John Larkin's LC oscillator
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From: Jim Thompson on 14 Jun 2010 16:34 On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Jun 14, 1:15�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >Web-Site.com> wrote: >> On Mon, 14 Jun 2010 10:50:58 -0700 (PDT), dagmargoodb...(a)yahoo.com >> wrote: >> >> >> >> >> >> >On Jun 14, 12:08�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On- >> >My-Web-Site.com> wrote: >> >> On Mon, 14 Jun 2010 09:49:09 -0700 (PDT), dagmargoodb...(a)yahoo.com >> >> wrote: >> [snip] >> >> >> > � � � � Vcc = +5v >> >> > � �--+--------------+------+-- >> >> > � � �| � � � � � � �| � � �| >> >> > � � �| � � � � � � �| � � .-. >> >> > � � �| � � � � � � �| � � | | e.s.r. = 1 ohm >> >> > � � �| � � � � � � �| � � | | >> >> > � � �| � � � � � � �| � � '-' >> >> > � � �| � � � � � � �| � � �| >> >> > � � �| � � � � � � �| � � �|_ || >> >> > � � �| � � � � � � �| � � � _)|| >> >> > � � .-. � � � � � �--- �L1a _)|| >> >> > Rb �| | � � � � C1 --- �1mH _)|| >> >> > 47k | | � � � � 1uF | � � � _)|| >> >> > � � '-' � � � � � � | � � � _)|| >> >> > � � �| � � � � � � �| � � *| �|| >> >> > � � �| � � � � � � �'---+--' �|| >> >> > � � �| � �R1 � � D1 � � | � � || >> >> > � � �| � 220r �schottky | � � || >> >> > � � �+--/\/\/----|>]----+ � � || >> >> > � � �| � � � � � � � � �| � � || >> >> > � � �| � � .------------' � � || >> >> > � � �| � |/ � � � � � � � � � || >> >> > � � �+---| � �Q1 � � � � � � �|| >> >> > � � �| � |>. 2n3904 � � � � � || >> >> > � � �| � � | � � � � � � � * �|| >> >> > �C2 --- � �+----------------. || >> >> > 1uF --- � �| � � � � � L1b �_)|| >> >> > � � �| � � | � � � � 100nH �_)|| >> >> > � � �| � � | � � � � � � � | >> >> > � � === � �| � � � � � � �=== >> >> > � � � � � �| >> >> > � � � � � �'--------------------> 5KHz output >> >> >> >Cheers, >> >> >James Arthur >> >> >> [snip LTspice Schematic] >> >> >> James, �How can you call it "class-A" when the emitter current is >> >> _not_linear_, _not_linear_, _not_linear_, _not_linear_ !! >> >> >True, the emitter current isn't linear, but it is continuous and non- >> >zero, so I call that "class-A." >> >> >> All you've done is use a Schottky bypassing the C-B junction... >> >> otherwise it's identical. >> >> >That makes a big difference. �It prevents Q1 saturating and from >> >conducting b-c. �And, without it Q1 conducts in reverse mode during >> >negative peaks, making the i(c) not just discontinuous, but reversing >> >in direction. �That loads the tank, obviously. >> >> "Obviously"? > >Yeah, if Q1 sucks energy out of the tank, that loads the tank. > >> 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. LTspice uses short-cuts to raise simulation speed. PSpice shows no such spike. > > >> >> I liken such oscillators to how you push your kid on a swing set. >> >> Giving a "nudge" every cycle. >> >> >That's exactly how I think of them too. �A "nudge" each cycle (short >> >conduction cycle) is what I did first. �I call that "class-C." >> >> >> To be "class-A" you'd need to sit upon the top bars and _continuously_ >> >> push and pull the ropes. >> >> >Or you can pull continuously, harder at some times, not as hard at >> >others. �That gives the swing position a d.c. bias, but is otherwise >> >the same, yes? >> >> Class-A implies _linear_, does it not? �Or do we have a Larkin >> definition for today ?:-) > >I've always used "class-A" to mean the transistor conduction angle = >360�. Class-B means mostly conducting but sometimes 'off', and Class- >C means 'mostly off.' Whatever ;-) ...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 16:43 On Mon, 14 Jun 2010 13:34:18 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodboat(a)yahoo.com >wrote: > >>On Jun 14, 1:15�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >>Web-Site.com> wrote: >>> On Mon, 14 Jun 2010 10:50:58 -0700 (PDT), dagmargoodb...(a)yahoo.com >>> wrote: >>> >>> >>> >>> >>> >>> >On Jun 14, 12:08�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On- >>> >My-Web-Site.com> wrote: >>> >> On Mon, 14 Jun 2010 09:49:09 -0700 (PDT), dagmargoodb...(a)yahoo.com >>> >> wrote: >>> [snip] >>> >>> >> > � � � � Vcc = +5v >>> >> > � �--+--------------+------+-- >>> >> > � � �| � � � � � � �| � � �| >>> >> > � � �| � � � � � � �| � � .-. >>> >> > � � �| � � � � � � �| � � | | e.s.r. = 1 ohm >>> >> > � � �| � � � � � � �| � � | | >>> >> > � � �| � � � � � � �| � � '-' >>> >> > � � �| � � � � � � �| � � �| >>> >> > � � �| � � � � � � �| � � �|_ || >>> >> > � � �| � � � � � � �| � � � _)|| >>> >> > � � .-. � � � � � �--- �L1a _)|| >>> >> > Rb �| | � � � � C1 --- �1mH _)|| >>> >> > 47k | | � � � � 1uF | � � � _)|| >>> >> > � � '-' � � � � � � | � � � _)|| >>> >> > � � �| � � � � � � �| � � *| �|| >>> >> > � � �| � � � � � � �'---+--' �|| >>> >> > � � �| � �R1 � � D1 � � | � � || >>> >> > � � �| � 220r �schottky | � � || >>> >> > � � �+--/\/\/----|>]----+ � � || >>> >> > � � �| � � � � � � � � �| � � || >>> >> > � � �| � � .