Active terminated current-mode pre-emphasis transmitter for PCI Express standard

Abstract

In this work we propose an active terminated current-mode pre-emphasis transmitter for high-speed chip-to-chip data communication. The salient feature of this current-mode transmitter is, it selectively provides high output port impedance while driving and 100-Ω differential impedance for the reflected signal coming back to the transmitter end. This feature helps in halving the signal current level for a specified signal swing at the output of the transmitter compared to traditional passive terminated current-mode transmitter. In the transmitter, a scaled down replica driver followed by a differential common drain is connected in parallel with the main driver. The output port impedance of this composite driver is matched with the characteristic impedance of the channel. However, while driving, the output signal appears to the output port through the replica and the main stage resulting in high impedance. The circuits have been implemented in a 1.8-V, 0.18-μm Digital CMOS technology meeting PCI Express standard. The simulated performance shows data transfer rate of 5 Gb/s, while transmitting the data over 15-in. FR4 PCB trace for a target bit-error rate (BER) of 10 12. The power consumed in the replica stage and main driver stage are 1.98 mW and 16.38 mW respectively for a target differential voltage swing of 800 mV.