Analysis of Transmitter Driver with High Output Resistance Using Gain-Boosted Current Source

Abstract

Analysis of Transmitter Driver with High Output Resistance Using Gain-Boosted Current Source Seungwoo Son Department of Nanoscale Semiconductor Engineering The Graduate School Hanyang University This thesis proposes a novel transmitter driver design used in memory-to-memory communication, characterized by high swing and high output resistance. This design ensures the safe transmission of PAM-8 signals without distortion or reflection. A current source with a stack structure different from the conventional current source is implemented to achieve high output resistance [3],[4]. Furthermore, the use of gain-boosting feedback significantly enhances the output resistance, with the output resistance of the transmitter driver being augmented by up to 58.7 times compared to non-feedback designs. The gain in the gain-boosting feedback amplifier is adjustable through a potentiometer. In addition, this thesis introduces a protective cascode circuit designed for high-swing operation [1],[2]. This circuit prevents the direct connection of the drain node to the output node. Even if the gate node voltage of the input transistor drops to 0V, because the drain node is not directly connected to the output node, the circuit can be protected from gate-oxide breakdown regardless of supply voltage. A bleeder current source is also proposed to prevent charge accumulation at the floating node created by the protective cascode, ensuring steady operation. According to post-layout simulations conducted in the 28-nm CMOS process, the proposed transmitter driver can safely communicate PAM-8 signals at a data rate of 150 Gb/s, consuming 98.22 mW of power at a supply voltage of 2.4V.