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[求助] bandgap can't work in post-simulation

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发表于 2013-8-20 15:12:24 | 显示全部楼层 |阅读模式

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i have designed a bandgap (opamp+bjt), in pre-simulation, the DC/AC/TRAN are all ok; but in post-simulation, the output of bandgap is only a few mV lower than vdd, when vdd is 2.1V,it is 2V.it should have to be adjacent to 1.2V in pre-simulation; i checked the simulation result, i found that, the voltage difference between positive and negative end of opamp is about 100mV (so big difference, only 10uV for pre-simulation), i think maybe it is the reason.
     later, i used non-parasitic post-layout netlist (NO RC or ONLY R, just like pre-simulation netlist), but i get the right result, so my layout have problems,but DRC and LVS have both passed,How can I correct my problem? or any other reasons? can anyone have met the same problem? or any advice?
    Thank you in advance.
发表于 2013-8-20 15:30:49 | 显示全部楼层
Check parasitic caps list, there is a big one, which delayed the circuit's start-up.
Give more time to the post tran simulation, or dig out the big cap.
 楼主| 发表于 2013-8-20 16:12:15 | 显示全部楼层
回复 2# xenolidar


    my start-up has the problem you say when I pin out start-up voltage, Thanks for your reply
发表于 2013-8-21 12:36:17 | 显示全部楼层
八成是你 提取寄生参数的 规则文件有问题,你自己看看提取后的网标,看看Bipolar或者电阻之类器件写的对不对。。。
发表于 2013-8-21 13:18:25 | 显示全部楼层
how about checking you pre-sim at some corner condition?
 楼主| 发表于 2013-8-21 15:36:58 | 显示全部楼层
回复 4# forest820


    规则文件没问题啊,后仿出来的网标我也看了,和电路是一致的
 楼主| 发表于 2013-8-21 15:41:40 | 显示全部楼层
回复 5# william_rx


    I did the sims separately and compare their waves.
发表于 2013-8-21 15:50:46 | 显示全部楼层
回复 6# davidleehust


    后仿真网表中BJT或者DIODE有无面积?如果有面积的话仿真软件可能不认,仿真结果会错的。
发表于 2013-8-23 19:01:49 | 显示全部楼层
删掉后仿真网表中BJT管的"area=??",保留“m=??”,如果其他流程正常,后仿应该就正常工作了。
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