Design Of Spread Spectrum Clock Generator Hershey Kiss Waveform Mudulation

Last year,the United States banned ZTE from trading with US companies on the grounds that ZTE illegally exported communication equipment.Therefore,it was unable to purchase key chips for the main communication equipment and smart phones,causing the whole equipment and smartphone business to stop production and stop selling.loss.After this incident,the chip localization replacement process has once again attracted widespread attention.As the world's largest semiconductor consumer market,China's demand for spread-spectrum clock chips in reducing electromagnetic interference(EMI)is also huge.The traditional method is to use a metal shielding box and an RCL passive filter to reduce EMI,but the complexity of the circuit system is getting higher and higher,and the method has been difficult to achieve the purpose of shielding.At present,there is no low-frequency spread-spectrum clock series in China,and the localization of such chips is imminent.The paper proposes a Hershey Kiss waveform-modulated spread-spectrum clock generation circuit,which can effectively reduce EMI.Its working principle is to reduce the electromagnetic energy from the source of the clock signal by broadening the signal energy of the output clock to a narrow band.radiation.The paper proposes the principle based on Hershey Kiss waveform modulation technology: the use of triangular wave generator and first-order Sigma-Delta modulator to generate Hershey Kiss waveform with approximate special slope.The advantage of this waveform modulation is that the spectral flatness modulated by the triangular wave and the sine wave is better,and the flatness is kept within 2 dB.The paper firstly analyzes the principle of central frequency modulation,and performs Matlab modeling and simulation on Sigma-Delta modulator.Subsequent sections perform circuit design and simulation on the key components of the spread spectrum generator.Finally,based on the design of each module,the overall design and simulation of the spread spectrum clock circuit based on Hershey Kiss waveform modulation is carried out,and the physical layout and package sample test are completed.Design specifications are input reference clock frequency of 25 MHz,output center frequency of 200 MHz,modulation frequency of 31.5kHz,loop bandwidth of 140 kHz,configurable spread frequency and radiation peak attenuation greater than 10 dB.This design is based on the circuit design and physical layout of the SMIC 0.13 um CMOS process,which completes the tape,package and sample test.The test result is that the output center frequency of the clock generator is 200 MHz,the modulation frequency is 32 kHz,the loop bandwidth is 139 kHz,and the spread frequency can be configured to be-0.75%,-0.5%,±0.25%,0%,and the fourth gear is adjustable.The radiation peak is reduced by 12.3dB@0.5% and 16dB@0.75%.The test results are basically consistent with the development goals and meet the expected design requirements of the target chip.The extended spectrum clock circuit in the paper has the advantages of digital circuit implementation,flexible configuration,and good output spectral flatness,which has achieved the expected results.