Saw/Ramp to Triangle and Inverted Ramp/Saw skewer circuit ideas?

[belzrebuth]

Hi all,
I was wondering if there is a circuit to be able, given a triangle wave or a saw wave to produce a continuously variable wave going from a downward ramp saw -> triangle -> inverted saw or upward ramp.
I really don't care about whether the input should be a saw or a triangle as I have both of them avalaible.
I initially thought to produce the inverted of a saw wave and then try to combine the two ramps  (the one going up and the other going down) at the same time essentially making a crossfader circuit of the two ramps to produce a half amplitude triangle but I get zero in the middle which is what one would get trying to add a signal with it's inverted copy. 
I then thought that I need to delay that by half a period or make the other half of the wave double the frequency of the first half so I can add the two halves essentially getting a triangle.
And then I stopped because I guess this is something more difficult to do that I anticipated.
 I would appreciate any help doing this!
From a quick search it doesn't seem to be an ordinary process so there isn't any obvious way to do that..

[Ian.M]

Integrate a PWM, but you'll also need to servo the PWM high and low levels to maintain output amplitude and mean level at zero.  50% duty cycle gives a triangle wave and the extremes close to  0% and 100% give the rising and falling sawtooths.

[belzrebuth]

By integrating a PWM you mean I need to use an OTA to produce a ramp from a pulse modulated square wave or just pass this square wave thru an opamp integrator? This latter seems simple enough
Do you have any examples?!


EDIT: I found this circuit here :
https://till.com/articles/VariableSaw/
Tried to simulate it but there are quite a few things missing that render it unusable as is..
also CA3280s are non existent anymore so I will eventually have to use a LM13700 for the circuit to be able to get built.

[Terry Bites]

Here's the classic aproach>>>> Control the ratio of charge to dischage of a simple integrator. OTAs indeed!
The volts feed back from the comparator control the ramp time. A buffer stops interaction of freq and symmetry controls.
You get a rectangular sync output for free.

[belzrebuth]

Do you have any circuit example for this?
Thanks!