John Larkin's LC oscillator
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From: John Larkin on 14 Jun 2010 19:01 On Mon, 14 Jun 2010 15:27:30 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Jun 14, 4:41�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodb...(a)yahoo.com >> wrote: >> >> >> Q1 doesn't conduct in reverse with your values, but no >> >> Schottky... the current is always out of the emitter... though it does >> >> get awfully close to zero: -376uA and -12.5mA peak. >> >> >Huh. �LTSpice says Q1 does conduct in reverse, a nasty little 5mA >> >spike's worth. �The schottky feedback prevents that by cutting the >> >base bias enough to make sure the collector never gets that low. >> >> Right; the schottly is a more pure AGC mode. The reverse emitter >> conduction depends on the inverse beta of the transistor. If the model >> includes inverse beta, when the collector dips down to close to >> ground, and the c-b junction forward biases, it essentially flips >> ends: collector becomes emitter, emitter becomes collector, emitter >> current flows upwards. >> >> ftp://jjlarkin.lmi.net/LC_YDx.gif >> >> Either way, the base cap gets discharged. > >It's interesting that Jim's PSpice doesn't show the same spike. He blames it on defects in LT Spice. That's crazy. I suspect it's actually different transistor models. Note that in my sim, the emitter current reverses exactly at the points in time when Vc swings through Ve. John
From: Jim Thompson on 14 Jun 2010 19:15 On Mon, 14 Jun 2010 16:01:55 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 14 Jun 2010 15:27:30 -0700 (PDT), dagmargoodboat(a)yahoo.com >wrote: > >>On Jun 14, 4:41�pm, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodb...(a)yahoo.com >>> wrote: >>> >>> >> Q1 doesn't conduct in reverse with your values, but no >>> >> Schottky... the current is always out of the emitter... though it does >>> >> get awfully close to zero: -376uA and -12.5mA peak. >>> >>> >Huh. �LTSpice says Q1 does conduct in reverse, a nasty little 5mA >>> >spike's worth. �The schottky feedback prevents that by cutting the >>> >base bias enough to make sure the collector never gets that low. >>> >>> Right; the schottly is a more pure AGC mode. The reverse emitter >>> conduction depends on the inverse beta of the transistor. If the model >>> includes inverse beta, when the collector dips down to close to >>> ground, and the c-b junction forward biases, it essentially flips >>> ends: collector becomes emitter, emitter becomes collector, emitter >>> current flows upwards. >>> >>> ftp://jjlarkin.lmi.net/LC_YDx.gif >>> >>> Either way, the base cap gets discharged. >> >>It's interesting that Jim's PSpice doesn't show the same spike. > >He blames it on defects in LT Spice. That's crazy. I suspect it's >actually different transistor models. Note that in my sim, the emitter >current reverses exactly at the points in time when Vc swings through >Ve. > >John > I didn't say that at all. I said I don't see it in PSpice, AND it's an advertised feature of LTspice that models are tweaked for speed. However I suspect it's that I assigned a resistance to the feedback winding proportionate to the Q assigned to the primary. You two did not. PSpice does model BR, so it's not that. It could also be that I'm looking way out at 1 second, where the loop is steady, and loop "replenishment current" is very small. It's quite possible that, during loop closure, you have some inverse transistor action. It's certainly not there at 1 second... and the spectral analysis does not show it either. However, it is dead clear, there is no AGC action controlling TRANSCONDUCTANCE :-) ...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 | The only thing bipartisan in this country is hypocrisy
