Gain...

[Cursitor Doom]

On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
<richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be better
to cascade two stages of 20? I\'d really prefer to use just one stage if
it can be done with stability. The input signal will be up to 20mV p-p
and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.
For the low-noise NPN, the AoE has table
with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people
to find.
1994_National_Linear_Applications_Handbook.pdf
page 435 (p. 460th in pdf)
https://archive.org/details/bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/1up

my point is, it\'s a \"2\" transistor low-noise
pre-amplifier. The LM394 could just as
well be any other low-noise NPN (or
multiple matched units in parallel).

in lieu of LM394 , many choices are given
in Horowitz&Hill Art of Electronics, in table
of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage. Guess
how many pairs I found? None! A few dozen matched pairs, but *all*
totally unsuitable for one reason or another. I was totally certain
I\'d have several to choose from at the end of my hunt but it was not
to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/

 

[Phil Hobbs]

Cursitor Doom wrote:

On Thu, 30 Dec 2021 19:11:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 30 Dec 2021 21:34:27 -0000, \"Kevin Aylward\"
kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

Why anyone would use a discrete transistor stage today is indeed a
mystery...


-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Some of the RF people are ashamed to admit they are selling
transistors. They label the pins RF IN and RF OUT and GROUND.

Sometimes a transistor is just what you need.

Yup, particularly in front ends.

FETs are better in that role IMHO.

For what in particular?

There are a very few JFETs that are competitive with or even superior to
BJTs in wideband, low-level front ends. (People have often used even
noisy JFETs such as J309s in receiver front ends, but below VHF, the
atmosphere is so noisy that you don\'t care very much, and the reduced
IMD is a help.)

I do a fair few mostly-discrete front ends for various things. ICs are
great at what they do well, and can often be repurposed for things their
designers never intended, but even in 2022 there are a lot, a lot of
things you can do with discrete front ends that no IC can touch.

The one we\'ve been discussing has an InGaAs pHEMT, two tiny GaN FETs,
and three 60-GHz Si BJTs. Good luck getting all that on a chip. (And
for Kevin\'s benefit: no, you couldn\'t integrate the equivalent function
in plain silicon.)

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

 

[Phil Hobbs]

Cursitor Doom wrote:

On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be better
to cascade two stages of 20? I\'d really prefer to use just one stage if
it can be done with stability. The input signal will be up to 20mV p-p
and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.
For the low-noise NPN, the AoE has table
with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people
to find.
1994_National_Linear_Applications_Handbook.pdf
page 435 (p. 460th in pdf)
https://archive.org/details/bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/1up

my point is, it\'s a \"2\" transistor low-noise
pre-amplifier. The LM394 could just as
well be any other low-noise NPN (or
multiple matched units in parallel).

in lieu of LM394 , many choices are given
in Horowitz&Hill Art of Electronics, in table
of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage. Guess
how many pairs I found? None! A few dozen matched pairs, but *all*
totally unsuitable for one reason or another. I was totally certain
I\'d have several to choose from at the end of my hunt but it was not
to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/

Why in the world do you need matched BJTs for this? That LM394 app note
was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\' device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will do
much better, and cost pennies.

The PNP wraparound trick helps reduce the Miller capacitance, for sure.
It\'s a bit like a cascode, but generally slower since the collector
swing is suppressed by feedback rather than the diode action. (I\'m a
big fan of local feedback in general.)

It\'s also much more likely to oscillate if you do it wrong.

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

 

[Rich S]

If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.
For the low-noise NPN, the AoE has table
with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people
to find.
1994_National_Linear_Applications_Handbook.pdf
page 435 (p. 460th in pdf)
https://archive.org/details/bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/1up

my point is, it\'s a \"2\" transistor low-noise
pre-amplifier. The LM394 could just as
well be any other low-noise NPN (or
multiple matched units in parallel).

in lieu of LM394 , many choices are given
in Horowitz&Hill Art of Electronics, in table
of \"low noise BJT transistors\"

Why in the world do you need matched BJTs for this? That LM394 app note
was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\' device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will do
much better, and cost pennies.

agreed, we don\'t need dual-matched NPNs
*If* one of those suitable singles will do.
For consumer gear, one is prob. OK.
(\"if\" = literature like AoE3 do show the benefit
of lowering noise by paralleling matched BJTs -
when one does need super-low noise voltage)
And the other point was that despite the fact
that the LM394 was obsolete, other duals/quads
are available. that is all.
happy new year! - RS

 

[Cursitor Doom]

On Fri, 31 Dec 2021 18:23:30 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be better
to cascade two stages of 20? I\'d really prefer to use just one stage if
it can be done with stability. The input signal will be up to 20mV p-p
and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.
For the low-noise NPN, the AoE has table
with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people
to find.
1994_National_Linear_Applications_Handbook.pdf
page 435 (p. 460th in pdf)
https://archive.org/details/bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/1up

my point is, it\'s a \"2\" transistor low-noise
pre-amplifier. The LM394 could just as
well be any other low-noise NPN (or
multiple matched units in parallel).

in lieu of LM394 , many choices are given
in Horowitz&Hill Art of Electronics, in table
of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage. Guess
how many pairs I found? None! A few dozen matched pairs, but *all*
totally unsuitable for one reason or another. I was totally certain
I\'d have several to choose from at the end of my hunt but it was not
to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/


Why in the world do you need matched BJTs for this? That LM394 app note
was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\' device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will do
much better, and cost pennies.