------------' � � || >>> >> > � � �| � |/ � � � � � � � � � || >>> >> > � � �+---| � �Q1 � � � � � � �|| >>> >> > � � �| � |>. 2n3904 � � � � � || >>> >> > � � �| � � | � � � � � � � * �|| >>> >> > �C2 --- � �+----------------. || >>> >> > 1uF --- � �| � � � � � L1b �_)|| >>> >> > � � �| � � | � � � � 100nH �_)|| >>> >> > � � �| � � | � � � � � � � | >>> >> > � � === � �| � � � � � � �=== >>> >> > � � � � � �| >>> >> > � � � � � �'--------------------> 5KHz output >>> >>> >> >Cheers, >>> >> >James Arthur >>> >>> >> [snip LTspice Schematic] >>> >>> >> James, �How can you call it "class-A" when the emitter current is >>> >> _not_linear_, _not_linear_, _not_linear_, _not_linear_ !! >>> >>> >True, the emitter current isn't linear, but it is continuous and non- >>> >zero, so I call that "class-A." >>> >>> >> All you've done is use a Schottky bypassing the C-B junction... >>> >> otherwise it's identical. >>> >>> >That makes a big difference. �It prevents Q1 saturating and from >>> >conducting b-c. �And, without it Q1 conducts in reverse mode during >>> >negative peaks, making the i(c) not just discontinuous, but reversing >>> >in direction. �That loads the tank, obviously. >>> >>> "Obviously"? >> >>Yeah, if Q1 sucks energy out of the tank, that loads the tank. >> >>> 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. > >LTspice uses short-cuts to raise simulation speed. PSpice shows no >such spike. > >> >> >>> >> I liken such oscillators to how you push your kid on a swing set. >>> >> Giving a "nudge" every cycle. >>> >>> >That's exactly how I think of them too. �A "nudge" each cycle (short >>> >conduction cycle) is what I did first. �I call that "class-C." >>> >>> >> To be "class-A" you'd need to sit upon the top bars and _continuously_ >>> >> push and pull the ropes. >>> >>> >Or you can pull continuously, harder at some times, not as hard at >>> >others. �That gives the swing position a d.c. bias, but is otherwise >>> >the same, yes? >>> >>> Class-A implies _linear_, does it not? �Or do we have a Larkin >>> definition for today ?:-) >> >>I've always used "class-A" to mean the transistor conduction angle = >>360�. Class-B means mostly conducting but sometimes 'off', and Class- >>C means 'mostly off.' > >Whatever ;-) > > ...Jim Thompson You distracted me... Where's the "AGC" ?:-) ...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: John Larkin on 14 Jun 2010 17:41 On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodboat(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. You can force this to work class-C if you jack around with the transformer ratio, and use a small base cap, but that's not the way I originally described the circuit. Maybe I'll try moving the feedback into the base circuit, one of these days. Cute circuit. John
From: Jim Thompson on 14 Jun 2010 17:45 On Mon, 14 Jun 2010 14:41:08 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 14 Jun 2010 12:27:57 -0700 (PDT), dagmargoodboat(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. > >You can force this to work class-C if you jack around with the >transformer ratio, and use a small base cap, but that's not the way I >originally described the circuit. > >Maybe I'll try moving the feedback into the base circuit, one of these >days. > >Cute circuit. > >John > If Q1 conducts in reverse what _class_ is the oscillator ?:-) ...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: dagmargoodboat on 14 Jun 2010 18:27
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. I put the schottky clamp in on theoretical grounds though--without it the collector _has_ to swing a diode-drop below the base to discharge the base cap, which puts Q1 at least on the verge if not frankly in reverse mode conduction. With the schottky, damping (via the bias) kicks in as the collector swing approaches 0.4v below Vb, preventing Vce ever going negative. > You can force this to work class-C if you jack around with the > transformer ratio, and use a small base cap, but that's not the way I > originally described the circuit. I did that first, with the savage versions. Theoretically I think that's more stable, letting the LC ring as it will, but with the effect of the reverse spike...I'm still not sure. Leaving the transistor on all the time gives a cleaner waveform, but manhandling the tank full-time slightly out-of-phase pulls the tank off its natural frequency. Hmmm. I guess it doesn't really matter--I was thinking RF oscillator here, but the feedback phase delays at audio are trivial. > Maybe I'll try moving the feedback into the base circuit, one of these > days. I did that too. Not much different really. > Cute circuit. I think so too. -- Cheers, James Arthur |