MMWave Cross Coupled CMOS VCO Layouts

Hello,

I want to layout a mmwave CMOS Cross Coupled (NMOS/PMOS) VCO.

I have questions about metal routing and the effects of the routing on the performance.

I have attached a few layout examples from papers about the cross coupled layout of the VCO.

In one of the papers, the routing is done by stacking many layers of interconnect and then routing on, what I assume, is the top metal of the process, metal 9. Is the advantage to this, the lower resistivity of the stacks of metals for better oscillator performance ?

In the other attachment, the layout of the cross coupled structure is shown. I also added another attachment showing the same thing - in both "M1" and "M2" mean the transistors and "OSC1" and "OSC2" mean the transistors of the cross coupled pair.

Here the drains are routed together on of the top metals, M6 while the drain of each finger is connected to the gate using metal 2, while sources are connected together using metal 1 to gnd.

So again, my question is, is it best to route the complete set of drain fingers together, just go all the way to a higher metal, like metal 6, or stack the interconnect on top of one another and then route on a higher metal layer.

Thanks.

Connect the Gates and Sources with M1, create the Coil with lower resistivity metal.

Hello,

And then route the drain to connect to the coil (in my process its on the top metal).

So use vias to route drain from say M2 up to top metal, say metal 9 and then to inductors ?

Correct ?

Puppet123 said:

Hello,
And then route the drain to connect to the coil (in my process its on the top metal).
So use vias to route drain from say M2 up to top metal, say metal 9 and then to inductors ?
Correct ?

Click to expand...

Yes, right..

Dont I get losses in vias going up to top metal ?

Puppet123 said:

Dont I get losses in vias going up to top metal ?

Click to expand...

Yes, there will inevitably be losses but if you connect the transistors on top metal, the inductor/capacitor effects will influence the operation of the oscillator.It may not oscillate ..