An Overview of the Electrical Validation of
`
`10BASE-T. 100BASE-TX. and 1000BASE-T
`
`Devices
`
`Application Note
`
`The number of devices that come
`with a built-in network interface card
`
`has risen steadily and will continue
`to rise as more and more digital
`entertainment devices with networking
`capabilities are designed and sold.
`Devices with network interface ports
`now range from personal computers
`to c|osed—circuit cameras. This is a far
`
`cry from the day when a 10-Mbit/s
`port could be found only on high-end
`servers and networking equipment.
`
`The technology used in these ports,
`commonly known as "LAN" or "N|C"
`ports, is usually one of the 10BASE-T,
`100BASE-TX, and 1000BASE-T
`standards or a combination of them.
`These standards transmit 10, 100
`or 1000 Mbit/s over UTP cable with
`
`an 8-pin RJ-45 connector. In this
`article, we will take a quick look
`at the electrical signals used in
`these technologies and how they
`can be probed for quick test and
`validation. This exploration will be
`useful for engineers involved in the
`electrical validation of the 10BASE-T,
`100BASE-TX, and 1000BASE-T
`
`implementations in their devices.
`
`10BASE-T
`
`The long-lived 10BASE-T standard
`has been around since 1990 and is
`
`showing no signs of going away,
`even though it is considered obsolete
`by many. It provides 10-Mbit/s data
`transmission over two pairs of a
`Category 3 or 5 cable, one pair for
`transmit and the other for receive.
`
`The other two pairs of the cable are
`unused.
`
`100BASE-TX
`
`100BASE-TX is the most widely
`used version of 100-Mbit/s Ethernet
`
`(also known as fast Ethernet) over
`UTP cable. It uses the same pairs as
`10BASE-T for transmit and receive but
`
`requires Category 5 or better cable.
`
`1000BASE-T
`1000BASE-T is the most common form
`
`of 1000-Mbit/s Ethernet (also known
`as Gigabit Ethernet) over UTP cable. It
`uses all four pairs of the UTP cable for
`both transmit and receive and requires
`Category 5e or better cable.
`
`Figure 1 and Table 1 below describe
`the pin assignment of the 8-pin RJ-45
`plug as used in a straight-through
`configuration.
`
`
`
`Figure 1. The 8-pin RJ-45 plug. also
`known as the 8P8C connector.
`
`Pin
`
`10BASE-T /
`100BASE-TX
`
`1000BASE-T
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`8
`
`TD+
`
`TD—
`
`RD+
`
`Unused
`
`Unused
`
`RD—
`
`Unused
`
`Unused
`
`B|_DA+
`
`B|_DA—
`
`B|_DB+
`
`B|_DC+
`
`B|_DC—
`
`B|_DB—
`
`B|_DD+
`
`B|_DD—
`
`Table 1. The pin assignment for 10BASE-T.
`100BASE-TX. and 1000BASE-T on the
`8-pin BJ-45 plug in a straight-through
`configuration. TD/ RD stands for transmit
`data/receive data. Bl_DX stands for
`bi-directional pair X.
`
`Agilent Technologies
`
`Aerohive - Exhibit 1036
`
`Aerohive - Exhibit 1036
`
`

`
`
`
`IUBASE-T transmits a differential
`
`circuit to the load, the standard also
`
`100 Q resistive load. This makes for a
`
`signal, and the most straightforward
`method to probe the signals is with
`the TD+ and TD— pins connected to
`a 100 Q resistive load as shown in
`Figure 2a. In addition to the 100 0
`resistive load, the standard specifies
`two additional loads to be used for
`
`describes the use of a “twisted-pair
`model" (also known as TPM in short).
`The TPM is an equivalent circuit that
`models the distortion introduced by
`a simplex link segment, and is made
`up of 4 segments of RLC circuitry
`not shown here. Tests for some of
`
`lot of tests!
`
`Let us take a look at the 10BASE-T
`waveforms. There are typically four
`different types of waveforms that
`need to be used for testing. All the
`waveforms in this article will be based
`
`testing. These two additional loads
`are illustrated in Figure 3. Apart from
`the direct connection from the TD
`
`the 10BASE-T parameters are done
`iteratively with and without the TPM
`and on loads 1 and 2 including the
`
`on the circuit in Figure 2a with a
`100 (1 resistive load unless otherwise
`mentioned.
`
`
`
`Figure 2a. The IIIBASE-T TD circuit directly
`connected to the load. The output voltage Vo is
`measured across the load.
`
`
`
`Figure 2b. The 1IlBASE-T TD circuit connected to the load through the
`twisted-pair model (TPM).
`
`L=
`1ll0uH
`
`L—
`220pH
`
`Br
`
`‘-8
`
`Rs
`
`LoAo1
`
`LOAD 2
`
`Figure 3. Loads 1 and 2. which are used to test 1llBASE-T.
`
`Ls=Li1%
`c,,=12pr¢2o%
`
`npzzkn
`nsso.5n
`
`L DEFINITION
`
`
`
`

