On 12/27/2016 11:47 AM, Piotr Wyderski wrote:> Phil Hobbs wrote: > >> Doesn't fix the polarization of the FET. It won't amplify if you >> come in via the drain. > > I'm afraid I don't understand what you mean, Phil. The only > polarization in a JFET I know of is the polarization of the gate > diode, which is a P region somehow embedded within the N silicon bar > which makes up D and S. Drain is the end with higher potential and > source with the lower, but it flips as the AC waveform changes. Is it > correct? > > Do you mean the problems with *external* gate polarization > circuitry, which would inject current through the gate if powered > incorrectly? > > Best regards, PiotrA symmetrical JFET is symmetrical with respect to interchanging gate and drain, but not with respect to inverting the supply polarity--otherwise there would be no difference between NFETs and PFETs. A common-gate amplifier can have gain if you come in via the source, but not if you come in via the drain. Inverting the power supply turns the one into the other. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Low-voltage AC-powered oscillator
Started by ●December 27, 2016
Reply by ●December 27, 20162016-12-27
Reply by ●December 27, 20162016-12-27
On 12/27/2016 12:27 PM, Jim Thompson wrote:> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski > <peter.pan@neverland.mil> wrote: > >> Phil Hobbs wrote: >> >>> Doesn't fix the polarization of the FET. It won't amplify if you come >>> in via the drain. >> >> I'm afraid I don't understand what you mean, Phil. The only polarization >> in a JFET I know of is the polarization of the gate diode, which is a >> P region somehow embedded within the N silicon bar which makes up D and >> S. Drain is the end with higher potential and source with the lower, but >> it flips as the AC waveform changes. Is it correct? >> >> Do you mean the problems with *external* gate polarization circuitry, >> which would inject current through the gate if powered incorrectly? >> >> Best regards, Piotr >> >> > > Phil only thinks discrete devices which (usually) have back > gate/substrate tied to source. In my I/C world it's trivial to have > both gates independent, so a _symmetrical_ grounded-gate situation is > quite possible. > > (I am currently working with a major ASIC foundry to get a good JFET > structure added to their repertoire.) > > ...Jim Thompson >The voltage gradient along the channel is what makes the drain different from the source, even in a perfectly symmetrical FET. (These exist in discretes, e.g. the BF862.) Inverting the supply in a common-gate amplifier moves the pinch from one end of the channel to the other, effectively interchanging drain and source. It'll amplify one way, but not the other. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●December 27, 20162016-12-27
Piotr Wyderski <no@mail.com> wrote:> If the power supply voltage is high, say >=3V, it is pretty simple > to design an oscillator (of unimportant output frequency and shape), > which can be powered from an AC power source: just add a diode bridge > at the power input lines and use any suitable DC-powered oscillator > circuit. But what if the supply voltage is really low, say 0.2V? > JFET-based oscillators can go really low, allegedly down to 25mV, > so it should be possible to pair two of them anti-paralelly and > power them directly from AC. However, the JFET structure exhibits > a high degree of symmetry, i.e. the D and S pins are called so > by convention and the device can work in "inversion mode". Is > it possible to use this fact to build an AC-powered oscillator > with a single JFET? > > Best regards, Piotr >This is not what you asked, but the LTC3108 uses a MOSFET and operates down to 20mV: http://www.linear.com/product/LTC3108 So it can be done and is available commercially.
