Help Volume
© 1992-97 Hewlett Packard Company. All rights reserved.
Instrument: HP 16533/34A
Digitizing Oscilloscope
HP 16533/34A Digitizing Oscilloscope
The HP 16533A and HP 16534A Digitizing Oscilloscopes offer basic
oscilloscope functionality. The oscilloscope can be easily correlated
with other instruments in the HP 16600A-series or HP 16700A logic
analysis system.
Getting Started
• “Calibrating the Oscilloscope” on page 10
• “Probing” on page 14
• “Acquiring a Waveform” on page 31
• “Combining the Oscilloscope with a Logic Analyzer” on page 36
Refining Your Measurement
• “Triggering” on page 39
• “Vertical and Horizontal Scaling” on page 53
• “Changing the Sample Rate” on page 55
• “Comparing Channels” on page 57
• “Using Markers” on page 75
Tip s
• “What Do the Display Symbols Mean?” on page 58
• “Changing Waveform Display and Grid” on page 47
• “Automatic Measurements and Algorithms” on page 62
• “Differences from a Standard Digitizing Oscilloscope” on page 77
• “Using Waveform Memories” on page 78
• “Loading and Saving Oscilloscope Configurations” on page 79
2
•“When Something Goes Wrong” on page 80
“Specifications and Characteristics” on page 85
Main System Help (see the HP 16600A/16700A Logic Analysis System
help volume)
Glossary of Terms (see page 97)
3
4
Contents
HP 16533/34A Digitizing Oscilloscope
1 HP 16533/34A Digitizing Oscilloscope
Calibrating the Oscilloscope 10
Calibration Reference 12
Probing 14
Table of Compatible Probes 14
Selecting the Proper Probe 15
Compensating the Compensated Passive Divider Probe 18
Probe Loading 19
Descriptions of Probe Types 23
Surface Mount Probing 30
Acquiring a Waveform 31
Autoscale 32
Specifying a Measurement 33
Combining the Oscilloscope with a Logic Analyzer 36
Oscilloscope Triggers Logic Analyzer 36
Logic Analyzer Triggers Oscilloscope 37
Logic Analyzer and Oscilloscope Correlate Data 37
Triggering 39
Trigger Concepts 39
Edge Triggering 41
Pattern Triggering 42
Delayed Triggering 43
Getting a Stable Trigger 44
The Trigger Setup Window 45
5
Contents
Changing Waveform Display and Grid 47
Zooming In 47
Changing the Persistence of the Waveform 47
Viewing Noisy Waveforms with Averaging 49
Changing Display Colors 51
Changing the Grid 51
Vertical and Horizontal Scaling 53
Changing the Sample Rate 55
Comparing Channels 57
What Do the Display Symbols Mean? 58
Display Setup Window 60
6
Contents
Automatic Measurements and Algorithms 62
How the Scope Makes Measurements 63
Average Voltage (Vavg) 64
Period 64
Rise Time 64
Fall Time 65
Negative and Positive Pulse Width (±Width) 65
Frequency 66
Base Voltage (Vbase) 67
Top Voltage (Vtop) 67
Preshoot 68
Overshoot 69
Peak-to-Peak Voltage (Vpp) 69
Minimum Voltage (Vmin) 70
Maximum Voltage (Vmax) 70
Time of Minimum Voltage (Tmin) 71
Time of Maximum Voltage (Tmax) 71
Voltage Amplitude (Vamp) 71
Vdcrms (Root Mean Square Voltage, DC) 71
About the Measurements 72
Increasing the Accuracy of Your Measurements 74
Using Markers 75
About Automatic Time Markers 76
Differences from a Standard Digitizing Oscilloscope 77
Using Waveform Memories 78
Loading and Saving Oscilloscope Configurations 79
When Something Goes Wrong 80
Error Messages 80
Calibration Problems 80
Triggering Problems 80
Other Problems 81
7
Contents
Specifications and Characteristics 85
What is a Specification 89
What is a Characteristic 89
What is a Calibration Procedure 90
What is a Function Test 90
Help - How to Navigate Quickly 91
Run/Group Run Function 92
Setting a tool for independent or Group Run 93
Setting Single or Repetitive Run 94
Checking Run Status 94
Demand Driven Data 95
Glossary
Index
8
1
HP 16533/34A Digitizing Oscilloscope
9
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Calibrating the Oscilloscope
Calibrating the Oscilloscope
The oscilloscope requires a full operational accuracy calibration by you
or a service department whenever
• it has been 6 months or 1,000 hours of use since last full calibration.
