MP1900A בערט סטרעס קאַליבראַציע בעסטע פּראַקטיקעס

PCI Express 6.0 CEM:
BERT Stress Calibration
בעסטער פּראַקטיסיז

טעכניש קורץ

PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

הקדמה

The PCI Express (PCIe) CEM Specification requires testing both transmitters and receivers to ensure that devices comply with the specification. Tektronix  provides automated BERT receiver (RX) stress calibration  and receiver test software for PCIe 6.0 CEM testing.  This software automates the calibration process for a  system composed of a Tektronix DPO70000SX real time  oscilloscope and Anritsu MP1900A Bit Error Rate Tester  (BERT). Features are implemented in TekRXTest Software  publicly available today supporting RX characterization,  debug, pre-compliance and compliance testing per the 6.0  CEM specification.

TekRxTest software offers a wizard-based approach  to intuitively guide users through the complex receiver  calibration process. The process, when done manually, can  easily take two to three days, while with this new solution  calibration can typically be completed in hours.

TekRxTest האט איינגעפירט די פאלגנדע אייגנארטיגע צוגאנגען צו מאכן עס מער עפעקטיוו ווי אנדערע פארהאן טעכניקן:

• Patented Tx EQ calibration shortens the process from several hours on comparable systems to ~30 mins, without compromising accuracy required by the specifications.
• Hardware accelerated FastFrame™ approach shortens the waveform averaging process required in the TP2 calibration process by hours.

דערצו, שטיצט TekRxTest אינטעגרירטע ריסיווער קאליבראציע און טעסטן טעסטן פאר אלע דורות פון די PCI Express סטאנדארט.

הינטערגרונט

PCIe receiver testing specifies the calibration of test signals. During actual operation of a high-speed serial link, numerous impairments will close an eye. PCIe standards  offer a well-defined CEM Test Spec that specifies  combinations of impairments to use for testing. Stressed  eye targets are defined with the full pad-to-pad channel,  with Compliance Base Board (CBB) and Compliance Load  Board (CLB) in the path through the CEM connector. The  BERT PPG acts as a surrogate PCIE transmitter in the  scenario of receiver testing. Once the recipe for the  stressed eye target is determined, one removes the  fixturing that isn’t used in testing — CLB for Add-In-Card  testing, or CBB for System testing. This effectively refunds  the loss budget permitted for the device-under-test (DUT).

Users must perform BERT stress calibration before RX  tests are conducted on a DUT. This BERT calibration  ensures the magnitude of stresses applied to the DUT  RX are in accordance with PCIe 6.0 spec limits. This RX  testing determines RX pass/fail and margin performance.  During BERT stress calibration, the user controls multiple  parameters during the calibration run. Receiver stressed  eye calibration is a complex, iterative process and human  error is a significant risk. As such, manual calibration is  unsustainable for routine testing. This technical brief  discusses those controls and provides recommendations  to maximize the probability of successful calibration  after all steps are complete. Guidance is given on when  different modes should be used, and troubleshooting tips  are provided.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

TekRXTest RX ווייכווארג

TekRXTest is a software framework that supports automated BERT stress calibration for multiple technologies including PCIe 6.0 CEM. פיגורע 1 shows the start screen for TekRXTest, and the RX personalities supported as of May 2025.

More info on TekRXTest is available דאָ.

פיגור 1. אָנהייב פאַרשטעלן פֿאַר TekRXTest און RX פּערזענלעכקייטן.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

בערט דרוק פֿאַר PCI Express 6.0 CEM

BERT stress calibration for PCIe 6.0 RX testing is broken into two parts: short channel (TP3, פיגורע 3) and long channel (TP2,  פיגורע 2). TP3 signal validation is performed first with BERT output signals connected directly through RF coaxial cables to  scope inputs. BERT tests using TP3 connections are pulse width jitter, differential amplitude, AC-DC balance, preset, random  jitter (RJ) and sinusoidal jitter (SJ). 6dB external attenuators should be installed on the front of each oscilloscope ATI channel  to ensure the best combination of voltage range and noise performance. These attenuators are available as part of the  DPO7RFKx connector kits from Tektronix.

פיגור 2. לאנג קאַנאַל BERT סטרעס קאַליבראַציע פֿאַר PCIe 6.0 RX טעסטינג.

