Try VIN in_p in_n ac=0.2 This then forces a differential voltage, so no math functions need to be performed. If you need a DC offset, you can add one with a single DC supply from in_n to ground. Pat > > Vin_p in_p 0 ac=0.2 > Vin_n 0 in_n ac=0.2 > > --- > > Vin_p in_p 0 ac=0.2 > Vin_n in_n 0 ac=-0.2 > > --- > > Vin_p in_p 0 ac=0.2 > Vin_n in_n 0 ac=0.2,180 > > --- > ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.org 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