Luciano wrote:
The CLC409 datasheet show all the test response up to +12dBm (around 1Vpp
on 75/50Ohm load)
see: pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS012748.PDF
I'm reporting what I have observed with the CLC409 (and LMH6702) when
operated on the "absolute max" supply rails of +/- 6v. Of course, I
would never design a commercial product using abs max specs without
having a serious conversation and understanding with the manufacturer
(if then).
Clipping commences at just over +/- 2v (a touch over +16dBm). This is
with a 50 ohm build-out or "back termination" resistor -- you can get an
additional 6dBm if you do without the build-out resistor and terminate
only the load end of the cable in 50 ohms, which actually works fine as
long as the output loads are matched at 50 ohms. I terminate both ends
"just in case" they aren't. Harmonic distortion does not rise until
there is visible clipping.
I agree that harmonic distortion is an important factor to keep in mind
however -45dBc is a very interesting value considering the market alternatives.
In my document I have enclosed on page 10 a little research I did online on
similar products and as you can see the -45 are positioned at a decidedly
higher level than other commercial solutions
see [table]:
IMO, pretty much all commercial distribution/isolation amplifiers fail
miserably to hold distortion down to tolerable levels -- one reason why
I have always designed my own. Interestingly, some older, vacuum-tube
models did better.
An extremely important factor not to be overlooked is the maximum output
power / level of the amplifier. Measurement systems such as the HP3048A for
phase noise measurement use mixers that require minimum signal levels of +
15dBm at higher PO1 and the CLC409 will never meet these requirements.
As noted above, it will if it is operated on abs max supplies, even with
a 50 ohm build-out resistor. Without the build-out resistor, it will
supply +22dBm (+20dBm on +/- 5v supplies).
In your modification document: Residual phase noise of <-165dBc at 10 MHz
I suppose you mean @100kHz, The buffer I propose is -170dBc @100KHz
I normally cite 10kHz measurements, but I don't recall if I cited 100kHz
or 10kHz measurements (my bad for the incomplete spec). One or the other.
In the end I don't think this should be a competition among Distribution
Amplifiers.
Nor I. I built a few dozen of the modified Extron DAs, which I've
passed on to other time nuts over the years. I still have one around,
but it is not in daily use. I currently use two different designs, both
scratch-built, one IC-based and one discrete. As I've said before, I
distinguish between distribution amplifiers (lots of outputs) and
isolation amplifiers (where only 2 or maybe 3 outputs are needed, but
distortion, residual PN, and transit delay must be truly
state-of-the-art for sensitive measurements).
On re-reading my original post, I see the tone could be taken as a bit
confrontational. That was certainly not my intent -- I just wanted to
defend IC designs against some "received wisdom" (*NOT* from you) that
they are inferior. Thank you for giving me the benefit of the doubt and
responding as a gentleman.
For a "ready" solution at low cost like DA the Extron I think is a great
solution.
Me, too, which is why my first efforts as a time-nuts newbie were made
in that direction.
Best regards,
Charles
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