A Coefficient-Error-Robust Feed-Forward Equalizing Transmitter for Eye-Variation and Power Improvement

This paper proposes a new feed-forward equalizing (FFE) transmitter (Tx) for a massively parallel I/Os to reduce calibration circuits and to save power consumption. The proposed FFE Tx improves its robustness to a coefficient error and its power efficiency by utilizing a high-pass digital difference filter and a channel loss to attenuate the effects of the coefficient errors. To verify the proposed FFE architecture, we fabricated the conventional and the proposed FFEs in 65 nm CMOS technology and tested eye sensitivity and eye variation at 8 Gb/s on 25 dB, 13.2 dB, and 9.6 dB PCB traces. Compared to the conventional FFE Tx, the proposed FFE Tx improves the eye sensitivity and the eye variation by about 230% on a 25 dB lossy channel without calibration. In addition, this improvement increases as the channel loss increases. The proposed FFE Tx also improves the power efficiency by 230% at 25% utilization on a 25 dB lossy channel. These results imply that the proposed FFE Tx can reduce calibration circuits in a massively parallel I/Os and the power consumption.