An FFE Transmitter Which Automatically and Adaptively Relaxes Impedance Matching

This paper proposes the first feed-forward equalizing transmitter (Tx) which adaptively relaxes impedance matching. Using an on-chip time-domain reflectometer monitor, the Tx accurately detects the impedances of the channel and the receiver (Rx), and then automatically configures its termination impedance to maximize the received signal by optimally relaxing the constraint of impedance matching at the cost of a negligible penalty in signal integrity. The Tx is universally compatible with arbitrary impedances of channels and Rxs, and achieves better performance and power efficiency than the conventional Tx with impedance matching. The proposed Tx was fabricated in 65-nm CMOS technology. The Tx successfully adapted to any combination of a channel impedance of 35–75 $\Omega $ and a receiver impedance of 30–200 $\Omega $ . When the impedance matching of the Tx is adaptively and optimally relaxed, the eye size and the power efficiency are improved by up to 3.8 times and 2 times, respectively, compared with the conventional Tx. These results verify that the proposed Tx can adapt to various impedances of the channel and the receiver while achieving better performance and power efficiency than the conventional Tx with impedance matching.