The PNP wraparound trick helps reduce the Miller capacitance, for sure.
It\'s a bit like a cascode, but generally slower since the collector
swing is suppressed by feedback rather than the diode action. (I\'m a
big fan of local feedback in general.)

It\'s also much more likely to oscillate if you do it wrong.

I really appreciate that, Phil! You saying \"if\" rather than *when*
LOL!
Seriously, you\'re so far above me I wouldn\'t even be able to see you
with that fancy new telescope they\'ve just put into space. :-D
More and more I\'m tempted to go down the IC route...

 

[whit3rd]

On Thursday, December 30, 2021 at 1:34:44 PM UTC-8, Kevin Aylward wrote:

\"Phil Hobbs\" wrote in message
news:905efb96-61d6-7cdc...@electrooptical.net...
Cursitor Doom wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or...

Realistically, one really needs two stages with this sort of spec.

In earlier days, realism was the reason for regenerative and superregenerative
circuitry. All the gain you need without the expensive second transistor.

> >How about a nice LM358A?

.... and without the third through thirtieth transistor

Why anyone would use a discrete transistor stage today is indeed a
mystery...

Yeah, the \'expensive\' word was, but is no longer, applicable.

 

[bitrex]

On 12/31/21 3:44 PM, Rich S wrote:

On Friday, December 31, 2021 at 5:54:11 PM UTC, bitrex wrote:
On 12/30/21 10:12 PM, Phil Allison wrote:
Rich Schmuck wrote:
================
CD.

Hi CD, > If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.

** The LM394 is long obsolete.

NOS examples go for $40 on Ebay.

CD is a massive troll and a moron - so are you.



.... Phil

Would you be interested in a Latvian equivalent:

https://www.ericasynths.lv/shop/ics/as394-matched-transistors/

Looks like \"ALFA RPAR\" specializes in repros of some ICs that were in
vintage synthesizers and effects

Cool! So Latvia rocks.
Only € 2.70 - not bad at all.

There was a decent-sized semiconductor manufacturing industry in Riga
during the Soviet era, they built a lot of electronics for the Soviet
military there.

Looks like they\'ve reoriented to supplying rad-hard/ruggedized
components for aerospace applications and \"legacy products\" generally:

<https://www.rdalfa.eu/>

Aside from LM394..
Other new-stock matched BJT duals or arrays live on...

http://thatcorp.com/300-series_Matched_Transistor_Array_ICs.shtml
https://www.analog.com/en/parametricsearch/10988#/
https://www.onsemi.com/products/discrete-power-modules/general-purpose-and-low-vcesat-transistors/nst45011mw6t1g

 

[bitrex]

On 12/31/21 3:44 PM, Rich S wrote:

On Friday, December 31, 2021 at 5:54:11 PM UTC, bitrex wrote:
On 12/30/21 10:12 PM, Phil Allison wrote:
Rich Schmuck wrote:
================
CD.

Hi CD, > If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.

** The LM394 is long obsolete.

NOS examples go for $40 on Ebay.

CD is a massive troll and a moron - so are you.



.... Phil

Would you be interested in a Latvian equivalent:

https://www.ericasynths.lv/shop/ics/as394-matched-transistors/

Looks like \"ALFA RPAR\" specializes in repros of some ICs that were in
vintage synthesizers and effects

Cool! So Latvia rocks.
Only € 2.70 - not bad at all.


Aside from LM394..
Other new-stock matched BJT duals or arrays live on...

http://thatcorp.com/300-series_Matched_Transistor_Array_ICs.shtml
https://www.analog.com/en/parametricsearch/10988#/
https://www.onsemi.com/products/discrete-power-modules/general-purpose-and-low-vcesat-transistors/nst45011mw6t1g

If you can accept \"relaxed\" specs and devices that maybe aren\'t
particularly well-matched and promise to buy a few hundred Rochester
Elec. seems to have tens of thousands of CA3096 in SOIC available for
well under a buck in quantity; in these times of chip shortages \"high
voltage\" analog ICs have seem particularly difficult to get a hold of so
could be useful to someone.

<https://www.rocelec.com/search?q=ca3096>

 

[Gerhard Hoffmann]

Am 01.01.22 um 07:09 schrieb bitrex:

On 12/31/21 3:44 PM, Rich S wrote:
On Friday, December 31, 2021 at 5:54:11 PM UTC, bitrex wrote:


** The LM394 is long obsolete.

NOS examples go for $40 on Ebay.

Renesas / ex Intersil HFA3046, HFA3096, HFA3127, HFA3128

They even contain 5.5 GHz PNPs, still available the last time
I needed them, even acceptable for space.

There is a data sheet from jan 2019, relatively fresh.



On Semi MBT6429DW1T1G NST45010MW6T1G UMZ1NT1G
AD MAT14 SSM2210 SSM2220
Fairchild MMPQ6700
Diodes/ex Zetex ZXTC2061E6

(from my .pdf collection)

Cheers, Gerhard

 

[Kevin Aylward]

\"Phil Hobbs\" wrote in message
news:cc9440bd-b699-d7a7-6b96-d985572889b0@electrooptical.net...

Cursitor Doom wrote:

On Thu, 30 Dec 2021 19:11:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 30 Dec 2021 21:34:27 -0000, \"Kevin Aylward\"
kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

Why anyone would use a discrete transistor stage today is indeed a
mystery...


-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Some of the RF people are ashamed to admit they are selling
transistors. They label the pins RF IN and RF OUT and GROUND.

