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<DIV><FONT face=Arial size=2>
<DIV><FONT face=Arial size=2>I've a question about the well known high freq.
tracking error in MOOG like VCO: <FONT face=Arial size=2>I think that is not Rbe
but the timing capacitor discharge time that degrade the VCO linearity at high
frequency !</FONT></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Looking at Chroma VCO I found that instead a
classic comparator + fet / bjt for the timing capacitor discharge they
used </FONT></DIV>
<DIV><FONT face=Arial size=2>a charge pump IC (4151). This make the frequency
linear because (balancing the charge into the capacitor):</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2> Iexp * T cycle = Ipump *
Tpump</FONT></DIV>
<DIV> </DIV>
<DIV>where Iexp is the current foem the expo converter, Tcycle the total charge
discharge time, Ipump the current from the Charge pump and Tpump the duration of
the Charge pump impulse. Thus:</DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2> f = 1/ Tcycle = Iexp / ( Ipump * Tpump)
</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>and the terms Ipump and Tpump are costants ! A very
smart solution that eliminate the effect of a costant discharge
time.</FONT></DIV>
<DIV>Right or I've omitted something ?</DIV>
<DIV><FONT face=Arial size=2> </FONT></DIV>
<DIV><FONT face=Arial size=2>Now I want to try the LM331 that appear to be
pin compatible with 4151 and make some test.</FONT></DIV>
<DIV><FONT face=Arial size=2>Ideas and suggestions are well
accepted</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Bye</FONT></DIV>
<DIV> </DIV></FONT></DIV></BODY></HTML>