On Mon, 15 May 2017 10:18:16 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 05/15/2017 10:09 AM, bitrex wrote: >> On 05/15/2017 10:01 AM, John Larkin wrote: >> >>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>> source and sink 88 mA. And there are lots of faster THS-series parts. >>> >>>> >>>> But indeed you can do that with a few NPNs of the old days, >>>> >>> >>> Post it. >> >> With discretes you can have: >> >> 1) wide bandwidth >> >> 2) low parts count >> >> 3) low quiescent current draw >> >> Pick two. > >The two transistor circuit Jan posted does have a pretty wide bandwidth >and a low parts count. It has a pretty nice small signal output >impedance, but its large-signal output impedance is bad. It also draws a >relatively large amount of quiescent current.Iq is undefined, and this is a poster child for thermal runaway. It needs more parts! -- John Larkin Highland Technology, Inc lunatic fringe electronics
Fast buffer idea
Started by ●May 14, 2017
Reply by ●May 15, 20172017-05-15
Reply by ●May 15, 20172017-05-15
On a sunny day (Mon, 15 May 2017 08:56:58 -0700) it happened John Larkin <jjlarkin@highlandtechnology.com> wrote in <6sjjhc1mm6atuu3ovmnnmtpke1iu2t4fgh@4ax.com>:>On Mon, 15 May 2017 10:18:16 -0400, bitrex ><bitrex@de.lete.earthlink.net> wrote: > >>On 05/15/2017 10:09 AM, bitrex wrote: >>> On 05/15/2017 10:01 AM, John Larkin wrote: >>> >>>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>>> source and sink 88 mA. And there are lots of faster THS-series parts. >>>> >>>>> >>>>> But indeed you can do that with a few NPNs of the old days, >>>>> >>>> >>>> Post it. >>> >>> With discretes you can have: >>> >>> 1) wide bandwidth >>> >>> 2) low parts count >>> >>> 3) low quiescent current draw >>> >>> Pick two. >> >>The two transistor circuit Jan posted does have a pretty wide bandwidth >>and a low parts count. It has a pretty nice small signal output >>impedance, but its large-signal output impedance is bad. It also draws a >>relatively large amount of quiescent current. > >Iq is undefined, and this is a poster child for thermal runaway. It >needs more parts!???? TWO transistor ????
Reply by ●May 15, 20172017-05-15
bitrex <bitrex@de.lete.earthlink.net> wrote:> On 05/15/2017 10:09 AM, bitrex wrote: >> On 05/15/2017 10:01 AM, John Larkin wrote: >> >>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>> source and sink 88 mA. And there are lots of faster THS-series parts. >>> >>>> >>>> But indeed you can do that with a few NPNs of the old days, >>>> >>> >>> Post it. >> >> With discretes you can have: >> >> 1) wide bandwidth >> >> 2) low parts count >> >> 3) low quiescent current draw >> >> Pick two. > > The two transistor circuit Jan posted does have a pretty wide bandwidth > and a low parts count. It has a pretty nice small signal output > impedance, but its large-signal output impedance is bad. It also drawsa> relatively large amount of quiescent current.I somehow missed the two transistor circuit that Jan posted. Can you please repost the link? Thanks
Reply by ●May 15, 20172017-05-15
On a sunny day (Mon, 15 May 2017 16:24:56 GMT) it happened Steve Wilson <no@spam.com> wrote in <XnsA7767E5052407idtokenpost@69.16.179.22>:>bitrex <bitrex@de.lete.earthlink.net> wrote: > >> On 05/15/2017 10:09 AM, bitrex wrote: >>> On 05/15/2017 10:01 AM, John Larkin wrote: >>> >>>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>>> source and sink 88 mA. And there are lots of faster THS-series parts. >>>> >>>>> >>>>> But indeed you can do that with a few NPNs of the old days, >>>>> >>>> >>>> Post it. >>> >>> With discretes you can have: >>> >>> 1) wide bandwidth >>> >>> 2) low parts count >>> >>> 3) low quiescent current draw >>> >>> Pick two. >> >> The two transistor circuit Jan posted does have a pretty wide bandwidth >> and a low parts count. It has a pretty nice small signal output >> impedance, but its large-signal output impedance is bad. It also draws >a >> relatively large amount of quiescent current. > >I somehow missed the two transistor circuit that Jan posted. Can you >please repost the link? > >ThanksFrom: http://panteltje.com/panteltje/quadcopter/hud.html the circuit diagram: http://panteltje.com/panteltje/quadcopter/hud-0.1_circuit_diagram_IMG_5984.JPG bottom left: that has a gain of 2, so can drive a 75 Ohm cable with reasonable Zi. The DC path requires an other 75 Ohm at the end of the cable.
