基于Duobinary信号调制的高速串行发射机建模与仿真

Modeling and simulation of high speed serial transmitter based on duobinary signal modulation

随着大数据产业急速发展,高速串行收发(SerDes)系统的数据传输速率不断提高,但高速信号传输时受到的高频衰减带来了更强的符号间干扰(ISI),这极大降低了信号质量,阻碍了传输速率的进一步提高。要抑制传输过程中的符号间干扰信号损耗,除了改进电路结构,另一个可行的思路是在保持信号波特率不变的情况下,让信号能量更集中在低频,降低高频衰减,从而缓解非理想信道带来的符号间干扰。讨论了双二进制编码(Duobinary)信号调制方式的调制原理并同不归零码(NRZ)编码进行了对比,分析了Duobinary信号调制的传递函数,并基于Duobinary调制方式在Cadence平台对56 Gb/s高速串行发射机进行了系统建模与仿真。发射机包含并行伪随机码(PRBS)发生器,树形结构合路器(MUX),3抽头前向反馈均衡器(Feedforward Equalization,FFE),非理想信道等电路模块。理论分析表明,相较传统的不归零码(NRZ),同速率的Duobinary编码信号功率谱更集中在低频成分。仿真结果表明,Duobinary编码信号在经过非理想信道后的眼图相较同速率NRZ信号更为清晰,受到的符号间干扰更小。因此Duobinary信号作为SerDes系统的调制方式,在抗信道干扰方面具有优势。

With the rapid development of the big data industry,the data transmission rate of the SerDes system continues to increase,but the high-frequency attenuation suffered during high-speed signal transmission brings stronger inter-symbol interference(ISI),which greatly reduces the signal quality and hinders further increase in transmission rate.To suppress the signal loss of intersymbol interference during transmission,in addition to improving the circuit structure,another feasible path is to concentrate the signal energy in the lower frequency and reduce the high frequency attenuation while keeping the signal baud rate unchanged,aiming to alleviating the Intersymbol interference caused by non-ideal channels.The modulation principle of Duobinary signal modulation is discussed and compared with NRZ coding,the transfer function of Duobinary signal modulation is analyzed,and the system modeling and simulation of 56 Gb/s high-speed serial transmitter is carried out with Cadence based on Duobinary modulation.The transmitter includes parallel PRBS generator,tree structure MUX,3-tap forward feedback equalizer(FFE),non-ideal channel and other circuit modules.Theoretical analysis shows that,compared with the traditional non-return-to-zero code(NRZ),the power spectrum of the Duobinary coded signal at the same rate is more concentrated in the low frequency components.The simulation results show that the eye diagram of the Duobinary coded signal after passing through the non-ideal channel is clearer than that of the NRZ signal at the same rate,and suffers less inter-symbol interference.Therefore,as the modulation method of the SerDes system,the Duobinary signal has advantages in resisting channel interference.