标题: | 次临界互补式金氧半匹配误差分析 Subthreshold CMOS Mismatch Analysis |
作者: | 林俊煌 Lin, Jiung-Huang 陳明哲 Chen Ming-Jer 電子研究所 |
关键字: | 次临界;互补式金氧半;匹配误差;subthreshold;CMOS;mismatch |
公开日期: | 1995 |
摘要: | 次临界互补式金氧半导体匹配误差分析在低功率、低电压的领域里是 众多重要的研究课题之一。我们已量测及分析不同大小、距离及方向的 N 型与 P 型金氧半导体之匹配误差。这些电晶体都被加以背闸逆向及顺向 偏压。我们首先观察到,电晶体在次临界区存在着比过临界区更大的误差 。此种现象是因为在次临界区中,电流与闸极电压及制程参数成指数关系 的结果。如将背闸逆向偏压加入考虑,我们发现电流误差随着背闸逆向偏 压的加剧而增大。另一方面,电流误差会随着背闸顺向偏压的增大而改善 。经由量测不同面积、距离及方向所得的数据,我们发现到:(1) 小尺寸 的电晶体不仅误差更大,并且对于背闸偏压更加敏感;(2) P 型电晶体的 误差较 N 型大,而且对于背闸电压也较不敏感;(3) 在布局时,电晶体 相距越近以及闸极保持水平方向将可改善匹配误差。除了实验,我们也推 导一个解析式的统计模型。此一模型可以成功地重现在次临界区对不同元 件在不同偏压下所量测的结果。在此模型中,电流误差被表达成以制程参 数变动为因子的函数。所粹取出的参数变动值与元件面积平方根倒数成正 比,符合前人所提的理论。 Subthreshold CMOS mismatch analysis is one of the most important issues in the low power, low voltage field. We have measured the current mismatch of identically drawn p- and n-type MOSFETs (similar to current mirror) operating in subthreshold or weak inversion to above-threshold regions with different gate width-to-length ratios, transistor spacing distances, and layout orientations. These transistors were characterized with back- gate reverse and forward biases. The first observation is that devices operating in subthreshold region exhibit larger mismatch than those in above-threshold region. This is due to the exponential dependence of current on gate and bulk voltages as well as process parameters. In the case of back-gate reverse bias, we have found that current mismatch increases as the magnitude of back-gate reverse bias increases. On the other hand, with the supply of back-gate forward bias, the current mismatch decreases with increasing the back-gate bias in all operation regions. With the data measured from devices with difference sizes, spacing distances, and layout orientations, we have found that (i) small size devices not only exhibit larger mismatch, but also are more sensitive to back-gate bias; (ii) p- type MOSFET exhibits larger mismatch and less sensitive to back- gate bias than n-type MOSFET; and (iii) drawing transistors closely and in horizontal orientation improves the match. We have also derived an analytical statistical model that has successfully reproduced the mismatch data in weak inversion for different back-gate biases and device dimensions. With this model, the current mismatch can be expressed as a function of the variations in process parameters, namely, flat-band voltage and body effect coefficient. The extracted process variations are shown to appropriately follow the inverse square root of the device area. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#NT840430038 http://hdl.handle.net/11536/60638 |
显示于类别: | Thesis |