does anyone has exp designing sawtooth generator?

[AMSA84]

Has the topic topic says, I would like to know if there is aomeone familiar with the design if sawtooth generator.

I havê design the BASIC sawtooth generator working até 500Mhz but it gails in corners.

I would appreciate any help.

 

[D.A.(Tony)Stewart]

What slew rate do you expect? for rising and falling edges?
Avalanche effect devices are usually needed.

 

[AMSA84]

What you mean by slew rate? Of what? Ota por sawtooth?

 

[BradtheRad]

It is a challenge to create a sawtooth at a fast frequency. You need to allow relatively large current pulses, for a fast discharge rate on the capacitor.

A unijunction transistor is a typical choice to make a simple sawtooth waveform. These may be difficult to find.

Or try a configuration of two transistors, referred to as a programmable unijunction transistor.

**broken link removed**

This is not necessarily the optimum design. You may have better luck with an oscillator known as a ring oscillator. It operates from the innate capacitance in mosfet gates.

 

[FvM]

You can make a simple experiment with the Falstad fourier series applet and visualize the effect of a 2.5 or 5 GHz bandwidth limitation and a 500 MHz sawtooth.

This should clarify a basic problem of a hugh frequency sawtooth generator. Then specify your requirements, or better explain what you want to achieve.

Any BJT transistor circuits based on saturated switching can be definitely excluded.

 

[dick_freebird]

I have enough experience, to have come to prefer a triangle
wave & comparators (LM555-style, quite often) for generating
a PWM master ramp signal. Benefits here can include a fair
degree of process / temperature insensitivity, and 0% - 100%
realizable duty cycle, and no fast discharge requirement at
all.

Now, 500MHz -is- fairly sporty and I would not expect much
purity out of the circuit. Consider that 2nS full cycle and a
desire to make a <=10% duty cycle position clean means
a 200pS high phase and in turn a desire for 20pS rise / fall.
That's tough territory for even the highest speed logic.
You're probably feeding this to a comparator somewhere,
which is going to be slower (and more variably slow) at low
overdrive than any bang-bang logic with a well driven input.
And you want an analog waveform to be all tight and pretty
across corners?

I think you might want to step back and think about what
you want for the real outcome - I'd assume this sawtooth
has a small part to play in a larger function, and maybe the
function can be had cleaner with some alternative approach.

 

[AMSA84]

Thanks for the reply. I forgot to tell that this will be implemented on a IC.