Sometimes a transistor is just what you need.

Yup, particularly in front ends.

FETs are better in that role IMHO.


For what in particular?

There are a very few JFETs that are competitive with or even superior to
BJTs in wideband, low-level front ends.

Probably true for most applications, especially for higher frequencies where
drive impedances are low. The gm is going to be significantly larger at the
same current.

The classic application that jfets win is the guitar pickup front end. Base
current noise is a problem when dropped across a 2 H inductor at 5kHz. even
the dc resistance is a tad on the high side, maybe up to 10k. One also
really requires an input resistance > 1M Ohm. 100k isn\'t enough.

(People have often used even noisy JFETs such as J309s in receiver front
ends, but below VHF, the atmosphere is so noisy that you don\'t care very
much, and the reduced IMD is a help.)

The 2SK162 for audio is actually very good. Gets down to a noise equivalent
of 26 ohms, matching bipolars

I do a fair few mostly-discrete front ends for various things. ICs are
great at what they do well, and can often be repurposed for things their
designers never intended, but even in 2022 there are a lot, a lot of things
you can do with discrete front ends that no IC can touch.

Sure, with off the shelf ics there are specialised gaps that they cant
fill.

If there is a large enough market, there is, nothing that can\'t be done by a
full ic implementation. It might require more than one ic though.

Most off the shelf ics such as op-amps are going to be \"general purpose\" not
ASIC (Application Specific)

If one takes an iPhone, its 100s of \"custom\" ICs.

The one we\'ve been discussing has an InGaAs pHEMT , two tiny GaN FETs, and
three 60-GHz Si BJTs. Good luck getting all that on a chip. (And for
Kevin\'s benefit: no, you couldn\'t integrate the equivalent function in
plain silicon.)

Its certainly difficult to get all types of devices in one process. However,
even Analog Devices might supply what looks like one ic package, but
actually has several die from different processes.

One can integrate any discrete device. An integrated circuit is just more
than one different discrete devices on one die.

ASIC design is fundamentally different to discrete. Transistors are cheap,
as is calibration. I would have to examine what your product spec is to
evaluate how one would do it in an ic.

I haven\'t checked all the combinations available in current processes, but
there are certainly \"standard\" (mos & bipolar) component processes that have
GaN FETs, and \"standard\" processes with SiGe 200GHz devices, and cmos
processes with pHEMT. There are a LOT of processes out there.

If the market size is there, its always possible to integrate anything. For
small markets, there may be be a few applications where discrete is the way
to go.

There are fundamental advantages to ic implementation. Routing capacitances
are at the ff level for starters.

-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[Joe Gwinn]

On Sat, 1 Jan 2022 18:59:06 -0000, \"Kevin Aylward\"
<kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

\"Phil Hobbs\" wrote in message
news:cc9440bd-b699-d7a7-6b96-d985572889b0@electrooptical.net...

Cursitor Doom wrote:
On Thu, 30 Dec 2021 19:11:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 30 Dec 2021 21:34:27 -0000, \"Kevin Aylward\"
kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

Why anyone would use a discrete transistor stage today is indeed a
mystery...


-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Some of the RF people are ashamed to admit they are selling
transistors. They label the pins RF IN and RF OUT and GROUND.

Sometimes a transistor is just what you need.

Yup, particularly in front ends.

FETs are better in that role IMHO.


For what in particular?

There are a very few JFETs that are competitive with or even superior to
BJTs in wideband, low-level front ends.

Probably true for most applications, especially for higher frequencies where
drive impedances are low. The gm is going to be significantly larger at the
same current.

The classic application that jfets win is the guitar pickup front end. Base
current noise is a problem when dropped across a 2 H inductor at 5kHz. even
the dc resistance is a tad on the high side, maybe up to 10k. One also
really requires an input resistance > 1M Ohm. 100k isn\'t enough.

Yes. I was doing such things about 15 years ago. The 2 H and 10 Kohms
(DC) values are typical. The coil has something like 10,000 turns of
AWG #42 enameled wire. An electric guitar pickup is a low-Q inductor
with a self resonant frequency around 3 KHz when loaded by the guitar
cable between pickup and the JFET input stage. The resonant Q might be
2.

I do have one detail to add:

It\'s useful to have a 100 K film resistor in series with the JFET
gate, to prevent output peak inversion on very strong input
transients, where the gate junction diode is driven solidly into
conduction.

Such transients are relatively common when the guitar is strummed
hard. The peak is some volts, as I recall.

I don\'t think it damages the JFET, but the peak inversion is probably
audible, more so than simply clipping the peak.

(People have often used even noisy JFETs such as J309s in receiver front
ends, but below VHF, the atmosphere is so noisy that you don\'t care very
much, and the reduced IMD is a help.)

The 2SK162 for audio is actually very good. Gets down to a noise equivalent
of 26 ohms, matching bipolars

Do you have any information on its flicker noise performance?

Joe Gwinn

 

[Phil Allison]

Joe Gwinn wrote:
\"Kevin Aylward\"
----------------------------

The classic application that jfets win is the guitar pickup front end. Base
current noise is a problem when dropped across a 2 H inductor at 5kHz. even
the dc resistance is a tad on the high side, maybe up to 10k. One also
really requires an input resistance > 1M Ohm. 100k isn\'t enough.
-----------------------------------------------------------
Yes. I was doing such things about 15 years ago. The 2 H and 10 Kohms
(DC) values are typical. The coil has something like 10,000 turns of
AWG #42 enameled wire. An electric guitar pickup is a low-Q inductor
with a self resonant frequency around 3 KHz when loaded by the guitar
cable between pickup and the JFET input stage. The resonant Q might be
2.

