On 8/14/19 11:39 AM, jlarkin@highlandsniptechnology.com wrote:> On Wed, 14 Aug 2019 08:24:28 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > >> On Wednesday, August 14, 2019 at 7:46:32 AM UTC-4, tabb...@gmail.com wrote: >>> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >>> >>>> Your formula is useless and misleading. You normally never run a transistor >>>> with the emitter grounded. >>> >>> odd thing to say >>> >>>> You need some way to stabilize the bias. Also, >>> >>> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >>> >>> >>> NT >> >> What's suicide bias? I went searching for biploar transistor and suicide bias... but got a lot of mental health sites. (maybe lithium doping would help. :^) >> >> GH > > A resistor from Vcc to the base, with the emitter grounded. That's > basically a constant base bias current, so Ic is proportional to beta. > > Early transistor circuits tended to do that. As do some cheap products > still. > > > I've done it in some special cases. One can now buy beta-graded > transistors, like BCX70J, that make the idea less silly. > > This is cool: > > https://www.dropbox.com/s/tqw2qe9mi4t8zmz/Suicide_Slicer.JPG?raw=1 > > I'm doing that as a CML-to-TTL converter.That's only suicide bias if the transistor doesn't saturate, or if the AC gets turned off. Otherwise you have a nice switched-cap resistor there, working through the low base Z of the saturated transistor. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Amplification factor for common emitter amplifier
Started by ●August 8, 2019
Reply by ●August 15, 20192019-08-15
Reply by ●August 15, 20192019-08-15
jlarkin@highlandsniptechnology.com wrote:> On Thu, 15 Aug 2019 06:35:17 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote:>>On Thursday, August 15, 2019 at 6:31:22 AM UTC-4, Jasen Betts wrote: >>> On 2019-08-14, George Herold <gherold@teachspin.com> wrote: >>> > On Wednesday, August 14, 2019 at 7:46:32 AM UTC-4, tabb...@gmail.com >>> > wrote: >>> >> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote:>>> >> > Your formula is useless and misleading. You normally never run a >>> >> > transistor with the emitter grounded.>>> >> odd thing to say>>> >> > You need some way to stabilize the bias. Also,>>> >> There's more than one way to do that. And despite the myths, >>> >> suicide bias IS used in commercial circuits.>>> >> NT>>> > What's suicide bias? I went searching for biploar transistor and >>> > suicide bias... but got a lot of mental health sites. (maybe >>> > lithium doping would help. :^)>>> It's been a term of art here (in sci.electronics) for as long as I can >>> remeber.>>> Basically the the base is connected to some sort of current source, >>> and the expression for emitter current is dominted by the beta.>>> --+-+--------+-----+-+-------+-- VCC >>> | | | | | R R | R +-+ R +-+ R | >>> | | | | | R | R | R | | c | c c >>> | | | | | | c +b +b >>> +b +b | e | e e e R | R | >>> | | | | | | >>> ----+--------+-----+-+-----+-+-- GND >>> Q1 Q2 Q3 Q4>>> Q1, Q2, Q3 suicide bias, Q4 maybe not> It's not. There's feedback, essentially a vbe-multiplier.> Q2 isn't suicidal because there's feedback there too. The transistor > can't saturate no matter how high the beta.>>> When I tried casting out nines I made a hash of it.>>Thanks, Isn't Q3 the 'first circuit' one learns to bias a common >>emitter? Well, it was the first circuit I learned.>>GH> Usually an emitter resistor would be added. Otherwise it's still > suicide bias.Then your formula for gain doesn't work.> One nice option is to use the circuit of Q4, but return the lower > resistor to a negative supply. That defines the operating point better > over temperature.Ground the base through a suitable resistor. Return the emitter to the negative supply to set the desired current. Bypass the emitter at a suitable point in the emitter resistor. Use Legg's formula for gain: Vg = Zc / Ze
Reply by ●August 15, 20192019-08-15