• the ambient temperature changes more than 10 degrees C from the
temperature at the time of the last full calibration.
• the frame configuration changes.
• you need to optimize measurement accuracy.
You will get more accurate measurements from the oscilloscope if you
perform the operational accuracy calibration at least once a year.
NOTE: Channel skew calibration requires a multi-board oscilloscope. The procedure
cannot be performed on single-board (2-channel) oscilloscopes.
To calibrate the oscilloscope
This is also covered in the Logic Analysis System Installation Guide.
Since this procedure requires you to turn off the system, print this
information if you do not have access to the Installation Guide.
1. If your oscilloscope has more than two channels, disconnect the short
cables on the back of the module that connect the boards.
2. Unprotect the memory.
a. Turn off the HP 16600A or HP 16700A frame.
b. Take the oscilloscope module out of the frame. See the Logic Analysis
System Installation Guide.
c. Set the PROTECT/UNPROTECT switch to UNPROTECT.
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Calibrating the Oscilloscope
d. Put the oscilloscope back in the frame.
3. Turn on the HP 16600A or HP 16700A and wait for it to finish booting.
You will get a more accurate calibration if you warm up the system for 30
minutes before calibrating the oscilloscope.
4. Select the oscilloscope icon with the right mouse button, and drag the
cursor to Calibration...
5. Select the procedure ADC through Logic Trigger.
The calibration software will tell you what cables need to be attached.
6. Click Run.
7. Select the procedure Ext Trig Skew and connect the cables as directed.
8. Click Run.
9. Optional - Calibrate the oscilloscope as a multi-board module.
a. Perform the ADC through Logic Trigger and Ext Trig Skew calibrations
on each oscilloscope board first.
b. Click Exit in the system window.
c. Connect the oscilloscopes together with the short board interconnect
cables. Connect the first board’s TRIG OUT to the next board’s TRIG IN
until all boards are connected.
d. Start a session.
e. Select the oscilloscope icon with the right mouse button, and drag the
cursor to Calibration.
f. Select the procedure Channel Skew and connect the cables as
directed.
10. After you have finished calibrating, protect the memory. Follow the steps
given above for unprotecting, setting the switch to PROTECT instead.
See Also Logic Analysis System Installation Guide
“Calibration Reference” on page 12
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Calibrating the Oscilloscope
Calibration Reference
ADC
The ADC calibration procedure produces a linearization table which is
applied to the data out of the analog-to-digital converters (ADC) to
undo the effects of a non-linear, analog-to-digital conversion.
Gain
The Gain calibration procedure measures the actual attenuation of the
attenuators and measures the actual gain of the preamps.
Offset
The Offset calibration procedure determines the actual offset value
that places a null signal in center screen.
Hysteresis
The Hysteresis calibration procedure determines the hardware setting
which is closest to achieving a hysteresis of 0.28 screen divisions.
Trigger Level
The Trigger Level calibration procedure determines the actual trigger
level values for all possible voltage levels across the screen.
Trigger Delay
The Trigger Delay calibration procedure determines a time delay which
correctly lines up the point at which a trace crosses the trigger level
with the trigger time.
Logic Trigger
The Logic Trigger calibration procedure determines settings which
affect the accuracy of duration trigger measurements.
Ext Trig Skew
The Ext Trig Skew calibration procedure lines up the external trigger
edge with the trigger time when triggering on the external channel.
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Calibrating the Oscilloscope
Channel Skew
The Channel Skew calibration procedure is only available for multiboard oscilloscope modules. It deskews the trigger channel and data
channels which are on different boards.
13
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
Probing
The probes covered in the topics below are 1:1 Passive Probes, Active
Probes, Current Probes, Compensated Passive Divider Probes,
Differential Probes, and Resistive Divider Probes.
