This paper presents an effective master-slave distributed voltage and frequency modulation circuit for processors in system-on-chip (SoC). This work achieves dynamic voltage and frequency scaling (DVFS) in a compact, simple, and scalable architecture. This all-digital control method does not need additional analog parts, such as comparators or analog reference voltages. This makes it more suitable for being integrated with digital circuits in the multi-core processor. The proposed work can provide independent power supply levels to different power domains, especially in sub-1V low voltage conditions, minimizing energy per operation. The proposed prototype circuit was fabricated in a 28-nm CMOS process.