# Pulse-amplitude modulation

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Form of signal modulation

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

Passband modulation Analog modulation AM SM SSB Angle modulation FM PM QAM Digital modulation ASK APSK CPM FSK MFSK MSK OOK PPM PSK QAM SC-FDE TCM TC-PAM WDM Hierarchical modulation QAM WDM Spread spectrum CSS DSSS FHSS THSS See also Capacity-approaching codes Demodulation Line coding Modem AnM PoM PAM PCM PDM PWM ΔΣM OFDM FDM Multiplexing v t e

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

## Types

### Polarities

There are two types of pulse amplitude modulation:

- In *single polarity PAM*, a suitable fixed [DC bias](/source/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](/source/Modulating_signal) transmission of digital data, with non-[baseband](/source/Baseband) applications having been largely replaced by [pulse-code modulation](/source/Pulse-code_modulation), and, more recently, by [pulse-position modulation](/source/Pulse-position_modulation).

### Amplitudes

The number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some natural number not less than 3 (PAM-2 would be a simple binary signal and is usually not considered to be PAM). Common choices for the number of amplitudes are: 3, 4, 5, 8, 16.

## Uses

### Ethernet

Some versions of the [Ethernet](/source/Ethernet) communication standard are an example of PAM usage.

- [100BASE-T4](/source/100BASE-T4) and [BroadR-Reach Ethernet standard](/source/BroadR-Reach_Ethernet_standard) use three-level PAM modulation (PAM-3).

- [1000BASE-T](/source/1000BASE-T) Gigabit Ethernet uses five-level PAM-5 modulation.[1][a]

- [10GBASE-T](/source/10GBASE-T) 10 Gigabit Ethernet uses a [Tomlinson–Harashima precoded](/source/Tomlinson-Harashima_precoding) (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16). The THP precoding provides for noise resistance. Two consecutive PAM-16-encoded symbols are interpreted according to a two-dimensional checkerboard pattern known as DSQ128, where 128 out of 256 possible combinations are picked to maximize their "distance" (again for noise resistance). This provides the same SNR as PAM-8 while increasing the data rate by 7⁄6.[2]

- [25 Gigabit Ethernet](/source/25_Gigabit_Ethernet) and some copper variants of [100 Gigabit Ethernet](/source/100_Gigabit_Ethernet) and [200 Gigabit Ethernet](/source/200_Gigabit_Ethernet) use PAM-4 modulation.

### USB

[USB4](/source/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.[3] [Thunderbolt 5](/source/Thunderbolt_5) uses the same PHY.[4]

### Video memory

[GDDR6X](/source/GDDR6_SDRAM), developed by Micron[5] and Nvidia and first used in the [Nvidia RTX 3080 and 3090](/source/GeForce_30_series) 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.[6][7]

[GDDR7](/source/GDDR7_SDRAM) utilizes PAM-3 signaling to achieve speeds of 36 Gbps/pin. The higher data transmission rate per cycle compared to [NRZ/PAM-2](/source/Non-return-to-zero)-signaling used by [GDDR6](/source/GDDR6) and prior generations improves power efficiency and signal integrity.[8] Compared to PAM-4 (GDDR6X), it is less strict on manufacturing equipment.[9]

### PCI Express

[PCI Express 6.0](/source/PCI_Express_6.0) has introduced PAM-4 usage.[10]

### Digital television

The North American [Advanced Television Systems Committee standards](/source/Advanced_Television_Systems_Committee_standards) for [digital television](/source/Digital_television) uses a form of PAM to broadcast the data that makes up the television signal. This system, known as [8VSB](/source/8VSB), is based on an eight-level PAM.[11] It uses additional processing to suppress one [sideband](/source/Single-sideband_modulation) and thus make more efficient use of limited [bandwidth](/source/Bandwidth_(signal_processing)). Using a single 6 MHz channel allocation, as defined in the previous [NTSC](/source/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.

