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

modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

in which 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 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 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 ...

applications having been largely replaced by

pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent 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 amplitud ...

, and, more recently, by

pulse-position modulation Pulse-position modulation (PPM) is a form of signal modulation in which ''M'' message bits are encoded by transmitting a single pulse in one of 2^M possible required time shifts. This is repeated every ''T'' seconds, such that the transmitted b ...

. The number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some natural number.

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 198 ...

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 and

10GBASE-T 10 Gigabit Ethernet (abbreviated 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. Unli ...

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 and some copper variants of

100 Gigabit Ethernet 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 ...

and 200 Gigabit Ethernet use PAM-4 modulation.

USB

USB4 Universal Serial Bus 4 (USB4), sometimes erroneously referred to as USB 4.0, is the most recent technical specification of the USB (Universal Serial Bus) data communication standard. The USB Implementers Forum originally announced USB4 in 201 ...

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. Thunderbolt 5 uses the same PHY.

GDDR6X

GDDR6X Graphics Double Data Rate 6 Synchronous Dynamic Random-Access Memory (GDDR6 SDRAM) is a type of Synchronous dynamic random-access memory#Synchronous graphics RAM .28SGRAM.29, synchronous graphics random-access memory (SGRAM) with a high Bandwidth ...

, developed by Micron 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.

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 Graphics Double Data Rate 6 Synchronous Dynamic Random-Access Memory (GDDR6 SDRAM) 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 con ...

and prior generations improves power efficiency and signal integrity.

PCI Express

PCI Express 6.0 has introduced PAM-4 usage.

Photo biology

The concept is also used for the study of

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

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 cyanobacterium, cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a #Membrane, thylakoid membrane surrounding a #Lumen, ...

membranes, thus querying various aspects of the state of the photosystems under different environmental conditions. Unlike the traditional dark-adapted

chlorophyll fluorescence Chlorophyll fluorescence is light re-emitted by chlorophyll molecules during return from Excited state, excited to non-excited states. It is used as an indicator of photosynthetic energy conversion in plants, algae and bacteria. Excited chlorop ...

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 device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...

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), also known as pulse-duration modulation (PDM) or pulse-length modulation (PLM), is any method of representing a signal as a rectangular wave with a varying duty cycle (and for some methods also a varying peri ...

(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 signal, digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an ...

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 c ...

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

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

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