From: Jim Thompson on 14 Jun 2010 19:36 On Mon, 14 Jun 2010 16:15:09 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 14 Jun 2010 16:01:55 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Mon, 14 Jun 2010 15:27:30 -0700 (PDT), dagmargoodboat(a)yahoo.com >>wrote: >> >>>On Jun 14, 4:41�pm, John Larkin >>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodb...(a)yahoo.com >>>> wrote: >>>> >>>> >> Q1 doesn't conduct in reverse with your values, but no >>>> >> Schottky... the current is always out of the emitter... though it does >>>> >> get awfully close to zero: -376uA and -12.5mA peak. >>>> >>>> >Huh. �LTSpice says Q1 does conduct in reverse, a nasty little 5mA >>>> >spike's worth. �The schottky feedback prevents that by cutting the >>>> >base bias enough to make sure the collector never gets that low. >>>> >>>> Right; the schottly is a more pure AGC mode. The reverse emitter >>>> conduction depends on the inverse beta of the transistor. If the model >>>> includes inverse beta, when the collector dips down to close to >>>> ground, and the c-b junction forward biases, it essentially flips >>>> ends: collector becomes emitter, emitter becomes collector, emitter >>>> current flows upwards. >>>> >>>> ftp://jjlarkin.lmi.net/LC_YDx.gif >>>> >>>> Either way, the base cap gets discharged. >>> >>>It's interesting that Jim's PSpice doesn't show the same spike. >> >>He blames it on defects in LT Spice. That's crazy. I suspect it's >>actually different transistor models. Note that in my sim, the emitter >>current reverses exactly at the points in time when Vc swings through >>Ve. >> >>John >> > >I didn't say that at all. I said I don't see it in PSpice, AND it's >an advertised feature of LTspice that models are tweaked for speed. > >However I suspect it's that I assigned a resistance to the feedback >winding proportionate to the Q assigned to the primary. You two did >not. > >PSpice does model BR, so it's not that. It could also be that I'm >looking way out at 1 second, where the loop is steady, and loop >"replenishment current" is very small. It's quite possible that, >during loop closure, you have some inverse transistor action. It's >certainly not there at 1 second... and the spectral analysis does not >show it either. > >However, it is dead clear, there is no AGC action controlling >TRANSCONDUCTANCE :-) > > ...Jim Thompson I re-measured: IE is _never_ less than 376uA OUT of the emitter... no reverse transistor action. ...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 | The only thing bipartisan in this country is hypocrisy
From: Jim Thompson on 14 Jun 2010 20:30 On Mon, 14 Jun 2010 16:36:19 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 14 Jun 2010 16:15:09 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Mon, 14 Jun 2010 16:01:55 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Mon, 14 Jun 2010 15:27:30 -0700 (PDT), dagmargoodboat(a)yahoo.com >>>wrote: >>> >>>>On Jun 14, 4:41�pm, John Larkin >>>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodb...(a)yahoo.com >>>>> wrote: >>>>> >>>>> >> Q1 doesn't conduct in reverse with your values, but no >>>>> >> Schottky... the current is always out of the emitter... though it does >>>>> >> get awfully close to zero: -376uA and -12.5mA peak. >>>>> >>>>> >Huh. �LTSpice says Q1 does conduct in reverse, a nasty little 5mA >>>>> >spike's worth. �The schottky feedback prevents that by cutting the >>>>> >base bias enough to make sure the collector never gets that low. >>>>> >>>>> Right; the schottly is a more pure AGC mode. The reverse emitter >>>>> conduction depends on the inverse beta of the transistor. If the model >>>>> includes inverse beta, when the collector dips down to close to >>>>> ground, and the c-b junction forward biases, it essentially flips >>>>> ends: collector becomes emitter, emitter becomes collector, emitter >>>>> current flows upwards. >>>>> >>>>> ftp://jjlarkin.lmi.net/LC_YDx.gif >>>>> >>>>> Either way, the base cap gets discharged. >>>> >>>>It's interesting that Jim's PSpice doesn't show the same spike. >>> >>>He blames it on defects in LT Spice. That's crazy. I suspect it's >>>actually different transistor models. Note that in my sim, the emitter >>>current reverses exactly at the points in time when Vc swings through >>>Ve. >>> >>>John >>> >> >>I didn't say that at all. I said I don't see it in PSpice, AND it's >>an advertised feature of LTspice that models are tweaked for speed. >> >>However I suspect it's that I assigned a resistance to the feedback >>winding proportionate to the Q assigned to the primary. You two did >>not. >> >>PSpice does model BR, so it's not that. It could also be that I'm >>looking way out at 1 second, where the loop is steady, and loop >>"replenishment current" is very small. It's quite