367:. 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;
347:. 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.
207:) 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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process includes a reciprocal network, called a de-emphasis network, to restore the original signal power distribution.
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624:"ECEN720 High Speed Links Circuits and Systems, Lecture 8: RX FIR, CTLE, and DFE Equalization"
593:"ECEN720 High Speed Links Circuits and Systems, Lecture 7: Equalization Intro & TX FIR EQ"
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IEC 60908:1999: Audio recording – Compact disc digital audio system
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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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570:. Geneva: International Electrotechnical Commission. 1999. pp. 29, 131.
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644:"Eye Doctor: Why Too Much Equalization is Bad for Your Serial Link Health"
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The effects of emphasis on a signal can be clearly seen in the
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403:. 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
610:"UltraScale Architecture GTY Transceivers User Guide"
371:, implemented at the transmit side of the channel.
60:. Unsourced material may be challenged and removed.
387:require transmitted signals to use de-emphasis.
264:of speech signals. One example of this is the
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120:Learn how and when to remove this message
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327:curve, from which one can calculate the
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268:curve on 33 rpm and 45 rpm
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58:adding citations to reliable sources
238:can be calculated from that value.
222:which is essentially a calibrated
69:"Emphasis" telecommunications
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241:Pre-emphasis is commonly used in
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411:modulation, typical for testing
218:Pre-emphasis is achieved with a
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678:General Services Administration
45:needs additional citations for
359:, emphasis is used to improve
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279:Pre-emphasis is employed in
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274:Dolby noise-reduction system
136:RIAA equalization curve for
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27:Process for reducing noise
199:In processing electronic
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311:In telecommunications,
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673:Federal Standard 1037C
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728:Broadcast engineering
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185:signal-to-noise ratio
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649:. Texas Instruments.
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54:improve this article
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413:10-Gigabit Ethernet
363:at the output of a
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52:Please help
47:verification
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688:MIL-STD-188
401:eye pattern
377:PCI Express
341:Red Book CD
313:de-emphasis
307:De-emphasis
249:recording,
177:PCI Express
154:de-emphasis
18:Preemphasis
717:Categories
554:References
213:saturation
80:newspapers
442:Optimized
421:overshoot
436:Baseline
319:Special
110:May 2019
547:Better
541:Better
509:Better
503:Better
405:PRBS-31
94:scholar
538:Worst
534:Jitter
515:Height
500:Worst
291:drive
289:signal
251:record
234:. The
226:. The
224:filter
171:(e.g.
167:) and
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669:from
647:(PDF)
627:(PDF)
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544:Best
525:Best
519:Good
506:Best
496:Width
293:power
169:vinyl
101:JSTOR
87:books
528:Bad
522:Bad
383:and
381:SATA
73:news
409:NRZ
393:ISI
385:SAS
355:In
283:or
211:or
143:In
56:by
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635:^
576:^
379:,
331:.
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173:LP
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