Clock and data recovery circuit for PAM4 receiver

Abstract

The invention discloses a clock and data recovery circuit for a PAM4 receiver, and the circuit comprises a waveform screening device which screens four types of jumps which pass through a central threshold and a central zero point from 12 types of jumping modes, guarantees that the jump edge density is high enough, and solves the problem of input jitter caused by the discretization of the jump zero crossing point; the phase discriminator is used for obtaining phase lead / lag information between the screening signal and the recovery clock; the differential V / I converter is used for converting the voltage pulse reflecting the phase difference into charging and discharging current, and the consistency of paths is fully considered; the loop filter is used for reflecting pulse current of the phase difference to charge and discharge a capacitor and filtering ripples of a voltage signal; and the voltage-controlled oscillator is used for realizing conversion from frequency change to phase deviation. The clock output by the PAM4CDR provided by the invention has the advantages of small jitter and large swing. And for waveform hopping selection of the CDR of the PAM4 receiver, low jitter and high stability are realized, and the method has a wide application prospect.

Description

technical field [0001] The invention relates to the field of high-speed communication, and relates to a clock and data recovery circuit for a PAM4 receiver. Background technique [0002] Facing the pressure brought by the limitation of transmission rate and circuit bandwidth, in order to achieve a higher rate of information transmission, consider using 4-level pulse amplitude modulation (4-level Pulse Amplitude Modulation, PAM4) or other multi-level modulation methods to break through this problem. [0003] The PAM4 receiver is composed of an analog front-end circuit, a clock data recovery circuit (Clock Data Recovery, CDR), a digital signal processing circuit and other circuits. Because there is usually no separate channel used to transmit the clock signal in serial communication, the clock needs to be recovered from the data at the receiving end. The clock data recovery circuit plays a vital role in the whole serial link, and its performance directly affects the quality ...

AI Technical Summary

Problems solved by technology

[0008] To sum up, the PAM4 signal has 4 levels and 12 jump modes, which make the zero-crossing points different. These discrete zero-crossing points cause the thermometer code period (pulse width) recovered by the PAM4 signal to be inconsistent, thus causing phase jitter

This not only causes timing errors in the subsequent decoding circuit, but also increases the instability of the receiver CDR circuit

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