•“Table of Compatible Probes” on page 14
•“Selecting the Proper Probe” on page 15
•“Compensating the Compensated Passive Divider Probe” on page 18
•“Probe Loading” on page 19
•“Descriptions of Probe Types” on page 23
•“Surface Mount Probing” on page 30
Table of Compatible Probes
* Most frequently used
Model Probe Type Band- Input Div Input R
Input C
Numbers width Z ratio
COMPENSATED DIVIDER
HP 10441A Compensated 500 1 Mohm 10:1 1 Mohm
9 pF
*HP 1160A Compensated 500 1 Mohm 10:1 10 Mohm
9 pF
Passive Divider MHz
HP 1161A Compensated 500 1 Mohm 10:1 10 Mohm
10 pF
Passive Divider MHz
HP 1162A High Impedance 25 1 Mohm 1:1 1 Mohm
50 pF +
Passive MHz
scope C
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
RESISTIVE DIVIDER
HP 1163A Resistive 1.5 50 ohm 10:1 500 ohm
1.5 pF
Divider GHz
HP 54006A Resistive 6 50 ohm 10:1 500 ohm
0.25 pF
Divider GHz 20:1 or 1Kohm
ACTIVE
*HP 1144A Active 800 50 ohm 10:1 1 Mohm
2 pF
MHz
*HP 1145A Dual Channel 750 50 ohm 10:1 1 Mohm
2 pF
Small Geometry MHz
Active
HP 1141A Differential 200 50 ohm 1:1 1 Mohm
7 pF
MHz 10:1 9 Mohm
3.5 pF
100:1 10 Mohm
2.0 pF
HP 54701A Active 2.5 50 ohm 10:1 100 Kohm
0.6 pF
GHz
CURRENT
HP 1146A Current 100 1 Mohm n/a n/a
n/a
kHz
See Also “Descriptions of Probe Types” on page 23
“Channel Setup Window” on page 34 for setting input impedance and
coupling
Selecting the Proper Probe
Use the flowchart below for selecting the proper type of probe. A
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
comparison of features, tradeoffs, and applications of the probes are
available after the flowchart.
1:1 Passive Probe
Features
Tradeoffs High capacitive loading and low bandwidth.
Applications Measuring small, low-bandwidth waveforms when no
No attenuation of waveform.
attenuation can be tolerated such as power supply ripple.
Active Probe
Features
Best overall combination of low resistive and capacitive
loading. High bandwidth.
Tradeoffs Higher cost, limited dynamic range, requires power.
Applications ECL, CMOS, GaAs probing, analog circuit probing,
transmission line probing, source resistance Š10 kohm, op amp
probing, most accurate for general measurements of circuits of
unknown impedance.
Compensated Passive Divider Probe
Features
Very low resistive loading, accurate amplitude measurements,
16
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
large dynamic range, and low cost.
Tradeoffs Capacitive loading <10 pF, lower bandwidth than active or
50-ohm resistive divider probes.
Applications General purpose probing, probing high-impedance nodes
(Š10 Kohm), op amp probing, CMOS probing (if bandwidth is
adequate), TTL probing (if bandwidth is adequate)
Current Probe
Features
Measures both ac and dc currents on a scope, with minimal
circuit loading.
Tradeoffs Large size.
Applications Power measurements, automotive measurements,
industrial measurements, motors, dynamoes, and alternators.
Differential Probe
Features
High common mode rejection ratio, easy viewing of small
waveforms with large dc offsets, more accurate than subtracting one
channel from another.
Tradeoffs Bigger than a passive probe, high cost, requires power, and
lower bandwidth than other probes.
Applications Measuring waveforms not referenced to the scope ground,
troubleshooting power supplies, and differential amplifier probing.
Resistive Divider Probe
Features
Highest bandwidth, lowest capacitive load, lower cost than
active probes, flat pulse response, good timing measurement accuracy.
Tradeoffs Relatively heavy resistive loading.
Applications ECL probing, GaAs probing, and transmission line probing.
See Also “Descriptions of Probe Types” on page 23
“Table of Compatible Probes” on page 14
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
Compensating the Compensated Passive Divider Probe
Before you can have a flat frequency response when using a
Compensated Passive Divider Probe, the probe’s cable capacitance and
scope input capacitance must be compensated. One of the
compensating capacitors in the probe is adjustable so you can optimize
the step response for flatness.
1. Connect the probe to the BNC Output, labeled AC/DC CAL, on the back of
the oscilloscope.
2. Connect the probe ground lead to ground.
3. Click the oscilloscope icon and select Calibration...
4. At the bottom of the calibration window, set BNC Output to Probe Comp
and close the window.
5. Click the oscilloscope icon and select Setup/Display...
6. Click Autoscale.
7. You should see a waveform similar to one of the following.
8. If necessary, adjust the probe’s compensating capacitor. Set the scope to
keep running by right-clicking Run, selecting repetitive, then clicking
Run.
