

Lcon = 10nH (~ 2 cm wire) 425 MHz 1.68 GHz 3.18 GHz

Resonance frequency with

Lcon = 150nH (~ 30 cm wire) 109 MHz 433 MHz 821 MHz


Never extend input leads !

l Adding extension wires to probe input leads increases the inductance, lowering

the resonance frequency.

l Only 1 cm added to tip and ground reduce Zin from 159 W to 8.3 W at 1 GHz!

100 kW 1 pF

10 nH

10 nH

Frequency (MHz)

Input Impedance

(Ohms)

0 cm

2 cm

5 cm

10 cm

1

10

100

1k

10 k

1 G 1 10 100 10 G


Probe loading – Active + Passive l Probe TTL B with the RT-ZS30 Active Probe, then add the RT-ZP10 Passive probe.


Frequency response accuracy

l +/- 2 dB response deviation is OK for routine digital design (S/H

timing, etc), but not serial data.

l Accurate weighting of fundamental to odd harmonics (3rd and 5th)

needed for eye patterns.

l Peaking or nulling harmonics create distortions:

l “Peanut shaped” eyes – possible mask violations

l Reduce or increase apparent Trise – reduced jitter accuracy


Probe vs. system bandwidth

l The graph displays a system behavior relative to a nominal BW

l Please note: the combination of probe and scope approximately determines the system bandwidth according to:

l Recommendation: choose the probe bandwidth at least 1.5 times higher than the scope BW

)BW(1/)BW(1/)BW(1/scopeprobe

system

22

nominal bandwidth


Frequency content in eyes

l The ideal eye pattern is a trapezoid – square wave with finite rise

and fall times.

l Each bit time slot (Unit Interval) occupies ½ of the square wave.

1 UI = ½ period

Fundamental frequency = ½ data rate


Harmonic weighting

l Problems result when data rate and 3rd harmonic fall on null and

peak.

1/ 2 Data Rate

3 / 2 Data Rate


Results in Peanut shaped eye

l Reduced mask margin.


Accessories

l Solder-in pins

l for small probing points

l insolated wires prevent short

circuits

l Maximize probe performance

with short length


Accessories

l Differential Probe Accessories

– Long reach solder in adapters for

tough to reach measurement

points

– Flexible square pin adapter

– Adjustable spacing browser

– Mini/Micro clips


Accessories – Adapter to 50 Ω inputs

l For high impedance

measurements on spectrum

and network analyzers

l Usable at any instrument with

USB for power supply

l On some analyzer types

(e.g. R&S FSV), the probe is

recognized by the firmware

and the scaling is

automatically adjusted


l Active Probe allows AC plus DC measurements

l DC flux compensation avoids core saturation

Current Probes Current Probe AC & DC


l The clamp introduces:

l An inductance that creates an „insertion impedance“ (or transfer

impedance). Careful with low impedance sources!

l A (parasitic) capacitance between conductor and ground. Together

with the impedance, a low-pass is created.

Current Probes Loading Effect

l The core in the current probe can retain its magnetized state

l This can cause a bias to appear on the DC output even before the

DUT is active

l Current probes have a demagnetizing feature (usually a button) that

creates a random magnetic field similar to erasing a magnetic

recording tape

l The probe should be demagnetized before each measurement

Demagnetization


l Ampere-Second product

l This specification is unique to current

probes

l The integral of current over time shall not

exceed the specification, otherwise the

core within the probe becomes saturated

and the measurement result is ‚clipped‘.

l Maximum AC Peak Current, DC Peak Current,

and RMS Current

l The measured current must not exceed either one of

these values.

Current Probes Key Specifications


l Current flow in the direction of the arrow

l Demagnetize before measuring

l Use high-res acquisition mode when

measuring low current

l Increase sensitivity by looping wire

through the probe several times

l Sensitivity increases by N = the number of

loops (Bandwidth is slightly reduced due

to phase delay of each loop)

Current Probes Connecting Current Probes







l Sampling Methods & Acquisition

l Horizontal System

l Trigger System




l Probe calibration

l Summary – But first, the MSO!


