- Catherine
- September 7, 2023
- 8:10 am
John Doe
Answered on 8:10 am
PAM-4 and NRZ are two different modulation techniques that are used to transmit data over an electrical or optical channel. Modulation is the process of changing the characteristics of a signal (such as voltage, amplitude, or frequency) to encode information. PAM-4 and NRZ have different advantages and disadvantages depending on the channel characteristics and the data rate.
PAM-4 stands for Pulse Amplitude Modulation 4-level. It means that the signal can have four different levels of amplitude (or voltage), each representing two bits of information. For example, a PAM-4 signal can use 0V, 1V, 2V, and 3V to encode 00, 01, 11, and 10 respectively. PAM-4 can transmit twice as much data as NRZ for the same symbol rate (or baud rate), which is the number of times the signal changes per second. However, PAM-4 also has some drawbacks, such as higher power consumption, lower signal-to-noise ratio (SNR), and higher bit error rate (BER). PAM-4 requires more sophisticated signal processing and error correction techniques to overcome these challenges. PAM-4 is used for high-speed data transmission such as 400G Ethernet.
NRZ stands for Non-Return-to-Zero. It means that the signal can have two different levels of amplitude (or voltage), each representing one bit of information. For example, a NRZ signal can use -1V and +1V to encode 0 and 1 respectively. NRZ does not return to zero voltage between symbols, hence the name. NRZ has some advantages over PAM-4, such as lower power consumption, higher SNR, and lower BER. NRZ is simpler and more robust than PAM-4, but it also has a lower data rate for the same symbol rate. NRZ is used for short-distance data transmission such as 100G Ethernet.
When a signal is referred to as “25Gb/s NRZ” or “25G NRZ”, it means the signal is carrying data at 25 Gbit / second with NRZ modulation. When a signal is referred to as “50G PAM-4”, or “100G PAM-4” it means the signal is carrying data at a rate of 50 Gbit / second, or 100 Gbit / second, respectively, using PAM-4 modulation.
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