On Thursday, August 15, 2019 at 2:11:31 PM UTC-4, Steve Wilson wrote:> jlarkin@highlandsniptechnology.com wrote: > > > On Thu, 15 Aug 2019 06:35:17 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote: > > >>On Thursday, August 15, 2019 at 6:31:22 AM UTC-4, Jasen Betts wrote: > >>> On 2019-08-14, George Herold <gherold@teachspin.com> wrote: > >>> > On Wednesday, August 14, 2019 at 7:46:32 AM UTC-4, tabb...@gmail.com > >>> > wrote: > >>> >> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: > > >>> >> > Your formula is useless and misleading. You normally never run a > >>> >> > transistor with the emitter grounded. > > >>> >> odd thing to say > > >>> >> > You need some way to stabilize the bias. Also, > > >>> >> There's more than one way to do that. And despite the myths, > >>> >> suicide bias IS used in commercial circuits. > > > >>> >> NT > > >>> > What's suicide bias? I went searching for biploar transistor and > >>> > suicide bias... but got a lot of mental health sites. (maybe > >>> > lithium doping would help. :^) > > >>> It's been a term of art here (in sci.electronics) for as long as I can > >>> remeber. > > >>> Basically the the base is connected to some sort of current source, > >>> and the expression for emitter current is dominted by the beta. > > >>> --+-+--------+-----+-+-------+-- VCC > >>> | | | | | R R | R +-+ R +-+ R | > >>> | | | | | R | R | R | | c | c c > >>> | | | | | | c +b +b > >>> +b +b | e | e e e R | R | > >>> | | | | | | > >>> ----+--------+-----+-+-----+-+-- GND > >>> Q1 Q2 Q3 Q4 > > >>> Q1, Q2, Q3 suicide bias, Q4 maybe not > > > It's not. There's feedback, essentially a vbe-multiplier. > > > Q2 isn't suicidal because there's feedback there too. The transistor > > can't saturate no matter how high the beta. > > >>> When I tried casting out nines I made a hash of it. > > >>Thanks, Isn't Q3 the 'first circuit' one learns to bias a common > >>emitter? Well, it was the first circuit I learned. > > >>GH > > > Usually an emitter resistor would be added. Otherwise it's still > > suicide bias. > > Then your formula for gain doesn't work. > > > One nice option is to use the circuit of Q4, but return the lower > > resistor to a negative supply. That defines the operating point better > > over temperature. > > Ground the base through a suitable resistor. Return the emitter to the > negative supply to set the desired current. Bypass the emitter at a > suitable point in the emitter resistor. > > Use Legg's formula for gain: Vg = Zc / ZeSteve, why don't you give it a rest? We all know how to estimate the gain of the CE amp. (well maybe not the OP) GH.
Reply by ●August 15, 20192019-08-15
On Thu, 15 Aug 2019 13:11:26 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 8/14/19 11:39 AM, jlarkin@highlandsniptechnology.com wrote: >> On Wed, 14 Aug 2019 08:24:28 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >>> On Wednesday, August 14, 2019 at 7:46:32 AM UTC-4, tabb...@gmail.com wrote: >>>> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >>>> >>>>> Your formula is useless and misleading. You normally never run a transistor >>>>> with the emitter grounded. >>>> >>>> odd thing to say >>>> >>>>> You need some way to stabilize the bias. Also, >>>> >>>> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >>>> >>>> >>>> NT >>> >>> What's suicide bias? I went searching for biploar transistor and suicide bias... but got a lot of mental health sites. (maybe lithium doping would help. :^) >>> >>> GH >> >> A resistor from Vcc to the base, with the emitter grounded. That's >> basically a constant base bias current, so Ic is proportional to beta. >> >> Early transistor circuits tended to do that. As do some cheap products >> still. >> >> >> I've done it in some special cases. One can now buy beta-graded >> transistors, like BCX70J, that make the idea less silly. >> >> This is cool: >> >> https://www.dropbox.com/s/tqw2qe9mi4t8zmz/Suicide_Slicer.JPG?raw=1 >> >> I'm doing that as a CML-to-TTL converter. > >That's only suicide bias if the transistor doesn't saturate, or if the >AC gets turned off. Otherwise you have a nice switched-cap resistor >there, working through the low base Z of the saturated transistor. > >Cheers > >Phil HobbsIf the RC tau is short compared to the input period, that becomes the "uni-shot" circuit. Before uPs, that was used to generate the control pulse train in R/C transmitters, where the pullup resistor was a joystick pot.
