356:. In transmitting signals at high data rates, the transmission medium may introduce distortions, so emphasis is used to distort the transmitted signal to correct for this distortion. When done properly this produces a received signal that more closely resembles the original or desired signal, allowing the use of higher data rates or producing fewer bit errors. Most real world channels have loss that increases with frequency (effectively a low pass filter), so emphasis needs to invert this effect (functioning as a high pass filter). This makes emphasis a form of
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at the receiver caused by bits which have not yet arrived (e.g. fields coupling across meanders in a delay-matched trace) and is typically zero or a very small negative value, as this is often not a major contribution to total ISI. The post cursor coefficient removes ISI at the receiver caused by the
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is a technique to protect against anticipated noise and loss. The idea is to boost (and hence distort) the frequency range that is most susceptible to noise and loss beforehand, so that after a noisy and lossy process (transmission over cable, tape recording...) more information can be recovered from
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One common implementation of emphasis in real SERDES is a 3-tap feed-forward equalizer (FFE): rather than driving the output pin with the desired output voltage directly, the actual output voltage is a weighted sum of the desired bit value (main cursor), the previous bit (post cursor), and the next
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is the complement of pre-emphasis, in the antinoise system called emphasis. De-emphasis is a system process designed to decrease, (within a band of frequencies), the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve
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Emphasis can be implemented either by boosting high frequencies (pre-emphasis, increasing the amplitude of transition bits) or attenuating low frequencies (de-emphasis, reducing the amplitude of non-transition bits). Both have the same net effect of producing a flatter system frequency response;
336:. After economies of scale eventually allowed full 16 bits, quantization noise became less of a concern, but emphasis remained an option. The pre-emphasis is described as a first-order filter with a gain of 10 dB (at 20 dB/decade) and time constants 50 μs and 15 μs.
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Excessive post-cursor emphasis. The eye is starting to close and transition bits have significant overshoot, indicating excessive equalization. The "double banding" artifact visible in the eye indicates the presence of significant ISI caused by the excessive emphasis.
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immediately preceding bit and is typically a larger negative value, with lossier channels requiring a larger tap value. Higher numbers of taps are possible but increase circuit complexity and tend to result in diminishing returns so are not commonly used.
196:) the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as
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bit to be transmitted (pre cursor). The main cursor coefficient controls the nominal amplitude of the bit and is always positive (as a negative coefficient would invert the bit value). The pre cursor coefficient removes
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Well-tuned post-cursor emphasis. The eye is open and transition and non-transition bits are well matched in amplitude, indicating a correct level of equalization. The signal is passing the mask test.
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of roughly 2 dB at the fundamental, 3 dB at the 2nd harmonic, and 4 dB at the 3rd. The goal is to achieve a well-equalized channel response in which the eye is maximally open without excessive
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the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.
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de-emphasis is typically more convenient to do in real circuits since it only requires attenuation rather than amplification. Well-known serial data standards such as
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Excessive pre-cursor emphasis. The eye is more closed than the baseline, indicating minimal pre-cursor ISI was present and the emphasis is doing more harm than good.
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mastering. As CD players were originally implemented with affordable 14-bit converters, a specification for pre-emphasis was included to compensate for
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Deemphasis – Frequency response and equalization EQ – Conversion: time constant to cut-off frequency and vice versa
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of recording media in subsequent parts of the system. The mirror operation is called de-emphasis, and the system as a whole is called emphasis.
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Emphasis – Frequency response and equalization EQ – Conversion: time constant to cut-off frequency and vice versa
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Baseline signal with no emphasis. Transition bits are clearly weaker than non-transition bits and the signal is touching the mask (fail).
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412:. Excessive equalization can worsen jitter, increase overshoot, and result in a less open eye than a properly equalized signal.
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process includes a reciprocal network, called a de-emphasis network, to restore the original signal power distribution.
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613:"ECEN720 High Speed Links Circuits and Systems, Lecture 8: RX FIR, CTLE, and DFE Equalization"
582:"ECEN720 High Speed Links Circuits and Systems, Lecture 7: Equalization Intro & TX FIR EQ"
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168:. For example, high-frequency signal components may be emphasized to produce a more equal
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that frequency range. Removal of the distortion caused by pre-emphasis is called
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Although rarely used, there exists the capability for standardized emphasis in
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559:. Geneva: International Electrotechnical Commission. 1999. pp. 29, 131.
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633:"Eye Doctor: Why Too Much Equalization is Bad for Your Serial Link Health"
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192:, pre-emphasis refers to a system process designed to increase (within a
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The effects of emphasis on a signal can be clearly seen in the
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392:. In the following demonstration, we consider a 10.3125 Gbps
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for a transmitted frequency spectrum, and therefore a better
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Emphasis is commonly used in many places ranging from
599:"UltraScale Architecture GTY Transceivers User Guide"
360:, implemented at the transmit side of the channel.
49:. Unsourced material may be challenged and removed.
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376:require transmitted signals to use de-emphasis.
253:of speech signals. One example of this is the
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109:Learn how and when to remove this message
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316:curve, from which one can calculate the
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257:curve on 33 rpm and 45 rpm
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47:adding citations to reliable sources
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227:can be calculated from that value.
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211:which is essentially a calibrated
58:"Emphasis" telecommunications
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230:Pre-emphasis is commonly used in
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400:modulation, typical for testing
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667:General Services Administration
34:needs additional citations for
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348:, emphasis is used to improve
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268:Pre-emphasis is employed in
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263:Dolby noise-reduction system
125:RIAA equalization curve for
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16:Process for reducing noise
188:In processing electronic
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340:In digital transmission
300:In telecommunications,
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662:Federal Standard 1037C
656:public domain material
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717:Broadcast engineering
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404:. The channel has an
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174:signal-to-noise ratio
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638:. Texas Instruments.
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43:improve this article
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402:10-Gigabit Ethernet
352:at the output of a
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396:test pattern with
334:quantization noise
314:frequency response
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261:. Another is the
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134:signal processing
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41:Please help
36:verification
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677:MIL-STD-188
390:eye pattern
366:PCI Express
330:Red Book CD
302:de-emphasis
296:De-emphasis
238:recording,
166:PCI Express
143:de-emphasis
706:Categories
543:References
202:saturation
69:newspapers
431:Optimized
410:overshoot
425:Baseline
308:Special
99:May 2019
536:Better
530:Better
498:Better
492:Better
394:PRBS-31
83:scholar
527:Worst
523:Jitter
504:Height
489:Worst
280:drive
278:signal
240:record
223:. The
215:. The
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160:(e.g.
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636:(PDF)
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533:Best
514:Best
508:Good
495:Best
485:Width
282:power
158:vinyl
90:JSTOR
76:books
517:Bad
511:Bad
372:and
370:SATA
62:news
398:NRZ
382:ISI
374:SAS
344:In
272:or
200:or
132:In
45:by
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624:^
565:^
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162:LP
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