פיגור 3. קורץ קאַנאַל BERT דרוק קאַליבראַציע פֿאַר PCIe 6.0 RX טעסטינג.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

Once TP3 calibrations are complete, a differential loss ISI channel is added between the BERT PPG and scope inputs. An  example connection diagram is shown in פיגורע 4. TP2 calibrations are performed including insertion loss (IL) verification,  common-mode interference (CMI) and differential mode interference (DMI), optimal preset and CTLE selection and stressed  eye. Final stressed eye parameters are compared to spec limits to determine successful completion of the BERT calibration.

פיגורע 4. עקסampדי פֿאַרבינדונג דיאַגראַמע וואָס ווײַזט אַ דיפערענציעל-פֿאַרלוסט ISI קאַנאַל צוגעגעבן צווישן די BERT PPG און אָסילאָסקאָפּ אינפּוטס.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

באַניצער קאָנטראָלס בעת BERT קאַליבראַציע

TekRXTest Software prompts the user to specify some settings prior to performing TP3 and TP2 BERT stress calibration.  טיש 1 lists these controls, their description, and how to set these values to complete a successful calibration.

Table 1. List of parameters set during calibration.

Note 1: Versions of Sigtest & SEASIM will be updated when fully tested and recommended by PCI-SIG.

Note 2: Although not required for PCIe 6.0 CEM-RX pass/fail testing, the user may enable JTOL testing with up to 14 SJ separate frequency tones to perform RX  margin testing. These SJ tones must be calibrated during TP3.

באַניצער סעטטינגס:

אָפּטיילונג	פּאַראַמעטער	פעליקייַט	רעקאַמענדיד	הערות
RT פאַרנעם	Positive ch	Ch1	Ch1
RT פאַרנעם	Negative ch	Ch2	Ch2
טעקארקס סערוויס	טיימאַוט	300 סעק	300 סעק
טעקארקס סערוויס	Sigtest   ווערסיע	6.1.10	6.1.10	באַמערקונג 1
טעקארקס סערוויס	Seasim   ווערסיע	2.0.103 f	2.0.103f	באַמערקונג 1
TP3 attenuator  settings	Acquisition  mode	שנעל   ראַם	שנעלע ראַם
TP3 attenuator  settings	דע-ימבעד	פאַרקריפּלט	פאַרקריפּלט
TP3 attenuator  settings	Ch1   אַטטענואַטיאָן	6 דב	6 דב
TP3 attenuator  settings	Ch2   אַטטענואַטיאָן	6 דב	6 דב
TP3   קאַלאַבריישאַנז	Ampליטוד	800 mV	800 mV
TP3   קאַלאַבריישאַנז	RJ	0.25 פּס   RMS	0.25 פּס רמס
TP3   קאַלאַבריישאַנז	SJ @   100 מהז	1.563 ps	1.563 ps
TP3   קאַלאַבריישאַנז	Multi-tone  Calibration	פאַרקריפּלט	באַניצער-דיפיינד	באַמערקונג 3
TP2 attenuator  settings	Acquisition  mode	שנעל   ראַם	שנעלע ראַם
TP2 attenuator  settings	דע-ימבעד	פאַרקריפּלט	פאַרקריפּלט
TP2 attenuator  settings	De-embed  (channel)	פאַרקריפּלט	פאַרקריפּלט
TP2 attenuator  settings	Ch1   אַטטענואַטיאָן	6dB	6dB

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אָפּטיילונג	פּאַראַמעטער	פעליקייַט	רעקאַמענדיד	הערות
TP2 attenuator  settings	Ch2   אַטטענואַטיאָן	6 דב	6 דב
TP2 DMI and   קמי	DMI	15 mV	15 mV
TP2 DMI and   קמי	קמי	75 mV	75 mV
TP2 stressed  eye params	# אקטן	3	3
TP2 stressed  eye params	אויג ברייט   ציל	3.125 פּס	3.125 פּס	System  Host
TP2 stressed  eye params	Eye height  target	6 mV	6 mV	System  Host
TP2 stressed  eye params	DMI מינימום	5 mV	5 mV	System  Host
TP2 stressed  eye params	DMI מאַקס	25 mV	25 mV	System  Host
TP2 stressed  eye params	SJ מין	1 פּס	1 פּס	System  Host
TP2 stressed  eye params	SJ מאַקס	3 פּס	3 פּס	System  Host
TP2 stressed  eye params	Amplitude  min	720 mV	720 mV	System  Host
TP2 stressed  eye params	Amplitude  max	800 mV	800 mV	System  Host
Remote access  – Config	לאקאלע IP   אַדרעס	האָסט פּיסי   IP	האָסט פּיסי IP
Remote access  – Config	צוגעהערט   פּאָרט	4004	4004
Remote access  – Config	טיימאַוט	20 סעק	20 סעק

PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

לאָנטש און לויפן TP3 קאַליבראַציע

When a user starts a short channel calibration, the RX software provides a connection diagram to ensure signals are connected properly from the BERT PPG to the scope inputs. Proper care should be used in making RF connections between cables and components. (Details are not covered in this technical brief). Refer to the High Performance Oscilloscopes Best  Practices Manual און DPO70000SX Quick Start User Manual, and use good lab practices. For assistance making proper  connections, please contact your local Tektronix field application engineer.

פיגור 5. TP3 קאליבראציע קאנעקשאן דיאגראם.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

With RX software launched and “connected” via IP address to scope and BERT, the user may INITIALIZE equipment for TP3  calibration. The RX software will automatically initialize instruments when the user clicks the INITIALIZE EQUIPMENT button  within TP3 calibration test flow. Initialization of the scope and BERT takes less than five minutes. By default, the scope will  perform signal validation during the initialization process. To speed up initialization, the user may select the check-box to  SKIP SIGNAL VALIDATION DURING INITIALIZATION. These controls are shown in פיגורע 6 אונטן.

פיגור 6. TP3 קאליבראציע קאנעקשאן וויזארד וואס ווייזט די איניציאליזאציע טריט.

The user may run all TP3 calibrations automatically, or one at a time. It is recommended that new users manually perform and  observe results for each calibration step. Manual mode is also recommended if hardware setup is new to ensure each TP3  calibration test completes correctly. For subsequent stress calibration runs, auto mode may be considered.

Baseline pulse width jitter (PWJ) is needed during TP3 to provide a reference for Seasim. During the PWJ Calibration  step, the user may opt for the scope to measure PWJ (default), or enter known values for PWJ RJ and PWJ DJ for their  specific setup.

ווען די PWJ קאליבראציע איז פארטיג, וועלן די נעקסטע דריי קאליבראציע טריט פארגיין אן קיין באנוצער אריינגאבע (AC-DC באלאנס,  Amplitude, Preset). During the Preset calibration step, all presets (Q0 to Q9) are calibrated. An IL measurement is performed  after Preset and is required only if the user plans to perform IL verification step during TP2. If the user will use VNA loss  measurements to establish and adjust ISI channel losses during TP2 calibration, TP3 IL measurement step can be skipped to  save time. If the IL measurement step is performed, the scope will measure short-channel loss (specify # scope acquisitions  and # averages) using step response from BERT and analysis via Seasim. The user may alternatively manually enter in the  short-channel loss (dB at 16 GHz) if known.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס

טעכניש קורץ

The next three calibration steps will proceed without user input (RJ, SJ, SJ@210MHz). After the last TP3 calibration step is  complete, the user may provide information to identify the calibration: Unique ID, Generated by, and comments field. Click  the SAVE button to save this TP3 calibration in the RX software for future use.

מולטי-טאָן SJ קאַליבראַציע

The user may enable multi-tone SJ calibration during TP3 to perform JTOL margin testing. The multi-tone SJ feature is  disabled by default but may be enabled in SETTINGS ➞ TP3 Calibrations via checkbox. Longer calibration times will be  incurred the more SJ frequencies that are specified (about five to seven minutes per SJ tone), and the higher number  calibration points tested between Min and Max SJ values. Even after passing compliance testing, it may be desirable to test  design margins. TekRXTest software makes it straightforward to retroactively add multi-tone SJ calibration to an existing  TP3 calibration.

פיגור 7. קאנפיגורירן מולטי-טאן SJ פרעקווענץ און ampליטוד.

