Editing Pulse-amplitude modulation

{{short description|Form of signal modulation where information is encoded in the amplitude of a series of pulses}}
{{Use American English|date=February 2020}}

[[File:PAM neutral.svg|class=skin-invert-image|thumb|Principle of PAM: (1) original signal, (2) PAM signal, (a) amplitude of signal, (b) time]]
{{Modulation techniques}}

'''Pulse-amplitude modulation''' ('''PAM''') is a form of signal [[modulation]] in which the message information is encoded in the [[amplitude]] of a [[pulse train]] interrupting the carrier frequency. Demodulation is performed by detecting the amplitude level of the carrier at every single period.

==Types==
There are two types of pulse amplitude modulation:
* In ''single polarity PAM'', a suitable fixed [[DC bias]] is added to the signal to ensure that all the pulses are positive. 
* In ''double polarity PAM'', the pulses are both positive and negative.

Pulse-amplitude modulation is widely used in [[modulating signal]] transmission of digital data, with non-[[baseband]] applications having been largely replaced by [[pulse-code modulation]], and, more recently, by [[pulse-position modulation]].

The number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some power of two. For example, in 4-level PAM there are <math>2^2</math> possible discrete pulse amplitudes; in 8-level PAM there are <math>2^3</math> possible discrete pulse amplitudes; and in 16-level PAM there are <math>2^4</math> possible discrete pulse amplitudes.

==Uses==

===Ethernet===
Some versions of the [[Ethernet]] communication standard are an example of PAM usage. In particular, [[100BASE-T4]] and [[BroadR-Reach Ethernet standard]] use three-level PAM modulation (PAM-3), while [[1000BASE-T]] Gigabit Ethernet uses five-level PAM-5 modulation<ref>{{cite magazine |title=What PAM5 means to you |magazine=EDN |url=https://www.edn.com/what-pam5-means-to-you/ |author=George Schroeder |date=2003-04-01 |access-date=2022-02-16}}</ref>{{efn|The first use of PAM-5 in Ethernet was in [[100BASE-T2]]. Although not widely adopted, the technology developed for 100BASE-T2 was subsequently used in the popular 1000BASE-T Gigabit Ethernet standard.}} and [[10GBASE-T]] 10 Gigabit Ethernet uses a [[Tomlinson-Harashima precoding|Tomlinson-Harashima precoded]]{{technical inline|date=October 2022}} (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern{{technical inline|date=October 2022}} known as DSQ128. [[25 Gigabit Ethernet]] and some copper variants of [[100 Gigabit Ethernet]] and [[200 Gigabit Ethernet]] use PAM-4 modulation.

===USB===
[[USB4]] Version 2.0 uses PAM-3 signaling for USB4 80&nbsp;Gbps (USB4 Gen 4×2) and USB4 120&nbsp;Gbps (USB4 Gen 4 Asymmetric) transmitting 3 bits per 2 clock cycles.<ref>{{Cite web |last=GraniteRiverLabs |first=Team |date=2023-01-17 |title=Welcome to the 80Gpbs Ultra-High Speed Era of USB4 {{!}} GraniteRiverLabs Taiwan |url=https://www.graniteriverlabs.com/en-us/technical-blog/usb4-80-cio80 |url-status=live |archive-url=https://web.archive.org/web/20230221162539/https://www.graniteriverlabs.com/en-us/technical-blog/usb4-80-cio80 |archive-date=2023-02-21 |access-date=2023-02-21 |website=www.graniteriverlabs.com |language=en-us}}</ref> [[Thunderbolt 5]] uses the same PHY.<ref>{{cite web |author1=Ian Cutress |date=2021-08-01 |title=Intel Executive Posts Thunderbolt 5 Photo then Deletes It: 80 Gbps and PAM-3 |url=https://www.anandtech.com/show/16858/intel-executive-posts-thunderbolt-5-photo-80-gbps-and-pam3-then-deletes-it |website=AnandTech |language=en}}</ref>

===GDDR6X===
[[GDDR6 SDRAM|GDDR6X]], developed by Micron<ref>{{cite web |title=Doubling I/O Performance with PAM4 - Micron Innovates GDDR6X to Accelerate Graphics Memory |url=https://media-www.micron.com/-/media/client/global/documents/products/technical-marketing-brief/gddr6x_pam4_2x_speed_tech_brief |website=Micron |access-date=11 September 2020}}</ref> and Nvidia and first used in the [[GeForce 30 series|Nvidia RTX 3080 and 3090]] graphics cards, uses PAM-4 signaling to transmit 2 bits per clock cycle without having to resort to higher frequencies or two channels or lanes with associated transmitters and receivers, which may increase power or space consumption and cost. Higher frequencies require higher bandwidth, which is a significant problem beyond 28&nbsp;GHz when trying to transmit through copper. PAM-4 costs more to implement than earlier NRZ (non return to zero, PAM-2) coding partly because it requires more space in integrated circuits, and is more susceptible to SNR (signal to noise ratio) problems.<ref>{{Cite web|url=https://www.anandtech.com/show/15978/micron-spills-on-gddr6x-pam4-signaling-for-higher-rates-coming-to-nvidias-rtx-3090|title=Micron Spills on GDDR6X: PAM4 Signaling For Higher Rates, Coming to NVIDIA's RTX 3090|first=Ryan|last=Smith|website=AnandTech.com}}</ref><ref>{{Cite web|url=https://www.edn.com/the-fundamentals-of-pam4/|title=EDN - The fundamentals of PAM4|first=David|last=Maliniak|date=January 14, 2016}}</ref>

