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Pulse-amplitude modulation
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.
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 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.
Some versions of the Ethernet communication standard are an example of PAM usage.
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. Thunderbolt 5 uses the same PHY.
GDDR6X, 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 utilizes 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. Compared to PAM-4 (GDDR6X), it is less strict on manufacturing equipment.
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Pulse-amplitude modulation
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.
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 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.
Some versions of the Ethernet communication standard are an example of PAM usage.
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. Thunderbolt 5 uses the same PHY.
GDDR6X, 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 utilizes 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. Compared to PAM-4 (GDDR6X), it is less strict on manufacturing equipment.