די מולטי-טאָן SJ פֿונקציע שטיצט:

• SJ sweep across frequencies from 30 kHz up to 100 MHz.

• ≤14 SJ frequencies.

• Two to eight calibration points per SJ frequency.

• Min SJ value determined by BERT hardware intrinsic jitter.

• Max SJ value determined by BERT hardware SJ limits.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

TP3 קאַליבראַציע צייט

TP3 קאליבראציע נעמט ארום 45 מינוט ניצנדיק די פעליקייט ווייכווארג סעטינגס. די לויף-צייט נעמט אן אז די הארדווער און ווייכווארג פארלאנגען זענען באגעגנט, עס עקזיסטירט געהעריגע קאמוניקאציע צווישן דעם גאסט קאמפיוטער וואס לויפט TekRXTest און די טעסט אינסטרומענטן, עס זענען געמאכט ריכטיקע פארבינדונגען לויט די פארבינדונג דיאגראמען און די אינסטרומענטן זענען אין גוטן ארבעטס ארדענונג.

Several factors allow TP3 calibrations to run faster:

• Skip signal validation during initialization.

• Manually enter BERT PWJ values.

• Skip IL measurement if using VNA to measure ISI channel loss in TP2.

• Use auto-calibration mode.

לאָנטש און לויפן TP2 קאַליבראַציע

Several factors will cause longer TP3 run-time including:

• Signal validation during initialization.

• Performing BERT PWJ measurement.

• Performing short-channel IL measurement.

• Using manual run mode, and pausing between  calibration steps.

The same RF cables used to connect the BERT PPG to the scope inputs during TP3 calibration should remain in place when  performing TP2 calibration. In the shift from TP3 to TP2 setup, these RF cables are disconnected from scope inputs and  connected to PCI-SIG 6.0 CEM test fixtures. These connections are shown in פיגורע 8 אונטן.

 

פיגור 8. TP3 און TP2 RF קאַבל פֿאַרבינדונג.

קאַנעקטער WORD? אַטטענואַטאָר

1.85 מ״מ צו 2.92 מ״מ אַדאַפּטער

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

The user must perform and save a TP3 short channel calibration prior to running a long channel calibration. TP2 stress  calibration will prompt the user for DUT type (System Host or Add-in Card) and the TP3 calibration to use for TP2 calibration.  Similar to TP3:

1. TekRXTest software provides a connection diagram to ensure signals are connected properly from BERT PPG to the  scope inputs. See פיגורע 8.

2. The user will initialize instruments using INITIALIZE EQUIPMENT button before performing TP2 calibration steps.

3. TP2 calibration settings are provided in the SETTINGS menu. These user settings are shown in Table 1.

4. TekRXTest software provides BERT calibration steps that may be run manually (one at a time) or in auto mode.

5. TP2 test report with plots and BERT calibrated values are available upon completion.

ISI קאַנאַל אָנווער

The user should acquire approved PCIe 6.0 fixtures including ISI board and cables from PCI- SIG to enable signal path  connections shown in פיגורע 8. VNA insertion loss measurements are recommended on ISI channel fixtures and associated  cables to ensure the prescribed amount of loss is in place during TP2 calibration.

Target ISI channel loss depends on whether a System Host or Add-in Card is being tested. For System Host, the total ISI  channel loss target is 24 dB @ 16 GHz (Add-in Card is 28 dB @ 16 GHz). These targets are shown in the RX software at the IL for  DMI/CMI calibration step shown in פיגורע 9 אונטן.

פיגור 9. TP2 קאליבראציע צילן.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

PCIe 6.0 ISI channel loss boards provide traces with about 0.5 dB loss increments to allow for adjustment. The user will vary  channel loss together with other BERT stress parameters to meet stress calibration closure requirements. Because each ISI  board will vary in its loss profile, it is recommended the user measure ISI channel loss on the fixture to be used prior to TP2  calibration. The goal is to identify a cable + ISI channel pair that exhibit the target channel loss (24 dB @ 16 GHz for System  Host, 28 dB @ 16 GHz for add-in card). It is Tektronix’ experience that lanes meeting ISI channel requirements do vary. Actual  convergence during the March 2025 pre-FYI plugfest was obtained using ISI pair 2 and 14 for System Host, ISI pair 23 and 0 for Add-in Card. This lane variation is dependent on RF cable, connector and fixture loss differences.