`
`Probing and Testing 10BASE-T Signals (continued)
`
`Hie Uunlrul
`
`§eI\-H Measure AIBIVZE Utlllfl HEIF
`
`
`
`First is the LTP or link test pulse, also
`known as the NLP or normal link pulse.
`The LTP is the first signal transferred
`by the 10BASE-T transmitter and
`is used to indicate the presence of
`an active transmitter. If there is an
`
`active device at the end of the link, it
`
`responds with its own LTP. The LTP
`is also used in bursts to form data
`
`words where device capability data is
`exchanged during auto-negotiation. In
`all cases, the LTP has to fit within a
`
`defined template with all combinations
`of loads with and without the
`
`twisted-pair model.
`
`
`
`._‘:1:-E/EEEEI.
`
`
`
`Figure 4. The link test pulse (LTP) waveform with and without the
`twisted-pair model.
`
`File mnrrnt Setup Neaslre Analyze unimes
`
`l-lain
`
`Figure 5. LTP signal with TPM in the LTP template.
`
`

`
`Probing and Testing 10BASE-T Signals (continued)
`
` ma [‘.(:nImI
`
`
`
`SFEIIII Analyze Utilities Help
`
`The next signal of interest is the
`TP_|DL signal. l0BASE-T data is
`transmitted in Manchester-encoded
`
`(transition indicates logical "1 ")
`data packets with a period of idle in
`between known as the interframe gap.
`The TP_|DL signal indicates the start
`of the idle period, and is therefore
`found at the end of each data packet.
`As with the LTP, the TP_|DL waveform
`also has to fit within a defined
`
`template with all combinations of
`loads with and without the
`
`twisted-pair model.
`
` Figure 6.
`
`Manchester-
`encoded random
`
`data packets.
`The waveform
`
`displayed in the
`lower half of the
`screen is the
`zoomed-in area
`contained in the
`white box on the
`waveform in the
`
`upper half.
`
`HIE flnnfrnl Selim Mnafilre Anfilwe
`
`llflllllefii
`
`Ilfllrl
`
`Anfilwe Uflllllefi
`
`Ilfllrl
`
`Figure 7. The
`TP_|DL is a
`positive-going
`pulse with a
`width of 300 ns
`or 350 ns
`
`depending on
`whether the
`last bit was
`one or zero
`
`respectively.
`
`Figure 8.
`The TP_lDL
`template test.
`
`

`
`Probing and Testing 10BASE-T Signals (continued)
`
`Anfiiwa Ufllllles Help
`
`The signaling rate for 10BASE-T
`is nominally 10 MHz. An all-l's
`Manchester-encoded signal will
`result in a 10-MHz waveform. This
`all-1's waveform is used to test
`that all harmonics measured on
`
`the transmitting circuit are at least
`27 dB below the fundamental. This
`
`is easily achieved, as most modern
`digitizing oscilloscopes come with
`an FFT function. Through the use of
`FFTs made with the Hanning window
`function for frequency accuracy, it is
`easy to measure the magnitude of the
`spectrum at 10 MHz and its harmonics.
`
`Apart from the template tests and the
`test for harmonic content. the other
`
`parameters that can be tested are
`the peak differential output voltage
`and common-mode voltage. These
`tests are performed with random
`data signals. as shown in Figure 6.
`and are relatively straightforward
`measurements.
`
`nu
`
`nsim __
`
`Mum
`
`Figure 9. All-1's Manchester-encoded signal.
`
`Analwa Uflllllfifi Help
`
`l%m' <lr-I>l
`
`‘
`
`.1 IFi'E;..’el :¢:l
`
`0'
`
`Figure 10. The oscilloscope display is divided into
`two, with the trace on the upper portion displaying
`the all-‘1's Manchester-encoded signal. The trace
`on the lower portion uses the oscilloscope FFT
`function to measure harmonic content of the all-1's
`
`Manchester-encoded signal. This example shows
`a marker at the fundamental frequency of 10 MHz
`and another marker on the third harmonic (30 MHz).
`The magnitude of the third harmonic shown here is
`-28.45 dB from the fundamental.
`
`