** Not true of those I have seen.
See actual measurements of popular PU types.
https://courses.physics.illinois.edu/phys406/sp2017/Lab_Handouts/Electric_Guitar_Pickup_Measurements.pdf

Self resonance is typically 6kHz and impedance up to 1Mohm.
The control pots in guitars are often 500kohm or 1Mohm.
Co-axial cables like RG58/59 can make good, low C guitar leads - 22pF per foot.

It\'s useful to have a 100 K film resistor in series with the JFET
gate,

** Adds noise and no benefit.

to prevent output peak inversion on very strong input
transients,

** Never an issue.

Such transients are relatively common when the guitar is strummed
hard. The peak is some volts, as I recall.

** Even a valve amp input would clip with that.



....... Phil

 

[Joe Gwinn]

On Sat, 1 Jan 2022 13:18:44 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

Joe Gwinn wrote:
\"Kevin Aylward\"
----------------------------
The classic application that jfets win is the guitar pickup front end. Base
current noise is a problem when dropped across a 2 H inductor at 5kHz. even
the dc resistance is a tad on the high side, maybe up to 10k. One also
really requires an input resistance > 1M Ohm. 100k isn\'t enough.
-----------------------------------------------------------
Yes. I was doing such things about 15 years ago. The 2 H and 10 Kohms
(DC) values are typical. The coil has something like 10,000 turns of
AWG #42 enameled wire. An electric guitar pickup is a low-Q inductor
with a self resonant frequency around 3 KHz when loaded by the guitar
cable between pickup and the JFET input stage. The resonant Q might be
2.

** Not true of those I have seen.
See actual measurements of popular PU types.
https://courses.physics.illinois.edu/phys406/sp2017/Lab_Handouts/Electric_Guitar_Pickup_Measurements.pdf

Self resonance is typically 6kHz and impedance up to 1Mohm.
The control pots in guitars are often 500kohm or 1Mohm.
Co-axial cables like RG58/59 can make good, low C guitar leads - 22pF per foot.

All true, but the artists seem to like the resonance lower than 6 KHz
(the no-cable value), and add cable to achieve. These folk do have
golden ears.

It\'s useful to have a 100 K film resistor in series with the JFET
gate,

** Adds noise and no benefit.

Adds some hiss for sure, benefit on balance is matter of opinion.

to prevent output peak inversion on very strong input
transients,

** Never an issue.

I thought it blurred the attack transients, but never made the
behind-curtain tests necessary to settle the issue.

Such transients are relatively common when the guitar is strummed
hard. The peak is some volts, as I recall.

** Even a valve amp input would clip with that.

Yes. Which is why I clipped it, once the inversion was prevented.

Joe Gwinn

 

[Phil Allison]

Joe Gwinn is a Dickhead wrote:
\"Kevin Aylward\"
---------------------------

** Not true of those I have seen.
See actual measurements of popular PU types.
https://courses.physics.illinois.edu/phys406/sp2017/Lab_Handouts/Electric_Guitar_Pickup_Measurements.pdf

Self resonance is typically 6kHz and impedance up to 1Mohm.
The control pots in guitars are often 500kohm or 1Mohm.
Co-axial cables like RG58/59 can make good, low C guitar leads - 22pF per foot.

All true, but the artists seem to like the resonance lower than 6 KHz

** What YOU think \" artists ? \" think is neither relevant or was claimed.

> (the no-cable value), and add cable to achieve.

** Made up horse poo.

It\'s useful to have a 100 K film resistor in series with the JFET
gate,

** Adds noise and no benefit.

Adds some hiss for sure, benefit on balance is matter of opinion.

** What YOU think is not relevant to simple facts.

to prevent output peak inversion on very strong input
transients,

** Never an issue.

I thought it blurred the attack transients,

** What YOU think is not relevant to simple facts .

Such transients are relatively common when the guitar is strummed
hard. The peak is some volts, as I recall.

** Even a valve amp input would clip with that.

Yes. Which is why I clipped it,

** Absurd drivel.

Been making and testing/repairing commercial guitar amps for all my 50 year career and must have dealt with 500 different guitar players.
( The ones I made all had JFET inputs )

FYI pal:

There is NO consensus among such \"artists\".

...... Phil

 

[Phil Hobbs]

Cursitor Doom wrote:

On Fri, 31 Dec 2021 18:23:30 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be better
to cascade two stages of 20? I\'d really prefer to use just one stage if
it can be done with stability. The input signal will be up to 20mV p-p
and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor
Linear Applications handbook, look at AN-222.
While its main topic is using the LM394, the
FIGURE 4 is fairly relevant to your project.
For the low-noise NPN, the AoE has table
with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people
to find.
1994_National_Linear_Applications_Handbook.pdf
page 435 (p. 460th in pdf)
https://archive.org/details/bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/1up

my point is, it\'s a \"2\" transistor low-noise
pre-amplifier. The LM394 could just as
well be any other low-noise NPN (or
multiple matched units in parallel).

in lieu of LM394 , many choices are given
in Horowitz&Hill Art of Electronics, in table
of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage. Guess
how many pairs I found? None! A few dozen matched pairs, but *all*
totally unsuitable for one reason or another. I was totally certain
I\'d have several to choose from at the end of my hunt but it was not
to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/


Why in the world do you need matched BJTs for this? That LM394 app note
was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\' device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will do
much better, and cost pennies.

The PNP wraparound trick helps reduce the Miller capacitance, for sure.
It\'s a bit like a cascode, but generally slower since the collector
swing is suppressed by feedback rather than the diode action. (I\'m a
big fan of local feedback in general.)

It\'s also much more likely to oscillate if you do it wrong.

I really appreciate that, Phil! You saying \"if\" rather than *when*
LOL!

Well, you can always reduce the collector current and stabilize almost
anything.
<snip>

> More and more I\'m tempted to go down the IC route...

To get a gain of 400 at 10 kHz, you\'ll need both sections of that LM358A.

To do it with discretes, you need to do a bit of algebra to understand
the issues. It\'s pretty simple though--there\'s no need to collect all
the effects into one giant opaque expression. It\'s better to follow all
the separate terms--the way the transconductance sets the maximum gain,
the Miller (C-B) rolloff due to source impedance and C-B capacitance,
and the Early effect that leads to an effective shunt resistance at the
collector.

You can ignore their interactions (e.g. the way the Early effect reduces
the gain, which reduces the Miller effect) because when any one effect
gets big enough for that to be an issue, you\'re already hosed.

Doing the math that way is about the fastest way to generate intuition
about how the circuit actually works.

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

 

[Cursitor Doom]

On Sun, 2 Jan 2022 09:22:40 -0500, Phil Hobbs wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 18:23:30 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom
wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be
better to cascade two stages of 20? I\'d really prefer to use just
one stage if it can be done with stability. The input signal will
be up to 20mV p-p and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor Linear
Applications handbook, look at AN-222.
While its main topic is using the LM394, the FIGURE 4 is fairly
relevant to your project.
For the low-noise NPN, the AoE has table with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people to find.
1994_National_Linear_Applications_Handbook.pdf page 435 (p. 460th in
pdf)
https://archive.org/details/

bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/
1up

my point is, it\'s a \"2\" transistor low-noise pre-amplifier. The
LM394 could just as well be any other low-noise NPN (or multiple
matched units in parallel).

in lieu of LM394 , many choices are given in Horowitz&Hill Art of
Electronics, in table of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage.
Guess how many pairs I found? None! A few dozen matched pairs, but
*all* totally unsuitable for one reason or another. I was totally
certain I\'d have several to choose from at the end of my hunt but it
was not to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/


Why in the world do you need matched BJTs for this? That LM394 app
note was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\'
device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will
do much better, and cost pennies.

The PNP wraparound trick helps reduce the Miller capacitance, for
sure. It\'s a bit like a cascode, but generally slower since the
collector swing is suppressed by feedback rather than the diode
action. (I\'m a big fan of local feedback in general.)

It\'s also much more likely to oscillate if you do it wrong.

I really appreciate that, Phil! You saying \"if\" rather than *when*
LOL!

Well, you can always reduce the collector current and stabilize almost
anything.
snip

More and more I\'m tempted to go down the IC route...

To get a gain of 400 at 10 kHz, you\'ll need both sections of that
LM358A.

To do it with discretes, you need to do a bit of algebra to understand
the issues. It\'s pretty simple though--there\'s no need to collect all
the effects into one giant opaque expression. It\'s better to follow all
the separate terms--the way the transconductance sets the maximum gain,
the Miller (C-B) rolloff due to source impedance and C-B capacitance,
and the Early effect that leads to an effective shunt resistance at the
collector.

You can ignore their interactions (e.g. the way the Early effect reduces
the gain, which reduces the Miller effect) because when any one effect
gets big enough for that to be an issue, you\'re already hosed.

Miller effect; Early effect. I\'ve got some reading up to do, clearly!
Seriously, I already have a future project in mind for an audio amp using
good old tubes just for the hell of it and will hold back til then from
studying the finer points. For *this* particular problem (the one under
discussion here; just getting this vintage radio working again) however,
I\'m coming around to your suggestion of the quickest solution and just
going for a suitable IC. I believe I\'ve found one in my copious treasury
of old bits. The only reservation I have is if it\'s suitable to use in
battery powered equipment. I\'ll post about this under a fresh thread title
shortly.

Doing the math that way is about the fastest way to generate intuition
about how the circuit actually works.

That mathematics don\'t lie, but hand calcs can be very, very time
consuming in certain circs. That\'s the outstanding benefit of the Spice
programs IMHO.

 

[Phil Hobbs]

Cursitor Doom wrote:

On Sun, 2 Jan 2022 09:22:40 -0500, Phil Hobbs wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 18:23:30 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Cursitor Doom wrote:
On Fri, 31 Dec 2021 10:01:45 -0800 (PST), Rich S
richsulinengineer@gmail.com> wrote:

On Friday, December 31, 2021 at 1:07:02 PM UTC, Cursitor Doom wrote:
On Thu, 30 Dec 2021 18:19:27 -0800 (PST), Rich S
richsuli...@gmail.com> wrote:

On Thursday, December 30, 2021 at 8:17:58 PM UTC, Cursitor Doom
wrote:
Gentlemen,

When talking about common-emitter configuration BJT stages, is it
feasible to get a voltage gain of 400 in one stage or would it be
better to cascade two stages of 20? I\'d really prefer to use just
one stage if it can be done with stability. The input signal will
be up to 20mV p-p and supply voltage 12V.
cheers,

CD.