TekRXTest software will embed the appropriate package loss onto the scope’s acquired waveform during TP2 calibration so that the step waveforms passed to Seasim represent the entire 30-33 dB ISI channel loss required for CEM compliance testing. This total loss is shown in the IL Measurement in פיגורע 10.

פיגור 10. גאַנץ פּעקל פארלוסט.

Once an ISI channel is chosen, TP2 stress calibration can begin. The recommendation from PCI- SIG is to begin with max  ISI channel loss for initial TP2 calibration run. The user may perform the IL measurement for DMI/CMI step, but this step is  optional and may be skipped if VNA measured data was used to verify target channel loss. DMI and CMI calibrations will run  without any user input. At the IL Measurement step, the user may select MANUAL ENTRY and enter in the total ISI channel  loss (i.e. VNA measured loss + embedded package loss). For System Host this target is 30-33 dB.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

Optimal preset calibration is performed next shown by פיגורע 11. The user may use the CONFIGURATION button to determine  what presets are considered during this step (Q0 to Q9). As shown in פיגורע 11, presets Q5, Q6, Q8, Q9 were selected based on  recommendation from PCIe 6.0 PHY Test spec working group. In Tektronix’ experience, successful calibrations have been  achieved using Q5, Q7 and Q8. The user may control the number of acquisitions for optimal preset step. The default number of acquisitions is three, but this value may be increased to ≥5, resulting in more waveform averages used to for preset eye area calculation.

פיגור 11. אָפּטימאַלע פאָרגעשטעלטע קאַליבראַציע.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

TekRXTest ווייכווארג וועט אויסקלויבן דעם פאָרגעשטעלטן פֿאָרשטעל וואָס וועט רעזולטירן אין דער גרעסטער דורכשניטלעכער אויג-שטח. אין דעם בייַשפּילampדי געוויזן אין פיגורע 12,  preset Q5 was found to yield the highest eye area of 5.274. In this example, the RX software will use Q5 in the final Stressed  Eye Cal step.

In some cases, more than one preset may result in a large eye area. To choose the best preset, the ratio of eye width /  eye height should be evaluated. With these ratios computed, the preset resulting in the ratio being closest to 50% is  recommended. An exampעס איז צוגעשטעלט אונטן:

Converged eye #1: Converged eye #2:

Preset = Q5 Preset = Q7

Eye width (EW) = 1.484 Eye width (EW) = 1.645

Eye height (EH) = 3.554 Eye height (EH) = 3.487

Ratio = EW / EH = 0.42 Ratio = EW / EH = 0.47

Choose this setting

פיגור 12. TP2 קאליבראציע אפטימאלע CTLE און פרעסעט סעלעקציע עקס.ample. Note that the “Bad” results for Q8, Q9 presets are normal in this case, when searching for the  optimum CTLE.

Final calibration step is Stressed Eye Cal. This step uses the preset determined in the previous step yielding the largest eye  area. With this preset configured in the BERT, a step waveform is captured and averaged then sent to Seasim for analysis.  Tektronix has implemented HW- assisted 10Ktrace averaging across 960 UIs to accelerate this process. Combinations of SJ,  DMI and amplitude are swept in Seasim. Tie-breakers are used to make decisions in cases where different values result in  similar final stressed eye conditions.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

TekRXTest software will use target values defined in TP2 STRESSED EYE PARAMETERS to adjust variable parameters to  meet eye target value. The default number of waveforms for Stressed Eye Cal is three, but this value may be adjusted by the  user. (A higher number of acquisitions yields more data but takes longer to acquire and process.) Tektronix recommends to  leave this value set to # acqs for stressed eye = 3 for initial TP2 runs. If three acquisitions are not sufficient, increase to ≥5 to  achieve stable results.

Nominal eye height and eye width targets for PCIe 6.0 are:

• Eye width: 3.125 ps (range of 2.825 ps to 3.425 ps)

• Eye height: 6 mV (range of 5.5 mV to 6.5 mV)

Figure 13. Configuring number of waveforms averaging for stressed eye.