### Photobiology

The concept is also used for the study of [photosynthesis](/source/Photosynthesis) using a specialized instrument that involves a [spectrofluorometric](/source/Fluorescence_spectroscopy) measurement of the kinetics of fluorescence rise and decay in the light-harvesting antenna of [thylakoid](/source/Thylakoid) membranes, thus querying various aspects of the state of the photosystems under different environmental conditions.[12] Unlike the traditional dark-adapted [chlorophyll fluorescence](/source/Chlorophyll_fluorescence) measurements, pulse amplitude fluorescence devices allow measuring under ambient light conditions, which made measurements significantly more versatile.[13]

### Electronic drivers for LED lighting

Pulse-amplitude modulation has also been developed for the control of [light-emitting diodes](/source/Light-emitting_diode) (LEDs), especially for lighting applications.[14] LED drivers based on the PAM technique offer improved [energy efficiency](/source/Efficient_energy_use) over systems based upon other common driver modulation techniques such as [pulse-width modulation](/source/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.

## See also

Wikimedia Commons has media related to [Pulse amplitude modulation](https://commons.wikimedia.org/wiki/Category:Pulse_amplitude_modulation).

- [8VSB](/source/8VSB)

- [Amplitude-shift keying](/source/Amplitude-shift_keying)

- [Carrier-sense multiple access](/source/Carrier-sense_multiple_access)

- [Pulse-density modulation](/source/Pulse-density_modulation)

- [Pulse-forming network](/source/Pulse-forming_network)

- [Quadrature amplitude modulation](/source/Quadrature_amplitude_modulation) (QAM)

## Notes

1. **[^](#cite_ref-2)** The first use of PAM-5 in Ethernet was in [100BASE-T2](/source/100BASE-T2). Although not widely adopted, the technology developed for 100BASE-T2 was subsequently used in the popular 1000BASE-T Gigabit Ethernet standard.

## References

1. **[^](#cite_ref-1)** George Schroeder (2003-04-01). ["What PAM5 means to you"](https://www.edn.com/what-pam5-means-to-you/). *EDN*. Retrieved 2022-02-16.

1. **[^](#cite_ref-3)** ["Why does 10Gbps ethernet claim PAM16 encoding then use a squared DSQ128 constellation?"](https://networkengineering.stackexchange.com/questions/42108). *Network Engineering Stack Exchange*.

1. **[^](#cite_ref-4)** GraniteRiverLabs, Team (2023-01-17). ["Welcome to the 80Gpbs Ultra-High Speed Era of USB4 | GraniteRiverLabs Taiwan"](https://www.graniteriverlabs.com/en-us/technical-blog/usb4-80-cio80). *www.graniteriverlabs.com*. [Archived](https://web.archive.org/web/20230221162539/https://www.graniteriverlabs.com/en-us/technical-blog/usb4-80-cio80) from the original on 2023-02-21. Retrieved 2023-02-21.

1. **[^](#cite_ref-5)** Ian Cutress (2021-08-01). ["Intel Executive Posts Thunderbolt 5 Photo then Deletes It: 80 Gbps and PAM-3"](https://web.archive.org/web/20210801175418/https://www.anandtech.com/show/16858/intel-executive-posts-thunderbolt-5-photo-80-gbps-and-pam3-then-deletes-it). *AnandTech*. Archived from [the original](https://www.anandtech.com/show/16858/intel-executive-posts-thunderbolt-5-photo-80-gbps-and-pam3-then-deletes-it) on August 1, 2021.

1. **[^](#cite_ref-6)** ["Doubling I/O Performance with PAM4 - Micron Innovates GDDR6X to Accelerate Graphics Memory"](https://media-www.micron.com/-/media/client/global/documents/products/technical-marketing-brief/gddr6x_pam4_2x_speed_tech_brief). *Micron*. Retrieved 11 September 2020.

1. **[^](#cite_ref-7)** Smith, Ryan. ["Micron Spills on GDDR6X: PAM4 Signaling For Higher Rates, Coming to NVIDIA's RTX 3090"](https://web.archive.org/web/20200814201640/https://www.anandtech.com/show/15978/micron-spills-on-gddr6x-pam4-signaling-for-higher-rates-coming-to-nvidias-rtx-3090). *AnandTech.com*. Archived from [the original](https://www.anandtech.com/show/15978/micron-spills-on-gddr6x-pam4-signaling-for-higher-rates-coming-to-nvidias-rtx-3090) on August 14, 2020.

