Amplification factor for common emitter amplifier

[Phil Hobbs]

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

--
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

 

[George Herold]

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 / Ze

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.

 

[Steve Wilson]

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

 

[Phil Hobbs]

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

 

>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.

 

[John Larkin]

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

 

[John Larkin]

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?

 

[John Larkin]

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 Hobbs

If 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.

 

[Phil Hobbs]

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

 

[John Larkin]

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!

 

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 Hobbs

Here'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

 

[Steve Wilson]

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?

 

[Steve Wilson]

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

 

[Jasen Betts]

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.

GH

No, 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.

 

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?

 

[Steve Wilson]

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

 

[Kevin Aylward]

"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

 

>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.

 

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

 

[whit3rd]

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!