possible that, >>during loop closure, you have some inverse transistor action. It's >>certainly not there at 1 second... and the spectral analysis does not >>show it either. >> >>However, it is dead clear, there is no AGC action controlling >>TRANSCONDUCTANCE :-) >> >> ...Jim Thompson > >I re-measured: IE is _never_ less than 376uA OUT of the emitter... no >reverse transistor action. > > ...Jim Thompson On closer examination I _am_ seeing some kind of burble on the emitter current. Applying a Schottky _does_ reduce the burble, but not completely, since you load the bias cap. No real change in spectrum. Perhaps tie base of Q1 to the juncture of R1/D1? Or a Baker clamp would certainly provide the isolation. But I doubt the ROI :-) ...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 | The only thing bipartisan in this country is hypocrisy
From: Jim Thompson on 14 Jun 2010 20:38
On Mon, 14 Jun 2010 17:30:55 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 14 Jun 2010 16:36:19 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Mon, 14 Jun 2010 16:15:09 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>>On Mon, 14 Jun 2010 16:01:55 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Mon, 14 Jun 2010 15:27:30 -0700 (PDT), dagmargoodboat(a)yahoo.com >>>>wrote: >>>> >>>>>On Jun 14, 4:41�pm, John Larkin >>>>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>> On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodb...(a)yahoo.com >>>>>> wrote: >>>>>> >>>>>> >> Q1 doesn't conduct in reverse with your values, but no >>>>>> >> Schottky... the current is always out of the emitter... though it does >>>>>> >> get awfully close to zero: -376uA and -12.5mA peak. >>>>>> >>>>>> >Huh. �LTSpice says Q1 does conduct in reverse, a nasty little 5mA >>>>>> >spike's worth. �The schottky feedback prevents that by cutting the >>>>>> >base bias enough to make sure the collector never gets that low. >>>>>> >>>>>> Right; the schottly is a more pure AGC mode. The reverse emitter >>>>>> conduction depends on the inverse beta of the transistor. If the model >>>>>> includes inverse beta, when the collector dips down to close to >>>>>> ground, and the c-b junction forward biases, it essentially flips >>>>>> ends: collector becomes emitter, emitter becomes collector, emitter >>>>>> current flows upwards. >>>>>> >>>>>> ftp://jjlarkin.lmi.net/LC_YDx.gif >>>>>> >>>>>> Either way, the base cap gets discharged. >>>>> >>>>>It's interesting that Jim's PSpice doesn't show the same spike. >>>> >>>>He blames it on defects in LT Spice. That's crazy. I suspect it's >>>>actually different transistor models. Note that in my sim, the emitter >>>>current reverses exactly at the points in time when Vc swings through >>>>Ve. >>>> >>>>John >>>> >>> >>>I didn't say that at all. I said I don't see it in PSpice, AND it's >>>an advertised feature of LTspice that models are tweaked for speed. >>> >>>However I suspect it's that I assigned a resistance to the feedback >>>winding proportionate to the Q assigned to the primary. You two did >>>not. >>> >>>PSpice does model BR, so it's not that. It could also be that I'm >>>looking way out at 1 second, where the loop is steady, and loop >>>"replenishment current" is very small. It's quite possible that, >>>during loop closure, you have some inverse transistor action. It's >>>certainly not there at 1 second... and the spectral analysis does not >>>show it either. >>> >>>However, it is dead clear, there is no AGC action controlling >>>TRANSCONDUCTANCE :-) >>> >>> ...Jim Thompson >> >>I re-measured: IE is _never_ less than 376uA OUT of the emitter... no >>reverse transistor action. >> >> ...Jim Thompson > >On closer examination I _am_ seeing some kind of burble on the emitter >current. Applying a Schottky _does_ reduce the burble, but not >completely, since you load the bias cap. No real change in spectrum. >Perhaps tie base of Q1 to the juncture of R1/D1? Or a Baker clamp >would certainly provide the isolation. But I doubt the ROI :-) > > ...Jim Thompson But it's weird, and counterproductive. The "burble" smoothes some, but at the price of peak emitter current going up to 20mA. Weird :-( ...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 | The only thing bipartisan in this country is hypocrisy |