Why not go back to basics and show how an ideal ramp voltage generator can be implemented in Virtuoso by using simple ideal components from the analogLib library.
We can use a voltage controlled current source (vccs) driving current into a capacitor and forming a negative feedback and employing a second voltage source which sets the maximum ramp voltage level. An ideal switch is ised for capacitor discharge (reset), and as long as we have the switch turned off our generator starts ramping.
The slew rate can be controlled by changing the maximum deliverable current by our vccs. Some cell parametrization seems useful in our case. You can get this component here.