1. **[^](#cite_ref-8)** Maliniak, David (January 14, 2016). ["EDN - The fundamentals of PAM4"](https://www.edn.com/the-fundamentals-of-pam4/).

1. **[^](#cite_ref-9)** Anton Shilov (2023-03-08). ["Cadence Delivers Technical Details on GDDR7: 36 Gbps with PAM3 Encoding"](https://web.archive.org/web/20230308232935/https://www.anandtech.com/show/18759/cadence-derlivers-tech-details-on-gddr7-36gbps-pam3-encoding). *AnandTech*. Archived from [the original](https://www.anandtech.com/show/18759/cadence-derlivers-tech-details-on-gddr7-36gbps-pam3-encoding) on March 8, 2023.

1. **[^](#cite_ref-10)** Anton Shilov (2023-07-19). ["GDDR7 Arrives: Samsung Outs World's First Chip, 32 GT/s for Next-Gen GPUs"](https://www.tomshardware.com/news/samsung-develops-worlds-first-gddr7-chip). *[Tom's Hardware](/source/Tom's_Hardware)*. Retrieved 2023-10-06.

1. **[^](#cite_ref-11)** Smith, Ryan. ["PCI Express Bandwidth to Be Doubled Again: PCIe 6.0 Announced, Spec to Land in 2021"](https://www.anandtech.com/show/14559/pci-express-bandwidth-to-be-doubled-again-pcie-60-announced-spec-to-land-in-2021). *www.anandtech.com*.{{[cite web](https://en.wikipedia.org/wiki/Template:Cite_web)}}: CS1 maint: deprecated archival service ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_deprecated_archival_service))

1. **[^](#cite_ref-12)** Sparano, David (1997). ["WHAT EXACTLY IS 8-VSB ANYWAY?"](http://www.arrl.org/files/file/Technology/TV_Channels/8_Bit_VSB.pdf) (PDF). Retrieved 8 Nov 2012.

1. **[^](#cite_ref-13)** 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](/source/Doi_(identifier)):[10.1007/978-1-4020-3218-9_11](https://doi.org/10.1007%2F978-1-4020-3218-9_11). [ISBN](/source/ISBN_(identifier)) [978-1-4020-3217-2](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4020-3217-2).

1. **[^](#cite_ref-14)** ["5.1 Chlorophyll fluorescence – ClimEx Handbook"](https://climexhandbook.w.uib.no/2019/11/03/chlorophyll-fluorescence/). Retrieved 2020-01-14.

1. **[^](#cite_ref-15)** Whitaker, Tim (January 2006). ["Closed-Loop Electronic Controllers Drive LED Systems"](http://www.ledsmagazine.com/articles/2006/01/closed-loop-electronic-controllers-drive-led-systems.html). *LEDs*. Retrieved 2020-10-29.

v t e Line coding (digital baseband transmission) Main articles Unipolar encoding Bipolar encoding On–off keying Mark and space Basic line codes Return to zero (RZ) Non-return-to-zero, level (NRZ/NRZ-L) Non-return-to-zero, inverted (NRZ-I) Non-return-to-zero, space (NRZ-S) Manchester Differential Manchester/biphase (Bi-φ) Extended line codes Conditioned diphase 4B3T 4B5B 2B1Q Alternate mark inversion Modified AMI code Coded mark inversion MLT-3 encoding Hybrid ternary code 6b/8b encoding 8b/10b encoding 64b/66b encoding Eight-to-fourteen modulation Delay/Miller encoding TC-PAM Optical line codes Carrier-Suppressed Return-to-Zero Alternate-Phase Return-to-Zero See also: Baseband Baud Bit rate Digital signal Digital transmission Ethernet physical layer Pulse modulation methods Pulse-amplitude modulation (PAM) Pulse-code modulation (PCM) Serial communication Category:Line codes

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