Han, I think you may have to use twice the capacitance to ensure at least on= e MOS is on. This will eat up twice the area. Even though you have a trip= le well process you have at least on well in a CMOS process. This well can= be isolated form the power supply. We use this "floating" well technique o= nce in a while but usually don't have the operating range to use this as a compensating technique. To insure that the PMOS Capacitor has enough Vgs(d) to maintain a channel is usually not possible. That's why I woul= d suggest using a big enough PMOS and NMOS to compensate even if the oth= er was not in the circuit. It is a brute force method but it will work wit= h a wide operating range. Bill Cohen Toshiba America = =20 Bi Han = =20 <mike_bihan@yahoo. To: Bill.Cohen@xxxxxxx= shiba.com, List` Si <si-list@xxxxxxxxxxxxx> =20 com.cn> cc: = =20 Sent by: Subject: [SI-LIST] Re:= op-amp compensation capacitor in digital cmos=20 si-list-bounce@fre process = =20 elists.org = =20 = =20 = =20 07/15/2003 09:23 = =20 PM = =20 Please respond to = =20 mike_bihan = =20 = =20 = =20 Bill: Thanks for your information! I agree that MOS gate cap is a good idea. But I may not be able to guarantee the working range of MOS cap in stro= ng inversion mode because the gain of the op-amp will be very high. Meanwhile, there is no triple well process, so all nmos's well is conne= cted to substrate, pmos to VCC. What should I do? Bill.Cohen@xxxxxxxxxxxxxxxx wrote: Han, It may not be a great idea but I compensate all my opamps with MOS gate= capacitors. Just make sure the device is in saturation otherwise you wi= ll get too much series resistance to the thin oxide device. If it is a rai= l to rail opamp you may need to used Both NMOS and PMOS devices to keep at l= east one device active depending on the common mode. Also, you will only be = able to use the device in the well if you need a compensating device with on= e end not tied to the power supply. Bill Cohen Toshiba America Bi Han com.cn> cc: Sent by: Subject: [SI-LIST] op-amp compensation capacitor in digital cm= os si-list-bounce@fre process elists.org 07/15/2003 07:34 AM Please respond to mike_bihan hi, experts: I am on a project designing high speed limiter in digital cmos process.= I need to design some op-amp as controlling circuits. So, I need capacitor to compensate them to stable. But, in my digital c= mos process(1p6m), there will be no MIM/PIP capacitor, so I can not compens= ate the op-amp!! Any people have good idea? Thanks, Han --------------------------------- Do You Yahoo!? =B9=FA=C4=DA=B5=E7=D3=CA=D3=C3=BB=A7=B7=B4=C0=AC=BB=F8=B5=F7=B2=E9=C0=AD= =BF=AA=E1=A1=C4=BB ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu --------------------------------- Do You Yahoo!? =B9=FA=C4=DA=B5=E7=D3=CA=D3=C3=BB=A7=B7=B4=C0=AC=BB=F8=B5=F7=B2=E9=C0=AD= =BF=AA=E1=A1=C4=BB ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu = ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu