SiGe:C transistors and Early effect...

[Phil Hobbs]

On 12/8/20 8:06 PM, Okkim Atnarivik wrote:

On 10/22/20 8:07 PM, Phil Hobbs wrote:
That\'s a good 20 times better than your average 10-GHz transistor, and
this is a 45-GHz one.  It\'s good enough (and the thermal is slow enough)
that I can mimic monolithic behaviour by equalizing the dissipation of
the two halves of the diff pair by dorking the V_CE of one side.

There is an old Tek trick, apparently re-invented by many others, to
put a bypassed resistor in the collectors of a discrete diff pair, so
the power dissipation is mostly constant with signal. That eliminated
some thermal hooks in vertical amplifiers.

Yup.  Makes a huge difference.  (The Tek \"Vertical Amplifiers\" book is
still a good read.)

...
If the transistors are at different temperatures, the splitting is
degraded because the same delta V_BE produces different ratios at
different tail currents.  Thus a symmetrical layout combined with
dorking V_CE as a function of I_C has a lot of charm.

It\'s happening at millisecond timescales, too, which makes it a good
match for some simple MCU magic.

The thermal servo trick is originally due to Tek? Interesting. I learned
it from Nikolay Ukhanski some years ago. He and his colleaques published
it, too, in a physics journal.

Regards,
Mikko

The Tek idea is to bias the transistors at the maximum-dissipation
point, so that small excursions don\'t cause thermal transients of any
appreciable size. That\'s an open-loop thing.

The thermal servoing idea may well not be original with me, but at least
I invented it independently in about 2010 or 2011. It\'s not much use
with normal RF transistors, because their Early voltages are so low, but
SiGe devices have VA ~ 250V at signal rates. (The datasheet curves even
tilt the other way, because the thermal effect on V_BE is bigger than
the Early effect.)

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

 

[JM]

On 09/12/2020 04:26, Phil Hobbs wrote:

On 12/8/20 8:19 PM, Okkim Atnarivik wrote:
On 12/8/20 8:06 PM, Okkim Atnarivik wrote:
On 10/22/20 8:07 PM, Phil Hobbs wrote:
That\'s a good 20 times better than your average 10-GHz transistor,
and
this is a 45-GHz one. It\'s good enough (and the thermal is slow
enough)
that I can mimic monolithic behaviour by equalizing the
dissipation of
the two halves of the diff pair by dorking the V_CE of one side.

There is an old Tek trick, apparently re-invented by many others, to
put a bypassed resistor in the collectors of a discrete diff pair, so
the power dissipation is mostly constant with signal. That eliminated
some thermal hooks in vertical amplifiers.

Yup. Makes a huge difference. (The Tek \"Vertical Amplifiers\" book is
still a good read.)

...
If the transistors are at different temperatures, the splitting is
degraded because the same delta V_BE produces different ratios at
different tail currents. Thus a symmetrical layout combined with
dorking V_CE as a function of I_C has a lot of charm.

It\'s happening at millisecond timescales, too, which makes it a good
match for some simple MCU magic.

The thermal servo trick is originally due to Tek? Interesting. I learned
it from Nikolay Ukhanski some years ago. He and his colleaques published
it, too, in a physics journal.

The paper I\'m thinking is older and more obscure, but judging
by the abstract, doi:10.1063.12335630 looks looks like same stuff.

The reference doesn\'t seem to work. Is there something after the slash?

Thanks

Phil Hobbs

High slew rate, ultrastable direct-coupled readout for dc superconducting
quantum interference devices

APPLIED PHYSICS LETTERS 89, 063502
2006

[DOI: 10.1063/1.2335630]

 

[Phil Hobbs]

On 12/12/20 11:19 AM, JM wrote:

On 09/12/2020 04:26, Phil Hobbs wrote:
On 12/8/20 8:19 PM, Okkim Atnarivik wrote:
On 12/8/20 8:06 PM, Okkim Atnarivik wrote:
On 10/22/20 8:07 PM, Phil Hobbs wrote:
That\'s a good 20 times better than your average 10-GHz transistor,
and
this is a 45-GHz one.  It\'s good enough (and the thermal is slow
enough)
that I can mimic monolithic behaviour by equalizing the
dissipation of
the two halves of the diff pair by dorking the V_CE of one side.

There is an old Tek trick, apparently re-invented by many others, to
put a bypassed resistor in the collectors of a discrete diff pair, so
the power dissipation is mostly constant with signal. That eliminated
some thermal hooks in vertical amplifiers.

Yup.  Makes a huge difference.  (The Tek \"Vertical Amplifiers\" book is
still a good read.)

...
If the transistors are at different temperatures, the splitting is
degraded because the same delta V_BE produces different ratios at
different tail currents.  Thus a symmetrical layout combined with
dorking V_CE as a function of I_C has a lot of charm.

It\'s happening at millisecond timescales, too, which makes it a good
match for some simple MCU magic.

The thermal servo trick is originally due to Tek? Interesting. I
learned
it from Nikolay Ukhanski some years ago. He and his colleaques
published
it, too, in a physics journal.

   The paper I\'m thinking is older and more obscure, but judging
by the abstract, doi:10.1063.12335630 looks looks like same stuff.

The reference doesn\'t seem to work.  Is there something after the slash?

Thanks

Phil Hobbs


High slew rate, ultrastable direct-coupled readout for dc superconducting
quantum interference devices

APPLIED PHYSICS LETTERS 89, 063502
2006

[DOI: 10.1063/1.2335630]

Thanks. It seems to be an MPU (minimum publishable unit) referencing
their other MPUs, none of which appear to tell what they\'re actually doing.

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