On 05/15/2017 03:05 PM, Jan Panteltje wrote:> On a sunny day (Mon, 15 May 2017 13:15:52 -0400) it happened bitrex > <bitrex@de.lete.earthlink.net> wrote in <cnlSA.15485$Qg.3753@fx14.iad>: > >>> >>> Actually when I did read that OP, I scribbled this on my 'desk': >>> http://panteltje.com/pub/maybe_this_amp_IMG_6183.JPG >>> that is a dual complementary emitter follower. >>> >>> The reason I did not jump into the discussion with that, is that _in this form_ >>> I am not sure about zero temp drift, it may need some resistors. >>> But it should have zero output offset versus input, low output impedance, >>> high input impedance, temp tracking, and I do not have spice running >>> to give an idea, so not a tested thing. >>> So if it melts you mega $ trannies so be it. >>> >> >> It's a regular "diamond buffer" topology. Without emitter degeneration >> resistors in the output emitters it's asking for thermal runaway, and >> the output waveform won't be particularly linear. >> >> Try adding 10 ohm degeneration resistors, and check the quiescent >> current on that bad boy with 10/-10 rails. Yikes! >> >> Taking feedback from the tops of the degeneration resistors to the input >> collectors makes it more linear by reducing Early effect variations. >> It's an even better idea with a MOSFET input stage, as ideally if the >> Vds is near constant you wont have the gm compromised due to >> channel-length modulation. > > OK, challenge? > I have the transistors: > http://panteltje.com/pub/have_those_transistors_in_quantity_IMG_6184.JPG > > So build it, used a 10K pot (single 10 V supply) to put the input at half way (5 V) 47k in series, > poly coupling cap, 1000Hz audio from eeePC: > http://panteltje.com/pub/build_it_and_testing_at_10V_IMG_6185.JPG > > NO resistors > here without flash so you can read the mA meter: > http://panteltje.com/pub/buid_it_and_testing_no_flash_IMG_6186.JPG > > Sorry for the crowded place, lots of things multitasking here. > > I did not load it, but it sure wanted to beep on my FM radio as I did not decouple the supply lines... > Old Trio Kenwood scope does not go that high. > Never underestimate El Pante > > Current does not increase from 5 to 10 V, did not try higher,, > The audio generator is Linux sgen. > > Now for the spice by those who have it!Yes, the basic topology is an _excellent_ performer at low quiescent bias current, low frequency, and into no load! ;-)
Fast buffer idea
Started by ●May 14, 2017
Reply by ●May 15, 20172017-05-15
Reply by ●May 15, 20172017-05-15
Jan Panteltje <pNa0nStpealmtje@yahoo.com> wrote:> On a sunny day (Mon, 15 May 2017 18:07:57 GMT) it happened Steve Wilson > <no@spam.com> wrote in <XnsA7768FC3A2F00idtokenpost@69.16.179.23>: >>These issues would be immediately apparent in a proper LTspiceanalysis.>> >>Unfortunately, with some users still devoted to ASCII-art or hand-drawn >>schematics, it is difficult or impossible to do a reasonablepreliminary>>analysis. > > Man you are way way out in the boonies, > > I can tell from just a few strokes if it wrks or not, > Van Gogh could too. > [My]Tronix is art, you are no art knower, just a wall painter usingspice> as paintbrush. > ;-) > > THIS is why US can no longer send humming beans to space, > You live in a virtual world. > Its all over. > The Matrix has you, no way back. > ....I am retired, so I am not so interested in hiring new enginers. If I were, I would use LTspice. SPICE has a huge learning curve that goes on forever. If a candidate cannot use LTspice, he is of no use to me. You cannot tell if a circuit will work by looking at it. You have to find a way to analyze it that is faster than pencil and paper. The old hybrid- pi models are useless to see if a circuit is usable. Unfortunately, these are stiil taught in engineering schools. My criteria for hiring a new employee would be to show how they are able to construct simple circuits in LTspice and show how they work. If they cannot do that, they are of very little use to me. Your claim that you can tell if a circuit works by simply looking at it is feeble. You need to prove it works, and LTspice is the best way to start.
