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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: fast NPN in LT Spice
Date: Tue, 4 Jun 2024 01:46:01 +1000
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On 4/06/2024 12:18 am, john larkin wrote:
> On Mon, 3 Jun 2024 09:58:52 +0200, Jeroen Belleman
> <jeroen@nospam.please> wrote:
> 
>> On 6/3/24 00:36, john larkin wrote:
>>> There are many NPNs in the standard LT Spice library.
>>>
>>> Does anyone know of a fast, RF type, transistor? It's hard to tell
>>> from the jillion lines of fine-print parameters.
>>>
>>> I want to make a model of the MC10EP89 gate.
>>>
>>
>> I always used the -now obsolete- BFR92A for such things.
>> That's a 5GHz Ft NPN that I used often. It's not in the
>> library, I think. Below the model. Mind the line wraps.
>>
>> Jeroen Belleman
>>
>> .model BFR92A NPN IS=4.11877E-016 BF=1.02639E+002 NF=9.97275E-001
>> VAF=6.26719E+001 IKF=3.20054E+000 ISE=4.01062E-015 NE=1.57708E+000
>> BR=1.81086E+001 NR=9.96202E-001 VAR=3.36915E+000 IKR=1.28155E+000
>> ISC=2.79905E-016       NC=1.07543E+000 RB=1.00000E+001 IRB=1.00000E-006
>> RBM=1.00000E+001 RE=1.16450E+000 RC=2.32000E+000 EG=1.11000E+000
>> XTI=3.00000E+000 CJE=8.90512E-013 VJE=6.00000E-001 MJE=2.58570E-001
>> TF=1.54973E-011 XTF=3.91402E+001 VTF=2.15279E+000       ITF=2.13776E-001
>> CJC=5.46563E-013 VJC=3.80824E-001 MJC=2.02935E-001
> 
> 2SC3838K is in the library, and has Ft = 3.5G typically. It's good
> enough for what I want to do now.
> 
> This is actually a bit faster than the MC10EP89:

<snipped two transistor model>

It is worth noting that even 3.5GHz transistors tend to need 
base-stopper resistors in real life. Collector-base capacitive feedback 
can make them self-oscillate without it. Phil Hobbs has found two Murata 
ferrite bead/chips which are specified as presenting resistive 
impedances of 60R and 200R at 5GHz which seems to do the job too.

Jim Thompson designed that kind of integrated circuit, but he's been 
dead for a while now.

-- 
Bill Sloman, Sydney