How to generate sawtooth voltage sweep in ns

Perhaps you need to think less, many regular logic families
will produce this kind of risetime just by loading.

Now if you want FM "modulation shape" fidelity you're on a
different sort of hook. But if all it wants is "there to here"
frequency sweep / chirp, maybe it's easier than you think.

The narrowest chirp you could get will be from an advanced
CMOS logic family, make a one-gate-delay positive-edge-only
"yip" with a quad NAND gate. Burden the output (incl the
varactor) with external C until you like the risetime (if too fast).
If too slow, pick another logic family.

A very linear ramp would need a fancier circuit. Like maybe a
current source charging a C, with a shunt switch to reset / hold
off driven by a suitably-matched one-shot.

ABIRAMIM said:

Hi there
I am a newbie working to generate chirp pulses for FMCW radars. I have a VCO to generate pulses in 5 - 6GHz frequency when Vtune of the VCO is varied from 2 to 12V. My understanding is I need to generate sawtooth voltage sweep in ns time duration to feed the Vtune so that the VCO will generate the required frequency shifts. Can someone help me how can I generate this voltage sweep to feed the vco. Because as far as I know, 555 timer ICs generate pulses in few hundred KHz only and I need the sawtooth sweep frequency to be in MHz (Ton = 13ns and Toff = 200ns)

Thanks

Click to expand...

Can you define any more what you expect?
Stepped ramp or linear ramp? When Ton << Toff that looks more like a 26 ns pulse with slew rate control of a triangular 13% pulse using the leading edge or 6.5% or 1/2 cycle of 38.46 MHz with a 5 MHz cycle. What Xtal and sync. counters be suitable for this in terms of stability (ppm) and phase noise). Do you need a Fractional-N Synth or can you adjust it to be an integer?
i.e. 12.5% instead of 13% for an integer of 8* f_rep or 16*f for on time duty factor.

This is usually created in a DSP and modeled by something like Visual System Simulator (VSS) software from AWR Corp https://kb.awr.com/display/awrfaq/Getting+Started+with+the+AWR+Software

Then you might need a $50k VNA to analyze it e.g. https://www.ni.com/en-ca/shop/model/pxie-5668.html

There is a confusion. In normal FMCW radars, the range of the period of the chirp is between few microseconds up to hundreds of microseconds.
I think your request for nanoseconds range is meaningless.

You have a duty to include design specs for range, BW .