Pulse-amplitude modulation (PAM) is a form of signal

modulation 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 informat ...

where the message information is encoded in the

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a

train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often ...

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.

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 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 informa ...

transmission of digital data, with non-

baseband 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 i ...

applications having been largely replaced by

pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the ...

, 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

2^2

possible discrete pulse amplitudes; in 8-level PAM there are

2^3

possible discrete pulse amplitudes; and in 16-level PAM there are

2^4

possible discrete pulse amplitudes.

Uses

Ethernet

Some versions of the

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...

communication standard are an example of PAM usage. In particular,

100BASE-T4 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. Fast Ether ...

and

BroadR-Reach Ethernet standard BroadR-Reach technology is an Ethernet physical layer standard designed for automotive connectivity applications. BroadR-Reach allows multiple in-vehicle systems to simultaneously access information over unshielded single twisted pair cable. Broad ...

use three-level PAM modulation (PAM-3), while

1000BASE-T In computer networking, Gigabit Ethernet (GbE or 1 GigE) 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 ...

Gigabit Ethernet uses five-level PAM-5 modulation and

10GBASE-T 10 Gigabit Ethernet (10GE, 10GbE, or 10 GigE) 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 ...

10 Gigabit Ethernet uses a Tomlinson-Harashima Precoded (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern known as DSQ128.

25 Gigabit Ethernet 25 Gigabit Ethernet and 50 Gigabit Ethernet are standards for Ethernet connectivity in a datacenter environment, developed by IEEE 802.3 task forces and and are available from multiple vendors. History An industry consortium, 25G Ethernet Con ...

and some copper variants of 100 Gigabit Ethernet and 200 Gigabit Ethernet use PAM-4 modulation.

GDDR6X

GDDR6X, developed by Micron and Nvidia and first used in the Nvidia RTX 3080 and 3090 graphics cards, uses PAM4 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. PAM4 costs more to implement than earlier NRZ (non return to zero, PAM2) coding partly because it requires more space in integrated circuits, and is more susceptible to SNR (signal to noise ratio) problems.

PCI Express

PCI Express 6.0 has introduced PAM usage.

Photo biology

The concept is also used for the study of

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

using a specialized instrument that involves a spectrofluorometric measurement of the kinetics of fluorescence rise and decay in the light-harvesting antenna of

thylakoid Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thyl ...

membranes, thus querying various aspects of the state of the photosystems under different environmental conditions. Unlike the traditional dark-adapted chlorophyll fluorescence measurements, pulse amplitude fluorescence devices allow measuring under ambient light conditions, which made measurements significantly more versatile.

Electronic drivers for LED lighting

Pulse-amplitude modulation has also been developed for the control of

light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

s (LEDs), especially for lighting applications. 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 Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...

(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 Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative adva ...

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. It uses additional processing to suppress one

sideband In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands ...

and thus make more efficient use of limited bandwidth. Using a single 6 MHz channel allocation, as defined in the previous

NTSC The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...

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.

Notes

References

{{Bit-encoding Quantized radio modulation modes