Reply by ●August 15, 20192019-08-15
On Thu, 15 Aug 2019 18:11:25 GMT, Steve Wilson <no@spam.com> wrote:>jlarkin@highlandsniptechnology.com wrote: > >> On Thu, 15 Aug 2019 06:35:17 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: > >>>On Thursday, August 15, 2019 at 6:31:22 AM UTC-4, Jasen Betts wrote: >>>> On 2019-08-14, George Herold <gherold@teachspin.com> wrote: >>>> > On Wednesday, August 14, 2019 at 7:46:32 AM UTC-4, tabb...@gmail.com >>>> > wrote: >>>> >> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: > >>>> >> > Your formula is useless and misleading. You normally never run a >>>> >> > transistor with the emitter grounded. > >>>> >> odd thing to say > >>>> >> > You need some way to stabilize the bias. Also, > >>>> >> There's more than one way to do that. And despite the myths, >>>> >> suicide bias IS used in commercial circuits. > > >>>> >> NT > >>>> > What's suicide bias? I went searching for biploar transistor and >>>> > suicide bias... but got a lot of mental health sites. (maybe >>>> > lithium doping would help. :^) > >>>> It's been a term of art here (in sci.electronics) for as long as I can >>>> remeber. > >>>> Basically the the base is connected to some sort of current source, >>>> and the expression for emitter current is dominted by the beta. > >>>> --+-+--------+-----+-+-------+-- VCC >>>> | | | | | R R | R +-+ R +-+ R | >>>> | | | | | R | R | R | | c | c c >>>> | | | | | | c +b +b >>>> +b +b | e | e e e R | R | >>>> | | | | | | >>>> ----+--------+-----+-+-----+-+-- GND >>>> Q1 Q2 Q3 Q4 > >>>> Q1, Q2, Q3 suicide bias, Q4 maybe not > >> It's not. There's feedback, essentially a vbe-multiplier. > >> Q2 isn't suicidal because there's feedback there too. The transistor >> can't saturate no matter how high the beta. > >>>> When I tried casting out nines I made a hash of it. > >>>Thanks, Isn't Q3 the 'first circuit' one learns to bias a common >>>emitter? Well, it was the first circuit I learned. > >>>GH > >> Usually an emitter resistor would be added. Otherwise it's still >> suicide bias. > >Then your formula for gain doesn't work.What is wrong with you?
Reply by ●August 15, 20192019-08-15
On Thu, 15 Aug 2019 13:07:20 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 8/14/19 7:46 AM, tabbypurr@gmail.com wrote: >> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >> >>> Your formula is useless and misleading. You normally never run a transistor >>> with the emitter grounded. >> >> odd thing to say >> >>> You need some way to stabilize the bias. Also, >> >> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >> >> >> NT >> >Sure, e.g. the late lamented BCV61/62 current mirrors, where the output >side will run away if its dissipation gets too large. (It's made of two >chips, so the thermal coupling is lousy.) There's a spec for that in >the datasheet. > >Cheers > >Phil HobbsSome engineers (and a lot of scientists!) have an undeserved affection for current mirrors, which seldom work well made from discretes, even "dual" transistors. https://www.dropbox.com/s/zdgjg8lv39s586d/UPA800_80mW_one-side.jpg?raw=1
Reply by ●August 15, 20192019-08-15
>Here is a picture of simple self bias. It is negative feedback, >broken at AC in the lower sketch.You realize the problems with both those circuits right ? Input Z is too damn low and too damn unpredictable. Doesn't mean it won't work but there are better ways to skin that cat.