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
Probe Loading
There are two major factors influencing probe selection: the load the
probe imposes on your circuit and the required bandwidth of your
circuit with the probe. This is discussed in three sections, below.
Probe Resistance and Capacitance Characteristics (see page 19)
Probe Ground Lead Characteristics (see page 20)
Understanding System Bandwidth at the Probe Tip (see page 21)
Probe Resistance and
Capacitance
Characteristics
The probe load has both resistive and capacitive components. In
addition, the inductance in the probe ground lead causes ringing.
The probe resistance to ground forms a voltage divider network with
the source resistance of your circuit. This reduces the waveform
amplitude and the dc offset. For example, if the probe’s resistance is 9
times the Thevenin equivalent resistance of your circuit, the waveform
amplitude is reduced by about 10 percent. Therefore, if your waveform
has a +5 V to 0.8 V range, the scope probe system shows a 4.5 V to 0.72
V range.
NOTE: At high frequencies, the probe reactance dominates the resistance.
The probe capacitive loading (Cin) to ground forms an RC circuit with
the resistance of your circuit (R
the probe and scope (R
). The time constant of this RC circuit slows
in
) and the resistance looking into
source
the rise time of any transitions, increases the slew rate, and introduces
delay in the actual transition time. The approximate rise time of a
simple RC circuit is:
t
R
RC
Tot al
= 2.2R
= [RinR
Tot alCin
source
where
]/[Rin + R
source
]
Thus, for circuit resistance of 100 ohm, a scope probe system
resistance of 1 Mohm, and a probe capacitance of 8 pF, the real rise
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
time due to probe loading is:
= [1 Mohm (100 ohm)]/[1 Mohm + 100 ohm], approximately 100
R
Tot al
ohm.
= 2.2(100 ohm)(8 pF), approximately 1.8 ns.
t
RC
Therefore, the rise time of your circuit cannot be faster than
approximately 1.8 ns, even though it might be faster without the probe.
If the output of the circuit under test is current-limited (as is often the
case for CMOS), the slew rate is limited by the relationship dV/dT = I/C.
Perhaps you have connected a scope to a circuit for troubleshooting
only to have the circuit operate correctly after connecting the probe.
The capacitive loading of the probe can attenuate a glitch, reduce
ringing or overshoot of your waveform, or slow an edge just enough
that a setup or hold time violation no longer occurs.
Probe Ground Lead
Characteristics
NOTE: If you print this page, subscripts and superscripts appear on the main line of
text. If a number seems to be in an odd place in the printed copy, it is probably
a superscript.
The inductance of the probe’s ground lead forms an LC circuit with the
probe’s capacitance and the output capacitance of the circuit under
test, including any parasitic capacitance of PC board traces, and so on.
The ringing frequency (F) of this circuit is:
20
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
Understanding
System Bandwidth at
the Probe Tip
F = (2 (3.14) (LC)
1/2)-1
If the rise time of the waveform is sufficient to stimulate this ringing,
the ringing can appear as part of your captured waveform. To calculate
the ringing frequency, you can assume that the probe’s ground lead has
an inductance of approximately 25 nH per inch. So, a probe with a
capacitance of 8 pF and a 4-inch ground lead has a ringing frequency of
approximately:
1/2)-1
F = (2 (3.14) [(25 nH) (4 inches) (8 pF)]
= 178 MHz
The 178 MHz does not include your circuit capacitance. Therefore, a
waveform with a rise time of less than 1.9 ns can stimulate ringing.
= 0.35/178 MHz = 1.9 ns
t
rise
To minimize the ringing effect, you should use a probe ground lead that
is as short as possible. Some probes add a ferrite bead to the ground
lead to reduce ringing. However, adding the ferrite bead also increases
the ground impedance which reduces the common mode rejection of
the probe.
System bandwidth is the bandwidth of the scope probe system. System
bandwidth affects measurements because the probe becomes part of
the circuit being measured. The rise time that is measured depends on
the actual rise time, the rise time of the scope probe system, and the
rise time of the RC circuit formed by the source resistance and the
scope probe system resistance and capacitance.
t
meas
= [t
act
2
+ t
RC
2
+ t
sys
2
1/2
]
where
= the measured rise time.
t
meas
= the actual rise time of the waveform being measured.
t
act
= the rise time of the RC circuit formed by the source resistance
t
RC
and the scope probe system resistance and capacitance.
