81110A Pulse Pattern Generator
81110A Pulse Pattern Generator
Simulating Distorted Signals
for Tolerance Testing
Application Note
Introduction
Industry sectors including computer and components, aerospace defense and education all require precise one or two channel signal sources. In
typical measurement setups, the Agilent
Technologies Pulse Pattern Generators are often
used as reference clocks, system trigger or simply
as data stimulus for transceiver tests. The analyzing is covered by Mixed-Signal Oscilloscopes
(MSO), Digital-Signal Oscilloscopes (DSO) or Logic
Analyzers.
The essential features for measurement equipment
to create the correct test conditions are two output channels, with channel adding, programmable
patterns, and adjustable delays and transitions.
The Agilent Technologies 81104A (80 MHz) and
81110A Pulse Pattern Generators meet all of
these conditions, with the 81110A having the
further flexibility of either Agilent Technologies
81111A (165 MHz) or 81112A (330 MHz) Output
Channels.
Noise, jitter, crosstalk and reflections can cause
distortions so valid clocks are not seen, spikes
are mistaken for valid clocks or data is misinterpreted. Such effects cause system failures and
must be minimized in the design to ensure accurate and reliable operation. Therefore, devices
need to be stressed with these kinds of distortion during design, validation and production.
This application note describes how to use the
81110A
• To create distorted signals
• To inject noise for full stress testing of devices
Figure 1: The setup of an Agilent Pulse Generator and an Agilent Infiniium oscilloscope
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
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Producing Distorted Signals
Principle of distorted signals
As shown in Figure 2, perfect data or clock
signals are defined by their rising and falling
edges, the width and the delay of the pulse. The
width and delay are defined at the 50 % points
of the edges. An ideal pulse pattern generator
lets the user define each of these parameters
individually.
Figure 3: Distorted signal composed from two independent
patterns
Figure 2: Perfect and distorted signal with clean rising and falling
edges
A distorted signal has either positive or negative
spikes added to the perfect signal at a specific
place. With the 81110A it is possible to create
such distorted signals by adding two pulse
signals. The first one is a perfect pulse, the
second reflects the distortion. This is why it is
necessary to have a pulse pattern generator with
two channels that can be added together. Also,
the pattern needs to be programmable and the
delay and transition of the rising and falling
edges need to be adjustable.
In Figure 3, we show how to define and combine the signals from each channel. The first channel has the perfect signal, including the logic patterns. On the second output channel, we define
the spikes. These can be either positive or negative. Adding the two (that is the perfect signal
and one of the spikes) we get the distorted signal.
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
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Setting Up the Pulse Pattern Generator
Figure 1 shows the setup used for the following
measurements. In this section we show the four
easy steps to set up the pulse pattern generator.
This is, defining the pattern mode, entering the
pattern, defining the pulse timing and finally, setting the signal levels. You can enter the parameters using either the front panel or SCPI programming.
Step Two:
2.1
Press PATTERN, and then set up the
following pattern for each channel.
Step One:
1.1
Reset the instrument by selecting
RECALL+0 (SHIFT, STORE+0).
1.2
Press MODE/TRG, and then select the
PATTERN mode.
Step Two (a): Parameters set in the PATTERN menu
2.2
Step One: Parameters set in the MODE/ TRG menu
Press PATTERN again and the pulse pattern generator shows the waveform for
each channel.
Step Two (b): The signal pattern
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
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Step Three:
Step Four:
3.1
3.2
Finally, define the voltage levels.
3.3
Press TIMING.
Set up the perfect signal with rising and
falling edges of 5 ns, a pulse width of
20 ns and a frequency of 30 MHz.
Set up the spike with rising and falling
edges of 2 ns, a pulse width of 5 ns.
For a negative spike, set a delay of 8 ns.
For a positive spike, set a delay of 25 ns.
4.1
4.2
4.3
4.4
Step Three: Parameters set in the TIMING menu
for the perfect signal and a negative spike
Press LEVELS.
Set up the perfect signal for a high level
of 2.5 V.
For a negative spike, set the high level to
0 V and the low level to - 800 mV. Select
COMPLEMENT mode.
For a positive spike, set the high level to
1 V and the low level to 0 V. Select
NORAMAL mode.
Finally, select that channel 2 (with the
spike) is added at output 1.
