<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">
<title></title>
</head>
<body text="#000000" bgcolor="#ffffff">
If you were interested in turning this circuit into an exponential
through-zero VCO: <br>
Instead of driving linear voltage to current converters, you could
drive the linear FM inputs of two expnential converters; i.e., on the
servo opamp that usually drives the emitters of the exponential
transistor pair, you would DC couple the modulation signals, one
inverted and one non-inverted, into the inputs of the servo opamps
where the voltage references usually go. If you used a quad pnp array
like the THAT120 for the exponential pairs, the exponential tracking
should be pretty good between the two current sources. You would have a
single CV summing amp that would drive both of the exponential pairs.
The rest of the quadrature circuit would be the same as in the article<br>
I think this would give you the benefit of the smooth through-zero
transition that the article purports, but with an exponential CV
response. Does this make sense or am I missing something?<br>
<br>
Daniel Araya wrote:<br>
<blockquote type="cite" cite="mids00e8ad7.042@gwia.sr.se">
<pre wrap="">Nice one!
<a class="moz-txt-link-freetext" href="http://www.reed-electronics.com/ednmag/article/CA341451">http://www.reed-electronics.com/ednmag/article/CA341451</a>
/d
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">Peter Blackett <a class="moz-txt-link-rfc2396E" href="mailto:dragon.servicing@virgin.net"><dragon.servicing@virgin.net></a> 2004-01-21 14:12:21
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap=""><!---->Hi,
I just thought you might be interested to know that in the latest
issue
of EDN Europe , Jan 2004 ,
there is an article in the design idea's section for a VCO that
produces
positive and negative output frequencies.the article mentions that
this
is traditionally done in analog music effect units such as they
Bode/Moog frequency shifters.
Article is written by Henry Walmsley from Farnborough .
edn's web address is <a class="moz-txt-link-abbreviated" href="http://www.edn-europe.com">www.edn-europe.com</a>
but I don't know if they have the article on line .
regards Peter
</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>
</body>
</html>