4 stage ring oscillator simulation...

[pnanda65675]

i q ring oscillator

im designing a VCO usin a 4stage ring oscillator for high speed operation 3.125GHz using 0.18um CMOS IBM foundry. Im vague in choosin a delay cell for my ring architecture. So when analyzed the circuit that given behzad razavi's book, it cant get oscillation.Im aware of various of delay cell. Can somebody tell how exactly u can get a frequency vs Vcont waveforms. I've explain very detaily in te attachment below...plz do hav a look on tat.Im rely vague n need ur kind help to proceed my next level of work.. Thanks in advance !!!!

 

[nibo_mmx]

When you simulate VCO, maybe you need set the initial condition of the output to let the VCO oscillate.

 

[amarnath]

can u tell me how u are going to make an even staged ring oscillator to oscillate.i have read and implemented only odd staged ring oscillators.i think an even stage ring oscillator will not oscillate at all,as far as i know.since if suppose u assume it is in an initial state of 1(vout),then i will be getting a 1 always at the output.correct me if iam wrong.

regards
amarnath

 

[khouly]

can u tell me how u are going to make an even staged ring oscillator to oscillate.i have read and implemented only odd staged ring oscillators.i think an even stage ring oscillator will not oscillate at all,as far as i know.since if suppose u assume it is in an initial state of 1(vout),then i will be getting a 1 always at the output.correct me if iam wrong

this is completly right for single ended ring oscillator
but if u can use differential mode ring oscillator it will work
and if u use 4 stage diff ring osc u can get the I.Q signals directly
for pnanda65675
u must put intial condition , for any volatge , or use ur DC supply as a step with finite rise time
it will work


khouly