Hi CD,
If it were me, I\'d grab a National Semiconducor Linear
Applications handbook, look at AN-222.
While its main topic is using the LM394, the FIGURE 4 is fairly
relevant to your project.
For the low-noise NPN, the AoE has table with many to choose from.
cheers, RS
I will; many thanks.



More details (for those who need it)
AN222 may be tricky for some people to find.
1994_National_Linear_Applications_Handbook.pdf page 435 (p. 460th in
pdf)
https://archive.org/details/
bitsavers_nationaldaLinearApplicationsHandbook_106847051/page/n459/mode/
1up

my point is, it\'s a \"2\" transistor low-noise pre-amplifier. The
LM394 could just as well be any other low-noise NPN (or multiple
matched units in parallel).

in lieu of LM394 , many choices are given in Horowitz&Hill Art of
Electronics, in table of \"low noise BJT transistors\"

cheers, RS

I have several thousands of all sorts of transistors \'in stock\' here
and have been rummaging through them all today trying to find a
matched pair of complimentary BJTs for the eventual power stage.
Guess how many pairs I found? None! A few dozen matched pairs, but
*all* totally unsuitable for one reason or another. I was totally
certain I\'d have several to choose from at the end of my hunt but it
was not to be.
What I *did* come across during the rummage, however, was a decent
selection of NOS TDA series chips. I\'m getting evil thoughts about
cheating now. Sigh...
:-/


Why in the world do you need matched BJTs for this? That LM394 app
note was just using it as a single low-noise BJT amplifier, which is
something only an apps guy would even contemplate. Besides being
expensive, there\'s no advantage whatsoever over a single low-Rbb\'
device.

A nice 2SD2704k or MPSA18, cascoded with a 2N3904 or something, will
do much better, and cost pennies.

The PNP wraparound trick helps reduce the Miller capacitance, for
sure. It\'s a bit like a cascode, but generally slower since the
collector swing is suppressed by feedback rather than the diode
action. (I\'m a big fan of local feedback in general.)

It\'s also much more likely to oscillate if you do it wrong.

I really appreciate that, Phil! You saying \"if\" rather than *when*
LOL!

Well, you can always reduce the collector current and stabilize almost
anything.
snip

More and more I\'m tempted to go down the IC route...

To get a gain of 400 at 10 kHz, you\'ll need both sections of that
LM358A.

To do it with discretes, you need to do a bit of algebra to understand
the issues. It\'s pretty simple though--there\'s no need to collect all
the effects into one giant opaque expression. It\'s better to follow all
the separate terms--the way the transconductance sets the maximum gain,
the Miller (C-B) rolloff due to source impedance and C-B capacitance,
and the Early effect that leads to an effective shunt resistance at the
collector.

You can ignore their interactions (e.g. the way the Early effect reduces
the gain, which reduces the Miller effect) because when any one effect
gets big enough for that to be an issue, you\'re already hosed.

Miller effect; Early effect. I\'ve got some reading up to do, clearly!
Seriously, I already have a future project in mind for an audio amp using
good old tubes just for the hell of it and will hold back til then from
studying the finer points. For *this* particular problem (the one under
discussion here; just getting this vintage radio working again) however,
I\'m coming around to your suggestion of the quickest solution and just
going for a suitable IC. I believe I\'ve found one in my copious treasury
of old bits. The only reservation I have is if it\'s suitable to use in
battery powered equipment. I\'ll post about this under a fresh thread title
shortly.

Doing the math that way is about the fastest way to generate intuition
about how the circuit actually works.

That mathematics don\'t lie, but hand calcs can be very, very time
consuming in certain circs. That\'s the outstanding benefit of the Spice
programs IMHO.

If you do them wrong, e.g. building that huge opaque expression that has
all the effects at once, that\'s true. But there\'s no need to do that in
most cases.

What I\'m talking about is like this:

1. Miller effect: The capacitive current at the base due to Miller
effect is

i_Miller = -C_cb * d V_cb / dt = (|A_V| + 1) C_cb dV_be / dt,

where as usual A_V is the voltage gain of the stage (-400 in this case).

Thus the effective input capacitance of an amp with a gain of -400 is

C_in ~= 401 C_cb.

So you have a rolloff with a 3-dB corner at

f_Miller = 1/(2 pi C_cb R_s) * 1/401.

With a 400-ohm source and a 3-pF C_cb, that comes out to 330 kHz. So
Miller doesn\'t do a lot at 10 kHz, and we can ignore him henceforward.

2. Early effect is similar, but more or less frequency independent: it
looks like a differential resistance in parallel with the collector, and
is characterized by the Early voltage V_A, which is the X-axis intercept
of the I_C vs. V_CE curve. (It\'s not a real DC resistance, so it
doesn\'t matter where the other end goes as long as it\'s signal ground.)

R_Early = (V_CE + V_A) / I_C.

Here all all quantities are assumed positive, even though the X
intercept is usually far out on the negative V axis. (That\'s why V-CE
gets added in--the slope is the rise over the run.) This shunt
resistance appears in parallel with the external collector resistor, and
reduces the gain exactly as you\'d expect if you had a real resistor there.

We talked about how to handle the transconductance earlier.

So from a math POV it\'s dead simple. You just need a clear idea of what
each effect actually does to the circuit, so you know what you can
ignore and what you have to work around.

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

 

[Phil Hobbs]

Kevin Aylward wrote:

\"Phil Hobbs\"  wrote in message
news:cc9440bd-b699-d7a7-6b96-d985572889b0@electrooptical.net...

