4-channel, 224Gb/s PAM-4 optical transmitter with group delay compensation in 130-nm BiCMOS technology

Abstract

A compact 4-channel 224 Gb/s PAM4 optical transmitter in 130nm SiGe BiCMOS technology is presented employing 3-tap feedforward equalizer (FFE) and continuous time linear equalizer (CLTE) techniques. One pre-emphasis tap and CLTE structures broadened the bandwidth to 26 GHz. Moreover, the peak-peak value of group delay for this system is reduced to 6.7 ps by adopting one pre-fall tap structure. The output stage employs current mode logic circuits to achieve high modulation currents. This chip occupies an area of 1.8 mm×1.95 mm with a 250 um channel pitch. An operating rate of 56 Gb/s/ch is achieved when inputting 28Gbaud PAM-4 signal. The single-ended output voltage amplitude is 240 mV, corresponding to 5.6 mA modulation currents.

A high-output-swing 64-Gb/s PAM-4 transmitter with a 4-tap hybrid FFE in 28-nm CMOS

“…The data-traffic explosion driven by cloud computing, 5G networks, industrial IoT, and virtual reality has accelerated the demand for high-speed SerDes transceivers to provide massive data throughput [1,2,3,4,5,6,7,8]. Previous studies have demonstrated that four-level pulse amplitude modulation (PAM-4) is superior to non-return-to-zero (NRZ) for the 56∼112-Gb/s serial data communications due to its doubled spectral efficiency, halved Nyquist frequency, and relaxed clock speeds [9,10,11,12,13,14,15]. However, the reduced symbol levels render the PAM-4 scheme less tolerant to the residual inter-symbol interference and amplitude noise [16,17].…”