Ring Oscillator using Sky130

The circuit designed for Marathon is Ring Oscillator using Sky130. The circuit is designed using total of 27 MOS devices. Pulse input is given to the circuit to drive and maintain a minimum voltage at the output during oscillation so that the lower potential does not attain zero voltage.

The main concept of circuit is derived from conventional ring oscillator which uses the nature of feedback circuit. The 27 MOS devices in the circuit are divided as 10 pMOS devices and 17 nMOS devices. 

The ideal output of the ring oscillator is similar to pulse signal. The real time simulation output simulated in ngspice gives us the output in such a way that when the signal transits from low voltage to high voltage, it experiences high noise. The noise effect on the circuit can be rectified using calculated resistors and capacitors. At the output, the lower potential of the oscillated waveform is not zero. Since the circuit is used in low-powered  applications, the signal is observed in units of nanoseconds.

The circuit was initially designed in esim and tested for default libraries which uses 180nm technology. When the desired output was achieved in ngspice simulation, the circuit was converted to 130nm technology models using sky130 pdk. For circuit the pulse input is provided with pulse width and period in nanoseconds  and oscillating output is achieved.

The challenges faced during the marathon were- initially, the problem was to understand the installation and integration of Sky130 pdk with esim. After resolving this issue, integrating Sky130 pdk with designed circuit was challenging in terms of understanding the change in sizing, input voltage, etc when compared to other technologies. All the challenges faced was resolved with the directions and help provided by mentors in Slack platform. 

By attending this Marathon, we got an opportunity in learning:
- The availability and use of opensource simulation tool (esim)
- How a circuit designed using GUI based tool gets converted to a netlist code at the backend
- How to edit the backend code of the circuit to achieve desired models, sizes and models by changing libraries.
- And one of the major non technical learning is being introduced to a new platform SLACK, which helped alot in resolving our doubts

I would like to thank all the mentors for being there to help all the partcipants all the time.
It was a pleasure attending the Marathon, and wish to be a part of few more in the future.