`
`Testing 100BASE-TX
`
`100BASE-TX uses a line encoding
`scheme known as MLT-3 where the
`
`data is alternated through three
`voltage levels with a transition
`indicating a logical 1. The MLT-3
`line coding enables the use of less
`bandwidth than would be required by a
`different coding scheme. such as NRZ.
`for the same data rate. 100BASE-TX
`
`is tested using an MLT-3 coded idle
`pattern. On most devices. setting the
`speed setting to 100 Mbit/s mode
`will automatically cause the device to
`output an idle pattern, part of which is
`shown in Figure 11. This same pattern
`is used for all 100BASE-TX tests.
`
`The TODBASE-TX standard provides
`the use of an eye pattern template
`that can be used to perform a quick
`check on the output of a 100BASE-TX
`transmitter. Note that the use of
`
`the eye template should not replace
`thorough testing of 1l]0BASE-TX
`parameters, but it can provide a
`reasonably good indication of the
`performance of a particular transmitter.
`
`Vertical Scale Offset
`
`i%fll'%<i°I>I
`
`.5l§~'9l
`
`3‘*1.|
`
`Figure 11. The MLT-3 coded idle pattern from a 100BASE-TX
`transmitter.
`
` ::xr,r::qa_1'a,<r
`
`Figure 12. The eye pattern template of a IMIBASE-TX signal. The
`oscilloscope used to create the eye-pattern is synchronized to the
`recovered clock from the transmit waveform.
`
`

`
`1000BASE-T transmits data over all
`
`four pairs of the tvvisted-pair and uses
`a five-level pulse amplitude modulation
`called PAM5 for data transmission.
`
`Performing tests on normal data
`transmission similar to 10BASE-T
`or 100BASE-TX is non-trivial, thus
`the standard defines the use of four
`
`
`
`different test modes for testing. These
`are named test modes 1 — 4 and are
`
`set by writing to bits 13 to 15 of the
`1000BASE-T control register (register
`9.13:15). Tests are performed over all
`four pairs of the transmitter.
`
`Figure 13. One cycle of a Test Mode 1 waveform with the test
`points A to M labeled.
`
`Test Mode 1 causes the transmitter
`
`to send out all five signal levels of
`the PAM5 coding, which are the
`"+2", "-2", "+1," "—1 " symbols
`alternating with 127 "0" symbols.
`This is then followed by long strings
`(128) of the "+2" and "—2" symbols
`repeated Mice. and ends with 1024
`"0" symbols. Various points in the
`waveform are then labeled from A
`
`to M (I is skipped) to mark points of
`interest for testing. Points A, B, C, and
`D corresponds to the "+2." "—2." "+1,"
`and "—1 " symbols respectively.
`
`Three tests are done using Test
`Mode 1. First, the peak voltages at
`points A, B. C, and D are measured.
`The voltages at points A and B are also
`compared to ensure their amplitudes
`are within 1%. These measurements
`
`are relatively straightforward to
`make. and it involves zooming in to
`the point of interest and making the
`measurement.
`
`
`
`