Reply by ●December 27, 20162016-12-27
On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 12/27/2016 12:27 PM, Jim Thompson wrote: >> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >> <peter.pan@neverland.mil> wrote: >> >>> Phil Hobbs wrote: >>> >>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>> in via the drain. >>> >>> I'm afraid I don't understand what you mean, Phil. The only polarization >>> in a JFET I know of is the polarization of the gate diode, which is a >>> P region somehow embedded within the N silicon bar which makes up D and >>> S. Drain is the end with higher potential and source with the lower, but >>> it flips as the AC waveform changes. Is it correct? >>> >>> Do you mean the problems with *external* gate polarization circuitry, >>> which would inject current through the gate if powered incorrectly? >>> >>> Best regards, Piotr >>> >>> >> >> Phil only thinks discrete devices which (usually) have back >> gate/substrate tied to source. In my I/C world it's trivial to have >> both gates independent, so a _symmetrical_ grounded-gate situation is >> quite possible. >> >> (I am currently working with a major ASIC foundry to get a good JFET >> structure added to their repertoire.) >> >> ...Jim Thompson >> > >The voltage gradient along the channel is what makes the drain different >from the source, even in a perfectly symmetrical FET. (These exist in >discretes, e.g. the BF862.) > >Inverting the supply in a common-gate amplifier moves the pinch from one >end of the channel to the other, effectively interchanging drain and >source. It'll amplify one way, but not the other. > >Cheers > >Phil HobbsWrong >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●December 27, 20162016-12-27
On 12/27/2016 01:27 PM, Jim Thompson wrote:> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>> <peter.pan@neverland.mil> wrote: >>> >>>> Phil Hobbs wrote: >>>> >>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>> in via the drain. >>>> >>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>> in a JFET I know of is the polarization of the gate diode, which is a >>>> P region somehow embedded within the N silicon bar which makes up D and >>>> S. Drain is the end with higher potential and source with the lower, but >>>> it flips as the AC waveform changes. Is it correct? >>>> >>>> Do you mean the problems with *external* gate polarization circuitry, >>>> which would inject current through the gate if powered incorrectly? >>>> >>>> Best regards, Piotr >>>> >>>> >>> >>> Phil only thinks discrete devices which (usually) have back >>> gate/substrate tied to source. In my I/C world it's trivial to have >>> both gates independent, so a _symmetrical_ grounded-gate situation is >>> quite possible. >>> >>> (I am currently working with a major ASIC foundry to get a good JFET >>> structure added to their repertoire.) >>> >>> ...Jim Thompson >>> >> >> The voltage gradient along the channel is what makes the drain different >>from the source, even in a perfectly symmetrical FET. (These exist in >> discretes, e.g. the BF862.) >> >> Inverting the supply in a common-gate amplifier moves the pinch from one >> end of the channel to the other, effectively interchanging drain and >> source. It'll amplify one way, but not the other. >> >> Cheers >> >> Phil Hobbs > > Wrong >:-} > > ...Jim Thompson >Show your work. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●December 27, 20162016-12-27
On Tue, 27 Dec 2016 13:36:17 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 12/27/2016 01:27 PM, Jim Thompson wrote: >> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>>> <peter.pan@neverland.mil> wrote: >>>> >>>>> Phil Hobbs wrote: >>>>> >>>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>>> in via the drain. >>>>> >>>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>>> in a JFET I know of is the polarization of the gate diode, which is a >>>>> P region somehow embedded within the N silicon bar which makes up D and >>>>> S. Drain is the end with higher potential and source with the lower, but >>>>> it flips as the AC waveform changes. Is it correct? >>>>> >>>>> Do you mean the problems with *external* gate polarization circuitry, >>>>> which would inject current through the gate if powered incorrectly? >>>>> >>>>> Best regards, Piotr >>>>> >>>>> >>>> >>>> Phil only thinks discrete devices which (usually) have back >>>> gate/substrate tied to source. In my I/C world it's trivial to have >>>> both gates independent, so a _symmetrical_ grounded-gate situation is >>>> quite possible. >>>> >>>> (I am currently working with a major ASIC foundry to get a good JFET >>>> structure added to their repertoire.) >>>> >>>> ...Jim Thompson >>>> >>> >>> The voltage gradient along the channel is what makes the drain different >>>from the source, even in a perfectly symmetrical FET. (These exist in >>> discretes, e.g. the BF862.) >>> >>> Inverting the supply in a common-gate amplifier moves the pinch from one >>> end of the channel to the other, effectively interchanging drain and >>> source. It'll amplify one way, but not the other. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Wrong >:-} >> >> ...Jim Thompson >> >Show your work. > >Cheers > >Phil Hobbs<http://www.analog-innovations.com/SED/PJFET_Construction.pdf> Which is drain and which is source is determined by potential direction... in this (PJFET) case drain is defined by the source/drain terminal that is negative relative to the other terminal. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●December 27, 20162016-12-27
On Tue, 27 Dec 2016 12:10:17 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Tue, 27 Dec 2016 13:36:17 -0500, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 12/27/2016 01:27 PM, Jim Thompson wrote: >>> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>>>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>>>> <peter.pan@neverland.mil> wrote: >>>>> >>>>>> Phil Hobbs wrote: >>>>>> >>>>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>>>> in via the drain. >>>>>> >>>>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>>>> in a JFET I know of is the polarization of the gate diode, which is a >>>>>> P region somehow embedded within the N silicon bar which makes up D and >>>>>> S. Drain is the end with higher potential and source with the lower, but >>>>>> it flips as the AC waveform changes. Is it correct? >>>>>> >>>>>> Do you mean the problems with *external* gate polarization circuitry, >>>>>> which would inject current through the gate if powered incorrectly? >>>>>> >>>>>> Best regards, Piotr >>>>>> >>>>>> >>>>> >>>>> Phil only thinks discrete devices which (usually) have back >>>>> gate/substrate tied to source. In my I/C world it's trivial to have >>>>> both gates independent, so a _symmetrical_ grounded-gate situation is >>>>> quite possible. >>>>> >>>>> (I am currently working with a major ASIC foundry to get a good JFET >>>>> structure added to their repertoire.) >>>>> >>>>> ...Jim Thompson >>>>> >>>> >>>> The voltage gradient along the channel is what makes the drain different >>>>from the source, even in a perfectly symmetrical FET. (These exist in >>>> discretes, e.g. the BF862.) >>>> >>>> Inverting the supply in a common-gate amplifier moves the pinch from one >>>> end of the channel to the other, effectively interchanging drain and >>>> source. It'll amplify one way, but not the other. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Wrong >:-} >>> >>> ...Jim Thompson >>> >>Show your work. >> >>Cheers >> >>Phil Hobbs > ><http://www.analog-innovations.com/SED/PJFET_Construction.pdf> > >Which is drain and which is source is determined by potential >direction... in this (PJFET) case drain is defined by the source/drain >terminal that is negative relative to the other terminal. > > ...Jim ThompsonPresently under analysis for practicality... <http://www.analog-innovations.com/SED/Circular_JFET.pdf> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●December 27, 20162016-12-27
On 12/27/2016 02:10 PM, Jim Thompson wrote:> On Tue, 27 Dec 2016 13:36:17 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 12/27/2016 01:27 PM, Jim Thompson wrote: >>> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>>>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>>>> <peter.pan@neverland.mil> wrote: >>>>> >>>>>> Phil Hobbs wrote: >>>>>> >>>>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>>>> in via the drain. >>>>>> >>>>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>>>> in a JFET I know of is the polarization of the gate diode, which is a >>>>>> P region somehow embedded within the N silicon bar which makes up D and >>>>>> S. Drain is the end with higher potential and source with the lower, but >>>>>> it flips as the AC waveform changes. Is it correct? >>>>>> >>>>>> Do you mean the problems with *external* gate polarization circuitry, >>>>>> which would inject current through the gate if powered incorrectly? >>>>>> >>>>>> Best regards, Piotr >>>>>> >>>>>> >>>>> >>>>> Phil only thinks discrete devices which (usually) have back >>>>> gate/substrate tied to source. In my I/C world it's trivial to have >>>>> both gates independent, so a _symmetrical_ grounded-gate situation is >>>>> quite possible. >>>>> >>>>> (I am currently working with a major ASIC foundry to get a good JFET >>>>> structure added to their repertoire.) >>>>> >>>>> ...Jim Thompson >>>>> >>>> >>>> The voltage gradient along the channel is what makes the drain different >>> >from the source, even in a perfectly symmetrical FET. (These exist in >>>> discretes, e.g. the BF862.) >>>> >>>> Inverting the supply in a common-gate amplifier moves the pinch from one >>>> end of the channel to the other, effectively interchanging drain and >>>> source. It'll amplify one way, but not the other. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Wrong >:-} >>> >>> ...Jim Thompson >>> >> Show your work. >> >> Cheers >> >> Phil Hobbs > > <http://www.analog-innovations.com/SED/PJFET_Construction.pdf> > > Which is drain and which is source is determined by potential > direction... in this (PJFET) case drain is defined by the source/drain > terminal that is negative relative to the other terminal. > > ...Jim Thompson >Right. So if you invert the power supply, the drain and source effectively get swapped. Seems like we're in violent agreement. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●December 27, 20162016-12-27
On Tue, 27 Dec 2016 15:20:28 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 12/27/2016 02:10 PM, Jim Thompson wrote: >> On Tue, 27 Dec 2016 13:36:17 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 12/27/2016 01:27 PM, Jim Thompson wrote: >>>> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>>>>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>>>>> <peter.pan@neverland.mil> wrote: >>>>>> >>>>>>> Phil Hobbs wrote: >>>>>>> >>>>>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>>>>> in via the drain. >>>>>>> >>>>>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>>>>> in a JFET I know of is the polarization of the gate diode, which is a >>>>>>> P region somehow embedded within the N silicon bar which makes up D and >>>>>>> S. Drain is the end with higher potential and source with the lower, but >>>>>>> it flips as the AC waveform changes. Is it correct? >>>>>>> >>>>>>> Do you mean the problems with *external* gate polarization circuitry, >>>>>>> which would inject current through the gate if powered incorrectly? >>>>>>> >>>>>>> Best regards, Piotr >>>>>>> >>>>>>> >>>>>> >>>>>> Phil only thinks discrete devices which (usually) have back >>>>>> gate/substrate tied to source. In my I/C world it's trivial to have >>>>>> both gates independent, so a _symmetrical_ grounded-gate situation is >>>>>> quite possible. >>>>>> >>>>>> (I am currently working with a major ASIC foundry to get a good JFET >>>>>> structure added to their repertoire.) >>>>>> >>>>>> ...Jim Thompson >>>>>> >>>>> >>>>> The voltage gradient along the channel is what makes the drain different >>>> >from the source, even in a perfectly symmetrical FET. (These exist in >>>>> discretes, e.g. the BF862.) >>>>> >>>>> Inverting the supply in a common-gate amplifier moves the pinch from one >>>>> end of the channel to the other, effectively interchanging drain and >>>>> source. It'll amplify one way, but not the other. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Wrong >:-} >>>> >>>> ...Jim Thompson >>>> >>> Show your work. >>> >>> Cheers >>> >>> Phil Hobbs >> >> <http://www.analog-innovations.com/SED/PJFET_Construction.pdf> >> >> Which is drain and which is source is determined by potential >> direction... in this (PJFET) case drain is defined by the source/drain >> terminal that is negative relative to the other terminal. >> >> ...Jim Thompson >> > >Right. So if you invert the power supply, the drain and source >effectively get swapped. Seems like we're in violent agreement. > >Cheers > >Phil HobbsYep. I should read more carefully :-( ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●December 27, 20162016-12-27
On 12/27/2016 05:54 AM, Piotr Wyderski wrote:> If the power supply voltage is high, say >=3V, it is pretty simple > to design an oscillator (of unimportant output frequency and shape), > which can be powered from an AC power source: just add a diode bridge > at the power input lines and use any suitable DC-powered oscillator > circuit. But what if the supply voltage is really low, say 0.2V? > JFET-based oscillators can go really low, allegedly down to 25mV, > so it should be possible to pair two of them anti-paralelly and > power them directly from AC. However, the JFET structure exhibits > a high degree of symmetry, i.e. the D and S pins are called so > by convention and the device can work in "inversion mode". Is > it possible to use this fact to build an AC-powered oscillator > with a single JFET? > > Best regards, PiotrInstead of a JFET, I think one could do some interesting things with a dual-gate depletion-mode MOSFET like so: http://cache.nxp.com/documents/data_sheet/BF992_N.pdf?pspll=1 For example, build an oscillator that starts out blocking, then creates its own boosted voltages to a) bias it up on the second gate into the linear region of operation, and b) develop enough negative voltage to half-wave rectify the input.