MSO – What does it stand for

Mixed Signal Oscilloscope

MSO is a hybrid test instrument combining measurement capabilities of a

l Digital Storage Oscilloscope (DSO) with

l some of the measurement capabilities of a logic analyzer,

l along with some serial protocol analysis

into a single, synergistic instrument.

+ =


Digital Oscilloscope

l Digital oscilloscopes have “Analog” channels

l Display the signal amplitude over time

l Typically 2 or 4 input channels

l High sample rate & bandwidth

Measure signal amplitudes & timing parameters

ADC


Logic Analyzer l Logic Analyzer “Digital" channels

l Display the logic level over time – comparator to distinguish between “high” and “low” state

l High number of input channels from 30 to hundreds

l Lower bandwidth & sample rate

Evaluate logic states

Threshold

Vth

Logic 0 Logic 1 Logic 0 Logic 1

Logic 0


MSO – Mixed Signal Oscilloscope MSO combines the strength of both the analog & digital channels

Display analog & digital signals on screen to give time-correlated comparison.


Typical MSO Applications Embedded System Design

Telecommunication

Systems

- Telephone Switches

- Mobile Phones

- Routers

- Network Bridges

Consumer

Electronics

- DVD Players

- MP3

- Microwave ovens

- Cellular Phone

Automotive - Airbag Controller

- Engineer Control Module (ECM)

- Tyre Pressure Controller

- Antilock brake controllers

Router Board

With WiFi

Embedded Computer

on Module

Engine Control Module

Definition

An embedded system is a computer system designed to do one or a few dedicated and/or

specific functions.

In contrast to that a PC is designed to be flexible to meet a wide range of end-user needs.

Embedded systems contain processing cores that are typically either microcontroller (MCU) or

digital signal processors (DSPs)

Variety of typical Embedded Design


Typical MSO Application Embedded System Design (II)

Mixed-signal embedded design that

generates analog “chirp” outputs

based on analog, digital, and serial I/O

Embedded Systems

l Consist of analog & digital modules

l The relationship between the analog & digital signal

needs to be measured

l Resolving signal integrity issues in the system will

need the resolution & bandwidth of the analog channel

l Logic issues in the system will need decode feature &

complex trigger to isolate.


MSO at a Glance

l Key specification

l 16 digital channels

l max input freq. at 500 mV (Vpp) signal amplitude: 400 MHz

l sampling rate: max 5 GSample/s

l acquisition memory: max 200 MSample

l rich set of trigger option

l high acquisition rate of > 200,000 waveforms /s

MSO board

2x 8 channels


RTO-B1 Block Diagram

. . .

Skew

Front end

Decimation

Acquisition

Memory

Trigger events

Protocol trigger

Acquisition

Trigger

Display

Interpolation Measurements Graphic

Engine

Acquisition Processing Measurement and Display

Cursors

Math Functions

FPGA

SW

D15

D14

Att

Att

Compare

Compare

. . . . . .

D1 Att Compare

D0 Att Compare

. . .

Mem

Con.

Generic Measurements


Architecture Highlights

Entire signal processing of a logic analyzer integrated into the

probe boxes …

l Decision of the logic levels

Comparators

Microcontroller

HDMI connector



… and the MSO board

l Sampling of the binary signals

l Trigger

l Math functions

l Measurements & cursors

l Graphic engine

l Acquisition memory

PCIe connector



Time-synchronous acquisition of analog and digital channels

l Necessity of the horizontal alignment

between analog and digital channels

l Automatic alignment between the

probe connectors of the analog channels

and the probe boxes of the digital channels

l Manual deskew of the analog probes

l Channel-to-channel skew <500ps

Automatic

Alignment


Definition - Input Impedance, Max. Input Freq.

Input Impedance The loading of the probe to the probe point.

Max Input Frequency Maximum toggle rate of the comparator determines the maximum input

frequency it can respond to.

Input Loading = 100 kΩ || ~ 4 pF

= 100 kΩ ~ 4 pF

Depending on the circuit nature, loading of the probes maybe cause

impact to the measurement or even cause circuit fail.