Cursitor Doom wrote:
On Thu, 30 Dec 2021 19:11:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 30 Dec 2021 21:34:27 -0000, \"Kevin Aylward\"
kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

Why anyone would use a discrete transistor stage today is indeed a
mystery...


-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Some of the RF people are ashamed to admit they are selling
transistors. They label the pins RF IN and RF OUT and GROUND.

Sometimes a transistor is just what you need.

Yup, particularly in front ends.

FETs are better in that role IMHO.


For what in particular?

There are a very few JFETs that are competitive with or even superior
to BJTs in wideband, low-level front ends.

Probably true for most applications, especially for higher frequencies
where drive impedances are low. The gm is going to be significantly
larger at the same current.

The classic application that jfets win is the guitar pickup front end.
Base current noise is a problem when dropped across a 2 H inductor at
5kHz. even the dc resistance is a tad on the high side, maybe up to 10k.
One also really requires an input resistance > 1M Ohm. 100k isn\'t enough.

(People have often used even noisy JFETs such as J309s in receiver
front ends, but below VHF, the atmosphere is so noisy that you don\'t
care very much, and the reduced IMD is a help.)

The 2SK162 for audio is actually very good. Gets down to a noise
equivalent of 26 ohms, matching bipolars

I do a fair few mostly-discrete front ends for various things.  ICs
are great at what they do well, and can often be repurposed for things
their designers never intended, but even in 2022 there are a lot, a
lot of things you can do with discrete front ends that no IC can touch.

Sure, with off the shelf ics there are  specialised gaps that they cant
fill.

If there is a large enough market, there is, nothing that can\'t be done
by a full ic implementation. It might require more than one ic though.

Your faith is touching, but misplaced. There are a lot of discrete GaN
FETs, IGBTs, and so on that aren\'t going away any time very soon. Many
front end things are like that too.

Most off the shelf ics such as op-amps are going to be \"general purpose\"
not ASIC (Application Specific)

If one takes an iPhone, its 100s of \"custom\" ICs.

The one we\'ve been discussing has an InGaAs pHEMT , two tiny GaN FETs,
and three 60-GHz Si BJTs.  Good luck getting all that on a chip.  (And
for Kevin\'s benefit: no, you couldn\'t integrate the equivalent
function in plain silicon.)

Its certainly difficult to get all types of devices in one process.
However, even Analog Devices might supply what looks like one ic
package, but actually has several die from different processes.

Sure, but that\'s a hybrid, not an IC. My front end would probably fit
in a 40-pin CERDIP too.

One can integrate any discrete device. An integrated circuit is just
more than one different discrete devices on one die.

If you can figure out how to get power GaN FETs really monolithically
integrated with silicon CMOS, you could make a lot of money. Ain\'t
happening soon.

Just the lattice matching, strain, and process compatibility issues are
horrendous.

(Yes, people have published papers on it, and have begun looking at
doing wafer bonding. The yield problems with that approach would make a
brave man blench.)

ASIC design is fundamentally different to discrete. Transistors are
cheap, as is calibration. I would have to examine what your product spec
is to evaluate how one would do it in an ic.

Sure, I\'ve collaborated on chip designs, so I know the drill. Getting 6
GHz f_max, very low noise (300 pV /sqrt(Hz) in the flatband, with
sub-nanoamp gate leakage on the one hand, with ~5-ns switching over a
500-MHz isolation barrier, all with low enough capacitance to sit on a a
fast bootstrapped node, is not something a chip design house would even
bother bidding on, regardless of the volume.

I haven\'t checked all the combinations available in current processes,
but there are certainly \"standard\" (mos & bipolar) component processes
that have GaN FETs, and \"standard\" processes with SiGe 200GHz devices,
and cmos processes with pHEMT. There are a LOT of processes out there.

SiGe, I believe. The others are all wafer-bonding or die-on-wafer AFAICT.

> If the market size is there, its always possible to integrate anything.

And I have a bridge to sell you.

For small markets, there may be be a few applications where discrete is
the way to go.

There are fundamental advantages to ic implementation. Routing
capacitances are at the ff level for starters.

Absolutely. And for most things those sorts of advantages, together
with monolithic matching and so forth, are enough that a clever designer
with a sufficiently-big budget can do a good job.

That time stretcher thing I was talking about works a lot better in an
IC--the proto used eight 2-GHz CFAs, each with three pHEMT T/Hs hung on it.

Each T/H hold cap was connected directly to an input of a
simultaneous-sampling ADC, and the channels were sampled sequentially
at much lower speed. The hold capacitors thus had to be several
picofarads, which confused the CFAs when the switches opened, so we had
to interleave the sampling to give the amps time to recover a bit.
Sucked power like anything, but did demonstrate that you can get
multiple well-behaved sub-nanosecond time slices in a single shot
without needing a big-iron digitizer/FPGA solution.

We\'re in the process of integrating that and scaling it up to 4096 APDs
x 24 samples per shot.

High performance front ends, not so much. A couple of CPH3910s, or a
SAV-551+ cascoded with a BFP640, can do things no available IC can
touch, even with no high voltage requirement.

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

 

[Phil Hobbs]

Phil Hobbs wrote:

Kevin Aylward wrote:
\"Phil Hobbs\"  wrote in message
news:cc9440bd-b699-d7a7-6b96-d985572889b0@electrooptical.net...