= the rise time of the scope probe system.
t
sys
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
NOTE: Often the bandwidth of the scope probe system is specified. The rise time is
calculated using the following equation.
= 0.35/SystemBW
t
sys
If the rise time of the scope probe system is not specified, it can be calculated
using the following formula.
probe
2
+ t
= [t
t
sys
scope
1/2
2
]
For example, if the scope probe system rise time is 600 ps, the probe
loading rise time (t
) is 600 ps, and the waveform has a 1-ns rise time,
RC
then the measured rise time is:
= [(1 ns)2 + (600 ps)2 + (600 ps)2]
t
meas
1/2
= 1.3 ns
The answer is in error by 30%.
However, if the scope probe system rise time is 190 ps, the probe
loading rise time is 190 ps, and the waveform has a 1-ns rise time, then
the measured rise time is:
= [(1 ns)2 + (190 ps)2 + (190 ps)2]
t
meas
1/2
= 1.03 ns
Now the error is only 3%.
You may find it useful to memorize three system bandwidth rules:
1. The combined rise time of the scope probe system and the probe loading
should be less than 1/3 of the rise time of the waveform you are measuring
to keep errors below 5%, and less than 1/7 of the rise time of the waveform
you are measuring to keep errors below 1%.
2. Rise time and bandwidth are related by the following approximations: rise
time = 0.35/bandwidth and bandwidth = 0.35/rise time.
3. Rise times add approximately as the square root of the sum of the squares
(for systems with minimal peaking).
NOTE: Because every scope probe has a different loading effect on your circuit, you
should use the equation given for the type of scope probe you are using.
See Also “Descriptions of Probe Types” on page 23
22
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
Descriptions of Probe Types
For each of the probe types listed below, the description gives a
summary of features and tradeoffs and a short text description. Most of
the probe types also give a sample rise time calculation.
•“1:1 Passive Probes” on page 23
•“Active Probes” on page 24
•“Compensated Passive Divider Probes” on page 26
•“Current Probes” on page 27
•“Differential Probes” on page 28
•“Resistive Divider Probes” on page 28
1:1 Passive Probes
Example Rise Time
Calculation
Features No attenuation of waveform.
Tradeoffs High capacitive loading and low bandwidth.
Applications Measuring small, low-bandwidth waveforms when no
attenuation can be tolerated such as power supply ripple.
The 1:1 passive probes provide a way to connect the input impedance
of the scope directly to your circuit with minimum attenuation due to
the resistive loading of the probe. However, 1:1 probes do have very
high capacitive loading which is much larger than that of the scope.
There are two types of 1:1 passive probes. One type is designed to work
with the scope’s input set to high impedance (1 Mohm) and uses a
lossy cable to keep the probe from ringing. The other type is designed
to work with the scope’s input set to low impedance (50 ohm) and uses
a 50-ohm coaxial cable.
Given the following circuit using the HP 1162A probe,
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
the input resistance is:
= R
R
in
= 1 Mohm
scope
The total resisitance is:
= (RinR
R
Tot al
= 1 Mohm(50 ohm)/(1 Mohm + 50 ohm) = 50 ohm
R
Tot al
source
)/(Rin + R
source
)
From the Table of Compatible Probes, the probe capacitance is 50 pF.
Therefore, the capacitive load is:
= C
C
in
probe
+ C
= 50 pF + 7 pF = 57 pF
scope
The rise time due to circuit loading is:
= 2.2R
t
RC
Tot alCin
tRC = 2.2(50 ohm)(57 pF) = 6.2 ns
From the Table of Compatible Probes, the scope probe system has a
bandwidth of 25 MHz. Therefore, the rise time of the scope probe
system is: t
= 0.35/25 MHz = 14 ns
t
Sys
The measured rise time is: t
2
ns)
+ (6.2 ns)2 + (14 ns)2]
= 0.35/SystemBW
Sys
= [t
meas
1/2
= 140.8 ns
act
2
+ t
RC
2
+ t
sys
2
1/2
]
t
= [(140
meas
Active Probes
Features Best overall combination of low resistive and capacitive
loading. High bandwidth.
Tradeoffs Higher cost, limited dynamic range, requires power.
Applications ECL, CMOS, GaAs probing, analog circuit probing,
transmission line probing, source resistance Š10 kohm, op amp
probing, most accurate for general measurements of circuits of
24
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
unknown impedance.
