 74HC4046 VCO duty cycle
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Marko
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Sun Nov 13 2011, 06:26PM
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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
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Hi guys
I have one problem I can't figure out - why does output duty cycle of this chip, which should be very well around 50% vary so wildly depending on how I set the minimum frequency resistance? I made a simple setup using phase comparator 2 and am trying to get a lock onto external sinewave signal fed into self-biased input at frequency of about 1.5Mhz. What happens is that I only get a lock with very careful adjustment of minimum frequency pot (while the max frequency one does almost nothing) and within this range I get very large variances of duty cycle depending even on strength of input signal.
Thought it must be poor power supply, but no amount of decoupling or begging helps it. Am I doomed to use a 74HC74 flip flop to divide the frequency in order to get out of this trouble? (I would like 8Mhz final output which would mean 16Mhz VCO frequency which is a stretch for this chip).
Marko
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