`
`Testing 1000BASE-T (continued)
`
`The next tests are the template tests.
`Points A, B, C, D, F, and H have to
`
`fit in defined templates after going
`through a 2-MHz high-pass filter
`and being normalized according to
`specific rules described in sub-clause
`40.6.1.2.3 of IEEE Standard 802.3-
`
`2005. These steps can be achieved
`using currently available digitizing
`oscilloscopes as shown in Figures 14a,
`14b and 14c below, using the template
`measurement for point A as an
`example.
`
`Apart from the template tests, there is
`also a droop test on the long strings
`of the "+2" and "-2" symbols. The
`voltage droop is measured from point
`F (minimum point at the start of "—2"
`symbol string) to point G (500 ns
`after point F) as well as from point H
`(maximum point of the waveform as
`indicated in Figure 3) to J (500 ns after
`point H).
`
`!J!l!Jfll
`Z
`V Display Oh
`0
`amr
`High pa55 Fine,
`SGJJFCQ 1
`F—
`Bandwidth
`
`|2_ooooo I\/Hz
`
`I
`Close
`Hem El
`
`'7 Scaling
`L * indicates User Defined Function
`
`5
`
`Figure 14a. The digitizing oscilloscope
`in this example allows the use
`of functions to he performed on
`waveforms. In this illustration, a
`high-pass filter with its lower cutoff
`at 2 MHz is applied on the Channel 1
`source using Function 2.
`
`my
`
`Ll
`
`W Scalirig
`* indicates L193’ Deflrm Rncfion
`Vertical
`*' Automatic
`" Automatic
`"- Manual
`Scale
`Scale
`
`Horizontal
`
`mogul
`
`:%l _ ‘°J":l
`Position
`
`Figure 14b. Function 3 then uses a magnify function to
`normalize the filtered waveform from Function 2. The
`
`point A waveform is normalized by dividing by the peak
`voltage value of the waveform at A.
`
`, Analwa Uflllllfifi Help
`
`wberuunzcnis. Mada Tusti tolor Grad:
`
`‘ ~l Pfifillélifil
`
`'
`
`Figure 14c. The filtered and normalized point A waveform is then
`aligned to best fit to the template.
`
`

`
`Next, we will take a look at test modes
`
`2 and 3. These test signals consist of
`alternating "+2" and "-2" symbols
`timed to a 125 MHz timing clock called
`the TX_TCLK. Test Modes 2 and 3
`differ in the timing source used. Test
`Mode 2 is called Master mode, and
`uses the device's own transmit clock,
`while Test Mode 3 is called Slave
`mode and uses a recovered clock from
`
`
`
`data transmitted by a link partner in
`Master mode. To be able to test the
`
`jitter of a 1ll00BASE-T device, the
`TX_TCLK of the device should be
`available for probing. The data sheet
`of the 1000BASE-T device should
`
`Figure 15. Test mode 2/3 waveform along with a 125MHz TX_TCLK.
`
`describe which pins should be
`probed to access the TX_TCLK. The
`waveforms for test modes 2 and 3
`
`are essentially the same: an example
`waveform and a TX_TCLK is displayed
`in Figure 13. Jitter testing will not be
`covered in detail here as it is beyond
`the scope of this article.
`
`
`
`

`
`The last test mode that we will look
`at is Test Mode 4. In Test Mode 4.
`
`the device outputs a 2047 symbol
`pseudo random bit pattern that is
`PAM5 encoded and then further
`
`
`
`filtered through a partial response
`filter. The resulting output from the
`filter is a 17-level signal, which can
`be seen in Figure 14. The Test Mode 4
`waveform gives an idea of what the
`waveform from an actively transmitting
`IUOOBASE-T device looks like. The Test
`
`Mode 4 output is used as the source to
`measure peak transmitter distortion.
`
`Figure 16. The Test Mode 4 waveform.
`
`The distortion measurement is
`
`not a straightforward oscilloscope
`measurement; it requires the use of
`post-processing to calculate distortion.
`Sample MATLAB® code is provided
`in the standard as a guidance to
`calculate distortion. In simple terms,
`what the code does is to sample each
`of the 2047 symbols at an arbitrary
`phase clocked from the TX_TCLK. The
`code then examines each sample for
`distortion and reports the highest value
`as the peak distortion. This usually
`involves obtaining a large record
`containing more than a few cycles
`of the Test Mode 4 waveform. This
`waveform record is then transferred
`
`to a personal computer and processed
`based on the guidance given in the
`MATLAB code.
`
`As in 10BASE—T where the standard
`calls for some tests to be run with a
`
`twisted-pair model. the 1000BASE-T
`standard also calls for the Test Mode 1
`and Test Mode 4 tests to be run in the
`
`presence of a disturbing signal. The
`disturbing signal is defined as a sine
`wave generator that simulates the
`potential interfering effect of another
`IUOOBASE-T transmitter. We will not
`
`cover testing with disturbing signal in
`detail in this article.
`
`
`
`

