<HTML><BODY><DIV style='font-family: "Verdana"; font-size: 10pt;'><DIV>
<DIV> Hi</DIV>
<DIV> The diodes in the 3080 are diode connected transistors,</DIV>
<DIV> Yes?</DIV>
<DIV> Jeri</DIV> <BR>-----Original Message-----<BR>From: Harry <SPAN class=correction id="">Bissell</SPAN> Jr <<SPAN class=correction id="">harrybissell</SPAN>@prodigy.net><BR>To: synth-diy@dropmix.xs4all.nl<BR>Sent: Fri, 3 <SPAN class=correction id="">Jun</SPAN> 2005 09:00:59 -0700 (PDT)<BR>Subject: Re: [<SPAN class=correction id="">sdiy</SPAN>] Humans are not Becoming Smaller<BR><BR>
<STYLE>
.AOLPlainTextBody {
margin: 0px;
font-family: Tahoma, Verdana, Arial, Sans-Serif;
font-size: 12px;
color: #000;
background-color: #fff;
}
.AOLPlainTextBody pre {
font-size: 9pt;
}
.AOLInlineAttachment {
margin: 10px;
}
.AOLAttachmentHeader {
border-bottom: 2px solid #E9EAEB;
background: #F9F9F9;
}
.AOLAttachmentHeader .Title {
font: 11px Tahoma;
font-weight: bold;
color: #666666;
background: #E9EAEB;
padding: 3px 0px 1px 10px;
}
.AOLAttachmentHeader .FieldLabel {
font: 11px Tahoma;
font-weight: bold;
color: #666666;
padding: 1px 10px 1px 9px;
}
.AOLAttachmentHeader .FieldValue {
font: 11px Tahoma;
color: #333333;
}
</STYLE>
<DIV class=AOLPlainTextBody id=AOLMsgPart_0_6fdaf702-ebc4-4345-a991-22a170bbea3c><PRE><TT>Another issue is the matching of the transistors
is very important. In a <SPAN class=correction id="">monolytic</SPAN> process you get this
almost for free. In <SPAN class=correction id="">discretes</SPAN> it is very hard to both
match AND keep the temperature similar.
I tried a 'spice' model of a <SPAN class=correction id="">CA3080</SPAN> from the
<SPAN class=correction id="">datasheet</SPAN>.
Using transistors and diodes... it did not work at
all. Offset was terrible. Then I figured out that if
I diode connected transistors, it would work (and it
did).
eventually we will have to move on and use other
technologies to get the results we want. Maybe after
my lifetime (I hope).
There is (of course)... always the desert island :^P
H^) <SPAN class=correction id="">harry</SPAN>
--- Ian Fritz <<A href="mailto:ijfritz%40earthlink.net"><SPAN class=correction id="">ijfritz</SPAN>@earthlink.net</A>> wrote:
> At 12:47 PM 6/2/05, <A href="mailto:laxt57%40aol.com">laxt57@aol.com</A> wrote:
>
> > Well what I am planning is this. A <SPAN class=correction id="">OTA</SPAN> made with
> <SPAN class=correction id="">SMD</SPAN> that
> > will fit the footprint of a <SPAN class=correction id="">ca3080</SPAN>. By input I
> guess I was not
> > asking about the design of the <SPAN class=correction id="">OTA</SPAN> itself, all
> that is freely
> > available on the web. I guess my question is with
> the available
> > <SPAN class=correction id="">smd</SPAN> devices 847s,3904 etc do you think this sdiy
> do able?
>
> Well, that's the question. I haven't found any good
> <SPAN class=correction id="">SMD</SPAN> well-matched,
> high-gain transistors. I've been stocking up on the
> popular Japanese
> matched pairs, some of which are quite good, but all
> discontinued. In my
> most recent discrete <SPAN class=correction id="">OTA</SPAN> I tried a pair of
> hand-matched <SPAN class=correction id="">ZTX795A's</SPAN> glued
> together, but they didn't work very well. They had
> too much <SPAN class=correction id="">LF</SPAN> noise,
> presumably due to temperature fluctuations.
>
> Maybe some of the non-monolithic <SPAN class=correction id="">SDMs</SPAN> could be made
> to work, I <SPAN class=correction id="">dunno</SPAN>.
>
> Another question is whether it is even a good idea
> to try to reproduce the
> 3080. The <SPAN class=correction id="">Iabc</SPAN> mirror has always been a pain,
> requiring a mirror in the
> <SPAN class=correction id="">expo</SPAN> converter. Why not work with the simpler
> discrete designs that don't
> have this "feature".
>
> Ian
>
>
</TT></PRE></DIV><!-- end of AOLMsgPart_0_6fdaf702-ebc4-4345-a991-22a170bbea3c --></DIV></DIV></BODY></HTML>