Reply by ●May 15, 20172017-05-15
On 05/15/2017 11:55 AM, John Larkin wrote:> On Mon, 15 May 2017 10:09:39 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> On 05/15/2017 10:01 AM, John Larkin wrote: >> >>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>> source and sink 88 mA. And there are lots of faster THS-series parts. >>> >>>> >>>> But indeed you can do that with a few NPNs of the old days, >>>> >>> >>> Post it. >> >> With discretes you can have: >> >> 1) wide bandwidth >> >> 2) low parts count >> >> 3) low quiescent current draw >> >> Pick two. > > But your circuit has 24 parts and doesn't even have a voltage gain of > 1. > > 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. Integrating the source you get that it's sourcing about 100uW, and a simple a 50 ohm load termination is dissipating 10mW. Assuming 100uW is the max the source could provide, what kind of length of wire has a a transducer gain of 100? That's a neat trick!
Reply by ●May 15, 20172017-05-15
On 05/15/2017 12:51 PM, bitrex wrote:> On 05/15/2017 11:55 AM, John Larkin wrote: >> On Mon, 15 May 2017 10:09:39 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 05/15/2017 10:01 AM, John Larkin wrote: >>> >>>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>>> source and sink 88 mA. And there are lots of faster THS-series parts. >>>> >>>>> >>>>> But indeed you can do that with a few NPNs of the old days, >>>>> >>>> >>>> Post it. >>> >>> With discretes you can have: >>> >>> 1) wide bandwidth >>> >>> 2) low parts count >>> >>> 3) low quiescent current draw >>> >>> Pick two. >> >> But your circuit has 24 parts and doesn't even have a voltage gain of >> 1. >> >> 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. > > Integrating the source you get that it's sourcing about 100uW, and a > simple a 50 ohm load termination is dissipating 10mW. > > Assuming 100uW is the max the source could provide, what kind of length > of wire has a a transducer gain of 100? That's a neat trick!If I had a square-wave source capable of providing say 200mA P2P with an infinite slew rate and zero output impedance then indeed, a piece of wire would be the perfect output buffer. Where do I get one of those?
Reply by ●May 15, 20172017-05-15
On 05/15/2017 12:56 PM, bitrex wrote:> > 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. > > Integrating the source you get that it's sourcing about 100uW, and a > simple a 50 ohm load termination is dissipating 10mW. > > Assuming 100uW is the max the source could provide, what kind of length > of wire has a a transducer gain of 100? That's a neat trick!Sorry, I screwed that up. The average current out of the source is 100uA
Reply by ●May 15, 20172017-05-15
On 05/15/2017 10:33 AM, Jan Panteltje wrote:> On a sunny day (Mon, 15 May 2017 07:01:06 -0700) it happened John Larkin > <jjlarkin@highlandtechnology.com> wrote in > <dpcjhclpajjafaf2nq0q7l7nt17jl40spo@4ax.com>: > >> On Mon, 15 May 2017 07:56:01 GMT, Jan Panteltje >> <pNa0nStpealmtje@yahoo.com> wrote: >> >>> On a sunny day (Sun, 14 May 2017 12:54:12 -0700) it happened John Larkin >>> <jjlarkin@highlandtechnology.com> wrote in >>> <auchhcp4h0898t9hatrh3017esf6dve1n5@4ax.com>: >>> >>>> If the object is to buffer a logic level, some 13-cent TinyLogic gate, >>>> like an NL37WZ16US or something. >>>> >>>> If it needs to be linear, there are tons of opamps to consider: >>>> THS4222, AD8007, whatever. >>> >>> THS4222 datasheet says open loop gain 0dB at 100 MHz? >> >> Where does it say that? >> >>> With a free 80 degrees phase shift? >>> Fig 17, see also Fig 1 for 500 Ohm load. >>> >>> It won't drive a 50 Ohm coax either.. >>> Maybe good for a 5 to 10 MHz wide video amp... >>> >> >> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >> source and sink 88 mA. And there are lots of faster THS-series parts. >> >>> >>> But indeed you can do that with a few NPNs of the old days, >>> >> >> Post it. > > Did not I ;-)? > > 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.