Cursitor Doom wrote:
On Thu, 30 Dec 2021 19:11:41 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Thu, 30 Dec 2021 21:34:27 -0000, \"Kevin Aylward\"
kevinRemoveandReplaceATkevinaylward.co.uk> wrote:

Why anyone would use a discrete transistor stage today is indeed a
mystery...


-- Kevin Aylward

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Some of the RF people are ashamed to admit they are selling
transistors. They label the pins RF IN and RF OUT and GROUND.

Sometimes a transistor is just what you need.

Yup, particularly in front ends.

FETs are better in that role IMHO.


For what in particular?

There are a very few JFETs that are competitive with or even superior
to BJTs in wideband, low-level front ends.

Probably true for most applications, especially for higher frequencies
where drive impedances are low. The gm is going to be significantly
larger at the same current.

The classic application that jfets win is the guitar pickup front end.
Base current noise is a problem when dropped across a 2 H inductor at
5kHz. even the dc resistance is a tad on the high side, maybe up to
10k. One also really requires an input resistance > 1M Ohm. 100k isn\'t
enough.

(People have often used even noisy JFETs such as J309s in receiver
front ends, but below VHF, the atmosphere is so noisy that you don\'t
care very much, and the reduced IMD is a help.)

The 2SK162 for audio is actually very good. Gets down to a noise
equivalent of 26 ohms, matching bipolars

I do a fair few mostly-discrete front ends for various things.  ICs
are great at what they do well, and can often be repurposed for
things their designers never intended, but even in 2022 there are a
lot, a lot of things you can do with discrete front ends that no IC
can touch.

Sure, with off the shelf ics there are  specialised gaps that they
cant fill.

If there is a large enough market, there is, nothing that can\'t be
done by a full ic implementation. It might require more than one ic
though.

Your faith is touching, but misplaced.  There are a lot of discrete GaN
FETs, IGBTs, and so on that aren\'t going away any time very soon.  Many
front end things are like that too.


Most off the shelf ics such as op-amps are going to be \"general
purpose\" not ASIC (Application Specific)

If one takes an iPhone, its 100s of \"custom\" ICs.

The one we\'ve been discussing has an InGaAs pHEMT , two tiny GaN
FETs, and three 60-GHz Si BJTs.  Good luck getting all that on a
chip.  (And for Kevin\'s benefit: no, you couldn\'t integrate the
equivalent function in plain silicon.)

Its certainly difficult to get all types of devices in one process.
However, even Analog Devices might supply what looks like one ic
package, but actually has several die from different processes.

Sure, but that\'s a hybrid, not an IC.  My front end would probably fit
in a 40-pin CERDIP too.

One can integrate any discrete device. An integrated circuit is just
more than one different discrete devices on one die.

If you can figure out how to get power GaN FETs really monolithically
integrated with silicon CMOS, you could make a lot of money.  Ain\'t
happening soon.

Just the lattice matching, strain, and process compatibility issues are
horrendous.

(Yes, people have published papers on it, and have begun looking at
doing wafer bonding.  The yield problems with that approach would make a
brave man blench.)


ASIC design is fundamentally different to discrete. Transistors are
cheap, as is calibration. I would have to examine what your product
spec is to evaluate how one would do it in an ic.

Sure, I\'ve collaborated on chip designs, so I know the drill.  Getting 6
GHz f_max, very low noise (300 pV /sqrt(Hz) in the flatband, with
sub-nanoamp gate leakage on the one hand, with ~5-ns switching over a
500-

volt

isolation barrier, all with low enough capacitance to sit on a a
fast bootstrapped node, is not something a chip design house would even
bother bidding on, regardless of the volume.

I haven\'t checked all the combinations available in current processes,
but there are certainly \"standard\" (mos & bipolar) component processes
that have GaN FETs, and \"standard\" processes with SiGe 200GHz devices,
and cmos processes with pHEMT. There are a LOT of processes out there.

SiGe, I believe. The others are all wafer-bonding or die-on-wafer AFAICT.

If the market size is there, its always possible to integrate anything.

And I have a bridge to sell you.

For small markets, there may be be a few applications where discrete
is the way to go.

There are fundamental advantages to ic implementation. Routing
capacitances are at the ff level for starters.

Absolutely.  And for most things those sorts of advantages, together
with monolithic matching and so forth, are enough that a clever designer
with a sufficiently-big budget can do a good job.

That time stretcher thing I was talking about works a lot better in an
IC--the proto used eight 2-GHz CFAs, each with three pHEMT T/Hs hung on it.

Each  T/H hold cap was connected directly to an input of a
simultaneous-sampling ADC, and  the channels were sampled sequentially
at much lower speed.  The hold capacitors thus had to be several
picofarads, which confused the CFAs when the switches opened, so we had
to interleave the sampling to give the amps time to recover a bit.
Sucked power like anything, but did demonstrate that you can get
multiple well-behaved sub-nanosecond time slices in a single shot
without needing a big-iron digitizer/FPGA solution.

We\'re in the process of integrating that and scaling it  up to 4096 APDs
x 24 samples per shot.

High performance front ends, not so much.  A couple of CPH3910s, or a
SAV-551+ cascoded with a BFP640, can do things no available IC can
touch, even with no high voltage requirement.

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

 

[LM]

On Sun, 2 Jan 2022 15:04:19 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

High performance front ends, not so much. A couple of CPH3910s, or a
SAV-551+ cascoded with a BFP640, can do things no available IC can
touch, even with no high voltage requirement.

OT: There are no CPH3910s in stock at Digikey. First microcontrollers
and now this.