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 19:51:11 +0100, "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote:>>"bitrex" wrote in message news:xW2SA.99882$jo6.643@fx33.iad... > >it... >> >>> Is your object to drive a length of coax? If it's terminated, you can >>> just ignore the cable entirely. Or poke in a Spice transmission line >>> to explore mismatch consequences. >> > >>Ya, exploring the "mismatch" consequences I'd like to do. How do I do that? >>I haven't used Spice transmission line models before... > >Well... in SS, you just place a transmission line symbol from the lib, and >double-click on it to pop up its setup box. :-)LT has a transmission line. It's fully symmetric, like an unshielded twisted pair. And it acts as if it has an ideal transformer inside; it tolerates any common-mode difference between ends. In fact, it makes a handy ideal transformer. To simulate an actual twisted pair, I use three of the LT Spice TXLINE things. https://dl.dropboxusercontent.com/u/53724080/Circuits/TxLines/Twist_1.jpg Probably the middle one should have a different prop delay. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 18:41:39 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Mon, 15 May 2017 13:38:11 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>>On 05/15/2017 01:28 PM, John Larkin wrote: >>> >>>>>> Snoop the input current of that buffer. At 20 MHz, the overall >>>>>> current gain is less than 1. At 100 MHz, the current gain is about >>>>>> 0.1. You'd be better off with a piece of wire. >>>>> >>>>> I'm not sure what "input current" you're looking at. I'm seeing an >>>>> average current of around 600uA into the MOSFET gates at 100MHz. >>>> >>>> I put a 1 mohm resistor in series with the signal generator and >>>> probed the current, with a sine wave signal input. Try it and see >>>> what you get. >>> >>>How are the gate capacitances of the input MOSFETs supposed to be >>>charged up and down with that fuckin' thing sitting in the way?! >>> >>>Fuck the circuit to hell and then complain it's bad?! Shit! :O >> >> mohm means milliohm, in SI units and in Spice. > >Megohm is MEG in spice. I don't know if caps are required in all >versions. > >However, to measure current, all you need is a voltage source in series >with zero volts output. Then plot the current through the device. > >But in LTspice, you can plot the current in any device using the current >probe.The current probe is twitchy. I like to add visible current-shunt resistors to make it easier to probe. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 15:05:51 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 05/15/2017 02:29 PM, John Larkin wrote: >> On Mon, 15 May 2017 13:38:11 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 05/15/2017 01:28 PM, John Larkin wrote: >>> >>>>>> Snoop the input current of that buffer. At 20 MHz, the overall current >>>>>> gain is less than 1. At 100 MHz, the current gain is about 0.1. You'd >>>>>> be better off with a piece of wire. >>>>> >>>>> I'm not sure what "input current" you're looking at. I'm seeing an >>>>> average current of around 600uA into the MOSFET gates at 100MHz. >>>> >>>> I put a 1 mohm resistor in series with the signal generator and probed >>>> the current, with a sine wave signal input. Try it and see what you >>>> get. >>> >>> How are the gate capacitances of the input MOSFETs supposed to be >>> charged up and down with that fuckin' thing sitting in the way?! >>> >>> Fuck the circuit to hell and then complain it's bad?! Shit! :O >> >> mohm means milliohm, in SI units and in Spice. > >Ok, I see what you mean; forgive my, uh, outburst. And there is a bug >with sine wave drive that isn't apparent with a square drive. > >Problem seems to be that with these slow transistors, I optimized R9 and >R10 to make a nice square wave. But those resistors aren't optimal for a >sine-wave of say 1V P2P; the boost transistors never turn on hard >enough, and if the output transistors can't get the current they need >they're going to try to pull it from somewhere, namely from the MOSFETs. >Or since Vds is fixed it can probably try to pull it right from the >input source. > >That's probably fixable.You might use some smaller mosfets; those are 10 amp beasts. Or bipolars. A spin on Jan's 4-transistor circuit should work. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 15, 20172017-05-15
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> The current probe is twitchy. I like to add visible current-shunt > resistors to make it easier to probe.Nothing wrong with that, except you have to add separate node names to either side of the resistor. Then instead of plotting Ib(Q2) you will plot I(R12). The polarity will depend on the orientation of the resistor. This is not so bad, except you will have to turn it around to get the flow in the direction you want. Or you could simply add a minus sign to the plot to get it to the direction you want. These are simple things, but are part of the huge learning curve in spice. This is why I wish people would post working LTspice schematics instead of ASCII or hand-drawn schematics that most likely do not function.
