Pulse-amplitude modulation

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Principle of PAM: (1) original signal, (2) PAM signal, (a) amplitude of signal, (b) time PAM neutral.svg
Principle of PAM: (1) original signal, (2) PAM signal, (a) amplitude of signal, (b) time

Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. Demodulation is performed by detecting the amplitude level of the carrier at every single period.

Contents

Types

There are two types of pulse amplitude modulation:

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 possible discrete pulse amplitudes; in 8-level PAM there are possible discrete pulse amplitudes; and in 16-level PAM there are 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 [1] [lower-alpha 1] and 10GBASE-T 10 Gigabit Ethernet uses a Tomlinson-Harashima precoded [ jargon ] (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern[ jargon ] 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 Gbps (USB4 Gen 4×2) and USB4 120 Gbps (USB4 Gen 4 Asymmetric) transmitting 3 bits per 2 clock cycles. [2] Thunderbolt 5 uses the same PHY. [3]

GDDR6X

GDDR6X, developed by Micron [4] and Nvidia and first used in the 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 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. [5] [6]

GDDR7

GDDR7 will utilize PAM-3 signaling to achieve speeds of 36 Gbps/pin. The higher data transmission rate per cycle compared to NRZ/PAM-2-signaling used by GDDR6 and prior generations improves power efficiency and signal integrity. [7]

PCI Express

PCI Express 6.0 has introduced PAM-4 usage. [8]

Photo biology

The concept is also used for the study of photosynthesis using a specialized instrument that involves a 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. [9] Unlike the traditional dark-adapted chlorophyll fluorescence measurements, pulse amplitude fluorescence devices allow measuring under ambient light conditions, which made measurements significantly more versatile. [10]

Electronic drivers for LED lighting

Pulse-amplitude modulation has also been developed for the control of light-emitting diodes (LEDs), especially for lighting applications. [11] LED drivers based on the PAM technique offer improved 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. [12] It uses additional processing to suppress one sideband and thus make more efficient use of limited bandwidth. Using a single 6 MHz channel allocation, as defined in the previous NTSC analog standard, 8VSB is capable of transmitting 32 Mbit/s. After accounting for error-correcting codes and other overhead, the data rate in the signal is 19.39 Mbit/s.

See also

Notes

  1. ↑ 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.

Related Research Articles

In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.

<span class="mw-page-title-main">Ethernet over twisted pair</span> Ethernet physical layers using twisted-pair cables

Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.

<span class="mw-page-title-main">Baseband</span> Range of frequencies occupied by an unmodulated signal

In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into an electrical signal. For example, the electronic output of a microphone is a baseband signal that is analogous to the applied voice audio. In conventional analog radio broadcasting, the baseband audio signal is used to modulate an RF carrier signal of a much higher frequency.

<span class="mw-page-title-main">Non-return-to-zero</span> Telecommunication coding technique

In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with no other neutral or rest condition.

In telecommunication, a ternary signal is a signal that can assume, at any given instant, one of three states or significant conditions, such as power level, phase position, pulse duration, or frequency.

<span class="mw-page-title-main">Fast Ethernet</span> Ethernet standards that carry data at the nominal rate of 100 Mbit/s

In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common.

<span class="mw-page-title-main">Gigabit Ethernet</span> Standard for Ethernet networking at a data rate of 1 gigabit per second

In computer networking, Gigabit Ethernet is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use in 1999, and has replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards. The first standard for faster 10 Gigabit Ethernet was approved in 2002.

8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM.

<span class="mw-page-title-main">Small Form-factor Pluggable</span> Modular communications interface

Small Form-factor Pluggable (SFP) is a compact, hot-pluggable network interface module format used for both telecommunication and data communications applications. An SFP interface on networking hardware is a modular slot for a media-specific transceiver, such as for a fiber-optic cable or a copper cable. The advantage of using SFPs compared to fixed interfaces is that individual ports can be equipped with different types of transceivers as required, with the majority including optical line terminals, network cards, switches and routers.

<span class="mw-page-title-main">Multi-mode optical fiber</span> Type of optical fiber mostly used for communication over short distances

Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 800 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.

The physical coding sublayer (PCS) is a networking protocol sublayer in the Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet standards. It resides at the top of the physical layer (PHY), and provides an interface between the physical medium attachment (PMA) sublayer and the media-independent interface (MII). It is responsible for data encoding and decoding, scrambling and descrambling, alignment marker insertion and removal, block and symbol redistribution, and lane block synchronization and deskew.

<span class="mw-page-title-main">Ethernet physical layer</span> Electrical or optical properties between network devices

The physical-layer specifications of the Ethernet family of computer network standards are published by the Institute of Electrical and Electronics Engineers (IEEE), which defines the electrical or optical properties and the transfer speed of the physical connection between a device and the network or between network devices. It is complemented by the MAC layer and the logical link layer. An implementation of a specific physical layer is commonly referred to as PHY.

40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) are groups of computer networking technologies for transmitting Ethernet frames at rates of 40 and 100 gigabits per second (Gbit/s), respectively. These technologies offer significantly higher speeds than 10 Gigabit Ethernet. The technology was first defined by the IEEE 802.3ba-2010 standard and later by the 802.3bg-2011, 802.3bj-2014, 802.3bm-2015, and 802.3cd-2018 standards. The first succeeding Terabit Ethernet specifications were approved in 2017.

