Current Source in Ring VCO

Hi all,

In three stage ring VCO, we feed the current by single current source to all inverter/delay cell. Can we feed each inverter/dela stage with separate current source? What will be theh effect? Thanks in advance.

niteshtripathi said:

Hi all,

In three stage ring VCO, we feed the current by single current source to all inverter/delay cell. Can we feed each inverter/dela stage with separate current source? What will be theh effect? Thanks in advance.

Click to expand...

I did not fully understand your question. What do you mean by

we feed the current by single current source to all inverter/delay cell

Click to expand...

Do you mean that each stage has its own current source and the current sources in each stage has the same value? Or do you mean that there is one large current source atop your three stage ring VCO? In the latter case, it becomes a voltage controlled oscillator rather than a current controlled oscillator.

In case you meant the first case, read on.

Why not? Ideally each stage will have a different delay and then your oscillation frequency would be different from the case where all three inverters have the same current. Your Kvco will also change and I have a feeling it will be more non-linear than the case where all the three stages have the same current. Phase noise will be dominated by the stage that has the lowest slew rate.