Current divider mirror
in [Design]
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From: John Larkin on 6 Feb 2010 00:02 On Fri, 5 Feb 2010 11:21:05 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"whit3rd" <whit3rd(a)gmail.com> wrote in message >news:152e5f52-6af1-4cb3-aa39-0ecf74e30db1(a)q4g2000yqm.googlegroups.com... >> The schemes John Larkin gave are unipolar, and 'current from +V or -V' >> sounds like bipolar to me. > >No, it's unipolar, I meant the currents are sourced from the +V rail, or >sunk into the -V rail. > >Your circuit reminds me of, >http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Current_Amplifer.gif >which isn't to be left alone on the breadboard unless the transistors are on >a fairly large heatsink. ;-) > >Tim Using the opamp rail currents gives essentially perfect crossover behavior. At zero signal, both mirrors run at their Iq. As you apply signal in one direction, one mirror current goes up and the other stays at Iq. That's different from most class AB stages, where as one side conducts, the other is turned off... which can lead to weird transient distortions. John
From: Tim Williams on 6 Feb 2010 20:42 "JosephKK" <quiettechblue(a)yahoo.com> wrote in message news:7anom5d66k5nn9k3epml4tm5q4hbuelh9g(a)4ax.com... > Do you need continuously adjustable or can you live with discrete steps > on the current ratio? Continuous, or sufficiently continuous (>= 8 bits?). I suppose an alternate formulation might be, if it can't be varied reliably over a wide range, then it could be varied over a small dither range while the switching handles the wide range, but that would quickly get ugly.. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: JosephKK on 6 Feb 2010 22:45 On Fri, 05 Feb 2010 21:02:46 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 5 Feb 2010 11:21:05 -0600, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>"whit3rd" <whit3rd(a)gmail.com> wrote in message >>news:152e5f52-6af1-4cb3-aa39-0ecf74e30db1(a)q4g2000yqm.googlegroups.com.... >>> The schemes John Larkin gave are unipolar, and 'current from +V or -V' >>> sounds like bipolar to me. >> >>No, it's unipolar, I meant the currents are sourced from the +V rail, or >>sunk into the -V rail. >> >>Your circuit reminds me of, >>http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Current_Amplifer.gif >>which isn't to be left alone on the breadboard unless the transistors are on >>a fairly large heatsink. ;-) >> >>Tim > >Using the opamp rail currents gives essentially perfect crossover >behavior. At zero signal, both mirrors run at their Iq. As you apply >signal in one direction, one mirror current goes up and the other >stays at Iq. That's different from most class AB stages, where as one >side conducts, the other is turned off... which can lead to weird >transient distortions. > >John And to think i cribbed that trick from datasheets and application notes in 1965 to build my first self designed stereo.
From: John Larkin on 6 Feb 2010 23:01 On Sat, 06 Feb 2010 19:45:38 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 05 Feb 2010 21:02:46 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 5 Feb 2010 11:21:05 -0600, "Tim Williams" >><tmoranwms(a)charter.net> wrote: >> >>>"whit3rd" <whit3rd(a)gmail.com> wrote in message >>>news:152e5f52-6af1-4cb3-aa39-0ecf74e30db1(a)q4g2000yqm.googlegroups.com... >>>> The schemes John Larkin gave are unipolar, and 'current from +V or -V' >>>> sounds like bipolar to me. >>> >>>No, it's unipolar, I meant the currents are sourced from the +V rail, or >>>sunk into the -V rail. >>> >>>Your circuit reminds me of, >>>http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Current_Amplifer.gif >>>which isn't to be left alone on the breadboard unless the transistors are on >>>a fairly large heatsink. ;-) >>> >>>Tim >> >>Using the opamp rail currents gives essentially perfect crossover >>behavior. At zero signal, both mirrors run at their Iq. As you apply >>signal in one direction, one mirror current goes up and the other >>stays at Iq. That's different from most class AB stages, where as one >>side conducts, the other is turned off... which can lead to weird >>transient distortions. >> >>John > >And to think i cribbed that trick from datasheets and application >notes in 1965 to build my first self designed stereo. This config is ideal for driving current into inductive loads, like MRI coils. The inherently high output impedance makes closed-loop dynamics mostly independent of load. For audio, where you want a low output impedance, it's not ideal. The fix is to apply massive negative feedback, which requires tons of GBW to waste at higher frequencies. That was probably hard to do in 1965. Got a schematic? John
From: Jim Thompson on 7 Feb 2010 11:21
On Sat, 06 Feb 2010 19:45:38 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 05 Feb 2010 21:02:46 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 5 Feb 2010 11:21:05 -0600, "Tim Williams" >><tmoranwms(a)charter.net> wrote: >> >>>"whit3rd" <whit3rd(a)gmail.com> wrote in message >>>news:152e5f52-6af1-4cb3-aa39-0ecf74e30db1(a)q4g2000yqm.googlegroups.com... >>>> The schemes John Larkin gave are unipolar, and 'current from +V or -V' >>>> sounds like bipolar to me. >>> >>>No, it's unipolar, I meant the currents are sourced from the +V rail, or >>>sunk into the -V rail. >>> >>>Your circuit reminds me of, >>>http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Current_Amplifer.gif >>>which isn't to be left alone on the breadboard unless the transistors are on >>>a fairly large heatsink. ;-) >>> >>>Tim >> >>Using the opamp rail currents gives essentially perfect crossover >>behavior. At zero signal, both mirrors run at their Iq. As you apply >>signal in one direction, one mirror current goes up and the other >>stays at Iq. That's different from most class AB stages, where as one >>side conducts, the other is turned off... which can lead to weird >>transient distortions. >> >>John > >And to think i cribbed that trick from datasheets and application >notes in 1965 to build my first self designed stereo. MC1524, actually was an I/C plus a 2N2222 and a 2N2906. ...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. |