Definition: Minimum Input Voltage Swing

Minimum Input Voltage Swing The smallest peak to peak swing across detection threshold required for

comparator to “sense” a toggle at the maximum input frequency.

Threshold Min Input

Voltage Swing


Input Hysteresis Noise rejection by requiring signal to

exceed a certain voltage, VH, before

detected as a input high or low.

- VH VH

≈ 114 mV

97 mV ≈

VH ≈ +/- 100mV

“Normal” Hysteresis Mode “Maximum” Hysteresis Mode

Threshold

1V

≈ 508 mV

509 mV ≈

Threshold

1V

VH ≈ +/- 500mV

Definition: Input Hysteresis


Definition: Sampling Rate

Sampling Rate Speed of the ADC latches analog signal & convert to digital signal.

Sampling Rate vs Max Input Frequency

Period

Pulse

Width

200 ps

Threshold

Rules of Thumb for oversampling:

Max input frequency = Sample Rate / > 5 Samples

R&S

Parameters RTO Opt. B1

Max Input Freq 400 MHz

Max Sampling Rate 5 GSa/s

Resolution 200 ps


Definition: Sampling Memory

Long Capture Time at 200 ps timing Resolution Maximum Time Length = Memory Length / Sampling Rate

= 200 MSa / 5 GSa/s

= 40 ms

Deep memory allows longer capture times


Definition: “Lost Pulse” Display

Detection of pulses lost due to decimation RTO-B1 detect minimum pulse width of 200 ps

Positions of lost pulses are highlighted in red color

1ns

Digitizing

Increase resolution

Low resolution causes decimation


Definition: Waveform Acquisition Rate

Wfm Acquisition Rate Speed of the waveform capture defined by number of waveform per second

Acquisition and analysis rate up to 200,000 wfms/s reduces blind time

and allow faster error detection

Fast detection of infrequent events on

both Analog and Digital Channels


Definition: Trigger Jitter

Low Trigger Jitter Trigger accuracy of digital channels depends on sample resolution

Timing measurement error = +/- 200 ps

Decision threshold

200ps 200ps

1

0

Analog

waveform

Binary

signal

1

0


Definition: Minimum Detectable Pulse Width

Minimum Detectable Pulse Width Smallest pulse duration that can be detected. This factor mainly depends on the

sampling rate and detection architecture.

Detect min 200 ps pulse width to

help locating error due to glitches

and noise on sensitive circuits.


Definition: Serial Pattern Trigger

Serial Pattern Trigger Logic channel detect and compare data against serial pattern to trigger on the

specified data pattern

0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1

Clock

Trigger

Serial Data


Definition: Automatic Measurements

Automatic Measurement Rich set of automated timing-related

measurements for digital channels

available

Additional features:

I Long term statistics

I Limit Test


Definition: Bus Display

Bus Display Flexible bus decoding definition

D0

D1

D2

D3

15 14 13 8 3 2 5 4 15 10 9 8

Digital

Channel

Digital Bus

Display

Analog Bus

Display

Displaying the integral value of the

bus in different code formats

Treat the logic signals like digital to

analog converter (DAC).


Definition: Analog Bus Display

Analog

Channel

“Analog”

BUS

Digital

Channel


Definition: Cursors

Cursor Vertical cursors can be used to read out bus values

20

21

22

23

24

25

26

25 128

4

2 2

8

16

32

64

Sum

Y1= 134 Sum

Y2= 122

Integral

Values

+

+

+ + +

+ =

=


Summary

l An oscilloscope is a very versatile instrument used in a lot of

different environments and applications (e.g. compliance testing)

l It displays voltage vs. time and most of the current available instruments are build up digitally

l The better the horizontal and the vertical system is implemented the higher the required signal fidelity is achieved

l A high trigger flexibility allows the user to set up the scope in a way to capture also infrequent signals

l A good probe is essential to get the signal under test into the measurement system; probe and oscilloscope are tightly connected and determine the key parameters (bandwidth, rise-time, signal fidelity etc.)

Documents

Oscilloscope Fundamentals - Oct 2013