A programmbale 8-channel multiphase clock generator with 360 phases for focus ultrasound applications

Abstract

An area efficient, programmable multichannel, multiphase clock generator is proposed to improve the phase resolution for focus ultrasound applications. By using the proposed phase-folding method, the cell amount for generating 360 phases are reduced from 360 to 38 cells. The proposed clock generator is able to provide 360 phases in real-time with 1° phase resolution, 1–51.9% 6-bit DPWM for each channel, and which output frequency varies from 0.1 to 1.5 MHz. Due to the proposed multiphase system is a real-time system, many independent multichannel applications such as focus ultrasound could easily adopt the proposed structure. A new phase-error calibration method for PLL is also present in this paper for reducing the static phase-error due to process voltage and temperature variation. It improves the accuracy of the phase difference in the multiphase system. The proposed ASIC was fabricated in a standard 0.18 μm CMOS process. Measured result shows that multiphase clock generator is able to provide 360 selective phases for each channel. The derived DNL is from −0.106 to +0.108 LSB, and the INL is from −0.284 to +0.449 LSB at 1 MHz.