TEST &


TEST & MEASUREMENT


NT


FEA


FEAT REATURE


TROUBLESHOOTING SPORADIC SIGNAL Ro


Philip Weige thatare


ilipp Weig ll,pro that are leading to faster identification of sporadi errors usi g osci releadingtofaster identifica


gell, product m fa


ct T oscilloscopes–challenge


in identifying sporadic errors using ges that can cost


est engineers face considera ra


valuable time during the development of new products.Debugging protocol-based buses or other pulsed signals is especially difficult and time-consuming because the pauseswithin these busses between individual data packets can be very long. Serial triggering and decoding options, togetherwith the history and segmentedmemory options, provide maj


ke ry ro


The issues are exemplified b ajor analysis advantages.


transmits a protocol packe y a sensor that


over the I2C bus every 10ms for a duration of 400µs. Errors that occur during this time are to be analysed and normally an oscilloscope would be used for debugging the I2C interf


re rface.Unfort


this class have only a very and this limits the record leng


DISADVAN AG ACQU SI ION


rtunately,most oscilloscopes in ry limi


th for analysing tedmemory,


errors and their history to a fewmilliseconds. DISA VANTAGES OF SINGLE-S OT


SADVA TAGES OF SINGLE-SHOT CQUISII TION


Normally, the user acquires long recordings in two steps. The first step is to select a sufficiently long timebase, 20ms/div for example,which in the example (right) corre


rd responds to 19pro rotocol packets fromthe


overwritten by the next trigge This pro


make the analysis of sporadic


sensor under test. The second step is to trigger a single-shot acquisition in order to prevent the acquire rw


red signal fro ge


rocess has two key dis rombeing


advantage r event.


rcentage of irrelevant ro


errors especially ges that


difficult for pulsed signalswith steep edges. Firstly, the large perc


ge


inactivitymeans that only a fewof the protocol packets of intere othermaj


ajor disadvantage


limited sampling ra memory


maximumrecord protocol packe ro rate.With 2Msample


ry and 2Gsample/s sampling rate, the rd length is only one


millisecond,which is just enough for one ket fromthe sensor under test.


The next packetwould bemissed because


desired 200ms - 20ms/div fo of the 10ms communications


require 10Msample/s. This is too low ror s. vercoming these re ro


r 10divisions - pause. The


res lowering the sampling rate to oweven for stable


decoding of the I2C signal, let alone finding signal integrity erro Ove


with deepmemory Figure 3:


requires an oscilloscope ry, such as that offered by


newinstruments like the RTM2000bench oscilloscope fromRohde&Schw rzarz.With a 20Msamplememory, sampling rate in this example can be increased to 100Msample/s, permitting seamless recording and analysis of


/ ELECTRONICS ELECTRONICS


Decoded I²C signal with analogue waveforms and acquisition table. The history function is accessed via the bottom menu


rest are acquired. The ge arises fromthe


Figure 2: Providing time, frequency, protocol and logic analysis plus a digital voltmeter in a single box, the R&S RT


development, production and servicing of embedded hardware


Figure 2: Providing time, frequency, protocol and logic analysis plus a digital voltmeter in a single box, the R&S RTM2000 bench oscilloscope is ideal for the development, production and servicing of embedded hardware


Figure 1: Figure 1:


Examples for acquiring and analysing short-term signals from a sensor


term ng


r


ket containing values ra


rable challenge ges cationof sporaporadicerro tmanager foger foroscilloscope for osc


cilloscopes at Rohde & Schwarz nvest ate rorsusingoscilloscopes


Schwarz inv scopes


cope all 19pro rotocol packets. Thismakes it


possible to analyse signal erro the pro


rors, however


robability of isolating the error is still lowbecause only very fewpackets are recorded.


ke


SEGMENTED ACQU SI ION Asmart


SEGMEN CQUISII TION rter approach is to limit acquisition to


only the data packets. This requires the definition of a dedicated protocol trigger, for example triggering on the start symbol of the I2C bus.Using the scope’s history in combinationwith the segmentedmemory option helps debugging ways. It increases the av


ge


ailablememory for in two significant


analogue and digital channels to


460Msamples and it divides thememory into equally sized segments,which ensure s that availablememory is used optimally. With a serial protocol, for example, the maximumpacket lengt


ry gth in the signal


determines the record length. Starting at the trigge intere


rest is store m ry ge


without activity are not acquired and store for subsequent analysis: the oscilloscope saves the pre at a re


ger point, the signal segment of red inme ory. Time periods re


recise time of the trigger event History ro


accessedlateron usingoscilloscopetool s suchas theQuickMeas function,masktest andprotocoldecoding.Masktest is ideal for findingadev


resolution of 3.2ns. rymodeallow ,


fo eviationinclocksignal fro sensorunder test, fo romthe for example.Thehistory ga ev ry


function’sPlay commandautomatically start acomparisonofall45000segmentsagainst themask.Violationsare


and, if enabled, thetest is stoppedandthe segmentdisplaye


The acquisition table that lists all RTM2000 bench oscilloscope is ideal for the


segments and their timestamps permits fast access to the acquired segments positioned before


re the faulty segment. Thismakes it possible to isolate the effects of preceding signals quickly. Periodicities can be exposed bymeans of a subsequent analysis of the trigge


segments can be save


analysis. Errors detected during standard opera


ration can be viewed fro and history


ger times for all faulty segments.All ved to a PCfor offline rd


romthe history.


Such techniques of segmented acquisition rymode enable the latest


generation of lab oscilloscopes to quickly and easily identify elusive sporadic errors in newdesigns - and gather the information needed to resolve


ro ve them. Rohde & Schwarz www.rohde-schwarz.com


www.rohde-schwarz T: 01252 818888


ELEC ELECTRONICS .com yedwhenamaskis violated. rts restatisticallyevaluated owsall acquisitions tobe vestigates thel test dvances vestigates the latest advances stadv va


TROUBLESHOOTI G SPORADI SIGNALS Rohde&Sc warz


red


| DECEMBER/JANUAR ECEMBER/J


JANUARY 2017


17 17


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