a pretty good definition of "wideband"
hawes at herald.ox.ac.uk
Tue Dec 22 16:43:02 CST 2009
I was wondering about the noise performance of a small-signal distributed amplifier. The stage gains add, but the noise in each stage is uncorrelated so will not add simply.
I have seen low-frequency amplifiers which achieve low noise by using several FET's in parallel - equivalent to reducing the
channel resistance. That would not work at h.f.because of the ever increasing capacitance, but I got to wondering if a distributed amplifier would achieve a similar noise reduction at r.f. and give lower I/P referred noise than a cascaded amplifier. It needn't be expensive, even done with CP666's it wouldn't break the bank (quite!), but perhaps the reduction is not enough to justify the complexity.
I need to think a bit more about that, or surf the 'net!
From: Mike O'Dell [mo at ccr.org]
Sent: 22 December 2009 17:04
To: Brian Hawes
Cc: Tacos AMRAD
Subject: Re: a pretty good definition of "wideband"
i believe Tek did build a hybrid solid state version
for the later high-end machines.
and i bet if you go looking for SSAs (solid-state amplifiers)
to replace TWTs aboard satellites, you'll find some hideously
expensive hybrids which look a lot like what you suggest.
Brian Hawes wrote:
> Looking closer at Fig 10 (it zooms quite a lot), I wonder if this is actually a hybrid?
> Did Tektronix ever make a Semiconductor version of their distributed amplifiers?
> Anyway, it's just seven cascode stages distributed along two delay lines: classic.
> Any thoughts on the noise properties of the d.a.? I guess that the noise contribution of each stage
> adds, but incoherently, unlike a cascaded amplifier where the noise of the first stage gets multiplied.
> Does a boxful of pHEMT's and two TX llines, on a PCB, give a super low-noise amplifier or is there
> no free lunch?
> Last one to submit a working prototype buys the Tacos!
> From: Mike O'Dell [mo at ccr.org]
> Sent: 21 December 2009 13:23
> To: Brian Hawes
> Cc: Tacos AMRAD
> Subject: Re: a pretty good definition of "wideband"
> i had the same flash-back!
> i remember the first time i saw a schematic for one of
> Tek's "distributed wideband amplifiers" and was completely
> blown away.
> "Everything old is new again, if you wait long enough."
> Brian Hawes wrote:
>> That is certainly a neat bit of chip design.
>> It reminds me of the distributed deflection amplifiers in the Tektronix 500 series 'scopes.
>> From: tacos-bounces+hawes=herald.ox.ac.uk at amrad.org [tacos-bounces+hawes=herald.ox.ac.uk at amrad.org] On Behalf Of Mike O'Dell [mo at ccr.org]
>> Sent: 20 December 2009 14:29
>> To: Tacos AMRAD
>> Subject: a pretty good definition of "wideband"
>> i bet it's expensive
>> Tacos mailing list
>> Tacos at amrad.org
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