<span class="mw-page-title-main">10 Gigabit Ethernet</span> Standards for Ethernet at ten times the speed of Gigabit Ethernet

10 Gigabit Ethernet is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlike previous Ethernet standards, 10GbE defines only full-duplex point-to-point links which are generally connected by network switches; shared-medium CSMA/CD operation has not been carried over from the previous generations of Ethernet standards so half-duplex operation and repeater hubs do not exist in 10GbE. The first standard for faster 100 Gigabit Ethernet links was approved in 2010.

Terabit Ethernet (TbE) is Ethernet with speeds above 100 Gigabit Ethernet. The 400 Gigabit Ethernet and 200 Gigabit Ethernet standard developed by the IEEE P802.3bs Task Force using broadly similar technology to 100 Gigabit Ethernet was approved on December 6, 2017. On February 16, 2024 the 800 Gigabit Ethernet standard developed by the IEEE P802.3df Task Force was approved.

25 Gigabit Ethernet and 50 Gigabit Ethernet are standards for Ethernet connectivity in a datacenter environment, developed by IEEE 802.3 task forces 802.3by and 802.3cd and are available from multiple vendors.

IEEE 802.3bz, NBASE-T and MGBASE-T are standards released in 2016 for Ethernet over twisted pair at speeds of 2.5 and 5 Gbit/s. These use the same cabling as the ubiquitous Gigabit Ethernet, yet offer higher speeds. The resulting standards are named 2.5GBASE-T and 5GBASE-T.

Graphics Double Data Rate 6 Synchronous Dynamic Random-Access Memory is a type of synchronous graphics random-access memory (SGRAM) with a high bandwidth, "double data rate" interface, designed for use in graphics cards, game consoles, and high-performance computing. It is a type of GDDR SDRAM, and is the successor to GDDR5. Just like GDDR5X it uses QDR in reference to the write command clock (WCK) and ODR in reference to the command clock (CK).

Coherent optical module refers to a typically hot-pluggable coherent optical transceiver that uses coherent modulation (BPSK/QPSK/QAM) rather than amplitude modulation (RZ/NRZ/PAM4) and is typically used in high-bandwidth data communications applications. Optical modules typically have an electrical interface on the side that connects to the inside of the system and an optical interface on the side that connects to the outside world through a fiber optic cable. The technical details of coherent optical modules were proprietary for many years, but have recently attracted efforts by multi-source agreement (MSA) groups and a standards development organizations such as the Optical Internetworking Forum. Coherent optical modules can either plug into a front panel socket or an on-board socket. Coherent optical modules form a smaller piece of a much larger optical module industry.

Graphics Double Data Rate 7 Synchronous Dynamic Random-Access Memory is a type of synchronous graphics random-access memory (SGRAM) specified by the JEDEC Semiconductor Memory Standard, with a high bandwidth, "double data rate" interface, designed for use in graphics cards, game consoles, and high-performance computing. It is a type of GDDR SDRAM, and is the successor to GDDR6.

References

  1. ↑ George Schroeder (2003-04-01). "What PAM5 means to you". EDN. Retrieved 2022-02-16.
  2. ↑ GraniteRiverLabs, Team (2023-01-17). "Welcome to the 80Gpbs Ultra-High Speed Era of USB4 | GraniteRiverLabs Taiwan". www.graniteriverlabs.com. Archived from the original on 2023-02-21. Retrieved 2023-02-21.
  3. ↑ Ian Cutress (2021-08-01). "Intel Executive Posts Thunderbolt 5 Photo then Deletes It: 80 Gbps and PAM-3". AnandTech.
  4. ↑ "Doubling I/O Performance with PAM4 - Micron Innovates GDDR6X to Accelerate Graphics Memory". Micron. Retrieved 11 September 2020.
  5. ↑ Smith, Ryan. "Micron Spills on GDDR6X: PAM4 Signaling For Higher Rates, Coming to NVIDIA's RTX 3090". AnandTech.com.
  6. ↑ Maliniak, David (January 14, 2016). "EDN - The fundamentals of PAM4".
  7. ↑ Anton Shilov (2023-03-08). "Cadence Delivers Technical Details on GDDR7: 36 Gbps with PAM3 Encoding". AnandTech.
  8. ↑ Smith, Ryan. "PCI Express Bandwidth to Be Doubled Again: PCIe 6.0 Announced, Spec to Land in 2021". www.anandtech.com.
  9. ↑ Schreiber, Ulrich (2004). "Pulse-Amplitude-Modulation (PAM) Fluorometry and Saturation Pulse Method: An Overview". Chlorophyll a Fluorescence. Advances in Photosynthesis and Respiration. Vol. 19. Dordrecht: Springer Netherlands. pp. 279–319. doi:10.1007/978-1-4020-3218-9_11. ISBN   978-1-4020-3217-2.
  10. ↑ "5.1 Chlorophyll fluorescence – ClimEx Handbook" . Retrieved 2020-01-14.
  11. ↑ Whitaker, Tim (January 2006). "Closed-Loop Electronic Controllers Drive LED Systems". LEDs. Retrieved 2020-10-29.
  12. ↑ Sparano, David (1997). "WHAT EXACTLY IS 8-VSB ANYWAY?" (PDF). Retrieved 8 Nov 2012.
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