`
`Return loss is a measurement of the
`
` From Zin, the reflection coefficients
`To perform the conversion, we use the
`sum of the reflected energy coming
`back from the receiving device to the
`transmitting device. Return loss is
`defined in the standards for 10BASE-
`T, 100BASE-TX, and 1000BASE-T. It is
`
`for the different impedances can be
`calculated.
`
`Zin-85
`ram: zin+85
`
`zin—1oo
`r‘"“"= 2. +100
`In
`
`zi,,—115
`rm“: 2. +115
`In
`
`And the resulting return loss in dB can
`be obtained by the following:
`
`Bl-ssn = 2" l°91u lrssol
`
`F“-moo = 2" l°91o lrmonl
`
`Bl-115n = 20l°91olr115nl
`
`following equations:
`
`Return Loss in dB, RLdB = 20 log",
`
`|Tu|
`
`Where To is the array of complex
`reflection coefficient values (vs
`frequency) of the measurement made
`on the VNA and is represented in
`terms of impedance by
`
`lo
`
`_ zin'zlJ
`_ zin "' 20
`
`Zin is the impedance of the DUT which
`is also a complex array (vs frequency).
`
`and Z0 is the standard reference
`impedance at which the measurement
`was made (real number).
`
`Since the measurement was made
`
`on the vector network analyzer at the
`standard reference of 500. but first
`
`going through a 2:1 conversion through
`
`the balun, Z0=2*50=100.
`
`Solving for Zin,
`
`especially important for 1000BASE-T
`devices as these devices use bi-
`
`directional signaling. These means
`that the same pins which transmit
`data also receives data. If the
`
`receiving device has bad return loss.
`the information originating from the
`transmit side will be reflected back,
`
`causing problems for the transmit side
`as it is also acts as a receiver, listening
`for data from the transmitter at the
`
`other end. Therefore return loss testing
`is important to ensure interoperability
`with other devices.
`
`Return loss testing is performed using
`a vector network analyzer. The N5395B
`or N5395C Ethernet electrical probing
`fixture can be used to facilitate the
`return loss measurement. As the
`
`signals from the Ethernet device are
`differential, a balun transformer on
`
`the fixture performs the differential to
`single-ended impedance conversion
`to the network analyzer input. The
`N5395B or N5395C fixture also
`
`provides a return loss calibration
`fixture with RJ-45 short, open, and
`load connections to calibrate the
`
`vector network analyzer.
`
`The return loss can be measured on
`
`a sing|e—port of the vector network
`analyzer using a forward reflection or
`S11 measurement in log magnitude.
`As this measurement is made in
`
`50 0 through a balun, it has to be
`conversion mathematically to its
`equivalent in 100 i 15 (1. Therefore
`return loss is calculated at 85 Q, 100
`
`(1, and 115 Q (111 0 additionally for
`10BASE-T).
`
`
`
`Figure 17. Return loss vs frequency plot of a 1I|0lIBASE-T device
`
`
`
`

`
`
`
`You now have an overview of the
`how the electrical validation of the
`
`popular 10BASE-T, 100BASE-TX, and
`1000BASE-T is done. The signals used
`in the transmission of Ethernet signals
`get more complex as the data rate
`increases exponentially from 10 to
`1000 Mbits/s. This trend will continue
`
`as designers try to transfer more data
`over the bandwidth-limited UTP cable
`
`using more complicated modulation
`schemes.
`
`The quality and signal integrity of your
`measurement tools play an important
`role in ensuring that you have the best
`representation of the signals you are
`measuring. Most of the measurements
`described here can be made manually
`on a modern digitizing real-time
`oscilloscope. The signals used in
`these illustrations were from an off-
`the-shelf network interface card and
`
`oscilloscope with an active differential
`probe. An Agilent N5395B or N5395C
`Ethernet electrical probing fixture was
`used to provide the probing circuits
`shown in Figures 2 and 3. There is also
`an automated test application available
`that can be used in conjunction with
`the N5395B or N5395C fixture. For
`
`more information regarding tools for
`Ethernet validation, visit
`
`captured using an Agilent 80000 Series
`
`www.agi|ent.com/find/n5392a.
`
`
`
`

`
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