一种高速高集成度MaskROM的设计与研究

Research and design of a high speed high density MaskROM

MaskROM在MCU设计应用中扮演着重要角色,而高速、高集成度是未来发展趋势。设计了一种混合结构MaskROM,兼有NAND的高集成度以及NOR的快速读出优点。子模块中串联的管子越多,集成度越高,但速度会降低。通过对行译码进行小的子模块划分,阵列被划分为多个子模块并联。选择每个子模块为5个MOS管串联,这样既能提高集成度又能保持快速读出的特点。在选中的子模块中,被进一步选中的WL(Word Line)为低,其他WL为高,串联的bit被导通的MOS管短路掉4行,WL为低的那一行MOS管关闭,从而其MOS管两端有没有被金属短接决定了cell是否产生电流。行译码的方式可以很容易地通过数学公式进行归纳和理解。SA采用伪差分方式,通过预设offset方式实现cell的快速读出。基于0.18μm 2P5M EEPROM工艺设计实现了一款32 K×34bit的MaskROM,芯片测试结果表明,在典型条件下其读出速度能达到170 MHz。

MaskROM plays an important role in MCU design and application,and high speed and high density is the future trend.A hybrid structure MaskROM is designed,which has the advantagesc of high integration of NAND and high speed of NOR.The more MOSFETs in series in the submodule,the higher the integration,but the speed will be reduced.By dividing the row decoding into small submodules,the array is divided into multiple submodules in parallel,and each submodule is selected as 5 MOSFETs in series.This not only improves integration but also maintains the characteristic of fast readout.In the selected submodule,the further selected Word Line(WL)is low,while the other WLs are high.The conducting MOS transistors short 4 rows,and the MOSFET with WL low is close.Therefore,whether the MOS transistor two ends are metal shorted determines whether the cell generates current.The way of wordline decoding can be summarized and understood through Formulas easily.SA adopts pseudo differential method and achieves fast cell reading through preset offset method.Based on 0.18μm 2P5M EEPROM process,a 32 K×34 bit MaskROM is designed and implemented.The chip test results show that the readout speed can reach 170 MHz under typical conditions.