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

On Thu, 5 Sep 2024 22:44:36 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

john larkin <jl@650pot.com> wrote:

On Thu, 5 Sep 2024 10:49:42 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

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

 
The CPH3910 is a jfet. Might an un-assisted PHEMT be better?
 
 

>
I’ve used them a fair amount in front ends, generally with a SiGe NPN
cascode-slash-drain bootstrap.  Their transconductance is a few times
higher than a CPH3910’s, but not as good as the local-feedback circuit’s.
>
pHEMTs have very low drain impedance—the late lamented ATF38143 had a
voltage gain of ~0.7 as a follower, even with a current sink in the tail. 
>
Their amazing noise floor (~0.3 nV in 1 Hz) makes them well worth patching
up, but they do take some patching.
>
Cheers
>
Phil Hobbs

What is the Vdd in your circuit above?

I learned about jfet impact ionization from AoE. Keep the drain
voltage low!