===GDDR7===
[[GDDR7 SDRAM|GDDR7]] will utilize PAM-3 signaling to achieve speeds of 36&nbsp;Gbps/pin. The higher data transmission rate per cycle compared to [[Non-return-to-zero|NRZ/PAM-2]]-signaling used by [[GDDR6]] and prior generations improves power efficiency and signal integrity.<ref>{{cite web |author1=Anton Shilov |title=Cadence Delivers Technical Details on GDDR7: 36 Gbps with PAM3 Encoding |url=https://www.anandtech.com/show/18759/cadence-derlivers-tech-details-on-gddr7-36gbps-pam3-encoding |website=AnandTech |language=en |date=2023-03-08}}</ref>

===PCI Express===
[[PCI Express 6.0]] has introduced PAM-4 usage.<ref>{{cite web|url=https://www.anandtech.com/show/14559/pci-express-bandwidth-to-be-doubled-again-pcie-60-announced-spec-to-land-in-2021|title=PCI Express Bandwidth to Be Doubled Again: PCIe 6.0 Announced, Spec to Land in 2021|first=Ryan|last=Smith|website=www.anandtech.com}}</ref>

===Photo biology===
The concept is also used for the study of [[photosynthesis]] using a specialized instrument that involves a [[fluorescence spectroscopy|spectrofluorometric]] measurement of the kinetics of fluorescence rise and decay in the light-harvesting antenna of [[thylakoid]] membranes, thus querying various aspects of the state of the photosystems under different environmental conditions.<ref>{{cite book|last1=Schreiber|first1=Ulrich|title=Chlorophyll a Fluorescence|volume=19|date=2004|publisher=Springer Netherlands|location=Dordrecht|isbn=978-1-4020-3217-2|pages=279–319|doi=10.1007/978-1-4020-3218-9_11|series=Advances in Photosynthesis and Respiration|chapter=Pulse-Amplitude-Modulation (PAM) Fluorometry and Saturation Pulse Method: An Overview}}</ref> Unlike the traditional dark-adapted [[chlorophyll fluorescence]] measurements, pulse amplitude fluorescence devices allow measuring under ambient light conditions, which made measurements significantly more versatile.<ref>{{Cite web|url=https://climexhandbook.w.uib.no/2019/11/03/chlorophyll-fluorescence/|title=5.1 Chlorophyll fluorescence – ClimEx Handbook|language=en-US|access-date=2020-01-14}}</ref>

===Electronic drivers for LED lighting===
Pulse-amplitude modulation has also been developed for the control of [[light-emitting diode]]s (LEDs), especially for lighting applications.<ref>{{cite magazine |first=Tim |last=Whitaker |date=January 2006 |url=http://www.ledsmagazine.com/articles/2006/01/closed-loop-electronic-controllers-drive-led-systems.html |title=Closed-Loop Electronic Controllers Drive LED Systems |magazine=LEDs |access-date=2020-10-29 }}</ref> LED drivers based on the PAM technique offer improved [[Efficient energy use|energy efficiency]] over systems based upon other common driver modulation techniques such as [[pulse-width modulation]] (PWM) as the forward current passing through an LED is relative to the intensity of the light output and the LED efficiency increases as the forward current is reduced.

Pulse-amplitude modulation LED drivers are able to synchronize pulses across multiple LED channels to enable perfect color matching. Due to the inherent nature of PAM in conjunction with the rapid switching speed of LEDs, it is possible to use LED lighting as a means of wireless data transmission at high speed.

===Digital television===
The North American [[Advanced Television Systems Committee standards]] for [[digital television]] uses a form of PAM to broadcast the data that makes up the television signal. This system, known as [[8VSB]], is based on an eight-level PAM.<ref>{{cite web|url=http://www.arrl.org/files/file/Technology/TV_Channels/8_Bit_VSB.pdf|title=WHAT EXACTLY IS 8-VSB ANYWAY?|last=Sparano|first=David|year=1997|access-date=8 Nov 2012}}</ref> It uses additional processing to suppress one [[Single-sideband modulation|sideband]] and thus make more efficient use of limited [[bandwidth (signal processing)|bandwidth]]. Using a single 6&nbsp;MHz channel allocation, as defined in the previous [[NTSC]] analog standard, 8VSB is capable of transmitting 32&nbsp;Mbit/s. After accounting for error-correcting codes and other overhead, the data rate in the signal is 19.39&nbsp;Mbit/s.

==See also==
{{Commons category|Pulse amplitude modulation}}
* [[8VSB]]
* [[Amplitude-shift keying]]
* [[Carrier Sense Multiple Access]]
* [[Pulse-density modulation]]
* [[Pulse forming network]]
* [[Quadrature amplitude modulation]] (QAM)

==Notes==
{{Notelist}}

==References==
{{Reflist}}

{{Bit-encoding}}

[[Category:Quantized radio modulation modes]]