I've been working about this ramp generator circuit (attached file) for my research. Initially I want to have a ramp output of frequency 100MHz to 1GHz but I have a problem because i can only get 20-30kHz ramp signal. In my reference paper, the formula of frequency is f =Vref/(RtCt(Vh-Vl)) or f = Io/CV, but no matter what value I change the parameters(Vref, Ct, Rt and Schmitt trigger sizes) it still would not get a high frequency output, instead the I only get a distorted one.

Here are the values of the parameters that I can get a clean ramp output but with small frequency:
Rt = 5k
Vref = 1V
Ct = 1nF
Vh = 0.7V
Vl = 0.25

using the formula f =Vref/(RtCt(Vh-Vl)); f = 444.44kHz
but in my simulation output, I only get 32kHz ramp signal.

I use TSMC 65nm technology in my simulation.
I attached my reference paper in this study.

Please someone expert in these things, please I need help. Thank you!

 

My supply voltage is 1.2V

 

If the supply is only 1.2V, what are the MOSFET threshold voltages, Vgs(th)?
Is would seem you have very little dynamic range to work with.

 

Are you sure the devices can run at such a high frequency?

 

Are you sure the devices can run at such a high frequency?

I don't know, but I hope it can run atleast 10MHz then I'll add frequency multiplier circuit to reach higher frequencies.

 

If the supply is only 1.2V, what are the MOSFET threshold voltages, Vgs(th)?
Is would seem you have very little dynamic range to work with.

all mosfet involved in the circuit have 0.4-0.55Vth and in strong inversion

 

The highest frequency mentioned in the paper is 700 kHz, and there is nothing to indicate or suggest that the circuit will function at any higher frequencies, let alone 100 MHz to 1 GHz.

ak

 

The highest frequency mentioned in the paper is 700 kHz, and there is nothing to indicate or suggest that the circuit will function at any higher frequencies, let alone 100 MHz to 1 GHz.

ak

I've seen HF stuff on silicon before and this is definitely not what it looks like.