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<DIV><FONT face=Arial size=2>it's all a bit obvious the more i think about it. i
knew the current is mirrored in both collectors due to both transistors sharing
the same base voltage (and temperature re the Ebers-Moll equation), but at 3 in
the morning, it didn't click that each transistor has its own
base Vbe v Ic current relationship. if the two transistors don't
share the same Vbe v Ic relationship, of course the current is going to be a
perfect mirror. duh</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>cheers all</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>B</FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=sbernardi@comcast.net href="mailto:sbernardi@comcast.net">Scott
Bernardi</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=synth-diy@dropmix.xs4all.nl
href="mailto:synth-diy@dropmix.xs4all.nl">Synth-DIY list</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, November 27, 2003 5:06
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [sdiy] current mirrors</DIV>
<DIV><BR></DIV>Ooo! Ooo! I know! (picture little kid jumping up and down
with his hand in the air).<BR>The Vbe vs. Ic curves should be matched.
I.e., for a given Vbe they should give the same collector current, and
visa-versa. The transistors should be at the same temperature also since that
greatly affects the Vbe vs. Ic relationship.<BR>A two transistor current
mirror will have an error due to the base currents. One way you can decrease
that error (by a factor of Beta) is to add a third transistor with its B-E
junction replacing the B-C short on the "input" side of the mirror.The
collector can go to the supply rail (positive rail for npn mirror, negative
rail for pnp) The transistor doesn't have to match.<BR>Here's a link I found
about current mirrors:<BR><A class=moz-txt-link-freetext
href="http://www.eas.asu.edu/~thornton/Teaching/ece334/lectures/lecture_16.pdf">http://www.eas.asu.edu/~thornton/Teaching/ece334/lectures/lecture_16.pdf</A><BR><BR>Paul
Schreiber wrote:<BR>
<BLOCKQUOTE cite=mid008001c3b44f$25bc0140$0201a8c0@speakeasy.net type="cite"><PRE wrap="">Yes, that's the whole *point* of being "matched" :)
Now, exactly WHAT is "matched" in a 'matched transistor pair'?
.....Anybody.....Buhler?........(yes, I know the answer, but I want you to find out yourself).
Paul S.
dang cold (cough cough)
----- Original Message -----
From: "Benjamin Riggs" <A class=moz-txt-link-rfc2396E href="mailto:benj@iinet.net.au"><benj@iinet.net.au></A>
To: "Synth-Diy" <A class=moz-txt-link-rfc2396E href="mailto:synth-diy@dropmix.xs4all.nl"><synth-diy@dropmix.xs4all.nl></A>
Sent: Wednesday, November 26, 2003 12:41 PM
Subject: [sdiy] current mirrors
</PRE>
<BLOCKQUOTE type="cite"><PRE wrap="">i am hardly an expert when it comes to transistor theory, but i think i
understand the basic operation of current mirrors. what i would like to know
is if in the basic two transistor curent mirror, do the transistors need to
be matched?
B
</PRE></BLOCKQUOTE><PRE wrap=""><!---->
</PRE></BLOCKQUOTE><BR><PRE class=moz-signature cols="72">--
Scott Bernardi
<A class=moz-txt-link-abbreviated href="mailto:sbernardi@comcast.net">sbernardi@comcast.net</A></PRE></BLOCKQUOTE></BODY></HTML>