Re: Drat. NTE is gone, and they took the last 5-GHz PNP with them.

On 2024-09-05 10:14, john larkin wrote:

On Thu, 5 Sep 2024 07:30:50 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

Jan Panteltje <alien@comet.invalid> wrote:

On a sunny day (Wed, 4 Sep 2024 17:54:19 -0400) it happened Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote in
<6b1217f0-f55b-95b4-6516-6914d18d0e91@electrooptical.net>:
>

The NTE2403, similar to the BFT92, but a bit better overall.  Dunno who
actually made them. (I saw the news on s.e.repair today.)
>
Rochester claims to have 1,500,000 of the 2SA1462 (1.8 GHz) for 20
cents, but that's all she wrote.
>
I have a couple of reels of BFT92s and one of BFG31s, so I'm good for
protos and small production, but I can't use PNP wraparound bootstraps
for customer designs anymore. :(
>
Barstids.
>
Cheers
>
Phil Hobbs

>
Lots if RF snall signal low noise stoff in LNBs:
  https://www.infineon.com/dgdl/Infineon-Design_guide_for_RF-transistors_and_diode_in_Low-Noise-Block-ApplicationNotes-v01_00-EN.pdf?fileId=8ac78c8c7e7124d1017f01f071aa5b8f
   Does that help?
>
>
Complete LNBs inclusive transistors and peeseebees are 5 dollies on ebay.
>
>

>
Thanks.  It’s not a 50-ohm system, so using those would be hard. I have
thousands  for personal use, but can’t put them in licensed designs, which
is what I’m moaning about.
>
Cheers
>
Phil Hobbs

 Can you use mmics? There are some really cool, fast, cheap, low-noise
things around. Just because the RF boys test everything at 50 ohms
doesn't mean we have to use them at 50 ohms.
 

For the wraparound topology, which is the second-best follower I know of,
  VDD 0------*---------*
             |         |
             R         |
             R         |
             R         /
             |       |V
             *-------|  BFT92
             |       |\
          |--*         \
  In  0-->|  CPH3910   |
          |--*         |
             |         |
             |         |
             *---------*----0   Follower output
             |
             V (tail current source)
the BJT needs to be a PNP.
It's a nice circuit, because the PNP reduces the output impedance a lot without adding much noise at all--way better than an NPN follower after the FET.
Because of the local feedback, the transistors need to be fairly different in speed to maintain stability.  The FET is about a 750-MHz device, so a 5-GHz PNP is great.  The alternative would be a 100-MHz PNP, which would be too depressing to contemplate. :(
The very best follower topology I know about is a fancy bootstrapped version of the White cathode follower, where the feedback is applied via the tail source.  That's much harder to stabilize, because there are three transistors in the local feedback loop, but on the other hand its gain is 0.9997 at baseband and above 0.995 at 10 MHz.  (You can't readily measure those sorts of numbers directly, so I inferred them from its performance as a bootstrap.)
The reason I care about getting such accurate bootstraps is a bit subtle--probably I'd have enough bandwidth improvement with a gain of 0.9, but that extra 10% shows up as a gnarly settling transient at late times, which screws up measurements.  0.9997 is dramatically better.
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