אויב די RX ווייכווארג קען נישט געפֿינען אַ קאָנווערדזשינג סכום פון וועריאַבאַל סטרעסאַז נאָך דורכקוקן אַלע בנימצא פּאַראַמעטערס, קען דער באַניצער נעמען עטלעכע אַקשאַנז:

• Change ISI lane pairs to reduce channel loss by 0.5 dB. This will require a re-run of TP2 calibrations with reduced  channel loss.

• In the case of changing the ISI pair, the user should rerun the two steps that are dependent on the ISI pair: the Preset  Selection, and the Stressed Eye Cal. These should be rerun to 1) find the optimal Preset and CTLE based on the current ISI  pair, and 2) find the final stress recipe based on the current ISI pair.

Consider using manual sweep settings while holding other variables constant. An addendum will be added to this document  providing guidance on how best to use sweep mode in this case.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס טעכניש קורץ

TP2 קאַליבראַציע צייט

TP2 calibration takes two and a half to four hours to run using standard software settings. This run time is affected by  several factors including:

• Is IL Verification step run, or is VNA data used?

• Is ISI channel loss within target range?

• Can convergence be obtained with combination of BERT variable stresses and ISI channel loss?

• Variable stress sweep settings (Min, Max, granularity).

• Run modes (explained in the following section).

דער באַניצער האט עטלעכע קאָנטראָלן צו געבן מעגלעכקייט צו דורכפירן סטרעסעד אויג קאַל, אַרייַנגערעכנט:

• סטאַנדאַרט מאָדע: This is the default and recommended run mode for Stressed Eye Cal. Preset and CMI/DMI stresses  are enabled, and BERT step response is captured and averaged, then passed to Seasim for analysis. This process is  repeated multiple times while sweeping stresses in the allowable range. Seasim computes eye width and eye height, and  TekRXTest software computes eye area then checks for convergence. A linear sweep of stresses (amplitude, SJ, DMI) is  performed to close the calibration.

• מאַנואַל מאָדע: Allows the user to manually enter SJ, DMI and amplitude values for Stressed Eye Cal. This mode is valuable  for “what-if” testing or debug to try discrete combinations of stresses for calibration closure.

• Exhaustive sweep mode: Allows the user to run Stressed Eye Cal for all combinations of amplitude, SJ and DMI within  the sweep range with defined step sizes. The user controls sweep ranges and step sizes as shown in פיגורע 14. The wider  the range and smaller the step size, the longer the run will take. This sweep וועט נישט האַלטן when a converged eye is found,  rather it will perform a complete sweep of parameters and ranges defined by the user. The user may stop the sweep prior  to completion. If the user sees a combination of stresses that is desired then enable manual mode and perform stressed  eye verification with these settings to test for convergence.

Figure 14. User can control sweep ranges and step sizes.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

TekRXTest ווייכווארג וועט איבערחזרן און צופּאַסן דרוק ביז עס געפינט אַ קאָמבינאַציע וואָס רעזולטירט אין אַ דורכשניטלעכע אויג ברייט און אויג הייך אין די ציל קייט.ampדי געוויזן אין פיגורע 15, a successfully converged stress calibration is shown in the green rows. In this example, דורכשניטלעכע אויג ברייט = 2.929 פּס און דורכשניטלעכע אויג הייך = 6.657 mV. די רעזולטאַטן זענען דערגרייכט געוואָרן מיט פּרעסעט Q5, CTLE = 6 dB, ampליכט = 726 mV, SJ = 1 ps, און DMI = 8.7 mV.

פיגור 15. גרינע רייען ווײַזן אַן עקס.ampלע פון ​​אַ סוקסעספול קאָנווערדזשד דרוק קאַליבראַציע.

בערט סטרעס קאַליבראַציע בעסטע פּראַקטיקעס

איידער ער לויפט BERT סטרעס קאליבראציע, זאל דער באנוצער זיכער מאכן אז די פאלגענדע פאראויסזעצונגען ווערן באגעגנט צו מאקסימיזירן גענויקייט און איבערחזרנדיקייט:

• Ensure scope and BERT have been powered on for ≥30 minutes. This ensures instruments are warmed up prior to  calibration.

• Ensure scope is running the latest versions of TekScope and waveform analysis software. To verify latest software  versions, please contact your local Tektronix field application engineer.

