1. Signal integrity
The phase locked loop (PLL, phase locked loop), CDR (clock and data recovery), 8B/10B codec and other mixed-signal modules in the transceiver are designed with analog signals, such as the voltage-controlled oscillator in the PLL, and there are also Digital signals, such as frequency dividers in PLLs, etc. In a chip, there are both analog and digital signals, which are prone to power synchronization noise, ground bounce and signal crosstalk. And the higher data rates of transceivers mean that non-ideal transmission line effects can make routing more difficult, with copper wires in layers creating a "skin effect," where high-frequency signals skim the surface of conductors, increasing signal attenuation.
2. Jitter
Jitter is the most important parameter to measure the robustness of the transceiver, because the jitter directly reflects the bit error rate of the transceiver. Factors that affect the jitter include the layout of power and ground, calibration circuits, package characteristics, etc. The most important of which is the high-speed clock generated by the PLL. The PLL is very important for clock and data recovery (CDR). The PLL is driven by the input reference clock, so the reference clock input needs to meet strict electrical and jitter requirements.
3. Equalization technology
Inter-symbol interference and various noise effects inevitably occur in the data transmitted in the channel. In the case of high speed, its interference will be more obvious. In order to overcome the transmission interference and loss, an equalizer is inserted into the transceiver system. After equalization correction, the system characteristics can be corrected and compensated, and the influence of inter-symbol interference can be reduced, so as to adapt to the random changes of the channel.
4. Pre-emphasis technology
At gigabit rates, designers cannot simply amplify the signal to address signal loss, as this would increase power consumption and cause eye closure. In layout, the intensity of the reflected energy exhibits proximal discontinuities. Pre-emphasis technology can pre-distort the transmitted signal by emphasizing the first data symbol after any signal change, eliminating the front-end overshoot and trailing-edge smear of the impulse response in the channel.