[sdiy] dual vco

[ASSI]

On Thursday 08 April 2010, Ian Fritz wrote:
> Has anyone made a pair of VCOs using dual chips?  I have one
> running using LM13700, TL072, CD4013, etc.  The two oscillators
> sync up a bit, and I'm not sure if this intrinsic or due to still
> being on a whiteboard.

If you look at the chip micrograph that Don Sauer put up on his web 
site www.idea2ic.com  you'll see that while the two halves of an 
LM13600/LM13700 are mirror symmetric, the power supply is not.  That's 
a bit unfortunate as it would have been possible to connect them both 
to V+ with a tow-under and get a slightly better isolation.  The first 
half (pin 1-8) has a better connection to V+, while the second half 
(pin 9-16) has a more direct connection to V-, so it may be possible 
to wring some improvement if the VCO are used in some known relation 
to each other.

So I'd say it is intrinsic to that chip to have some coupling through 
the power rails.


Achim.
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