ramp generator question

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anotherbrick

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hello dear forum,

I want to design a ramp generator

here is my circuit and the simulation result



my question ;

how can I seperately adjust rise and fall times ?

thank you
 

Hi,

I'd use a simple "integrator circuit"

... at least I don't see a benefit in your circuit.

Klaus
 
hello thank you,

I dont want Vout exeeds Vin

Vout must be equal to Vin at the end of ramp

is it posible with integrator circuit ?
 

Hi,

No, not with the simple integrator circuit.

Klaus

- - - Updated - - -

Hi,

Try with individual resistors in series with the diodes.

Klaus
 
The simplest ramp generator I've seen / done, is a timing
cap and a pair of current sources, one fixed and one
switched. For a "sawtooth" the switched source is much
higher value and for a triangle wave it would be 2X the
fixed value (so sum, +fixed and -fixed).

Now you would also want endpoint control meaning a
pair of comparators for top and bottom phase termination.

I think about 20 transistors all told, in a DC-DC chip design.


If you aren't dead-set on absolute linearity then a switched-R
scheme could be simpler (and I prefer it for PVT with a pair
of supply-ratiometric thresholds). You could also use supply-tracking
current sources to get V rejection -and- linearity.
 
Hi,

Maybe useful if you haven't seen it, RAMP GENERATORS

The linear ramp (sawtooth) I know works, not sure about Vout = Vin at end of ramp with it 'though, is the current source into a cap, with oscillator transistor draining cap.

- - - Updated - - -

Apologies for the circuit being backwards to standard layout, in a rush right now... The input to BJT base is any old squarewave. I seem to remember you can make it more triangle wave-like changing (R)C values. Again, doubt it can go to Vin, not sure.

 
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