pulse generator circuit (digital ckt supported by cadence)

[sai]

hai folks,
i need to design a circuit in cadence which works as a square wave
generator or rather ( a circuit which trigers to 0 and 1
alternatively).the main problem is with speed and I am looking for 20
GHz (50 pico secs).

i have taken give an input to the nand gate which is '0'.this is for
initialisation , later i changed it to '1'. later i have given this
out put to the not gate and this and i gave a feedback from the
middle.
cadence is not supporting for the simulation.

can anybody plz help regading to this problem?


regards,
sai

 

[Jeroen Vriesman]

If I understand you, you are trying to make a 20GHz oscillator with digital
gates and feedback?

To make an oscillator with a gate you need a schmidt-trigger, otherwise you
just have a stable DC-feedback, the gates then work as a bad analog
amplifier.

For as far as I know, there are no schmidt-triggers for 20GHz.

To make oscillators like in the 20GHz range, you can use your pcb layout as
a transmission line for 180deg. phase shift and feedback with one (very
high frequency) transistor. (e.g. BFG425W). But that's hard for 20GHz, if
you get a signal, it won't be stable. You can also build a series of
frequency doublers if you want a stable signal.

Or tunnel diodes inside microwave resonators. But logic gates?

And it will never be a square wave ofcourse if your amplifier doesn't even
amplify the second harmonic.