An instant-switching ∆–Σ fractional-N frequency synthesizer with adjustable duty cycles

Abstract

A Phase-Locked Loop (PLL)-based frequency synthesizer (FS) with adjustable duty cycle is presented. By employing digital processing circuitry and the ?---Σ fractional-N technique, the FS is capable of generating arbitrary frequencies in a wide frequency range, and capable of adjusting the clock duty cycles. In addition, the switching between different frequencies is instant except when a very fine frequency resolution is required. The adjustable duty cycle and instant switching are desired features in applications such as time-interleaved Analog-to-Digital-Converters (ADCs), switched-capacitor circuits, and DC---DC converters. The design was fabricated using a 0.13 μm CMOS process. This paper gives the theories, analysis, implementation, and measurement results of this FS.