Reply by ●May 15, 20172017-05-15
John Larkin <jjlarkin@highland_snip_technology.com> wrote:>>That's probably fixable.> You might use some smaller mosfets; those are 10 amp beasts.> Or bipolars. A spin on Jan's 4-transistor circuit should work.If you are speaking of the complmentary emitter-follower circuit, it is not new. I used it in 1979 and shipped it in millions of dollars worth of products in 1980's dollars. HP thought it was excellent, which led to several hundred thousand dollar sales. I don't know if it has a name, but it is also shown in numerous web sites today.
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 20:46:14 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> The current probe is twitchy. I like to add visible current-shunt >> resistors to make it easier to probe. > >Nothing wrong with that, except you have to add separate node names to >either side of the resistor. Then instead of plotting Ib(Q2) you will plot >I(R12). The polarity will depend on the orientation of the resistor.LT Spice defaults to getting that backwards. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 15, 20172017-05-15
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Mon, 15 May 2017 20:46:14 GMT, Steve Wilson <no@spam.com> wrote: > >>John Larkin <jjlarkin@highland_snip_technology.com> wrote: >> >>> The current probe is twitchy. I like to add visible current-shunt >>> resistors to make it easier to probe. >> >>Nothing wrong with that, except you have to add separate node names to >>either side of the resistor. Then instead of plotting Ib(Q2) you will >>plot I(R12). The polarity will depend on the orientation of the >>resistor. > > LT Spice defaults to getting that backwards.So plot the twitchy base, emitter or collector current, and add a minus sign if needed to make it correspond with the waveform. No matter how painful or inconvenient, LTspice is still orders of magnitude more useful than ASCII or hand-drawn schematics.
Reply by ●May 15, 20172017-05-15
On 05/15/2017 04:21 PM, John Larkin wrote:> On Mon, 15 May 2017 15:05:51 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> On 05/15/2017 02:29 PM, John Larkin wrote: >>> On Mon, 15 May 2017 13:38:11 -0400, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 05/15/2017 01:28 PM, John Larkin wrote: >>>> >>>>>>> Snoop the input current of that buffer. At 20 MHz, the overall current >>>>>>> gain is less than 1. At 100 MHz, the current gain is about 0.1. You'd >>>>>>> be better off with a piece of wire. >>>>>> >>>>>> I'm not sure what "input current" you're looking at. I'm seeing an >>>>>> average current of around 600uA into the MOSFET gates at 100MHz. >>>>> >>>>> I put a 1 mohm resistor in series with the signal generator and probed >>>>> the current, with a sine wave signal input. Try it and see what you >>>>> get. >>>> >>>> How are the gate capacitances of the input MOSFETs supposed to be >>>> charged up and down with that fuckin' thing sitting in the way?! >>>> >>>> Fuck the circuit to hell and then complain it's bad?! Shit! :O >>> >>> mohm means milliohm, in SI units and in Spice. >> >> Ok, I see what you mean; forgive my, uh, outburst. And there is a bug >> with sine wave drive that isn't apparent with a square drive. >> >> Problem seems to be that with these slow transistors, I optimized R9 and >> R10 to make a nice square wave. But those resistors aren't optimal for a >> sine-wave of say 1V P2P; the boost transistors never turn on hard >> enough, and if the output transistors can't get the current they need >> they're going to try to pull it from somewhere, namely from the MOSFETs. >> Or since Vds is fixed it can probably try to pull it right from the >> input source. >> >> That's probably fixable. > > You might use some smaller mosfets; those are 10 amp beasts. > > Or bipolars. A spin on Jan's 4-transistor circuit should work. >I think I found a way to resolve the problems to make it have a nice linear boost proportional to signal amplitude for all types of signals. Requires rearranging the feedback from the output emitters to the inner transistors a little bit. Stay tune...