Step Four: Parameters set in the LEVELS menu for the perfect signal and a negative spike
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
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Examining the Output Signal
Injecting Noise
The two following screen shots (made with an
Agilent oscilloscope) show the resulting distorted
signal.
Devices can and need to be stressed in different
ways by applying distorted signals, jitter or noise.
For low speed applications, analyzing the behavior
under common mode or differential noise conditions is the second important test. Common mode
noise means the same noise signal is on both the
data and the data complement line. Differential
(also known as cross-talk) noise means the noise
is on one data line only.
The pulse width of the positive spike is long
when compared with the negative spike. Varying
the delay, moves the spike forwards and backwards. If the delay of the positive spike is reduced, the spike merges with the perfect signal
and creates a "multilevel signal".
Noise is added as AM (amplitude modulation) to
the data sequence. Using a function generator this
noise can be sinusoidal, rectangular or random.
For the high-speed data, the AM is achieved by
connecting to the terminating resistors. By applying the modulating signal to the far side of the
terminating resistors, normally the ground, this
signal is added to the data sequence at the receiver (RX) input.
Figure 6 shows the set up for noise injection. The
pattern generator provides the data sequence on
the differential lines. A power divider is included
into both signal lines to add the modulation
signal. This must be done in a way that keeps the
electrical length of both data lines, between generator output and receiver input, the same.
Figure 4: Distorted signal with a negative spike
Please Note: Though the timing system of the
81110A has a frequency up to 330 MHz, the
81111A output channel has a maximum frequency of 165 MHz. If you set the frequency of an
81111A channel to 330 MHz, you will receive a
warning. This over-programming is not critical,
but means the specifications are no longer guaranteed.
For the measurement, we connect an oscilloscope
(as shown in Figure 1.0) instead of the device
under test (DUT) in Figure 6. Configure one output channel of the pulse pattern generator
(81110A) (either an 81111A, 165 MHz channel or
an 330 MHz 81110A channel) is enough. To stress
the DUT with noise, the pulse pattern generator
creates a simple pattern - for channel 1 and the
strobe, as shown in steps 1 to 3 above.
The power dividers use three resistors to ensure
proper termination in each direction, though this
means an amplitude loss of 50 % through the
divider. For a specific swing, we need to double
the amplitude on the pattern generator.
Figure 5: Distorted signal with a positive spike
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
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Figure 6: Test setup for noise testing with an 81110A/11A and
Agilent Technologies 33250A Function Generator
For common mode noise we need to modulate
both data lines with the same signal. Therefore
we also need a power divider to split the noise
from the function generator. This will provide the
noise signal on both data lines with clean isolation of the data and data complement lines. To
compensate for the modulation signals passing
through two power dividers, the amplitude of the
function generator must be set to 4-times the
desired noise floor at the receiver input.
Figure 7 shows the principal influence of common
mode noise on a signal. The injected noise causes a voltage range on the high and low levels of
the signal. Jitter, on the other hand, would result
in increasing the width of the rising and falling
edges. For differential noise, we only need to connect the modulation signal to one of the power
dividers in the data path. In this case, it is
important to terminate both open ends. Some
function generators may not have a good backwards termination, so it may be helpful to add a
3dB attenuator between the function generator
and the power divider. This improves backwards
termination significantly.
Figure 7: Influence of noise on the eye diagram
81110A Pulse Pattern Generator Simulating Distorted Signals for Tolerance Testing Application Note
Page 7
Related Literature
Pulse Pattern and Data Generators
Digital Stimulus Solutions, Brochure
Publication Number www.agilent.com
5980-0489EN
81100 Family of Pulse Pattern Generators
Technical Specifications
5980-1215E
81100 Family of Pulse Pattern Generators
Radar Distance Test to Airborne Planes
Product Note 1
5968-5843E
81100 Family of Pulse Pattern Generators
The Dual Clock Gbit Chip Test
Product Note 2
5968-5844E
81100 Family of Pulse Pattern Generators
Magneto-Optical Disk Drive Research
Product Note 3
5968-5845E
Infiniium 54850 Series Oscilloscopes
Data sheet
5988-7976E
Signal Integrity Solutions
Brochure
5988-5405EN
Function/Arbitrary Waveform Generator
Data Sheet
5968-8807EN
www.agilent.com/find/81100family_81110a
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© Agilent Technologies, Inc. 2006
Printed in USA, 1 June, 2006
5989-4709EN
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