• On the scope with all RF cables disconnected, run signal path compensation (SPC) under UTLITITES ➞ INTRUMENT  CALIBRATION. SPC is recommended once every 30 days or if ambient temperature changes by >5 degrees C.

• Characterize PCIe 6.0 CEM fixture loss with VNA for TP2 ISI pair combination. For System Host, ISI trace pairs + RF cables  should measure ~24 dB loss @ 16 GHz (Add-in Card ~28 dB loss @ 16 GHz). Refer to PCIe 6.0 PHY Test Spec, Appendix C for more details.

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PCI Express 6.0 CEM: BERT סטרעס קאַליבראַציע בעסטע פּראַקטיקעס 

טעכניש קורץ

די ציל פון BERT סטרעס קאליבראציע איז צו געפֿינען אַ קאָמבינאַציע פֿון פֿיר אַדזשאַסטאַבאַל סטרעס פּאַראַמעטערס (ISI קאַנאַל פֿאַרלוסט, SJ, DMI, ampליטוד) ווען קאמבינירט מיט פעסטע סטרעסארן (למשל RJ, CMI) וואס גיט דורכשניטלעכע אויג הייך און אויג ברייט ווערטן אין די ספעציפיצירטע קייט. די ציל קייטן זענען:

• Eye width: 2.825 ps to 3.425 ps (nominally 3.125 ps).

• Eye height: 5.5 mV to 6.5 mV (nominally 6 mV).

The PCIe 6.0 PHY Test Specification specifies BERT stress calibration flow as follows:

1. Start with maximum ISI channel of 33 dB (HW ISI channel loss + embedded package model) for capturing the  step response.

2. Post process BERT step response with Seasim to find optimal preset and CTLE.

3. Post process BERT step response with Seasim to sweep adjustable parameters.

4. If a converged solution can be found, the calibration is successful. Record these values.

5. If no solution can be found with any combination of SJ, DMI, and amplitude, reduce ISI channel loss by one pair (nominally  0.5 dB step).

6. Repeat steps two through five until a solution converges within target eye width and eye height ranges.

VNA characterization of PCIe 6.0 fixtures along with RF cables is highly recommended prior to running BERT stress  calibration. TekRXTest software does provide a step-response based ISI channel verification, but this value may deviate  from a VNA-based measurement by several dB. The goal is to find a combination of ISI channel + RF cable loss that is ~24 dB  @ 16 GHz for System Host, ~28 dB @ 16 GHz for Add-in card. Once the ISI channel + RF cable combination is found, this is the  starting point for the TP2 portion of the calibration.

טראָובלעשאָאָטינג

In cases where TekRXTest does not successfully provide a converged BERT stress calibration at the end of TP2, below are  several areas to assess what changes should be made in the test setup or calibration settings:

• Check software revisions (scope, BERT, Sigtest, Seasim, etc.).

• Perform scope self-test and signal path compensation.

• Ensure scope channels are correctly deskewed <1 ps.

• Ensure coaxial connections in the signal path are tight and torqued to the proper value where appropriate.

• With no signal applied, measure pk-pk ACrms voltage on scope ATI Channel 1 and Channel 2 using auto measurements.  This ACrms value should be in the range of 1.1 to 1.3 mV. The measured ACrms mean value should also match between  Channel 1 and Channel 2 within a tight tolerance (≤.3 mV). If either condition is not met, ensure proper airflow into and out  of the scope to provide proper cooling. A minimum six-inch clearance is recommended on all sides of the scope. Ensure  instruments sitting in close proximity to the scope are not blowing hot air into the scope air inlet located on the bottom of  each scope unit.

Your Tektronix field application engineer is standing by to assist you. If you have followed this guide and are still not achieving  convergence during BERT stress calibration, reach out to your local Tektronix application engineer for assistance.

For more information on Tektronix’ PCI Express test solutions, please visit tek.com.

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געפֿינען מער ווערטפול רעסורסן ביי TEK.COM

Copyright © Tektronix. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supersedes that  in all previously published material. Specification and price change privileges reserved. TEKTRONIX and TEK are registered trademarks of Tektronix, Inc. All other trade names  referenced are the service marks, trademarks or registered trademarks of their respective companies.

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