tri lfo with 90deg lag?(blush)

[Paul Perry]

I asked recently for anything on a 90deg  lag sine oscilator
and as usual got some very good & useful replies..

Today I seemed to remember somethng slightly familiar fron the
National Semi LM13600 data sheet, an oscillator with 3 OTA
stages giving 60 deg in each stage.. which made me think if there were 2 
stages there would be 90 deg difference.. which made me thnk about what 
my LP filter (clone of the LM13600 Korg MS20 filter) must be doing..
got out the scope (thanks Barry!) and viola, there it is, when
it oscillates one of the OTA stages is 90 deg behind the other..

Boy is my face red! who else would ask the list for a quadrature
oscillator when he has one running on the bench!! 
Well I guess this list is educational :-)

paul perry melbourne australia

BTW the outputs aren't perfect sine/cos waveforms, but plenty good enough 
for LFO panning applications. And, putting a fet before the buffer stage
(thanks JH) should give a nice big range..