Current divider mirror
in [Design]
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From: Tim Williams on 3 Feb 2010 19:08 I need a current mirror that has a current coming in from +V or -V, reproduces that current from +V, and produces a current to -V which is about 0.1 to 10 times the input current. I'd just do it with one of those ten emitter transistors that ICs are so fond of using, but they aren't variable geometry... Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 3 Feb 2010 20:31 On Wed, 3 Feb 2010 18:08:04 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >I need a current mirror that has a current coming in from +V or -V, >reproduces that current from +V, and produces a current to -V which is about >0.1 to 10 times the input current. > >I'd just do it with one of those ten emitter transistors that ICs are so >fond of using, but they aren't variable geometry... > >Tim Do you mean things like this? ftp://jjlarkin.lmi.net/Mirror1.JPG ftp://jjlarkin.lmi.net/Mirror2.JPG John
From: Jim Thompson on 3 Feb 2010 20:43 On Wed, 03 Feb 2010 17:31:16 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 3 Feb 2010 18:08:04 -0600, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>I need a current mirror that has a current coming in from +V or -V, >>reproduces that current from +V, and produces a current to -V which is about >>0.1 to 10 times the input current. >> >>I'd just do it with one of those ten emitter transistors that ICs are so >>fond of using, but they aren't variable geometry... >> >>Tim > >Do you mean things like this? > >ftp://jjlarkin.lmi.net/Mirror1.JPG > >ftp://jjlarkin.lmi.net/Mirror2.JPG > > >John > Version #1 is NOT accurately made variable/adjustable. Version #2 is. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Jamie on 3 Feb 2010 21:03 Tim Williams wrote: > I need a current mirror that has a current coming in from +V or -V, > reproduces that current from +V, and produces a current to -V which is about > 0.1 to 10 times the input current. > > I'd just do it with one of those ten emitter transistors that ICs are so > fond of using, but they aren't variable geometry... > > Tim > Are you looking for a totem pole current mirror?
From: Tim Williams on 3 Feb 2010 21:28
On Feb 3, 7:31 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > Do you mean things like this? > > ftp://jjlarkin.lmi.net/Mirror1.JPG > > ftp://jjlarkin.lmi.net/Mirror2.JPG No, offset is an issue. Example: a bipolar current mirror will work over as many decades as the transistors do (assuming equal temperatures, which works for monolithic, not as well for discrete, but is capable of working roughly), but an op-amp mirror gets lost in Vos. I'd rather not tune microvolts of offset, or amplify the noise. A bipolar mirror would work if I basically had a 1:100 variable emitter width. Specifically I want something that works well from 1uA to 5mA within +/-5 or 10V rails. Tim |