An active probe has a buffer amplifier at the probe tip. This buffer
amplifier drives a 50-ohm cable terminated in 50 ohms at the scope
input. Active probes offer the best overall combination of resistive
loading, capacitive loading, and bandwidth.
Example Rise Time
Calculation
Given the following circuit using the HP 1152A probe,
the input resistance is:
R
= 100 kohm. The total input resistance is:
in
= (RinR
R
Tot al
= 100 ohm(50 ohm)/(100 ohm + 50 ohm) = 50 ohm
R
Tot al
source
)/(Rin + R
source
)
The rise time due to circuit loading is:
= 2.2R
t
RC
Tot alCtip
tRC = 2.2(50 ohm)(0.6 pF) = 66 ps
Because the rise time of the scope probe system is not given in the
Table of Compatible Probes, we will have to calculate it using the
bandwidth of the probe (2.5 GHz) and the bandwidth of the scope (500
MHz). Therefore, the rise time of the scope probe system is:
= 0.35/ProbeBW = 0.35/2.5 GHz = 140 ps
t
probe
= 0.35/ScopeBW = 0.35/500 MHz = 700 ps
t
scope
t
= [t
sys
t
= [(140 ps)2 + (700 ps)2]
sys
probe
2
+ t
scope
2
1/2
]
1/2
= 714 ps
The measured rise time is:
25
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
t
meas
= [t
act
2
+ t
RC
2
+ t
sys
2
1/2
]
t
= [(2 ns)2 + (66 ps)2 + (714 ps)2]
meas
1/2
= 2.12 ns
Compensated Passive Divider Probes
Features Very low resistive loading, accurate amplitude measurements,
large dynamic range, and low cost.
Tradeoffs Capacitive loading <10 pF, lower bandwidth than active or
50-ohm resistive divider probes.
Applications General purpose probing, probing high-impedance nodes
(Š10 Kohm), op amp probing, CMOS probing (if bandwidth is
adequate), TTL probing (if bandwidth is adequate).
The compensated passive divider probe is the most common type of
scope probe. The 9-Mohm resistor in the tip forms a 10:1 voltage
divider with the 1-Mohm input resistance of the scope.
To have a flat frequency response, the probe tip capacitance is
compensated by the probe's cable capacitance, a compensating
capacitor, and the scope input capacitance. The compensating
capacitor is adjustable so you can optimize the step response for
flatness.
Example Rise Time
Calculation
Not all 9-Mohm divider probes work with all 1-Mohm scope inputs. The
probe data sheet shows the range of scope input capacitance it can
accommodate. You must make sure that the input capacitance of the
scope is within that range.
Given the following circuit using an HP 1160A probe,
26
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
the input resistance is:
= R
R
in
= 9 Mohm + 1 Mohm = 10 Mohm
R
in
probe
+ R
scope
The capacitive load is:
= C
C
in
[C
probe+Ccable+Ccomp+Cscope
tip
+ {[C
probe(Ccable+Ccomp+Cscope
]}
)]/
This number is calculated for the scope and scope probe combination,
and is shown in the Table of Compatible Probes.
The total resistance is: R
= 10 Mohm(50ohm)/(10 Mohm + 50ohm) = 50 ohm
R
Tot al
Total
= (RinR
The rise time due to circuit loading is: t
source
RC
)/(Rin + R
= 2.2R
TotalCin
source
)
tRC = 2.2(50 ohm)(7.5 pF) = 825 ps
From the Table of Compatible Probes, the bandwidth of the scope
probe system is 500 MHz. Therefore, the rise time of the scope probe
system is:
= 0.35/SystemBW
t
sys
= 0.35/500 MHz = 700 ps
t
sys
The measured rise time is:
= [(t
t
meas
t
= [(2 ns)2 + (825 ps)2 + (700 ps)2]
meas
)2 + (tRC)2 + (t
act
sys
)2]
1/2
1/2
= 2.27 ns
Remember that probe input impedance for compensated passive
divider probes is complex. A simple RC network serves only as a firstorder approximation.
Current Probes
Features Measures both ac and dc currents on a scope, with minimal
circuit loading.
Tradeoffs Large size.
Applications Power measurements, automotive measurements,
industrial measurements, motors, dynamoes, and alternators.
Scopes are designed to measure voltage, but by using a current probe
27
Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
you can measure current. A current probe measures current in a wire
by enclosing the wire. Therefore, no electrical connection is needed.
Current probes generally use one of two technologies. The simplest
uses the principle of a transformer, with one winding of the
transformer being the measured wire. Because transformers only work
with alternating voltages and currents, current probes of this type
cannot measure direct current.
The other type of current probe uses the Hall effect principle. The Hall
effect produces an electric field in response to an applied magnetic
field. While this technique requires a power supply, it measures both
alternating and direct current.
Differential Probes
Features High common mode rejection ratio, easy viewing of small
waveforms with large dc offsets, more accurate than subtracting one
channel from another.
Tradeoffs Bigger than a passive probe, high cost, requires power, and
lower bandwidth than other probes.
Applications Measuring waveforms not referenced to the scope ground,
troubleshooting power supplies, and differential amplifier probing.
A differential probe is a high-impedance differential amplifier with two
probe tips; a non-inverting input and an inverting input. These two
inputs feed a differential amplifier which in turn drives the 50-ohm
input of the scope. The main advantage of differential probes is their
ability to reject waveforms that are common to both inputs. This type
of probe is often used in floating ground applications.
You could duplicate a differential probe by using two passive probes
and subtracting the two scope channels. However, the electrical paths
of the differential probe are carefully matched to give a high common
mode rejection ratio (CMRR). The higher the CMRR, the smaller the
waveforms you can view in the presence of unwanted noise.
Resistive Divider Probes
Features Highest bandwidth, lowest capacitive load, lower cost than
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
active probes, flat pulse response, good timing measurement accuracy.
Tradeoffs Relatively heavy resistive loading.
Applications ECL probing, GaAs probing, and transmission line
probing.
Resistive divider probes are designed for scopes with a 50-ohm input
impedance. The probe tips of the HP 1163A or HP 54006A have either
a 450-ohm or 950-ohm series resistor. The probe cable is a 50-ohm
transmission line. Because the cable is terminated in 50 ohms at the
scope input, it looks like a purely resistive 50-ohm load when viewed
from the probe tip. Therefore, the resistive divider probe is flat over a
wide range of frequencies, limited primarily by the parasitic
capacitance and inductance of the 450-ohm or 950-ohm resistor and
the fixture that holds it. The resistive load of the probe to your circuit
is either 500 ohm or 1 kohm, depending on the probe.
This type of probe has the smallest capacitive load of any probe. The
small capacitance and wide bandwidth make this probe type a good
choice for wide bandwidth measurements or time-critical
measurements.
Example Rise Time
Calculation
Given the following circuit using the HP 1163A probe,
the input resistance is:
R
= R
in
R
in
+ R
tip
= 450 ohm + 50 ohm = 500 ohm
scope
The total resistance is:
R
Tot al
= (RinR
source
)/(Rin + R
source
)
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Chapter 1: HP 16533/34A Digitizing Oscilloscope
Probing
R
= 500 ohm(50ohm)/(500 ohm + 50ohm) = 45 ohm
Tot al
The rise time due to circuit loading is:
= 2.2R
t
RC
Tot alCtip
tRC = 2.2(45 ohm)(1.5 pF) = 165 ps
From the Table of Compatible Probes, the bandwidth of the scope
probe system is 1.5 GHz. Therefore, the rise time of the scope probe
system is:
= 0.35/SystemBW
t
sys
= 0.35/1.5 GHz = 230 ps
t
sys
The measured rise time is:
= [(t
t
meas
t
= [(2 ns)2 + (165 ps)2 + (230 ps)2]
meas
)2 + (tRC)2 + (t
act
sys
)2]
1/2
1/2
= 2.02 ns
Surface Mount Probing
The HP 10467A 0.5 mm MicroGrabber Accessory Kit is designed for
using the HP 116x family of probes when you are probing fine-pitch
(0.5 mm to 0.8 mm) SMT (Surface Mount Technology) devices. The kit
contains enough parts for two probes.
The HP 116x probe tip plugs into the single-lead end of the dual-lead
adapter. The MicroGrabber connects to the red lead. You can also use a
MicroGrabber on the black lead, which you should connect to your
circuit’s ground. You can also connect the dual-lead end to circuit pins
that are 0.635 mm (0.025 inch) in diameter.
The kit is intended for use with voltages no greater than ±40 V (dc and
ac peak).
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