Reply by ●August 15, 20192019-08-15
On 8/15/19 3:18 PM, John Larkin wrote:> On Thu, 15 Aug 2019 13:07:20 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 8/14/19 7:46 AM, tabbypurr@gmail.com wrote: >>> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >>> >>>> Your formula is useless and misleading. You normally never run a transistor >>>> with the emitter grounded. >>> >>> odd thing to say >>> >>>> You need some way to stabilize the bias. Also, >>> >>> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >>> >>> >>> NT >>> >> Sure, e.g. the late lamented BCV61/62 current mirrors, where the output >> side will run away if its dissipation gets too large. (It's made of two >> chips, so the thermal coupling is lousy.) There's a spec for that in >> the datasheet. >> >> Cheers >> >> Phil Hobbs > > Some engineers (and a lot of scientists!) have an undeserved affection > for current mirrors, which seldom work well made from discretes, even > "dual" transistors. > > https://www.dropbox.com/s/zdgjg8lv39s586d/UPA800_80mW_one-side.jpg?raw=1 >They can be useful in some cases, especially where you have to supply bias with practically no headroom. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●August 15, 20192019-08-15
On Thu, 15 Aug 2019 15:26:17 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 8/15/19 3:18 PM, John Larkin wrote: >> On Thu, 15 Aug 2019 13:07:20 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 8/14/19 7:46 AM, tabbypurr@gmail.com wrote: >>>> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >>>> >>>>> Your formula is useless and misleading. You normally never run a transistor >>>>> with the emitter grounded. >>>> >>>> odd thing to say >>>> >>>>> You need some way to stabilize the bias. Also, >>>> >>>> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >>>> >>>> >>>> NT >>>> >>> Sure, e.g. the late lamented BCV61/62 current mirrors, where the output >>> side will run away if its dissipation gets too large. (It's made of two >>> chips, so the thermal coupling is lousy.) There's a spec for that in >>> the datasheet. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Some engineers (and a lot of scientists!) have an undeserved affection >> for current mirrors, which seldom work well made from discretes, even >> "dual" transistors. >> >> https://www.dropbox.com/s/zdgjg8lv39s586d/UPA800_80mW_one-side.jpg?raw=1 >> > >They can be useful in some cases, especially where you have to supply >bias with practically no headroom. > >Cheers > >Phil HobbsBut most of the fixes add headroom!
Reply by ●August 15, 20192019-08-15
On 8/15/19 3:55 PM, John Larkin wrote:> On Thu, 15 Aug 2019 15:26:17 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 8/15/19 3:18 PM, John Larkin wrote: >>> On Thu, 15 Aug 2019 13:07:20 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 8/14/19 7:46 AM, tabbypurr@gmail.com wrote: >>>>> On Wednesday, 14 August 2019 11:09:55 UTC+1, Steve Wilson wrote: >>>>> >>>>>> Your formula is useless and misleading. You normally never run a transistor >>>>>> with the emitter grounded. >>>>> >>>>> odd thing to say >>>>> >>>>>> You need some way to stabilize the bias. Also, >>>>> >>>>> There's more than one way to do that. And despite the myths, suicide bias IS used in commercial circuits. >>>>> >>>>> >>>>> NT >>>>> >>>> Sure, e.g. the late lamented BCV61/62 current mirrors, where the output >>>> side will run away if its dissipation gets too large. (It's made of two >>>> chips, so the thermal coupling is lousy.) There's a spec for that in >>>> the datasheet. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Some engineers (and a lot of scientists!) have an undeserved affection >>> for current mirrors, which seldom work well made from discretes, even >>> "dual" transistors. >>> >>> https://www.dropbox.com/s/zdgjg8lv39s586d/UPA800_80mW_one-side.jpg?raw=1 >>> >> >> They can be useful in some cases, especially where you have to supply >> bias with practically no headroom. >> >> Cheers >> >> Phil Hobbs > > But most of the fixes add headroom!What I have in mind is a diff pair whose emitters can be very near the supply. A good mirror is the business for that. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
