Design Of The Spread Spectrum Clock Signal Generator

With the development of the integrated circuit industry,the integration of electronic products is more and more powerful and the running speed is getting higher and higher.Under the impetus of the Moore's Law,the smallest feature size of a chip components is 0.35?m in 1995 gradually developed to 0.1?m in 2005,and now,the smallest feature size of the MOS device has reached 10 nm below,and the number of transistors on a single chip will reach 100 billion or more,so the electromagnetic interference problem of a chip system internal is more and more prominent.This paper aims at using the clock spread spectrum technology studying and designing a double loop spread spectrum clock signal generator to reduce the system electromagnetic interference problem.The design requirements of this paper are as follows: the input frequency of the system is 1.92 MHz,the center frequency of the output signal is 800 MHz,power supply voltage of 3.3V and the spread depth is controlled within 0.5%.In this paper,the design idea of the spread spectrum clock generator is using the charge and discharge principle of the charge pump,that the square wave signals which the reference signal is divided and is a lower frequency signals,the duty cycle of this signal is 50%,the same frequency and phase,and the cycle is from 30 KHz to 60 KHz,which controls the switches of the charge pump and produces a periodic and the swing controlling of the triangular wave on the capacitor to achieve the modulation of the oscillator control voltage.After the modulation,without modulation spectrum of the system clock is extended to broadband,so that the peak energy of the baseband and harmonic containing significantly to be reduced,thus effectively reducing the electromagnetic interference of the system.First,this paper introduces the background of the development of spread spectrum clock technology,the research status at home and abroad and the method of the spread spectrum clock technology to achieve.Then,the structural block diagram of the clock signal generator and the working principle of each module are analyzed and studied in detail.Third,according to the requirements of the system,the design of the system structure related circuit are completed,and establish a mathematical model and analysis,analyzed and researched in detail the principle of working and process of the spread spectrum and the control of the spread depth.Then,design of the system circuit is completed basing on the SMIC 0.35?m CMOS process and simulated and analyzed to ensure that the performance parameters of the circuit meet the requirements of the index.Finally,the simulation results show that the output frequency is 800 MHz,the spread depth of less than or equal to 0.5% and the electromagnetic interference is reduced by 11.23 d B,which satisfies the whole Chip design requirements.