All-digital delay-locked loop for 3D-IC die-to-die clock synchronization

In this paper, an all-digital delay-locked loop (ADDLL) for 3D-IC die-to-die clock synchronization with through silicon vias (TSVs) is presented. The proposed ADDLL can tolerate delay variations in TSVs and synchronize the clock signals in multiple layers of a given 3D-IC. Firstly, after system is reset, the proposed ADDLL uses two high resolution delay lines which composed of digital controlled varactors (DCVs) to compensate for the delay variations in TSVs. Subsequently, the proposed ADDLL can further compensate for the clock skew of clock signals in multiple layers of a 3D-IC. After ADDLL is locked, the clock skew or phase error is eliminated, and data transfer between dies can be performed synchronously. The proposed design can operate from 300MHz to 1GHz. The proposed ADDLL is implemented in a standard performance 90nm CMOS process, and the area of the ADDLL per die is 0.045mm². The power consumption of the proposed ADDLL is 3.27mW at 1GHz, and the maximum phase error of clock signals in multiple layers of a given 3D-IC is 21.9ps.