multiplier: was Re: 3280 and AD533 availability, EN frequency shifter

[Martin Czech]

:::>The best thing would be a 1495, same topology as 633 or my diy, but
:::>unavailable for some mysterious reason.
:::>
:::It is 'missing' because it hasn't been manufactured for a couple of years 
now.
:::And, I personally think the AD633 is just fine ;-)

I know that most people disagree in this point.  I had only one chip,
could be that it was not typical. Let me explain: I used "Horowitz
playing Moscow" piano music CD as program input and sine wave at the
modulator input.  I found the AD633 to be very noisy (hissing), compared
with my own homebrew.

I expect NO additional audible noise with a critical recording like that
when using a multiplier intended for audio. I mean it is piano music with
fff and ppp. If the sine wave is slow, I expect amplitude modulation,
and faster I expect sidebands. But NO noise.  This methode means that the
noise is -80dB down, but still audible.  It is better then a tape deck,
for shure.  And this is too much for me and the application.


If I put in Megadeth "Tornado of Souls" instead, I'll not notice any
noise, of course not. ;_>

Less current draw and internal zener reference (zeners are known to be
noisy) in the AD 633 data sheet are additional hints that I might be right.
My discrete design also uses a zener diode reference, but it is filtered with
a 100uF electrolytic.


btw. ESD can also heavily degrade noise figures, I forgot to mention.
It is a pain in the @ss if you are doing noise figure measurements
on MOST on the wafer. Is this device still ok? Is it degraded?
Why does this curve look so funny?


m.c.