Reply by ●May 15, 20172017-05-15
Jan Panteltje <pNa0nStpealmtje@yahoo.com> wrote:> On a sunny day (Mon, 15 May 2017 16:24:56 GMT) it happened Steve > Wilson <no@spam.com> wrote in > <XnsA7767E5052407idtokenpost@69.16.179.22>: > >>bitrex <bitrex@de.lete.earthlink.net> wrote: >> >>> On 05/15/2017 10:09 AM, bitrex wrote: >>>> On 05/15/2017 10:01 AM, John Larkin wrote: >>>> >>>>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>>>> source and sink 88 mA. And there are lots of faster THS-series >>>>> parts. >>>>> >>>>>> >>>>>> But indeed you can do that with a few NPNs of the old days, >>>>>> >>>>> >>>>> Post it. >>>> >>>> With discretes you can have: >>>> >>>> 1) wide bandwidth >>>> >>>> 2) low parts count >>>> >>>> 3) low quiescent current draw >>>> >>>> Pick two. >>> >>> The two transistor circuit Jan posted does have a pretty wide >>> bandwidth and a low parts count. It has a pretty nice small signal >>> output impedance, but its large-signal output impedance is bad. It >>> also draws a relatively large amount of quiescent current. >> >>I somehow missed the two transistor circuit that Jan posted. Can you >>please repost the link? >> >>Thanks > > From: > http://panteltje.com/panteltje/quadcopter/hud.html > the circuit diagram: > http://panteltje.com/panteltje/quadcopter/hud-0.1_circuit_diagram_IMG > _5984.JPG bottom left: > that has a gain of 2, so can drive a 75 Ohm cable with reasonable Zi. > The DC path requires an other 75 Ohm at the end of the cable.OK, thanks. That is a Sziklai Pair with a voltage divider in the feedback path: https://en.wikipedia.org/wiki/Sziklai_pair It would normally have the same thermal drift as a simple base-emitter junction, but the divide by two may increase it. The output impedance may be increased due to the low loop gain. The bandwidth is determined by the transistors you use. But it is difficult to tell what the transistors are due to the poor clarity of the handwritten numbers. I can't read them even when I expand the drawing. I really wish you could convert some of your critical circuits to LTspice so we can see the operation a bit better. That would have a far greater impact for the value of your work.
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 12:51:03 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 05/15/2017 11:55 AM, John Larkin wrote: >> On Mon, 15 May 2017 10:09:39 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 05/15/2017 10:01 AM, John Larkin wrote: >>> >>>> BW is 230 MHz as a unity-gain buffer. Each half of the dual will >>>> source and sink 88 mA. And there are lots of faster THS-series parts. >>>> >>>>> >>>>> But indeed you can do that with a few NPNs of the old days, >>>>> >>>> >>>> Post it. >>> >>> With discretes you can have: >>> >>> 1) wide bandwidth >>> >>> 2) low parts count >>> >>> 3) low quiescent current draw >>> >>> Pick two. >> >> But your circuit has 24 parts and doesn't even have a voltage gain of >> 1. >> >> 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. Assume 1 volt peak input at 100 MHz. And 600 uA peak (not average!) current. That works out to a capacitance of 1 pF. That sounds improbable. Ciss of that fet is 3600 pF.> >Integrating the source you get that it's sourcing about 100uW, and a >simple a 50 ohm load termination is dissipating 10mW.Apply a 1 volt 100 MHz sine input and measure the V+ supply current.> >Assuming 100uW is the max the source could provide, what kind of length >of wire has a a transducer gain of 100? That's a neat trick!-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
