A Comprehensive Study On LPDDR4X's Signal Integrity And Power Integrity Issues

With the popularity of smart phones and the rise of social network,stricter requirements are imposed on mobile device performance,specifically on the data transfer speed between the central processing unit and DRAM,DRAM capacity and power consumption.LPDDR4 X,as the latest generation of mobile memory,has 50% I/O output voltage drop and 15% power consumption decrease,compared with LPDDR4,which significantly enable longer battery life without lowered performance.However,lowered supply voltage results in severe noise margin decrease,which causes severe signal integrity and power integrity problems.Therefore,this paper analyzes the signal integrity and power integrity problems of LPDDR4 X,and the main topics are as follows.Firstly,this paper presents a channel model,which starts from the cellphone baseband chip and ends at the LPDDR4 X chip.This channel model also includes the power distribution network of the baseband chip package,PCB and LPDDR4 X chip package.Secondly this paper analyzes the impact of crosstalk,stimulus pattterns and Cdie to power dilivery network and singal quality.Thirdly,this paper performs time domain and frequency domain analysis of package level routing and PCB level routing,and gives suggestion for modification.Fourthly,this paper analyzes stimulus pattern and presents several stimulus patterns specified to LPDDR4 X and its related circuits to study ISI triggered problems,as well as the relationship between pattern's sub frequency and power distribution network resonance frequency,and concludes the worst pattern for power distribution network noise.Fifthly,this paper analyzes board decoupling capacitors and gets the best decoupling path.In the last,this paper performs power integrity and signal integrity co-simulation with multiple Cdie value,to distinctly show the influence of Cdie to the research and development engineers.To sum up,this paper draws the conclusion that crosstalk imposes utmost impact on LPDDR4X's signal integrity issues after the analyze of crosstalk and ISI.Meanwhile,the analysis of Cdie draws the conclusion that the increase of Cdie causes the decrease of PDN noise and jitter within certain range.