On Thu, 15 Aug 2019 16:24:31 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>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 HobbsHere's a diff pair where the bases and collectors all run about at nominal ground. https://www.dropbox.com/s/degnb00z3l5xqec/Soar_RT1.JPG?raw=1
Amplification factor for common emitter amplifier
Started by ●August 8, 2019
Reply by ●August 15, 20192019-08-15
Reply by ●August 16, 20192019-08-16
George Herold <gherold@teachspin.com> wrote:> Steve, 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.True. Why don't you try to convince him?
Reply by ●August 16, 20192019-08-16
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:> What is wrong with you?Absolutely nothing. I proposed a circuit that reduces the temperature drift. In the following ASC file, the temperature changes from 25C to 80C. The drift is 50mV vs 854mV, an improvement of a factor of 17.08. Version 4 SHEET 1 1288 680 WIRE 560 -208 288 -208 WIRE 1104 -208 560 -208 WIRE 288 -192 288 -208 WIRE 560 -144 560 -208 WIRE 1104 -144 1104 -208 WIRE 288 -96 288 -112 WIRE 560 -48 560 -64 WIRE 608 -48 560 -48 WIRE 656 -48 608 -48 WIRE 1104 -48 1104 -64 WIRE 1152 -48 1104 -48 WIRE 1200 -48 1152 -48 WIRE 560 -32 560 -48 WIRE 1104 -32 1104 -48 WIRE 320 16 288 16 WIRE 496 16 320 16 WIRE 1008 16 992 16 WIRE 1040 16 1008 16 WIRE 288 32 288 16 WIRE 560 96 560 64 WIRE 624 96 560 96 WIRE 656 96 624 96 WIRE 1104 96 1104 64 WIRE 1168 96 1104 96 WIRE 1248 96 1168 96 WIRE 560 112 560 96 WIRE 1104 112 1104 96 WIRE 1248 112 1248 96 WIRE 288 128 288 112 WIRE 1248 192 1248 176 WIRE 560 224 560 192 WIRE 560 224 288 224 WIRE 1104 224 1104 192 WIRE 1104 224 560 224 WIRE 288 240 288 224 WIRE 288 336 288 320 FLAG 320 16 Vin FLAG 288 128 0 FLAG 608 -48 Q1C FLAG 624 96 Q1E FLAG 288 -96 0 FLAG 288 336 0 FLAG 1152 -48 Q2C FLAG 1168 96 Q2E FLAG 1008 16 Vin FLAG 1248 192 0 SYMBOL npn 496 -32 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL voltage 288 16 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value SINE(0 0.005 1k) SYMBOL res 544 -160 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res 544 96 R0 SYMATTR InstName R2 SYMATTR Value 1.856k SYMBOL voltage 288 -208 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 10 SYMBOL voltage 288 224 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value -10 SYMBOL npn 1040 -32 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 1088 -160 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL res 1088 96 R0 SYMATTR InstName R4 SYMATTR Value 1.856k SYMBOL cap 1232 112 R0 SYMATTR InstName C1 SYMATTR Value 1 TEXT 720 -352 Left 2 !.tran 0 10m 0 1u TEXT 720 -384 Left 2 ;'Voltage Gain TEXT 464 288 Left 2 ;Vg = 5.35e-3 / 10e-3 = 0.535 TEXT 1016 288 Left 2 ;Vg = 1.767/ 10e-3 = 176.7 TEXT 552 256 Left 2 ;A TEXT 1096 248 Left 2 ;B
Reply by ●August 16, 20192019-08-16
On 2019-08-15, 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 >> >> -- >> 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. > > GHNo, that circuit has an emitter resistor. without an emitter resistor Q3 is equivalent to Q1 but with the base resistor fed from a lower voltage. -- When I tried casting out nines I made a hash of it.
Reply by ●August 16, 20192019-08-16
On Wed, 14 Aug 2019 13:23:08 -0700 (PDT), jurb6006@gmail.com wrote:>>But you can also apply local resistive feedback from the >collector to the base > >Sure. If you apply that to the bias divider fine, it will further stabilise the stage but will lower input Z. It may even clip off the top of the output if you really want the stability. The lower the Z of the bias the better Re works. I could put you together a stage that has near infinite voltage gain, but has one ohm input Z and 32 megohn output Z.Can you do that with one transistor?
Reply by ●August 16, 20192019-08-16
>Can you do that with one transistor?Why not if the hfe can handle it. Low current, small signal, possibly a transistor meant for RF amplification at the front end. High hfe and low Icmax. So you got say a 33 meg collector resistor and say a 100 meg from collector to base to bias it. No Re at all. The 100 meg is going to clip your top end you know, but it can work. And don't come crying to me when it is thermally unstable. You either find another transistor or heat sink it. Now imagine putting a heat sink on one that has a maximum Pd of 30mW. But then there are instruments that actually do put certain components in an oven, I shit you not. Like the crystal that controls the frequency of a TV or radio station. They need that by law and it is not cheap. Yes, you can have a million voltage gain with one transistor and two well chosen resistors. Stability is a different story. Now remember you can't just feed this to anything. Lower input Z in subsequent stages will just short it out. I you want all that gain, feed it to an FET, infinite input impedance. You have the first stage as described, a kagillion gain. Then the FET is enough of a current amplifier, that is with current gain but no voltage gain (but you supplied that) to drive a transistor base, and then subsequently more current gain stages to where you can burn the house down by coughing.
Reply by ●August 16, 20192019-08-16
"John Larkin" wrote in message news:3qbblel6gsurh5f9nehlq47nkq7ije82fi@4ax.com...>Some engineers (and a lot of scientists!) have an undeserved affection >for current mirrors, which seldom work well made from discretes, even >"dual" transistors.It would be fair to say, that without current mirrors, analog ic design would be pretty much impossible. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●August 16, 20192019-08-16
On Wednesday, August 14, 2019 at 4:23:12 PM UTC-4, jurb...@gmail.com wrote:> Sure. If you apply that to the bias divider fine, it will further stabilise the stage but will lower input Z. It may even clip off the top of the output if you really want the stability. The lower the Z of the bias the better Re works. I could put you together a stage that has near infinite voltage gain, but has one ohm input Z and 32 megohn output Z. Pretty much useless. (PRETTY MUCH, THERE ARE TIMES...)Can you post the circuit? In LTspice? Thanks
Reply by ●August 16, 20192019-08-16
On Thursday, August 15, 2019 at 12:18:47 PM UTC-7, John Larkin wrote:> Some engineers (and a lot of scientists!) have an undeserved affection > for current mirrors, which seldom work well made from discretes, even > "dual" transistors.Anyone who designs an op amp uses a current mirror or three. For an LM13700, it's eight to twelve. For a CD4046, it's only three or four, but redesigning without 'em would be a nightmare. Speaking dismissively of "even dual transistors" seems to indicate you don't care about integrated circuits? You needn't share the affection, but it is never undeserved!
Reply by ●August 16, 20192019-08-16
On Thursday, 15 August 2019 20:20:37 UTC+1, jurb...@gmail.com wrote:> >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.yes and no. It doesn't get cheaper than suicide bias. If you don't need much output swing & won't diss enough P to make it suicidal, it works. NT
